ESS Tech (GWH) 10-K 1 Mar 23 2022 FY Annual report Financial data

Cover

Cover - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Feb. 24, 2023	Jun. 30, 2022
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2022
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-39525
Entity Registrant Name	ESS Tech, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	98-1550150
Entity Address, Address Line One	26440 SW Parkway Ave.
Entity Address, Address Line Two	Bldg. 83
Entity Address, City or Town	Wilsonville
Entity Address, State or Province	OR
Entity Address, Postal Zip Code	97070
City Area Code	855
Local Phone Number	423-9920
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Public Float			$ 250
Entity Common Stock, Shares Outstanding		154,307,976
Entity Central Index Key	0001819438
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Amendment Flag	false
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s definitive proxy statement relating to the 2023 Annual Meeting of Stockholders are incorporated herein by reference in Part III of this Annual Report on Form 10-K to the extent stated herein. Such proxy statement will be filed with the Securities and Exchange Commission within 120 days of the registrant’s fiscal year ended December 31, 2022.
Common Stock
Entity Information [Line Items]
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	GWH
Security Exchange Name	NYSE
Common Stock Warrants
Entity Information [Line Items]
Title of 12(b) Security	Warrants, each whole warrant exercisable for one share of common stock at an exercise price of $11.50
Trading Symbol	GWH.W
Security Exchange Name	NYSE

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2022
Auditor Information [Abstract]
Auditor Firm ID	42
Auditor Name	Ernst & Young LLP
Auditor Location	Portland, Oregon

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 34,767	$ 238,940
Restricted cash, current	1,213	1,217
Accounts receivable, net	4,952	451
Accounts receivable, net - related parties	0	66
Short-Term Investments	105,047	0
Prepaid expenses and other current assets	5,657	4,844
Total current assets	151,636	245,518
Property and equipment, net	17,570	4,501
Operating lease right-of-use assets	3,401	0
Restricted cash, non-current	675	75
Other non-current assets	271	105
Total assets	173,553	250,199
Current liabilities:
Accounts payable	3,036	1,572
Accrued and other current liabilities	14,125	6,487
Accrued product warranties	1,643	0
Operating lease liabilities, current	1,421	0
Deferred revenue	6,168	3,663
Notes payable, current	1,600	1,900
Total current liabilities	27,993	13,622
Notes payable, non-current	315	1,869
Operating lease liabilities, non-current	2,535	0
Deferred revenue, non-current	2,442	0
Earnout warrant liabilities	163	1,476
Public warrant liabilities	2,066	18,666
Private warrant liabilities	980	8,855
Other non-current liabilities	85	552
Total liabilities	36,579	45,040
Commitments and contingencies (Note 11)
Stockholders’ equity:
Preferred stock ($0.0001 par value, 200,000,000 shares authorized, none issued and outstanding as of December 31, 2022 and 2021)	0	0
Common stock ($0.0001 par value; 2,000,000,000 shares authorized, 153,821,339 and 151,839,058 shares issued and outstanding as of December 31, 2022 and 2021, respectively)	16	16
Additional paid-in capital	755,537	745,753
Accumulated deficit	(618,579)	(540,610)
Total stockholders’ equity	136,974	205,159
Total liabilities and stockholders’ equity	$ 173,553	$ 250,199

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Preferred stock, par value (in USD per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	200,000,000	200,000,000
Preferred stock, shares outstanding (in shares)	0	0
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (in USD per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	2,000,000,000	2,000,000,000
Common stock, shares issued (in shares)	153,821,339	151,839,058
Common stock, shares outstanding (in shares)	153,821,339	151,839,058

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Revenue:
Total revenue	$ 894	$ 0
Operating expenses:
Research and development	71,979	30,275
Sales and marketing	6,938	3,041
General and administrative	27,469	27,286
Total operating expenses	106,386	60,602
Loss from operations	(105,492)	(60,602)
Other income (expenses), net:
Interest income (expense), net	2,187	(1,886)
Gain (loss) on revaluation of warrant liabilities	24,475	(37,584)
Loss on revaluation of derivative liabilities	0	(223,165)
Gain (loss) on revaluation of earnout liabilities	1,313	(154,806)
Other (expenses) income, net	(452)	926
Total other income (expenses), net	27,523	(416,515)
Net loss to common stockholders	(77,969)	(477,117)
Comprehensive loss to common stockholders	$ (77,969)	$ (477,117)
Net loss per share, basic (in USD per share)	$ (0.51)	$ (5.73)
Net loss per share, diluted (in USD per share)	$ (0.51)	$ (5.73)
Weighted average shares used in per share calculation, basic (in shares)	152,676,155	83,256,431
Weighted average shares used in per share calculation, diluted (in shares)	152,676,155	83,256,431
Revenue
Revenue:
Total revenue	$ 610	$ 0
Revenue - related parties
Revenue:
Total revenue	$ 284	$ 0

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Legacy ESS Common Stock	Series C-2 Redeemable Convertible Preferred Stock	Common Stock	Common Stock Legacy ESS Common Stock	Common Stock Series C-2 Redeemable Convertible Preferred Stock	Common Stock Warrants	Common Stock Warrants Legacy ESS Common Stock	Additional Paid-In Capital	Additional Paid-In Capital Legacy ESS Common Stock	Additional Paid-In Capital Series C-2 Redeemable Convertible Preferred Stock	Accumulated Deficit
Balance at beginning of period (in shares) at Dec. 31, 2020	0
Balance at beginning of period at Dec. 31, 2020	$ 0
Balance at end of period (in shares) at Dec. 31, 2021	0
Balance at end of period at Dec. 31, 2021	$ 0
Balance at beginning of period (in shares) at Dec. 31, 2020				58,919,345
Balance at beginning of period at Dec. 31, 2020	(27,888)			$ 6			$ 153		$ 35,446			$ (63,493)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued (in shares)				5,746,003
Issuance of Legacy ESS Redeemable Convertible Preferred Stock	$ 29,516			$ 1					29,515
Issuance of common stock upon exercise of options (in shares)	2,496,070			13,112	2,482,958
Issuance of common stock upon exercise of options	$ 7	$ 664							7	$ 664
Issuance of common stock upon exercise of warrants (in shares)				955,374	3,398,214
Issuance of Legacy ESS common stock upon exercise of warrants	15,130	$ 26,185						$ (153)	15,130	$ 26,338
Issuance of Legacy ESS Series C-2 Redeemable Convertible Preferred Stock upon exercise of C-2 Purchase Right and warrant (in shares)						29,153,806
Issuance of Legacy ESS Series C-2 Redeemable Convertible Preferred Stock upon exercise of the Series C-2 Redeemable Convertible Preferred Stock Issuance Right and Series C-2 warrant			$ 238,483			$ 3					$ 238,480
Net business Combination and PIPE Financing (in shares)				35,495,281
Net Business Combination and PIPE Financing	128,917			$ 4					128,913
Issuance of common stock upon achievement of earnout (in shares)				15,674,965
Issuance of common stock upon achievement of earnout	263,340			$ 2					263,338
Stock-based compensation expense	7,922								7,922
Net loss	$ (477,117)											(477,117)
Balance at end of period (in shares) at Dec. 31, 2021	151,839,058			151,839,058
Balance at end of period at Dec. 31, 2021	$ 205,159			$ 16			0		745,753			(540,610)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued (in shares)	25,000,000
Net business Combination and PIPE Financing (in shares)	64,649,087
Balance at end of period (in shares) at Oct. 08, 2021	135,195,607
Balance at end of period (in shares) at Dec. 31, 2022	0
Balance at end of period at Dec. 31, 2022	$ 0
Balance at beginning of period (in shares) at Dec. 31, 2021	151,839,058			151,839,058
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options (in shares)	529,832
Issuance of common stock upon exercise of warrants (in shares)				20
Stock-based compensation expense	$ 11,889								11,889
Issuance of common stock under employee stock plans (in shares)				2,226,463
Issuance of common stock under employee stock plans	657								657
Cancellation of shares used to settle payroll tax withholding (in shares)				(244,202)
Cancellation of shares used to settle payroll tax withholding	(2,808)								(2,808)
Warrants issued	46								46
Net loss	$ (77,969)											(77,969)
Balance at end of period (in shares) at Dec. 31, 2022	153,821,339			153,821,339
Balance at end of period at Dec. 31, 2022	$ 136,974			$ 16			$ 0		$ 755,537			$ (618,579)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities:
Net loss	$ (77,969)	$ (477,117)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,523	572
Non-cash lease expense	1,134	0
Stock-based compensation expense	11,889	7,922
Change in fair value of warrant liabilities	(24,475)	37,584
Change in fair value of derivative liabilities	0	223,165
Change in earnout liabilities	(1,313)	154,806
Other non-cash income and expenses, net	(866)	(868)
Changes in operating assets and liabilities:
Accounts receivable	(1,886)	0
Prepaid expenses and other assets	(311)	(4,673)
Accounts payable	1,464	886
Accrued and other current liabilities	6,789	2,211
Accrued product warranties	1,643	0
Deferred revenue	1,881	3,663
Operating lease liabilities	(1,123)	0
Net cash used in operating activities	(81,620)	(51,849)
Cash flows from investing activities:
Purchases of property and equipment	(14,180)	(2,767)
Purchases and maturities of short-term investments, net	(103,704)	0
Net cash used in investing activities	(117,884)	(2,767)
Cash flows from financing activities:
Borrowings on notes payable	0	20,000
Payments on notes payable	(1,900)	(21,067)
Repurchase of shares from employees for income tax withholding purposes	(2,808)	0
Proceeds from contributions to Employee Stock Purchase Plan	492	0
Net cash contributions from Business Combination and PIPE Financing	0	258,730
Payments made towards offering costs	0	(7,895)
Proceeds from warrants exercised	165	10,995
Proceeds from exercise of Legacy ESS Series C-2 Redeemable Convertible Preferred Stock Issuance Rights and C-2 warrants upon Business Combination	0	15,559
Proceeds from sale of Legacy ESS Series C-2 Redeemable Convertible Preferred Stock, net of issuance costs	0	11,461
Other, net	(22)	671
Net cash (used in) provided by financing activities	(4,073)	288,454
Net change in cash, cash equivalents and restricted cash	(203,577)	233,838
Cash, cash equivalents and restricted cash, beginning of period	240,232	6,394
Cash, cash equivalents and restricted cash, end of period	36,655	240,232
Supplemental disclosures of cash flow information:
Cash paid for operating leases included in cash used in operating activities	1,625	0
Cash paid for interest	154	1,799
Non-cash investing and financing transactions:
Purchase of property and equipment included in accounts payable and accrued and other current liabilities	1,358	526
Right-of-use operating lease assets obtained in exchange for lease obligations	4,534	0
Right-of-use finance lease assets obtained in exchange for lease obligations	123	0
Warrant vested under contracts with customers	46	0
Extinguishment of derivative liabilities upon sale of Legacy ESS Series C-2 redeemable convertible preferred stock, net of amount allocated to warrants	0	18,055
Extinguishment of warrant liabilities upon exercise of Legacy ESS Series B, Series C-1 and Series C-2 redeemable convertible preferred stock warrants	0	26,178
Assumption of accrued expenses upon Business Combination	0	75
Assumption of private and public warrant liabilities upon Business Combination	0	11,833
Assumption of earnout warrant liabilities upon Business Combination	0	502
Assumption of earnout liability upon Business Combination	0	109,507
Extinguishment of earnout liability upon achievement of earnout and issuance of shares	0	263,338
Extinguishment of derivative liability upon exercise of Legacy ESS Series C-2 Issuance Right and related Series C-2 warrant liability upon Business Combination	0	222,924
Extinguishment of public warrant liability upon exercise of warrants	0	4,143
Cash and cash equivalents	34,767	238,940
Restricted cash, current	1,213	1,217
Restricted cash, non-current	675	75
Total cash, cash equivalents and restricted cash shown in the consolidated statements of cash flows	$ 36,655	$ 240,232

DESCRITPION OF BUSINESS, BASIS

DESCRITPION OF BUSINESS, BASIS OF PRESENTATION AND RISKS AND UNCERTAINTIES	12 Months Ended
	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
DESCRITPION OF BUSINESS, BASIS OF PRESENTATION AND RISKS AND UNCERTAINTIES	DESCRIPTION OF BUSINESS, BASIS OF PRESENTATION AND RISKS AND UNCERTAINTIES Description of Business —ESS Tech, Inc. (“ESS” or the “Company”) is a long-duration energy storage company specializing in iron flow battery technology. ESS develops long-duration iron flow batteries for commercial and utility-scale energy storage applications requiring four or more hours of flexible energy capacity. The Company designs and produces long-duration batteries predominantly using earth-abundant materials that the Company believes can be cycled over 20,000 times without capacity fade. The Company continues to be in the research and development phase. The Company was originally incorporated as a Cayman Islands exempted company on July 21, 2020 as a publicly traded special purpose acquisition company under the name ACON S2 Acquisition Corp. (“STWO”) for the purpose of effecting a merger, share exchange, asset acquisition, share purchase, reorganization or similar business combination involving STWO and one or more businesses. On October 8, 2021 (the “Closing Date”), the Company consummated the merger provided for under the merger agreement (the “Merger Agreement”) dated May 6, 2021, by and among STWO, SCharge Merger Sub, Inc., a Delaware corporation and wholly owned direct subsidiary of STWO (“Merger Sub”), and ESS Tech, Inc., a Delaware corporation (“Legacy ESS”). Pursuant to the terms of the Merger Agreement, STWO deregistered by way of continuation under the Cayman Islands Companies Act (2021 Revision) and registered as a corporation in the State of Delaware under Part XII of the Delaware General Corporation Law, and a business combination between STWO and Legacy ESS was effected through the merger of Merger Sub with and into Legacy ESS, with Legacy ESS surviving as a wholly owned subsidiary of STWO (together with the other transactions described in the Merger Agreement, the “Business Combination”). On the Closing Date, STWO changed its name from “ACON S2 Acquisition Corp” to “ESS Tech, Inc.”, and its shares of common stock and warrants for shares of common stock commenced trading on the New York Stock Exchange under the new ticker symbols “GWH” and “GWH.W”, respectively. Basis of Presentation —The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiary and have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). Pursuant to the Merger Agreement, the merger between Merger Sub and Legacy ESS was accounted for as a reverse recapitalization in accordance with U.S. GAAP (the “Reverse Recapitalization”). Under this method of accounting, STWO was treated as the “acquired” company and Legacy ESS was treated as the acquirer for financial reporting purposes. Accordingly, for accounting purposes, the Reverse Recapitalization was treated as the equivalent of Legacy ESS issuing stock for the net assets of STWO, accompanied by a recapitalization. The net assets of STWO were stated at historical cost, with no goodwill or other intangible assets recorded. Legacy ESS was determined to be the accounting acquirer based on the following predominant factors: • Legacy ESS existing stockholders had the greatest voting interest in the Company; • Legacy ESS directors represented all of the new board of directors of the Company; • Legacy ESS senior management continued as the senior management of the Company; and, • Legacy ESS had the larger employee base. The assets, liabilities and results of operations prior to the Reverse Recapitalization are those of Legacy ESS. The shares and corresponding capital amounts and losses per share, prior to the Reverse Recapitalization, have been retroactively restated based on shares reflecting the exchange ratio of approximately 1.47 (the “Per Share Consideration”) established in the Business Combination. Risks and Uncertainties —The Company is subject to a number of risks associated with companies of similar size in its industry, including, but not limited to, the need for successful development of products, the need for additional capital and financing to fund operations, competition from substitute products and services from larger companies, legal protection of proprietary technology, patent litigation, dependence on key individuals, and risks associated with changes in information technology. COVID-19 presents material uncertainty and risk with respect to the Company, its performance, and its financial results and could adversely affect the Company’s financial position and results. Segment Information —The Company has determined that its Chief Executive Officer (“CEO”) is its chief operating decision maker. The CEO reviews financial information for purposes of assessing performance and making decisions on how to allocate resources. The Company has determined that it operates in a single reportable segment. Substantially all of the Company’s operations and long-lived assets were attributable to operations in the United States as of December 31, 2022 and 2021. Use of Estimates —The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and disclosure of commitments and contingencies as of the date of the financial statements and the reported amounts of expenses during the reporting periods. Such estimates relate to, among others, the useful lives and assessment of recoverability of property and equipment, deferred tax assets valuation, determination of the fair value of the Company’s investments, Bridge Loan, warrant liabilities, Series C-2 Redeemable Convertible Preferred Stock Issuance Right, earnout liabilities, earnout warrant liabilities, public warrants, private warrants, and determination of variable consideration, standalone selling price, product warranty liabilities, as well as other accruals. These estimates are based on historical trends, market pricing, current events and other relevant assumptions and data points. Actual results could differ from those estimates and such differences may be material to the financial statements. Concentration of Credit Risk —Financial instruments that potentially subject the Company to concentration of credit risk consist of cash and cash equivalents and restricted cash. The Company’s cash and cash equivalents include cash in bank accounts, money market funds, and investments with a maturity of three months or less at the date of purchase. The Company’s restricted cash includes a certificate of deposit, collateral associated with a standby letter of credit, and a performance and payment bond. Deposits held with banks may exceed the amount of insurance provided on such deposits. Reclassifications —Certain prior year amounts have been reclassified to conform with current year presentation. These reclassifications had no effect on the reported results of operations.

SIGNIFICANT ACCOUNTING POLICIES

SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
SIGNIFICANT ACCOUNTING POLICIES	SIGNIFICANT ACCOUNTING POLICIES Net Loss Per Share —The Company will use the two-class method when computing net loss per common share when shares are issued that meet the definition of participating securities. Under this method, net earnings are reduced by the amount of dividends declared in the current period for common stockholders and participating security holders. The remaining earnings or “undistributed earnings” are allocated between common stock and participating securities to the extent that each security may share in earnings as if all the earnings for the period had been distributed. Once calculated, the earnings per common share is computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding during each year presented. Diluted loss attributable to common stockholders per common share has been computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding plus the dilutive effect of outstanding options, warrants, and restricted stock units (“RSUs”) during the respective periods. In cases where the Company has a net loss, no dilutive effect is shown as options, warrants, and RSUs become anti-dilutive. Cash and Cash Equivalents —Cash and cash equivalents include cash in bank accounts, money market funds, and investments with a maturity of three months or less at the date of purchase. Cash equivalents are recorded at carrying value, which approximates fair value. Restricted Cash — Restricted cash is required as collateral for certain of the Company’s lease agreements and contractual supply and service arrangements. Restricted cash includes a certificate of deposit for the Company’s lease agreements, collateral associated with a standby letter of credit issued to a customer, and a performance and payment bond for the Company’s supply and service arrangements. The certificate of deposit and bond are recorded at carrying value, which approximates fair value. Restricted cash amounts are reported in the consolidated balance sheets as current or non-current depending on when the cash will be contractually released. Accounts Receivable, Net —The Company evaluates the creditworthiness of its customers. If the collection of any specific receivable is doubtful, an allowance is recorded in the allowance for doubtful accounts which is included in accounts receivable, net in the consolidated balance sheets. The Company had no allowance for doubtful accounts recorded at either December 31, 2022 or 2021. Property and Equipment, Net —Property and equipment are stated at cost, net of depreciation. Depreciation is provided using the straight-line method over the estimated useful lives of the assets, which range from three The Company evaluates the recoverability of property and equipment for possible impairment whenever events or circumstances indicate that the carrying amount of such assets may not be recoverable. The Company assesses the alternative use of an asset, the condition of the asset and the current market demand to determine if an asset is impaired. No impairment loss was recognized during the years ended December 31, 2022 and 2021. Investments —Investments consist primarily of U.S. Treasury securities, U.S. agency securities, and commercial paper and are classified as trading securities as they are bought and held principally for the purpose of selling them in the near term. Trading securities are carried on the consolidated balance sheets at fair value. Unrealized gains and losses on trading securities are included in other income (expense), net in the consolidated statements of operations and comprehensive loss. For trading securities still held at the reporting date, the Company recorded net losses of $45 thousand and zero for the years ended December 31, 2022 and 2021, respectively. Revenue Recognition —Revenue is earned from the sale, installation and commissioning of energy storage systems and is derived from customer contracts. Revenue is recognized in an amount that reflects the consideration to which the Company expects to be entitled in exchange for transferring the promised goods and/or services to the customer, when or as the Company’s performance obligations are satisfied, which includes estimates for variable consideration (e.g., liquidated damages). For sales of energy storage systems, the Company’s performance obligations are satisfied at the point in time when the customer obtains control of the system. Revenue recognition is deferred until written customer acceptance has been received, after site acceptance testing, or until the Company has established a history of successfully obtaining customer acceptance. In the near term, as the Company’s products are newly developed, this is likely to be a longer process than when the products are mature and the Company has an established history of customer acceptance. No right of return exists on sales of energy storage systems. Performance obligations for services, including the optional Ironclad Services Plan (“ISP”) extended warranty and ongoing operations and maintenance program provided to customers, are satisfied over time as the respective services are performed. The transaction price of the underlying customer agreement is allocated to each performance obligation based on its relative standalone selling price. When the standalone selling price is not directly observable, revenue is determined based on an estimate of selling price using the observable market price that the good or service sells for separately in similar circumstances and to similar customers, and/or an expected cost plus margin approach when the observable selling price of a good or services is not known and is either highly variable or uncertain. Costs to obtain a contract relate primarily to commissions paid to the Company’s sales personnel related to the sale of energy storage systems. The Company expenses costs associated with obtaining new contracts as incurred if the amortization period of the asset recognized by the Company is one year or less. The Company invoices customers in accordance with customer agreements and in advance of recognizing revenue as the Company has not satisfied certain performance obligations that transfer control to the customer. Payment terms generally include advance payments to reserve capacity and/or upon issuance of the customer’s purchase order with the remainder due upon the achievement of various milestones including but not limited to shipment readiness, delivery, commissioning of the system, and completion of final site testing. Advanced customer payments and unsatisfied performance obligations are recognized as deferred revenue in the consolidated balance sheets. Sales tax collected from customers is recorded on a net basis and therefore, not included in revenue. Sales tax is recorded as a liability until remitted to governmental authorities. Shipping and handling, freight costs and other reimbursable costs are accounted for as fulfillment activities and included in revenue. Related costs are included in research and development expenses while the Company is in the research and development phase. Product Warranties —Warranty obligations are incurred in connection with the sale of the Company’s products. The Company generally provides a standard warranty for a period of one year and an extended warranty through the optional ISP. The standard warranty is accounted for as an assurance-type warranty, which provides customers with assurance that the product complies with agreed-upon specifications and does not represent a separate performance obligation. The ISP warranty is considered a service-type warranty which is a distinct service and a portion of the transaction price is allocated to that performance obligation. Costs to provide for standard warranty obligations are estimated and recorded as a liability at the time revenue is recognized on the sale of the energy storage system. Warranty reserves include management’s best estimate of the projected costs to repair or to replace any items under warranty, which is based on various factors, including the use of actual claim data to date. Adjustments to warranty reserves are recorded to research and development expenses while the Company is in the research and development phase. Sales and Marketing —Sales and marketing expenses consist primarily of salaries, benefits and stock-based compensation for marketing and sales personnel and related support teams. To a lesser extent, sales and marketing expenses also include professional services costs, travel costs, and trade show sponsorships and participation. Advertising costs are expensed as incurred. The Company incurred advertising costs of $173 thousand and $45 thousand for the years ended December 31, 2022 and 2021, respectively. Research and Development —The Company continues to be in the research and development phase. Research and development costs are expensed as incurred and consist primarily of direct product development material costs, including freight charges, and product development personnel-related expenses, warranty-related costs, depreciation charges, overhead related costs, consulting services, and other direct expenses. Personnel-related expenses consist of salaries, benefits and stock-based compensation. The Company receives funding from federal agencies for research and development activities related to its products. Under certain circumstances, up to the entire amount of funding may need to be repaid to the grantor in the form of a success fee in future periods if the Company monetized the results of the activities funded by the grantor. The portion of such funding the Company may be required to pay in certain circumstances is recorded in accrued and other current liabilities in the consolidated balance sheets and was $452 thousand as of December 31, 2022 and 2021. General and Administrative —General and administrative expenses consist of personnel-related expenses for the Company’s corporate, executive, finance, legal, and other administrative functions, as well as expenses for outside professional services and insurance costs. Personnel-related expenses consist of salaries, benefits and stock-based compensation. To a lesser extent, general and administrative expenses include depreciation and other allocated costs, such as facility-related expenses and supplies. Stock-Based Compensation —The Company accounts for stock-based compensation in accordance with ASC 718, Compensation – Stock Compensation (“ASC 718”) . The Company measures and recognizes compensation expense for all stock-based awards based on estimated fair values on the date of the grant, recognized over the requisite service period. For awards that vest solely based on a service condition, the Company recognizes stock-based compensation expense on a straight-line basis over the requisite service period. The compensation expense related to awards with performance conditions is recognized over the requisite service period when the performance conditions are probable of being achieved. The compensation expense related to awards with market conditions is recognized on an accelerated attribution basis over the requisite service period identified as the derived service period over which the market conditions are expected to be achieved, and is not reversed if the market condition is not satisfied. The Company accounts for forfeitures as they occur. Stock-based awards granted to employees are primarily stock options and RSUs. The fair value of each stock option granted is estimated using the Black-Scholes Merton option-pricing model using the single-option award approach. The following assumptions are used in the Black-Scholes Merton option-pricing model: Risk-Free Interest Rate —The risk-free interest rate is based on the implied yield available on the date of grant on U.S. Treasury zero-coupon issued with a term that is equal to the option’s expected term at the grant date. Expected Volatility —The Company estimates the volatility for option grants by evaluating the average historical volatility of a peer group of companies for the period immediately preceding the option grant for a term that is approximately equal to the option’s expected term. Expected Term —The expected term for employees represents the period over which options granted are expected to be outstanding using the simplified method, as the Company’s historical share option exercise experience does not provide a reasonable basis upon which to estimate the expected term. The simplified method deems the term to be the average of the time-to-vesting and contractual life of the stock-based awards. Dividend Yield —The Company has not declared or paid dividends to date and does not anticipate declaring dividends. As such, the dividend yield has been estimated to be zero. Income Taxes —The Company accounts for income taxes under the asset and liability method. Under this method, deferred taxes are determined based on the temporary differences between the financial statement and tax bases of assets and liabilities using tax rates expected to be in effect during the years in which the bases differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in the consolidated statement of operations and comprehensive loss in the period that includes the enactment date. The Company provides for a valuation allowance when it is more likely than not that some portion of, or all of the Company’s deferred tax assets will not be realized. In making such determination, the Company considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. As of December 31, 2022 and 2021, the Company has recorded a full valuation allowance against its deferred tax assets. ASC 740, Accounting for Income Taxes (“ASC 740”), requires that the tax benefit of net operating losses, temporary differences and credit carryforwards be recorded as an asset to the extent that management assesses that realization is “more likely than not.” Realization of the future tax benefits is dependent on the Company’s ability to generate sufficient taxable income within the carryforward period. Because of the Company’s history of operating losses, management believes that recognition of the deferred tax assets arising from the above-mentioned future tax benefits is currently not likely and, accordingly, has provided a full valuation allowance for these tax benefits for the years ended December 31, 2022 and 2021. The Company recognizes accrued interest and penalties related to unrecognized tax benefits as a component of income tax expense. No amounts were accrued for the payment of interest and penalties as of December 31, 2022 and 2021 as the Company is currently not aware of any issues under review that could result in significant payments, accruals, or material deviation from its position. Fair Value —The Company follows ASC 820, Fair Value Measurements (“ASC 820”) , which establishes a common definition of fair value to be applied when U.S. GAAP requires the use of fair value, establishes a framework for measuring fair value, and requires certain disclosure about such fair value measurements. ASC 820 establishes a hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that observable inputs be used when available. Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about what market participants would use in pricing the asset or liability based on the best information available in the circumstances. The hierarchy is broken down into three levels based on the reliability of inputs as follows: Level 1: Observable inputs such as quoted prices in active markets for identical assets or liabilities to which the Company has access at a measurement date. Level 2: Observable inputs other than Level 1 quoted prices that are observable for the asset or liability, either directly or indirectly; these include quoted prices for similar assets or liabilities in an active market, quoted prices for identical assets and liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3: Unobservable inputs for which little or no market data exists and for which the Company must develop its own assumptions regarding the assumptions that market participants would use in pricing the asset or liability, including assumptions regarding risk. Because of the uncertainties inherent in the valuation of assets or liabilities for which there are no observable inputs, those estimated fair values may differ significantly from the values that may have been used had a ready market for the assets or liabilities existed. Recent Accounting Pronouncements —Pursuant to the Jumpstart Our Business Startups Act (“JOBS Act”), an emerging growth company is provided the option to adopt new or revised accounting standards that may be issued by the FASB or the SEC either (i) within the same periods as those otherwise applicable to non-emerging growth companies or (ii) within the same time periods as private companies. The Company has elected to use the extended transition period for complying with any new or revised financial accounting standards. As a result, the Company’s consolidated financial statements may not be comparable to the financial statements of issuers who are required to comply with the effective date for new or revised accounting standards that are applicable to public companies. The Company also intends to continue to take advantage of some of the reduced regulatory and reporting requirements of emerging growth companies pursuant to the JOBS Act so long as the Company qualifies as an emerging growth company. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”), which requires the measurement and recognition of expected credit losses for financial assets held at amortized cost. ASU 2016-13 replaces the existing incurred loss impairment model with a forward-looking expected credit loss model, which will result in earlier recognition of credit losses. ASU 2016-13 is effective for emerging-growth companies for fiscal years beginning after December 15, 2022, and interim periods within those fiscal years. The Company has determined that the adoption of ASU 2016-13 will not have a material impact on its consolidated financial statements or related disclosures. In future periods, as revenue and accounts receivable increase, ASU 2016-13 could have a material impact on its consolidated financial statements. Recently Adopted Accounting Pronouncements —On January 1, 2022, the Company adopted ASU 2016-02, Leases (ASC 842), which superseded previous guidance related to accounting for leases within Topic 840, Leases . The Company elected the practical expedient provided under ASU 2018-11, Leases (Topic 842) Targeted Improvements , which amended ASU 2016-02 to provide entities an optional transition practical expedient to adopt the new standard with a cumulative effect adjustment as of the beginning of the year of adoption with prior year comparative financial information and disclosures remaining as previously reported. As a result, no adjustments were made to the consolidated balance sheet prior to January 1, 2022 and amounts are reported in accordance with historical accounting under Topic 840, while the consolidated balance sheets as of December 31, 2022 are presented under Topic 842. The Company elected the package of practical expedients permitted under the transition guidance, which allowed it to carry forward historical lease classification, its assessment of whether a contract was or contains a lease, and its assessment of initial direct costs for any leases that existed prior to January 1, 2022. The Company also elected to combine its lease and non-lease components and to keep leases with an initial term of 12 months or less off the consolidated balance sheets and recognize the associated lease payments in the consolidated statements of operations and comprehensive loss on a straight-line basis over the lease term. For new required disclosures and further information see Note 9, Leases . Adoption of the new standard resulted in the recording of lease assets and lease liabilities of $4,534 thousand and $5,229 thousand, respectively, as of January 1, 2022. The transition did not have a material impact on the Company’s results of operations, cash flows or liquidity measures. For the year ended December 31, 2022, the Company adopted ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes , which simplifies the accounting for income taxes. The adoption did not result in a material impact to the Company’s consolidated financial statements or related disclosures.

BUSINESS COMBINATION

BUSINESS COMBINATION	12 Months Ended
	Dec. 31, 2022
Business Combination and Asset Acquisition [Abstract]
BUSINESS COMBINATION	BUSINESS COMBINATION As discussed in Note 1, on October 8, 2021, the Company consummated the Business Combination pursuant to the Merger Agreement, with Legacy ESS surviving the Business Combination as a wholly owned subsidiary of the Company. Upon the Business Combination closing, each share of Legacy ESS common stock, par value $0.0001 per share (“Legacy ESS Common Stock”) and preferred stock, par value $0.0001 per share (“Legacy ESS Preferred Stock”), were converted into the right to receive shares of the Company’s common stock at the Per Share Consideration as calculated pursuant to the Merger Agreement. The aggregate consideration paid to Legacy ESS stockholders in connection with the Business Combination (excluding any potential Earnout Shares (as defined below)), was 99,700,326 shares of the Company’s common stock (including 125,958 shares of common stock issued following the Closing as a result of a transaction expense adjustment as disclosed in the Company’s Form 8-K filed with the SEC on November 15, 2021). Upon the closing of the Business Combination, the Company’s certificate of incorporation was amended and restated to, among other things, increase the total number of authorized shares of capital stock to 2,200,000,000, of which 2,000,000,000 shares are common stock, $0.0001 par value per share, and 200,000,000 shares are preferred stock, $0.0001 par value per share. In connection with the Business Combination, on the Closing Date, STWO issued and sold an aggregate of 25,000,000 shares of the Company’s common stock for a selling price of $10.00 per share and an aggregate selling price of $250,000 thousand pursuant to subscription agreements, dated as of May 6, 2021, with certain accredited investors, in a Private Investment in Public Equity (“PIPE Financing”). Each issued and outstanding warrant of Legacy ESS was exercised in full in exchange for the issuance of shares of the Company’s common stock immediately prior to the Closing. Each issued and outstanding vested and unvested Legacy ESS option was converted into options of the Company exercisable for shares of the Company’s common stock with the same terms except for the number of shares exercisable and the exercise price, each of which was adjusted using the Per Share Consideration. Legacy ESS allocated to Legacy ESS employees 824,998 RSUs (the “Incentive RSU Pool”) of which 757,448 were vested upon meeting certain Earnout Milestone Events on November 9, 2021. A total of 67,550 RSUs were cancelled or not awarded as the holders did not meet the continued service requirement through the vesting date. Pursuant to the Merger Agreement, the Company was permitted to issue to eligible Legacy ESS securityholders, on a pro rata basis, up to 16,500,000 shares of additional common stock (the “Earnout Shares”) less any RSUs issued pursuant to the Incentive RSU Pool, issuable in two equal tranches upon the occurrence of the respective Earnout Milestone Events. The Earnout Milestone Events were achieved on November 9, 2021 and Legacy ESS issued 15,674,965 shares to securityholders. 6,707,318 of the Earnout Shares were delivered subsequent to December 31, 2021 upon satisfaction of a regulatory holding period and were excluded from the calculation of diluted weighted-average common shares outstanding for the period. See Note 4, Loss per Share . The Business Combination is accounted for as a reverse recapitalization in accordance with U.S. GAAP. Under this method of accounting, STWO was treated as the “acquired” company and Legacy ESS was treated as the acquirer for financial reporting purposes. Accordingly, for accounting purposes, the Business Combination was treated as the equivalent of Legacy ESS issuing stock for the net assets of STWO, accompanied by a recapitalization. The net assets of STWO were stated at historical cost, with no goodwill or other intangible assets recorded. The following table reconciles the elements of the Business Combination to the consolidated statement of cash flows and the consolidated statement of stockholders’ equity (deficit) for the year ended December 31, 2021 (in thousands): Cash contributions from Business Combination and PIPE Financing, net of redemptions $ 258,730 Less: transaction costs paid by ESS (7,895) Net cash contributions from Business Combination and PIPE Financing 250,835 Less: non-cash fair value of Public and Private Common Stock Warrants (11,833) Less: non-cash fair value of Earnout Shares and Warrants (110,010) Less: liabilities assumed from STWO (75) Net Business Combination and PIPE Financing $ 128,917 The number of shares of common stock issued immediately following the consummation of the Business Combination: Class A Common Stock, outstanding prior to Business Combination 25,000,000 Class B Common Stock, outstanding prior to Business Combination 6,250,000 Less: redemption of STWO shares (20,754,719) Common Stock of STWO 10,495,281 ESS common stock issued upon exercise of C-2 Right and Warrant 29,153,806 Shares issued in PIPE Financing 25,000,000 Business Combination and PIPE Financing shares - common stock 64,649,087 Legacy ESS Convertible Preferred Stock converted to ESS common stock 57,104,322 Legacy ESS Common Stock converted to ESS common stock 13,442,198 Total shares of common stock immediately after Business Combination 135,195,607

LOSS PER SHARE

LOSS PER SHARE	12 Months Ended
	Dec. 31, 2022
Earnings Per Share [Abstract]
LOSS PER SHARE	LOSS PER SHARE The following table presents the calculation of basic and diluted net loss per share attributable to common shareholders for the years ended December 31, 2022 and 2021 (in thousands, except per share data): 2022 2021 Net loss attributable to common stockholders $ (77,969) $ (477,177) Weighted-average shares outstanding – basic and diluted 152,676,155 83,256,431 Net loss per share – basic and diluted $ (0.51) $ (5.73) Due to the net losses for the years ended December 31, 2022 and 2021, basic and diluted net loss per common share were the same, as the effect of potentially dilutive securities would have been anti-dilutive. The following outstanding balances of common share equivalent securities have been excluded from the calculation of diluted weighted-average common shares outstanding because the effect is anti-dilutive for the periods presented: 2022 2021 Stock options 3,223,109 3,796,530 Restricted stock units 6,346,955 3,392,153 Warrants 11,473,727 11,461,247 Earnout shares pending satisfaction of regulatory holding period — 6,707,318 Number of securities outstanding 21,043,791 25,357,248

PREPAID EXPENSES AND OTHER CURR

PREPAID EXPENSES AND OTHER CURRENT ASSETS	12 Months Ended
	Dec. 31, 2022
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
PREPAID EXPENSES AND OTHER CURRENT ASSETS	PREPAID EXPENSES AND OTHER CURRENT ASSETS Prepaid expenses and other current assets consist of the following (in thousands): December 31, 2022 December 31, 2021 Insurance $ 2,033 $ 3,482 Vendor advances 3,147 1,103 Other 477 259 Total prepaid expenses and other current assets $ 5,657 $ 4,844

PROPERTY AND EQUIPMENT, NET

PROPERTY AND EQUIPMENT, NET	12 Months Ended
	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT, NET	PROPERTY AND EQUIPMENT, NET Property and equipment, net consist of the following (in thousands): December 31, 2022 December 31, 2021 Machinery and equipment $ 13,699 $ 2,868 Furniture and fixtures 184 90 Leasehold improvements 3,115 746 Software 183 — Construction in process 3,230 2,517 Total property and equipment 20,411 6,221 Less accumulated depreciation (2,841) (1,720) Total property and equipment, net $ 17,570 $ 4,501

ACCRUED AND OTHER CURRENT LIABI

ACCRUED AND OTHER CURRENT LIABILITIES	12 Months Ended
	Dec. 31, 2022
Payables and Accruals [Abstract]
ACCRUED AND OTHER CURRENT LIABILITIES	ACCRUED AND OTHER CURRENT LIABILITIES Accrued and other current liabilities consist of the following (in thousands): December 31, 2022 December 31, 2021 Payroll and related benefits $ 2,948 $ 1,876 Materials and related purchases 6,892 2,108 Amounts due to customers 770 — Deferred rent — 142 Professional and consulting fees 1,011 1,820 Accrued capital purchases 1,093 — Other 1,411 541 Total accrued and other current liabilities $ 14,125 $ 6,487

ACCRUED PRODUCT WARRANTIES

ACCRUED PRODUCT WARRANTIES	12 Months Ended
	Dec. 31, 2022
Guarantees and Product Warranties [Abstract]
ACCRUED PRODUCT WARRANTIES	ACCRUED PRODUCT WARRANTIES The following table summarizes product warranty activity (in thousands): Year Ended December 31, 2022 2021 Accrued product warranties - beginning of period $ — $ — Accruals for warranties issued 2,612 — Repairs and replacements (969) — Accrued product warranties - end of period $ 1,643 $ —

LEASES

LEASES	12 Months Ended
	Dec. 31, 2022
Leases [Abstract]
LEASES	LEASES The Company determines if an arrangement is a lease at inception and whether the arrangement is classified as an operating or finance lease. At commencement of the lease, the Company records a right-of-use (“ROU”) asset and lease liability in the consolidated balance sheets based on the present value of lease payments over the term of the arrangement. ROU assets represent the right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. As the Company’s leases do not provide an implicit rate, it uses its incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. The Company determines its incremental borrowing rate based on publicly available data for instruments with similar characteristics, including recently issued debt, as well as other factors. Contract terms may include options to extend or terminate the lease, and when the Company deems it reasonably certain that ESS will exercise that option it is included in the ROU asset and lease liability. Operating leases will reflect lease expense on a straight-line basis, while finance leases will result in the separate presentation of interest expense on the lease liability and amortization expense of the ROU asset. ROU assets related to the Company’s operating leases are included in operating lease ROU assets, while the corresponding lease liabilities are included in current and non-current operating lease liabilities on the Company’s consolidated balance sheets. ROU assets related to the Company’s finance leases are included in other non-current assets, while the corresponding lease liabilities are included in accrued and other current liabilities and other non-current liabilities The Company does not record leases with a term of 12-months or less in the consolidated balance sheets. Short-term lease costs were immaterial for the year ended December 31, 2022. The Company leases office and manufacturing space in Wilsonville, Oregon under operating leases and printers and copiers under finance leases. Each of the operating leases provides the Company an option to renew the lease for an additional 60 months which have not been included in the operating lease obligations. Operating lease costs for the year ended December 31, 2022 were $1,483 thousand. Finance lease costs for the year ended December 31, 2022 were immaterial. As of December 31, 2022, the weighted-average remaining term for the operating leases was 2.6 years and the weighted-average discount rate was 7.5%. The weighted-average remaining term for the finance lease was 4.3 years and the weighted-average discount rate was 7.5%. As of December 31, 2022, future maturities of lease liabilities are as follows (in thousands): Operating Leases Finance Leases 2023 $ 1,670 $ 30 2024 1,720 30 2025 986 30 2026 — 30 2027 — 6 Thereafter — — Total minimum lease payments $ 4,376 $ 126 Less imputed interest (420) (19) Total $ 3,956 $ 107 2021 Lease Disclosures Future minimum lease payments from the Company’s 2021 Form 10-K as filed in accordance with Leases (Topic 840) under non-cancelable operating lease agreements for the years ending December 31, are as follows (in thousands): 2022 $ 1,625 2023 1,670 2024 1,720 2025 983 Total $ 5,998 Rent expense related to operating leases recorded in accordance with Leases (Topic 840) was $1,491 thousand for the year ended December 31, 2021.
LEASES	LEASES The Company determines if an arrangement is a lease at inception and whether the arrangement is classified as an operating or finance lease. At commencement of the lease, the Company records a right-of-use (“ROU”) asset and lease liability in the consolidated balance sheets based on the present value of lease payments over the term of the arrangement. ROU assets represent the right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. As the Company’s leases do not provide an implicit rate, it uses its incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. The Company determines its incremental borrowing rate based on publicly available data for instruments with similar characteristics, including recently issued debt, as well as other factors. Contract terms may include options to extend or terminate the lease, and when the Company deems it reasonably certain that ESS will exercise that option it is included in the ROU asset and lease liability. Operating leases will reflect lease expense on a straight-line basis, while finance leases will result in the separate presentation of interest expense on the lease liability and amortization expense of the ROU asset. ROU assets related to the Company’s operating leases are included in operating lease ROU assets, while the corresponding lease liabilities are included in current and non-current operating lease liabilities on the Company’s consolidated balance sheets. ROU assets related to the Company’s finance leases are included in other non-current assets, while the corresponding lease liabilities are included in accrued and other current liabilities and other non-current liabilities The Company does not record leases with a term of 12-months or less in the consolidated balance sheets. Short-term lease costs were immaterial for the year ended December 31, 2022. The Company leases office and manufacturing space in Wilsonville, Oregon under operating leases and printers and copiers under finance leases. Each of the operating leases provides the Company an option to renew the lease for an additional 60 months which have not been included in the operating lease obligations. Operating lease costs for the year ended December 31, 2022 were $1,483 thousand. Finance lease costs for the year ended December 31, 2022 were immaterial. As of December 31, 2022, the weighted-average remaining term for the operating leases was 2.6 years and the weighted-average discount rate was 7.5%. The weighted-average remaining term for the finance lease was 4.3 years and the weighted-average discount rate was 7.5%. As of December 31, 2022, future maturities of lease liabilities are as follows (in thousands): Operating Leases Finance Leases 2023 $ 1,670 $ 30 2024 1,720 30 2025 986 30 2026 — 30 2027 — 6 Thereafter — — Total minimum lease payments $ 4,376 $ 126 Less imputed interest (420) (19) Total $ 3,956 $ 107 2021 Lease Disclosures Future minimum lease payments from the Company’s 2021 Form 10-K as filed in accordance with Leases (Topic 840) under non-cancelable operating lease agreements for the years ending December 31, are as follows (in thousands): 2022 $ 1,625 2023 1,670 2024 1,720 2025 983 Total $ 5,998 Rent expense related to operating leases recorded in accordance with Leases (Topic 840) was $1,491 thousand for the year ended December 31, 2021.

BORROWINGS

BORROWINGS	12 Months Ended
	Dec. 31, 2022
Debt Disclosure [Abstract]
BORROWINGS	BORROWINGS Borrowings consist of the following (in thousands): December 31, 2022 December 31, 2021 Total notes payable $ 1,915 $ 3,769 Less current portion of notes payable 1,600 1,900 Notes payable, non-current $ 315 $ 1,869 Notes Payable In 2018, the Company entered into a $1,000 thousand note payable with a bank that was secured by all property of the Company, except for its intellectual property. The note payable’s original maturity date was July 1, 2021. In March 2020, the Company amended the note payable and borrowed an additional $4,000 thousand. The additional $4,000 thousand borrowing changed the present value of cash flows by more than 10% and, as such, was treated as a debt extinguishment. The Company recognized a $62 thousand loss on extinguishment of debt for the year ended December 31, 2020. The Company’s notes payable to the bank were recorded at fair value as part of the extinguishment. The $4,000 thousand note payable’s original maturity date was January 1, 2023. In April 2020, the Company entered into a deferral agreement (“Deferral Agreement”) to extend the maturity date of the original $1,000 thousand note payable to September 1, 2022 and extend the maturity date of the additional $4,000 thousand note payable to January 1, 2024. The Company accounted for the Deferral Agreement as a debt modification based on an analysis of cash flows before and after the debt modification. The original $1,000 thousand note payable was fully repaid in September 2022, pursuant to the terms of the Deferral Agreement. The notes payable bear interest at 0.50% below the bank’s prime rate (7.50% on December 31, 2022). The Company makes monthly interest and principal payments on the note payable based on the schedule defined in the agreement. Annual maturities on notes payable outstanding at December 31, 2022 are as follows (in thousands): 2023 $ 1,600 2024 333 Total maturities 1,933 Less unamortized debt premium (18) Total notes payable $ 1,915 Payroll Protection Program Loan In April 2020, the Company entered into an unsecured promissory note under the Payroll Protection Program (“PPP Loan”) administered by the United States Small Business Administration. The principal amount of the PPP Loan was $936 thousand. The PPP Loan bore interest of 1.0% per annum and had a maturity date of April 20, 2022. In July 2021, the Company applied for and received forgiveness on the $936 thousand PPP Loan plus $12 thousand in accrued interest. The gain on extinguishment of debt of $948 thousand is recorded within other income (expense), net in the Company’s consolidated statements of operations and comprehensive loss for the year ended December 31, 2021. Bridge Loan In July 2021, the Company entered into a six-month $20,000 thousand bridge loan (“Bridge Loan”), maturing on the earlier of January 12, 2022 or consummation of the Business Combination, which ultimately closed on October 8, 2021. See Note 3, Business Combination . The Bridge Loan bore interest of 9%, of which 2.25% was payable monthly and 6.75% paid-in-kind (“PIK”) interest was due upon maturity. At maturity, a final payment of $1,250 thousand was due in addition to all outstanding principal and accrued interest. The Bridge Loan was paid off pursuant to the terms of the Business Combination. The Company elected the fair value option to account for the Bridge Loan, which contained embedded derivatives. The Company recorded the Bridge Loan at fair value of $20,000 thousand at issuance. Interest expense of $1,578 thousand was recognized related to the paid in-kind interest and final payment on the Bridge Loan for the year ended December 31, 2021.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES The Company, from time to time, is a party to various claims, legal actions, and complaints arising in the ordinary course of business. The Company is not aware of any legal proceedings or other claims, legal actions, or complaints through the date of issuance of these consolidated financial statements. As of December 31, 2022, and 2021, the Company had a standby letter of credit with First Republic Bank totaling $725 thousand as security for an operating lease of office and manufacturing space in Wilsonville, Oregon. As of December 31, 2022 the letter of credit was secured by a restricted certificate of deposit account totaling $75 thousand. There were no draws against the letter of credit during the years ended December 31, 2022 and 2021. On September 1, 2022, the Company executed a standby letter of credit with CitiBank, N.A., for $600 thousand as security for the performance and payment of the Company’s obligations under a customer agreement. The letter of credit is in effect until the date on which the warranty period under the agreement expires, which is anticipated to be in 2025. As of December 31, 2022, $600 thousand was pledged as collateral for the letter of credit and recorded as restricted cash, non-current. There were no draws against the letter of credit during the year ended December 31, 2022. The Company purchases materials from several suppliers and has entered into agreements with various contract manufacturers, which include cancelable and noncancelable purchase commitments. As of December 31, 2022 and 2021, total unfulfilled noncancelable purchase commitments were $21,540 thousand and $10,160 thousand, respectively. In addition, total unfulfilled cancellable purchase commitments amounted to $5,663 thousand and $10,446 thousand as of December 31, 2022, and 2021, respectively. These purchase commitments were not recorded in the consolidated financial statements.

LEGACY ESS REDEEMABLE CONVERTIB

LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK	12 Months Ended
	Dec. 31, 2022
Temporary Equity Disclosure [Abstract]
LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK	LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK All Legacy ESS redeemable convertible preferred stock classified as redeemable was converted into Legacy ESS common stock, which was subsequently exchanged for the Company’s common stock as a result of the Business Combination using the Per Share Consideration of approximately 1.47. All preferred stock amounts have been retroactively adjusted to reflect the Business Combination. Immediately prior to the completion of the Business Combination on October 8, 2021, all outstanding shares of Legacy ESS redeemable convertible preferred stock converted into an aggregate 57,104,332 shares of common stock. Legacy ESS Rights to Purchase Series C-2 Redeemable Convertible Preferred Stock Legacy ESS Series C redeemable convertible preferred stock financing agreement initially provided additional committed funding of up to $79,999 thousand, through the purchase of up to 39,971,716 shares of Series C-2 redeemable convertible preferred stock based on the completion of certain operational milestones at a predetermined price of $2.00 per share, to certain Series C-1 Investors. Legacy ESS determined that its obligation to issue, and Legacy ESS investors’ obligation to purchase shares of Series C-2 redeemable convertible preferred stock at a fixed price represents a freestanding derivative financial instrument (the “Series C-2 Redeemable Convertible Preferred Stock Issuance Right”). The Series C-2 Redeemable Convertible Preferred Stock Issuance Right was initially recorded at fair value and was adjusted to fair value at each reporting date, with the change in fair value recorded as a revaluation of derivative liabilities as a component of other income (expense), net in the consolidated statement of operations and comprehensive loss. The Series C-2 Redeemable Convertible Preferred Stock Issuance Right was initially scheduled to expire in August 2021 and was classified as a non-current derivative liability as of December 31, 2020. The Series C-2 Redeemable Convertible Preferred Stock Issuance Right was initially valued at a fair value of $11,379 thousand. Sale of Legacy ESS Series C-2 Redeemable Convertible Preferred Stock In March 2021, Legacy ESS issued 5,746,003 shares of Series C-2 redeemable convertible preferred stock for $2.00 per share, totaling $11,500 thousand. Legacy ESS incurred $39 thousand in costs associated with the issuance. In connection with the sale of the Series C-2 redeemable convertible preferred stock, Legacy ESS issued warrants to purchase 861,896 shares of Series C-2 redeemable convertible preferred stock and extinguished a portion of the Series C-2 Redeemable Convertible Preferred Stock Issuance Right for 5,746,003 shares. The warrants were exercisable at a price of $0.0001 per share. The extinguishment of a portion of the Series C-2 Redeemable Convertible Preferred Stock Issuance Right reduced Legacy ESS derivative liabilities and increased the amount attributable to the issuance by $23,152 thousand. Total transaction value of $34,613 thousand was allocated to the Series C-2 redeemable convertible preferred stock and warrants in the amounts of $29,516 thousand and $5,096 thousand, respectively. Amendment to Legacy ESS Series C-2 Redeemable Convertible Preferred Stock Issuance Right and Related Warrants On May 7, 2021, Legacy ESS amended its Series C-2 Preferred Stock Purchase Agreement and Amendment to Series C Preferred Stock Purchase Agreement. Under the terms of the amended agreement, the number of shares of Series C-2 convertible redeemable preferred stock required to be issued by Legacy ESS and purchased by investors under the Series C-2 Redeemable Convertible Preferred Stock Issuance Right were adjusted, and Legacy ESS issued Series C-2 warrants. The Series C-2 warrants were exercisable at a price of $0.00007 per share upon a successful Business Combination with STWO. The investors were permitted to purchase shares subject to the Series C-2 Redeemable Convertible Preferred Stock Issuance Right at any time and must purchase the shares upon the Company’s achievement of specific milestones. The number of shares subject to and potential proceeds from the Series C-2 Redeemable Convertible Preferred Stock Purchase Agreement and related Series C-2 warrants were as follows: As of May 7, 2021 Upon completion of the Business Combination Quantity Price Series C-2 Redeemable Convertible Preferred Stock Issuance Right 7,994,442 $ 2.00 Series C-2 Warrant exercisable upon completion of the Business Combination 21,159,364 $ 0.00007 The Series C-2 warrants and the Series C-2 Redeemable Convertible Preferred Stock Issuance Right were exercised in conjunction with the Business Combination which cl osed on October 8, 2021 and the Company received proceeds of $15,559 thousand, which were net of $439 thousand in issuance costs. The Company recorded a net increase in the derivative liability of $223,165 thousand for the year ended December 31, 2021 for changes in the estimated fair value of the Series C-2 Redeemable Convertible Preferred Stock Issuance Right and Series C-2 warrant exercisable upon completion of the Business Combination. Legacy ESS Warrants Legacy ESS Series B redeemable convertible preferred stock warrants were issued at exercise prices ranging from $0.0007 per share to $0.83 per share. 100,161 shares of Series B redeemable convertible preferred stock warrants had a ten-year exercise period and the remainder did not expire until a significant transaction had occurred, as defined by the warrant purchase agreement. The warrants were fully vested at the issuance date. Legacy ESS Series C-1 and C-2 redeemable convertible preferred stock warrants were issued with prices ranging from $0.00007 per share to $1.25 per share, a life of ten years and were fully vested at issuance. Legacy ESS common stock warrants, all issued at a price of $0.0007 per share, were recorded at fair value within equity. Legacy ESS common stock warrants were fully vested at issuance and did not expire until a significant transaction has occurred, as defined by the Warrant Purchase Agreement. In connection with the Business Combination, all Legacy ESS warrants were exercised during the year ended December 31, 2021.

COMMON STOCK WARRANTS

COMMON STOCK WARRANTS	12 Months Ended
	Dec. 31, 2022
Equity [Abstract]
COMMON STOCK WARRANTS	COMMON STOCK WARRANTS Common stock warrant balances consist of the following: December 31, 2022 December 31, 2021 Public Warrants outstanding 7,377,893 7,377,913 Private Warrants outstanding: Other Private Warrants outstanding 3,500,000 3,500,000 Earnout Warrants outstanding 583,334 583,334 Total common stock warrants 11,461,227 11,461,247 As part of STWO’s initial public offering, 8,333,287 warrants to purchase common stock listed on the New York Stock Exchange (“NYSE”) under the ticker symbol “GWH.W” (the “Public Warrants”) were sold. The Public Warrants entitle the holder thereof to purchase one share of common stock at a price of $11.50 per share, subject to adjustments. The Public Warrants may be exercised only for a whole number of shares of common stock. No fractional shares will be issued upon exercise of the warrants. The Public Warrants will expire five years after completion of the business combination, on October 8, 2026, or earlier upon redemption or liquidation. The Company may call the Public Warrants for redemption starting anytime, in whole and not in part, at a price of $0.01 per warrant, so long as the Company provides not less than 30 days prior written notice of redemption to each warrant holder, and if, and only if, the reported last sale price of common stock equals or exceeds $18.00 per share or $10.00 per share for any 20 trading days within a 30-trading day period ending on the third trading day prior to the date the Company sends the notice of redemption to the warrant holders provided there is an effective registration statement covering the shares of common stock issuable upon exercise of the warrants. The Company may call the Public Warrants for redemption starting anytime, in whole and not in part, at a price of $0.10 per warrant, so long as the Company provides not less than 30 days prior written notice of redemption to each warrant holder; provided that holders will be able to exercise their warrants on a cashless basis prior to redemption and receive a number of shares determined based on the redemption date fair market value of the shares, and if, and only if, the reported last sale price of common stock equals or exceeds $10.00 per share or $10.00 per share for any 20 trading days within a 30-trading day period ending on the third trading day prior to the date the Company sends the notice of redemption to the warrant holders provided there is an effective registration statement covering the shares of common stock issuable upon exercise of the warrants. Simultaneously with STWO’s initial public offering, STWO issued in a private placement 4,666,667 warrants to purchase common stock (the “Private Warrants”) to STWO’s sponsor. In connection with the Business Combination, STWO’s sponsor agreed to forfeit 583,333 Private Warrants. Of the remaining 4,083,334 Private Warrants, 3,500,000 were immediately vested and 583,334 warrants (the “Earnout Warrants”) were vested upon meeting certain Earnout Milestone Events on November 9, 2021. Each Private Warrant and Earnout Warrant is exercisable for one share of common stock at a price of $11.50 per share, subject to adjustment. The Private Warrants and Earnout Warrants, post vesting on November 9, 2021, are identical to the Public Warrants, except that the Private Warrants and Earnout Warrants and the shares of common stock issuable upon exercise of the Private Warrants are not transferable, assignable or salable until 30 days after the completion of a Business Combination, subject to certain limited exceptions. Additionally, the Private Warrants and Earnout Warrants are non-redeemable so long as they are held by the initial purchasers or such purchasers’ permitted transferees. If the Private Warrants and Earnout Warrants are held by someone other than their initial purchasers or their permitted transferees, then the Private Warrants and Earnout Warrants will be redeemable by the Company and exercisable by such holders on the same basis as the Public Warrants. Additionally, if the Company redeems the Public Warrants when the common stock equals or exceeds $10.00 per share for any 20 trading days within a 30-day period ending on the third trading day prior to the date the Company sends the notice of redemption to warrant holders and the closing price of the common share for any 20 trading days within the same period is less than $18.00 per share, the Company must concurrently redeem the Private Warrants and Earnout Warrants. The table below shows the common stock warrant activities during the year ended December 31, 2022: December 31, 2021 Issued Exercised December 31, 2022 Earnout Warrants 583,334 — — 583,334 Public Warrants 7,377,913 — 20 7,377,893 Private Warrants (excluding Earnout Warrants) 3,500,000 — — 3,500,000 Total common stock warrants 11,461,247 — 20 11,461,227 The table below shows the common stock warrant activities during the year ended December 31, 2021: December 31, 2020 Issued Exercised December 31, 2021 Earnout Warrants — 583,334 — 583,334 Public Warrants — 8,333,287 955,374 7,377,913 Private Warrants (excluding Earnout Warrants) — 3,500,000 — 3,500,000 Total common stock warrants — 12,416,621 955,374 11,461,247 The Company’s common stock warrants were initially recorded at fair value upon completion of the Business Combination and are adjusted to fair value at each reporting date based on the market price of the Public Warrants, with the change in fair value recorded as a component of other income and expense in the consolidated statements of operations. For the year ending December 31, 2022, the Company recorded a net decrease to the liabilities for Earnout Warrants, Public Warrants and Private Warrants (excluding Earnout Warrants) of $1,313 thousand, $16,600 thousand and $7,875 thousand, respectively. For the year ending December 31, 2021, the Company recorded a net increase to the liabilities for Earnout Warrants, Public Warrants and Private Warrants (Excluding Earnout Warrants) of $974 thousand, $14,476 thousand and $5,355 thousand, respectively. SMUD Warrant On September 16, 2022, the Company entered into a warrant agreement with the Sacramento Municipal Utility District (“SMUD”), whereby the Company agreed to issue a warrant for up to 500,000 shares of the Company’s common stock at an exercise price of $4.296 per share. The vesting of the shares underlying the warrant will be subject to the achievement of certain commercial milestones through December 31, 2030 pursuant to a related commercial agreement. As of December 31, 2022, vesting conditions had been met for 12,500 of the shares.

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	12 Months Ended
	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION Stock-based compensation expense is allocated on a departmental basis based on the classification of the award holder. The following table presents the amount of stock-based compensation related to stock-based awards to employees on the Company’s consolidated statements of operations and comprehensive loss during the years ended December 31, 2022 and 2021 (in thousands): 2022 2021 Research and development $ 2,856 $ 2,233 Sales and marketing 456 213 General and administrative 8,577 5,476 Total stock-based compensation $ 11,889 $ 7,922 2021 Equity Incentive Plan In October 2021, the Board of Directors of the Company adopted the ESS Tech, Inc. 2021 Equity Incentive Plan (the “2021 Plan”). The 2021 Plan became effective upon consummation of the Business Combination. The stock awards may be issued as Incentive Stock Options (“ISO”), Non-statutory Stock Options (“NSO”), Stock Appreciation Rights, Restricted Stock Awards, or Restricted Stock Unit Awards. Only employees are eligible to receive ISO awards. Employees, directors, and consultants who are providing continuous service to the Company are eligible to receive stock awards other than ISOs. The number of shares available for issuance under the 2021 Plan will be increased on the first day of each fiscal year beginning with the 2022 fiscal year and ending with the 2031 fiscal year, in an amount equal to the lesser of (i) 15,260,000 Shares, (ii) five percent (5%) of the outstanding shares on the last day of the immediately preceding fiscal year, or (iii) such number of shares determined by the Company no later than the last day of the immediately preceding fiscal year. As of January 1, 2023, the number of shares available for issuance under the 2021 Plan was increased by 4,614,640 shares in accordance with the plan and as approved by the Board. Under the 2021 Plan, the Company is authorized to issue 17,610,000 shares of common stock as of December 31, 2022. Option prices for incentive stock options are set at the fair market value of the Company’s common stock at the date of grant. The fair market value of RSUs is set at the closing sales price of the Company’s common stock at the date of grant. Employee new hire grants generally cliff vest at the end of the first year and then 1/48 th of the original grant over the remaining three years. Grants expire 10 years from the date of grant. As of December 31, 2022, there were 10,626,299 shares available for future grant under the 2021 Plan. Stock Options and Restricted Stock Units Stock option and RSU activity, prices, and values during the years ended December 31, 2022 and 2021 are as follows (in thousands, except for share, per share, and contractual term data): Options Outstanding RSUs Number of Weighted Weighted Aggregate Number of plan shares outstanding Weighted average Balances at December 31, 2020 5,732,422 $ 0.30 8.23 $ 4,333 — $ — Options and RSUs granted 1,454,549 1.75 3,392,153 10.69 Options exercised and RSUs released (2,496,070) 0.27 — — Options and RSUs forfeited (894,371) 0.46 — — Balances as of December 31, 2021 3,796,530 $ 0.83 8.08 $ 40,274 3,392,153 $ 10.69 Options and RSUs granted 65,717 8.00 5,602,206 4.68 Options exercised and RSUs released (529,832) 4.28 (1,526,784) 8.02 Options and RSUs forfeited (109,306) 2.53 (1,120,620) 10.46 Balances as of December 31, 2022 3,223,109 $ 1.01 7.39 $ 4,583 6,346,955 $ 6.10 Options vested and exercisable - December 31, 2021 1,827,374 $ 0.31 7.20 $ 20,337 Options vested and exercisable - December 31, 2022 1,947,123 $ 0.76 7.06 $ 3,244 The aggregate intrinsic value is the fair market value on the reporting date less the exercise price for each option. The aggregate intrinsic value of the options exercised was $2,107 thousand and $6,244 thousand during the years ended December 31, 2022 and 2021, respectively. The fair value of each stock option award is estimated on the date of the grant using the Black-Scholes Merton option-pricing model. For options granted during the years ended December 31, 2022 and 2021, respectively, the weighted average estimated fair value using the Black-Scholes Merton option pricing model was $5.23 and $5.63 per option, respectively. In accordance with ASC 718, the fair value of each option grant has been estimated as of the date of grant using the following weighted average assumptions: 2022 2021 Risk-free rate 1.64 % 1.01 % Expected volatility 73.95 % 75.14 % Expected term 6 years 6 years Expected dividends — — As of December 31, 2022, there was approximately $28,129 thousand of unamortized stock-based compensation cost related to unvested stock options and RSUs, which was expected to be recognized over a weighted average period of 2.81 years. Employee Stock Purchase Plan In May 2022, the Company commenced its first offering period under the ESS Tech, Inc. Employee Stock Purchase Plan (the “ESPP”), which assists employees in acquiring a stock ownership interest in the Company. The ESPP permits eligible employees to purchase common stock at a discount through payroll deductions during specified offering periods. No employee may purchase more than $25,000 worth of stock in any calendar year. The price of shares purchased under the ESPP is equal to 85% of the fair market value of the common stock on the first or last day of the offering period, whichever is lower. The total ESPP expense for the year ended December 31, 2022 was $270 thousand.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2022
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS The Company follows ASC 820, which establishes a common definition of fair value to be applied when U.S. GAAP requires the use of fair value, establishes a framework for measuring fair value, and requires certain disclosure about such fair value measurements. The following table presents the Company’s fair value hierarchy for its financial assets and liabilities measured at fair value on a recurring basis (in thousands): December 31, 2022 Total Assets at Fair Value Cash Equivalents and Restricted Cash Short-Term Investments Level 1: Money market funds $ 27,993 $ 27,993 $ — U.S. Treasury securities 19,944 — 19,944 Total Level 1 47,937 27,993 19,944 Level 2: Certificate of deposit 75 75 — U.S. agency securities 55,319 — 55,319 Commercial paper 35,756 5,972 29,784 Total Level 2 91,150 6,047 85,103 Total assets measured at fair value $ 139,087 $ 34,040 $ 105,047 December 31, 2021 Total Assets at Fair Value Cash Equivalents and Restricted Cash Short-Term Investments Level 1: Money market funds $ 237,897 $ 237,897 $ — Level 2: Certificate of deposit 125 125 — Total assets measured at fair value $ 238,022 $ 238,022 $ — The following tables present the Company’s fair value hierarchy for its financial liabilities measured at fair value on a recurring basis (in thousands): December 31, 2022 Level 1 Level 2 Level 3 Total Liabilities: Earnout warrant liabilities $ — $ 163 $ — $ 163 Public common stock warrants 2,066 — — 2,066 Private common stock warrants — 980 — 980 Total liabilities measured at fair value $ 2,066 $ 1,143 $ — $ 3,209 December 31, 2021 Level 1 Level 2 Level 3 Total Liabilities: Earnout warrant liabilities $ — $ 1,476 $ — $ 1,476 Public common stock warrants 18,666 — — 18,666 Private common stock warrants — 8,855 — 8,855 Total liabilities measured at fair value $ 18,666 $ 10,331 $ — $ 28,997 There were no transfers among Level 1, Level 2, or Level 3 categories during the periods presented. The carrying amounts of the Company’s notes payable and accounts payable approximate their fair values due to their short maturities. Level 1 Assets: The Company invests in money market funds and U.S. Treasury securities that have maturities of 90 days or less. These assets are valued using observable inputs that reflect quoted prices for securities with identical characteristics. Level 2 Assets: The Company invests in a certificate of deposit, U.S. agency securities, and commercial paper. These assets are valued using observable inputs that reflect quoted prices for securities with similar characteristics and other observable inputs (such as interest rates that are observable at commonly quoted intervals). Level 1 Liabilities: The Company values its public common stock warrants based on the market price of the warrants. Level 2 Liabilities: The Company values its earnout warrant liabilities and private common stock warrants based on the market price of the Company’s public common stock warrants. Level 3 Liabilities: The Company values the following as Level 3 liabilities: Bridge Loan The Company accounted for the Bridge Loan under the fair value option election wherein the Bridge Loan was initially measured at its issue-date fair value and then subsequently re-measured at estimated fair value on a recurring basis at each reporting date. As a result of applying the fair value option, direct costs and fees related to the Bridge Loan were expensed as incurred. The fair value of the Bridge Loan was based on significant inputs including, estimated time to maturity, which causes them to be classified as a Level 3 measurement within the fair value hierarchy. The valuation used assumptions and estimates the Company believed would be made by a market participant in making the same valuation. The Bridge Loan was repaid on October 8, 2021 as part of the Business Combination. See Note 10, Borrowings for further details. Legacy ESS Warrants Freestanding warrants to purchase redeemable convertible preferred stock were accounted for as liability awards and recorded at fair value on their initial issuance date and adjusted to fair value at each reporting date, with the change in fair value being recorded in the consolidated statements of operations and other comprehensive loss. The warrants were accounted for as liabilities as the underlying preferred shares were contingently redeemable upon occurrence of a change in control, which was outside the control of the Company. The Company measured its warrant liabilities using Level 3 unobservable inputs within the Black-Scholes Merton option-pricing model. The Company used various key assumptions, such as the fair value of redeemable convertible preferred stock Series B and Series C, the volatility of peer companies’ stock prices, the risk-free interest rate based on the U.S. treasury yield, and the expected term (based on remaining term to a significant event). The Company measured the fair value of the redeemable convertible preferred stock warrants at each reporting date, with subsequent gains and losses from remeasurement of Level 3 financial liabilities recorded through other expense, net in the consolidated statements of operations and comprehensive loss. In connection with the Business Combination, all Legacy ESS warrants were exercised during the year ended December 31, 2021. Rights to Purchase Legacy ESS Series C-2 Redeemable Convertible Preferred Stock Legacy ESS Series C Preferred Stock Purchase Agreement initially provided additional committed funding of up to $79,999 thousand, through the purchase of up to 39,971,716 shares of Series C-2 redeemable convertible preferred stock based on the completion of certain operational milestones at a predetermined price of $2.00 per share, to certain Series C-1 Investors. This commitment was called the Series C-2 Redeemable Convertible Preferred Stock Issuance Right, see Note 12, Legacy ESS Redeemable Convertible Preferred Stock . The value of the Series C-2 Redeemable Convertible Preferred Stock Issuance Right was determined based on significant inputs not observable in the market, which represented a Level 3 measurement within the fair value hierarchy. The Company utilized a probability weighting of successful completion of the Business Combination versus probability of the Company staying private in establishing the quantity of purchase rights to value and the fair value of the Series C-2 Redeemable Convertible Preferred Stock Issuance Right. The fair value of the Series C-2 Redeemable Convertible Preferred Stock Issuance Right was determined using a discounted cash flow model, which took into account the estimated value of Series C-2 stock, estimated time to purchase, probability of purchase and the risk-free interest rate based on the U.S. treasury yield. The Company measured the fair value of the Series C-2 Redeemable Convertible Preferred Stock Issuance Right at each reporting date, with subsequent gains and losses from remeasurement of Level 3 financial liabilities recorded through other expense, net in the consolidated statements of operations and comprehensive loss. The Company included the valuation of the related Series C-2 warrants that were only exercisable upon completion of the Business Combination with the valuation of the Series C-2 Redeemable Convertible Preferred Stock Issuance Right. The following table sets forth a summary of changes in the fair value of the Company’s Level 3 liabilities at fair value on a recurring basis for the years ended December 31, 2022 and 2021 (in thousands): 2022 2021 Bridge loan: Beginning balance January 1 $ — $ — Fair value of Bridge loan funded — 20,000 Accrued interest — 1,578 Change in fair value — — Repayment of loan principal and interest — (21,578) Ending balance December 31 — — Legacy ESS Warrant liabilities: Beginning balance January 1 — 3,329 Change in fair value — 17,753 Fair value of warrants issued — 5,096 Fair value of warrants exercised — (26,178) Ending balance December 31 — — Series C-2 Redeemable Convertible Preferred Stock Issuance Right liability: Beginning balance January 1 — 22,911 Change in fair value — 223,165 Fair value of derivatives extinguished — (23,152) Fair value of Series C-2 Redeemable Convertible Preferred Stock Issuance Right exercised — (222,924) Ending balance December 31 — — Total $ — $ —

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. The significant components of deferred tax assets and liabilities are as follows (in thousands): As of December 31, 2022 2021 Deferred tax assets: Net operating losses $ 34,454 $ 24,655 Tax credit carryforward 909 292 Equity compensation 737 1,143 Capitalized research and development expenses 16,946 — Other 2,153 1,231 Total deferred tax assets 55,199 27,321 Valuation allowance (54,261) (27,321) Deferred tax assets, net of valuation allowance 938 — Deferred tax liabilities: Right-of-use assets (938) — Net deferred tax $ — $ — The Tax Cuts and Jobs Act (the “Act”) was enacted on December 22, 2017. Included in the Act is the requirement to capitalize and amortize research and development expenditures beginning in 2022. Prior to 2022, the Company had been expensing these costs as incurred for tax purposes. The capitalization of the research and development expenditures resulted in a new deferred tax asset of $16,946 thousand, which was offset by a valuation allowance, resulting in no significant impact to income tax expense for the year ending December 31, 2022. ASC 740 requires that the tax benefit of net operating losses, temporary differences and credit carryforwards be recorded as an asset to the extent that management assesses that realization is “more likely than not.” Realization of the future tax benefits is dependent on the Company’s ability to generate sufficient taxable income within the carryforward period. Because of the Company’s history of operating losses, management believes that recognition of the deferred tax assets arising from the above-mentioned future tax benefits is currently not likely and, accordingly, has provided a valuation allowance for fiscal years 2022 and 2021. The valuation allowance increased by $26,940 thousand during the year ended December 31, 2022. As of December 31, 2022, the Company has federal and state net operating loss carryforwards of $130,708 thousand and $130,578 thousand, respectively. Federal net operating losses generated prior to 2018 will start to expire in 2032. Federal net operating losses generated after 2017 do not expire. The state net operating losses will begin to expire in 2027. The Company also has federal and state research and development tax credit carryforwards totaling $1,795 thousand and $28 thousand, respectively. The federal research and development credit carryforwards begin to expire in 2039, unless previously utilized. The state research and development credit carryforwards do not expire. The effective tax rate of the Company’s provision for income taxes differs from the federal statutory rate as follows: Years Ended December 31, 2022 2021 Federal statutory tax rate 21.0 % 21.0 % State tax, net of federal tax benefit 7.2 0.6 Stock compensation (0.2) 0.0 Non-deductible officer compensation (1.4) (0.1) Transaction costs related to the Business Combination — (0.2) Warrant liabilities revaluation 6.6 (1.7) Derivative liabilities revaluation — (9.8) Earnout Shares liabilities revaluation 0.4 (6.8) Permanent differences 0.1 0.0 R&D tax credits 0.8 0.0 Other 0.1 0.1 Valuation allowance (34.6) (3.1) Effective tax rate — % — % The changes in the Company's uncertain tax positions are summarized as follows (in thousands): Balance as of December 31, 2020 $ 47 Additions in 2021 245 Balance as of December 31, 2021 292 Additions in 2022 613 Balance as of December 31, 2022 $ 905 During the years ended December 31, 2022 and 2021, the Company recognized uncertain tax positions of $613 thousand and $245 thousand, respectively, related to a reduction of the research and development credit deferred tax asset. Unrecognized tax benefits may change during the next twelve months for items that arise in the ordinary course of business. The Company does not expect a material change to its unrecognized tax benefits over the next twelve months that would have an adverse effect on its operating results. The Company recognizes interest and penalties accrued on any unrecognized tax benefits as a component of income tax expense. The Company had no accrued interest or penalties related to uncertain tax positions as of 2022 and 2021. The Company files federal and certain state income tax returns, which provide varying statutes of limitations on assessments. However, because of net operating loss carryforwards, substantially all tax years since inception remain open to federal and state tax examination.

REVENUE

REVENUE	12 Months Ended
	Dec. 31, 2022
Revenue from Contract with Customer [Abstract]
REVENUE	REVENUE Disaggregated Revenue The following table presents the Company’s revenue, disaggregated by source (in thousands): Year Ended December 31, 2022 2021 Product revenue $ 803 $ — Service and other revenue 91 — Total revenue $ 894 $ — The majority of the Company’s revenue is derived from the product sales of energy storage systems. See Note 2, Significant Accounting Policies for further information regarding revenue recognition. Contract Balances Deferred revenues primarily relate to consideration received from customers in advance of the Company satisfying performance obligations under contractual arrangements. Contract balances are reported in a net contract asset or deferred revenue liability position on a contract-by-contract basis at the end of each reporting period. The following table summarizes deferred revenue activity (in thousands): Year Ended December 31, 2022 2021 Deferred revenue - beginning of period $ 3,663 2,258 Deferral of revenue 7,704 1,405 Recognition of previously unearned revenue (830) — Deposits returned to customers (1,157) — Reclassification to accrued liabilities due to estimation of variable consideration (770) — Deferred revenue - ending of period $ 8,610 $ 3,663

DEFINED CONTRIBUTION PLAN

DEFINED CONTRIBUTION PLAN	12 Months Ended
	Dec. 31, 2022
Retirement Benefits [Abstract]
DEFINED CONTRIBUTION PLAN	DEFINED CONTRIBUTION PLANThe Company has a 401(k) plan to provide defined contribution retirement benefits for all employees who have completed six months of service. Employees may elect to contribute a portion of their pretax compensation to the 401(k) plan, subject to annual limitations. The Company may make profit-sharing contributions at the discretion of the Board of Directors. Employee contributions are always fully vested. For the years ended December 31, 2022 and 2021, the Company contributed $674 thousand and $292 thousand, respectively.

RELATED PARTY TRANSACTIONS

RELATED PARTY TRANSACTIONS	12 Months Ended
	Dec. 31, 2022
Related Party Transactions [Abstract]
RELATED PARTY TRANSACTIONS	RELATED PARTY TRANSACTIONS In April 2021, the Company signed a framework agreement with one of its investors, SB Energy Global Holdings One Ltd (“SBE”), to supply energy storage products to SBE in support of its market activities. Under this agreement, the Company has made various commitments to meet SBE’s potential need for energy storage products and is obligated to reserve a certain percentage of manufacturing capacity to meet SBE’s future needs, subject to periodic reviews of its firm and anticipated orders. To date, no orders have been placed under the framework agreement. Additionally, the Company entered into a preferred financing equity transaction with SBE and Breakthrough Energy Ventures, LLC as discussed in Note 12, Legacy ESS Redeemable Convertible Preferred Stock . These related parties were also issued 6,707,318 of the Earnout Shares discussed in Note 3, Business Combination . As of December 31, 2021, the Company had recorded accounts receivable of $66 thousand and deferred revenue of $171 thousand for sales of energy storage systems to related parties. During the year ended December 31, 2022, the Company recognized revenue of $284 for sales of energy storage systems and extended warranty services to related parties. As of December 31, 2022, the Company had recorded deferred revenue of $5 thousand for sales of extended warranty services to related parties.

SIGNIFICANT ACCOUNTING POLICI_2

SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation —The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiary and have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). Pursuant to the Merger Agreement, the merger between Merger Sub and Legacy ESS was accounted for as a reverse recapitalization in accordance with U.S. GAAP (the “Reverse Recapitalization”). Under this method of accounting, STWO was treated as the “acquired” company and Legacy ESS was treated as the acquirer for financial reporting purposes. Accordingly, for accounting purposes, the Reverse Recapitalization was treated as the equivalent of Legacy ESS issuing stock for the net assets of STWO, accompanied by a recapitalization. The net assets of STWO were stated at historical cost, with no goodwill or other intangible assets recorded. Legacy ESS was determined to be the accounting acquirer based on the following predominant factors: • Legacy ESS existing stockholders had the greatest voting interest in the Company; • Legacy ESS directors represented all of the new board of directors of the Company; • Legacy ESS senior management continued as the senior management of the Company; and, • Legacy ESS had the larger employee base.
Risks and Uncertainties	Risks and Uncertainties —The Company is subject to a number of risks associated with companies of similar size in its industry, including, but not limited to, the need for successful development of products, the need for additional capital and financing to fund operations, competition from substitute products and services from larger companies, legal protection of proprietary technology, patent litigation, dependence on key individuals, and risks associated with changes in information technology. COVID-19 presents material uncertainty and risk with respect to the Company, its performance, and its financial results and could adversely affect the Company’s financial position and results.
Segment Information	Segment Information —The Company has determined that its Chief Executive Officer (“CEO”) is its chief operating decision maker. The CEO reviews financial information for purposes of assessing performance and making decisions on how to allocate resources. The Company has determined that it operates in a single reportable segment.
Use of Estimates	Use of Estimates—The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and disclosure of commitments and contingencies as of the date of the financial statements and the reported amounts of expenses during the reporting periods. Such estimates relate to, among others, the useful lives and assessment of recoverability of property and equipment, deferred tax assets valuation, determination of the fair value of the Company’s investments, Bridge Loan, warrant liabilities, Series C-2 Redeemable Convertible Preferred Stock Issuance Right, earnout liabilities, earnout warrant liabilities, public warrants, private warrants, and determination of variable consideration, standalone selling price, product warranty liabilities, as well as other accruals. These estimates are based on historical trends, market pricing, current events and other relevant assumptions and data points. Actual results could differ from those estimates and such differences may be material to the financial statements.
Concentration of Credit Risk	Concentration of Credit Risk —Financial instruments that potentially subject the Company to concentration of credit risk consist of cash and cash equivalents and restricted cash. The Company’s cash and cash equivalents include cash in bank accounts, money market funds, and investments with a maturity of three months or less at the date of purchase. The Company’s restricted cash includes a certificate of deposit, collateral associated with a standby letter of credit, and a performance and payment bond. Deposits held with banks may exceed the amount of insurance provided on such deposits.
Reclassifications	Reclassifications —Certain prior year amounts have been reclassified to conform with current year presentation. These reclassifications had no effect on the reported results of operations.
Net Loss Per Share	Net Loss Per Share —The Company will use the two-class method when computing net loss per common share when shares are issued that meet the definition of participating securities. Under this method, net earnings are reduced by the amount of dividends declared in the current period for common stockholders and participating security holders. The remaining earnings or “undistributed earnings” are allocated between common stock and participating securities to the extent that each security may share in earnings as if all the earnings for the period had been distributed. Once calculated, the earnings per common share is computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding during each year presented. Diluted loss attributable to common stockholders per common share has been computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding plus the dilutive effect of outstanding options, warrants, and restricted stock units (“RSUs”) during the respective periods. In cases where the Company has a net loss, no dilutive effect is shown as options, warrants, and RSUs become anti-dilutive.
Cash and Cash Equivalents	Cash and Cash Equivalents—Cash and cash equivalents include cash in bank accounts, money market funds, and investments with a maturity of three months or less at the date of purchase. Cash equivalents are recorded at carrying value, which approximates fair value.
Restricted Cash	Restricted Cash — Restricted cash is required as collateral for certain of the Company’s lease agreements and contractual supply and service arrangements. Restricted cash includes a certificate of deposit for the Company’s lease agreements, collateral associated with a standby letter of credit issued to a customer, and a performance and payment bond for the Company’s supply and service arrangements. The certificate of deposit and bond are recorded at carrying value, which approximates fair value. Restricted cash amounts are reported in the consolidated balance sheets as current or non-current depending on when the cash will be contractually released.
Accounts Receivable, Net	Accounts Receivable, Net —The Company evaluates the creditworthiness of its customers. If the collection of any specific receivable is doubtful, an allowance is recorded in the allowance for doubtful accounts which is included in accounts receivable, net in the consolidated balance sheets. The Company had no allowance for doubtful accounts recorded at either December 31, 2022 or 2021.
Property and Equipment, Net	Property and Equipment, Net —Property and equipment are stated at cost, net of depreciation. Depreciation is provided using the straight-line method over the estimated useful lives of the assets, which range from three
Investments	Investments —Investments consist primarily of U.S. Treasury securities, U.S. agency securities, and commercial paper and are classified as trading securities as they are bought and held principally for the purpose of selling them in the near term. Trading securities are carried on the consolidated balance sheets at fair value. Unrealized gains and losses on trading securities are included in other income (expense), net in the consolidated statements of operations and comprehensive loss. For trading securities still held at the reporting date, the Company recorded net losses of $45 thousand and zero for the years ended December 31, 2022 and 2021, respectively.
Revenue Recognition	Revenue Recognition —Revenue is earned from the sale, installation and commissioning of energy storage systems and is derived from customer contracts. Revenue is recognized in an amount that reflects the consideration to which the Company expects to be entitled in exchange for transferring the promised goods and/or services to the customer, when or as the Company’s performance obligations are satisfied, which includes estimates for variable consideration (e.g., liquidated damages). For sales of energy storage systems, the Company’s performance obligations are satisfied at the point in time when the customer obtains control of the system. Revenue recognition is deferred until written customer acceptance has been received, after site acceptance testing, or until the Company has established a history of successfully obtaining customer acceptance. In the near term, as the Company’s products are newly developed, this is likely to be a longer process than when the products are mature and the Company has an established history of customer acceptance. No right of return exists on sales of energy storage systems. Performance obligations for services, including the optional Ironclad Services Plan (“ISP”) extended warranty and ongoing operations and maintenance program provided to customers, are satisfied over time as the respective services are performed. The transaction price of the underlying customer agreement is allocated to each performance obligation based on its relative standalone selling price. When the standalone selling price is not directly observable, revenue is determined based on an estimate of selling price using the observable market price that the good or service sells for separately in similar circumstances and to similar customers, and/or an expected cost plus margin approach when the observable selling price of a good or services is not known and is either highly variable or uncertain. Costs to obtain a contract relate primarily to commissions paid to the Company’s sales personnel related to the sale of energy storage systems. The Company expenses costs associated with obtaining new contracts as incurred if the amortization period of the asset recognized by the Company is one year or less. The Company invoices customers in accordance with customer agreements and in advance of recognizing revenue as the Company has not satisfied certain performance obligations that transfer control to the customer. Payment terms generally include advance payments to reserve capacity and/or upon issuance of the customer’s purchase order with the remainder due upon the achievement of various milestones including but not limited to shipment readiness, delivery, commissioning of the system, and completion of final site testing. Advanced customer payments and unsatisfied performance obligations are recognized as deferred revenue in the consolidated balance sheets. Sales tax collected from customers is recorded on a net basis and therefore, not included in revenue. Sales tax is recorded as a liability until remitted to governmental authorities. Shipping and handling, freight costs and other reimbursable costs are accounted for as fulfillment activities and included in revenue. Related costs are included in research and development expenses while the Company is in the research and development phase.
Product Warranties	Product Warranties —Warranty obligations are incurred in connection with the sale of the Company’s products. The Company generally provides a standard warranty for a period of one year and an extended warranty through the optional ISP. The standard warranty is accounted for as an assurance-type warranty, which provides customers with assurance that the product complies with agreed-upon specifications and does not represent a separate performance obligation. The ISP warranty is considered a service-type warranty which is a distinct service and a portion of the transaction price is allocated to that performance obligation. Costs to provide for standard warranty obligations are estimated and recorded as a liability at the time revenue is recognized on the sale of the energy storage system. Warranty reserves include management’s best estimate of the projected costs to repair or to replace any items under warranty, which is based on various factors, including the use of actual claim data to date. Adjustments to warranty reserves are recorded to research and development expenses while the Company is in the research and development phase.
Sales and Marketing	Sales and Marketing —Sales and marketing expenses consist primarily of salaries, benefits and stock-based compensation for marketing and sales personnel and related support teams. To a lesser extent, sales and marketing expenses also include professional services costs, travel costs, and trade show sponsorships and participation. Advertising costs are expensed as incurred. The Company incurred advertising costs of $173 thousand and $45 thousand for the years ended December 31, 2022 and 2021, respectively.
Research and Development	Research and Development —The Company continues to be in the research and development phase. Research and development costs are expensed as incurred and consist primarily of direct product development material costs, including freight charges, and product development personnel-related expenses, warranty-related costs, depreciation charges, overhead related costs, consulting services, and other direct expenses. Personnel-related expenses consist of salaries, benefits and stock-based compensation. The Company receives funding from federal agencies for research and development activities related to its products. Under certain circumstances, up to the entire amount of funding may need to be repaid to the grantor in the form of a success fee in future periods if the Company monetized the results of the activities funded by the grantor. The portion of such funding the Company may be required to pay in certain circumstances is recorded in accrued and other current liabilities in the consolidated balance sheets and was $452 thousand as of December 31, 2022 and 2021.
General and Administrative	General and Administrative —General and administrative expenses consist of personnel-related expenses for the Company’s corporate, executive, finance, legal, and other administrative functions, as well as expenses for outside professional services and insurance costs. Personnel-related expenses consist of salaries, benefits and stock-based compensation. To a lesser extent, general and administrative expenses include depreciation and other allocated costs, such as facility-related expenses and supplies.
Stock-Based Compensation	Stock-Based Compensation —The Company accounts for stock-based compensation in accordance with ASC 718, Compensation – Stock Compensation (“ASC 718”) . The Company measures and recognizes compensation expense for all stock-based awards based on estimated fair values on the date of the grant, recognized over the requisite service period. For awards that vest solely based on a service condition, the Company recognizes stock-based compensation expense on a straight-line basis over the requisite service period. The compensation expense related to awards with performance conditions is recognized over the requisite service period when the performance conditions are probable of being achieved. The compensation expense related to awards with market conditions is recognized on an accelerated attribution basis over the requisite service period identified as the derived service period over which the market conditions are expected to be achieved, and is not reversed if the market condition is not satisfied. The Company accounts for forfeitures as they occur. Stock-based awards granted to employees are primarily stock options and RSUs. The fair value of each stock option granted is estimated using the Black-Scholes Merton option-pricing model using the single-option award approach. The following assumptions are used in the Black-Scholes Merton option-pricing model: Risk-Free Interest Rate —The risk-free interest rate is based on the implied yield available on the date of grant on U.S. Treasury zero-coupon issued with a term that is equal to the option’s expected term at the grant date. Expected Volatility —The Company estimates the volatility for option grants by evaluating the average historical volatility of a peer group of companies for the period immediately preceding the option grant for a term that is approximately equal to the option’s expected term. Expected Term —The expected term for employees represents the period over which options granted are expected to be outstanding using the simplified method, as the Company’s historical share option exercise experience does not provide a reasonable basis upon which to estimate the expected term. The simplified method deems the term to be the average of the time-to-vesting and contractual life of the stock-based awards.
Income Taxes	Income Taxes —The Company accounts for income taxes under the asset and liability method. Under this method, deferred taxes are determined based on the temporary differences between the financial statement and tax bases of assets and liabilities using tax rates expected to be in effect during the years in which the bases differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in the consolidated statement of operations and comprehensive loss in the period that includes the enactment date. The Company provides for a valuation allowance when it is more likely than not that some portion of, or all of the Company’s deferred tax assets will not be realized. In making such determination, the Company considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. As of December 31, 2022 and 2021, the Company has recorded a full valuation allowance against its deferred tax assets. ASC 740, Accounting for Income Taxes (“ASC 740”), requires that the tax benefit of net operating losses, temporary differences and credit carryforwards be recorded as an asset to the extent that management assesses that realization is “more likely than not.” Realization of the future tax benefits is dependent on the Company’s ability to generate sufficient taxable income within the carryforward period. Because of the Company’s history of operating losses, management believes that recognition of the deferred tax assets arising from the above-mentioned future tax benefits is currently not likely and, accordingly, has provided a full valuation allowance for these tax benefits for the years ended December 31, 2022 and 2021. The Company recognizes accrued interest and penalties related to unrecognized tax benefits as a component of income tax expense. No amounts were accrued for the payment of interest and penalties as of December 31, 2022 and 2021 as the Company is currently not aware of any issues under review that could result in significant payments, accruals, or material deviation from its position.
Fair Value	Fair Value —The Company follows ASC 820, Fair Value Measurements (“ASC 820”) , which establishes a common definition of fair value to be applied when U.S. GAAP requires the use of fair value, establishes a framework for measuring fair value, and requires certain disclosure about such fair value measurements. ASC 820 establishes a hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that observable inputs be used when available. Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about what market participants would use in pricing the asset or liability based on the best information available in the circumstances. The hierarchy is broken down into three levels based on the reliability of inputs as follows: Level 1: Observable inputs such as quoted prices in active markets for identical assets or liabilities to which the Company has access at a measurement date. Level 2: Observable inputs other than Level 1 quoted prices that are observable for the asset or liability, either directly or indirectly; these include quoted prices for similar assets or liabilities in an active market, quoted prices for identical assets and liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3: Unobservable inputs for which little or no market data exists and for which the Company must develop its own assumptions regarding the assumptions that market participants would use in pricing the asset or liability, including assumptions regarding risk. Because of the uncertainties inherent in the valuation of assets or liabilities for which there are no observable inputs, those estimated fair values may differ significantly from the values that may have been used had a ready market for the assets or liabilities existed.
Recent Accounting Pronouncements and Recently Adopted Accounting Pronouncements	Recent Accounting Pronouncements —Pursuant to the Jumpstart Our Business Startups Act (“JOBS Act”), an emerging growth company is provided the option to adopt new or revised accounting standards that may be issued by the FASB or the SEC either (i) within the same periods as those otherwise applicable to non-emerging growth companies or (ii) within the same time periods as private companies. The Company has elected to use the extended transition period for complying with any new or revised financial accounting standards. As a result, the Company’s consolidated financial statements may not be comparable to the financial statements of issuers who are required to comply with the effective date for new or revised accounting standards that are applicable to public companies. The Company also intends to continue to take advantage of some of the reduced regulatory and reporting requirements of emerging growth companies pursuant to the JOBS Act so long as the Company qualifies as an emerging growth company. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”), which requires the measurement and recognition of expected credit losses for financial assets held at amortized cost. ASU 2016-13 replaces the existing incurred loss impairment model with a forward-looking expected credit loss model, which will result in earlier recognition of credit losses. ASU 2016-13 is effective for emerging-growth companies for fiscal years beginning after December 15, 2022, and interim periods within those fiscal years. The Company has determined that the adoption of ASU 2016-13 will not have a material impact on its consolidated financial statements or related disclosures. In future periods, as revenue and accounts receivable increase, ASU 2016-13 could have a material impact on its consolidated financial statements. Recently Adopted Accounting Pronouncements —On January 1, 2022, the Company adopted ASU 2016-02, Leases (ASC 842), which superseded previous guidance related to accounting for leases within Topic 840, Leases . The Company elected the practical expedient provided under ASU 2018-11, Leases (Topic 842) Targeted Improvements , which amended ASU 2016-02 to provide entities an optional transition practical expedient to adopt the new standard with a cumulative effect adjustment as of the beginning of the year of adoption with prior year comparative financial information and disclosures remaining as previously reported. As a result, no adjustments were made to the consolidated balance sheet prior to January 1, 2022 and amounts are reported in accordance with historical accounting under Topic 840, while the consolidated balance sheets as of December 31, 2022 are presented under Topic 842. The Company elected the package of practical expedients permitted under the transition guidance, which allowed it to carry forward historical lease classification, its assessment of whether a contract was or contains a lease, and its assessment of initial direct costs for any leases that existed prior to January 1, 2022. The Company also elected to combine its lease and non-lease components and to keep leases with an initial term of 12 months or less off the consolidated balance sheets and recognize the associated lease payments in the consolidated statements of operations and comprehensive loss on a straight-line basis over the lease term. For new required disclosures and further information see Note 9, Leases . Adoption of the new standard resulted in the recording of lease assets and lease liabilities of $4,534 thousand and $5,229 thousand, respectively, as of January 1, 2022. The transition did not have a material impact on the Company’s results of operations, cash flows or liquidity measures. For the year ended December 31, 2022, the Company adopted ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes , which simplifies the accounting for income taxes. The adoption did not result in a material impact to the Company’s consolidated financial statements or related disclosures.

BUSINESS COMBINATION (Tables)

BUSINESS COMBINATION (Tables)	12 Months Ended
	Dec. 31, 2022
Business Combination and Asset Acquisition [Abstract]
Schedule Of Reverse Recapitalization	The following table reconciles the elements of the Business Combination to the consolidated statement of cash flows and the consolidated statement of stockholders’ equity (deficit) for the year ended December 31, 2021 (in thousands): Cash contributions from Business Combination and PIPE Financing, net of redemptions $ 258,730 Less: transaction costs paid by ESS (7,895) Net cash contributions from Business Combination and PIPE Financing 250,835 Less: non-cash fair value of Public and Private Common Stock Warrants (11,833) Less: non-cash fair value of Earnout Shares and Warrants (110,010) Less: liabilities assumed from STWO (75) Net Business Combination and PIPE Financing $ 128,917 The number of shares of common stock issued immediately following the consummation of the Business Combination: Class A Common Stock, outstanding prior to Business Combination 25,000,000 Class B Common Stock, outstanding prior to Business Combination 6,250,000 Less: redemption of STWO shares (20,754,719) Common Stock of STWO 10,495,281 ESS common stock issued upon exercise of C-2 Right and Warrant 29,153,806 Shares issued in PIPE Financing 25,000,000 Business Combination and PIPE Financing shares - common stock 64,649,087 Legacy ESS Convertible Preferred Stock converted to ESS common stock 57,104,322 Legacy ESS Common Stock converted to ESS common stock 13,442,198 Total shares of common stock immediately after Business Combination 135,195,607

LOSS PER SHARE (Tables)

LOSS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2022
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Net Loss per Share Attributable to Common Shareholders	The following table presents the calculation of basic and diluted net loss per share attributable to common shareholders for the years ended December 31, 2022 and 2021 (in thousands, except per share data): 2022 2021 Net loss attributable to common stockholders $ (77,969) $ (477,177) Weighted-average shares outstanding – basic and diluted 152,676,155 83,256,431 Net loss per share – basic and diluted $ (0.51) $ (5.73)
Schedule of Securities Excluded from Calculation of Diluted Weighted-Average Common Shares Outstanding	The following outstanding balances of common share equivalent securities have been excluded from the calculation of diluted weighted-average common shares outstanding because the effect is anti-dilutive for the periods presented: 2022 2021 Stock options 3,223,109 3,796,530 Restricted stock units 6,346,955 3,392,153 Warrants 11,473,727 11,461,247 Earnout shares pending satisfaction of regulatory holding period — 6,707,318 Number of securities outstanding 21,043,791 25,357,248

PREPAID EXPENSES AND OTHER CU_2

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Tables)	12 Months Ended
	Dec. 31, 2022
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consist of the following (in thousands): December 31, 2022 December 31, 2021 Insurance $ 2,033 $ 3,482 Vendor advances 3,147 1,103 Other 477 259 Total prepaid expenses and other current assets $ 5,657 $ 4,844

PROPERTY AND EQUIPMENT, NET (Ta

PROPERTY AND EQUIPMENT, NET (Tables)	12 Months Ended
	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, net	Property and equipment, net consist of the following (in thousands): December 31, 2022 December 31, 2021 Machinery and equipment $ 13,699 $ 2,868 Furniture and fixtures 184 90 Leasehold improvements 3,115 746 Software 183 — Construction in process 3,230 2,517 Total property and equipment 20,411 6,221 Less accumulated depreciation (2,841) (1,720) Total property and equipment, net $ 17,570 $ 4,501

ACCRUED AND OTHER CURRENT LIA_2

ACCRUED AND OTHER CURRENT LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2022
Payables and Accruals [Abstract]
Schedule of Accrued and Other Current Liabilities	Accrued and other current liabilities consist of the following (in thousands): December 31, 2022 December 31, 2021 Payroll and related benefits $ 2,948 $ 1,876 Materials and related purchases 6,892 2,108 Amounts due to customers 770 — Deferred rent — 142 Professional and consulting fees 1,011 1,820 Accrued capital purchases 1,093 — Other 1,411 541 Total accrued and other current liabilities $ 14,125 $ 6,487

ACCRUED PRODUCT WARRANTIES (Tab

ACCRUED PRODUCT WARRANTIES (Tables)	12 Months Ended
	Dec. 31, 2022
Guarantees and Product Warranties [Abstract]
Schedule of Product Warranty Activity	The following table summarizes product warranty activity (in thousands): Year Ended December 31, 2022 2021 Accrued product warranties - beginning of period $ — $ — Accruals for warranties issued 2,612 — Repairs and replacements (969) — Accrued product warranties - end of period $ 1,643 $ —

LEASES (Tables)

LEASES (Tables)	12 Months Ended
	Dec. 31, 2022
Leases [Abstract]
Finance Lease Liability Maturities	As of December 31, 2022, future maturities of lease liabilities are as follows (in thousands): Operating Leases Finance Leases 2023 $ 1,670 $ 30 2024 1,720 30 2025 986 30 2026 — 30 2027 — 6 Thereafter — — Total minimum lease payments $ 4,376 $ 126 Less imputed interest (420) (19) Total $ 3,956 $ 107
Operating Lease Liability Maturities	As of December 31, 2022, future maturities of lease liabilities are as follows (in thousands): Operating Leases Finance Leases 2023 $ 1,670 $ 30 2024 1,720 30 2025 986 30 2026 — 30 2027 — 6 Thereafter — — Total minimum lease payments $ 4,376 $ 126 Less imputed interest (420) (19) Total $ 3,956 $ 107
Schedule of Future Minimum Lease Payments	Future minimum lease payments from the Company’s 2021 Form 10-K as filed in accordance with Leases (Topic 840) under non-cancelable operating lease agreements for the years ending December 31, are as follows (in thousands): 2022 $ 1,625 2023 1,670 2024 1,720 2025 983 Total $ 5,998

BORROWINGS (Tables)

BORROWINGS (Tables)	12 Months Ended
	Dec. 31, 2022
Debt Disclosure [Abstract]
Schedule of Borrowings	Borrowings consist of the following (in thousands): December 31, 2022 December 31, 2021 Total notes payable $ 1,915 $ 3,769 Less current portion of notes payable 1,600 1,900 Notes payable, non-current $ 315 $ 1,869
Schedule of Annual Maturities on Notes Payable	Annual maturities on notes payable outstanding at December 31, 2022 are as follows (in thousands): 2023 $ 1,600 2024 333 Total maturities 1,933 Less unamortized debt premium (18) Total notes payable $ 1,915

LEGACY ESS REDEEMABLE CONVERT_2

LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK (Tables)	12 Months Ended
	Dec. 31, 2022
Temporary Equity Disclosure [Abstract]
Schedule of Warrants	The number of shares subject to and potential proceeds from the Series C-2 Redeemable Convertible Preferred Stock Purchase Agreement and related Series C-2 warrants were as follows: As of May 7, 2021 Upon completion of the Business Combination Quantity Price Series C-2 Redeemable Convertible Preferred Stock Issuance Right 7,994,442 $ 2.00 Series C-2 Warrant exercisable upon completion of the Business Combination 21,159,364 $ 0.00007 Common stock warrant balances consist of the following: December 31, 2022 December 31, 2021 Public Warrants outstanding 7,377,893 7,377,913 Private Warrants outstanding: Other Private Warrants outstanding 3,500,000 3,500,000 Earnout Warrants outstanding 583,334 583,334 Total common stock warrants 11,461,227 11,461,247 December 31, 2021 Issued Exercised December 31, 2022 Earnout Warrants 583,334 — — 583,334 Public Warrants 7,377,913 — 20 7,377,893 Private Warrants (excluding Earnout Warrants) 3,500,000 — — 3,500,000 Total common stock warrants 11,461,247 — 20 11,461,227 The table below shows the common stock warrant activities during the year ended December 31, 2021: December 31, 2020 Issued Exercised December 31, 2021 Earnout Warrants — 583,334 — 583,334 Public Warrants — 8,333,287 955,374 7,377,913 Private Warrants (excluding Earnout Warrants) — 3,500,000 — 3,500,000 Total common stock warrants — 12,416,621 955,374 11,461,247

COMMON STOCK WARRANTS (Tables)

COMMON STOCK WARRANTS (Tables)	12 Months Ended
	Dec. 31, 2022
Equity [Abstract]
Schedule of Common Stock Warrant Activity	The number of shares subject to and potential proceeds from the Series C-2 Redeemable Convertible Preferred Stock Purchase Agreement and related Series C-2 warrants were as follows: As of May 7, 2021 Upon completion of the Business Combination Quantity Price Series C-2 Redeemable Convertible Preferred Stock Issuance Right 7,994,442 $ 2.00 Series C-2 Warrant exercisable upon completion of the Business Combination 21,159,364 $ 0.00007 Common stock warrant balances consist of the following: December 31, 2022 December 31, 2021 Public Warrants outstanding 7,377,893 7,377,913 Private Warrants outstanding: Other Private Warrants outstanding 3,500,000 3,500,000 Earnout Warrants outstanding 583,334 583,334 Total common stock warrants 11,461,227 11,461,247 December 31, 2021 Issued Exercised December 31, 2022 Earnout Warrants 583,334 — — 583,334 Public Warrants 7,377,913 — 20 7,377,893 Private Warrants (excluding Earnout Warrants) 3,500,000 — — 3,500,000 Total common stock warrants 11,461,247 — 20 11,461,227 The table below shows the common stock warrant activities during the year ended December 31, 2021: December 31, 2020 Issued Exercised December 31, 2021 Earnout Warrants — 583,334 — 583,334 Public Warrants — 8,333,287 955,374 7,377,913 Private Warrants (excluding Earnout Warrants) — 3,500,000 — 3,500,000 Total common stock warrants — 12,416,621 955,374 11,461,247

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	12 Months Ended
	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
Schedule of Stock-Based Compensation	The following table presents the amount of stock-based compensation related to stock-based awards to employees on the Company’s consolidated statements of operations and comprehensive loss during the years ended December 31, 2022 and 2021 (in thousands): 2022 2021 Research and development $ 2,856 $ 2,233 Sales and marketing 456 213 General and administrative 8,577 5,476 Total stock-based compensation $ 11,889 $ 7,922
Schedule of Share-based Payment Arrangement, Option, Activity	Stock option and RSU activity, prices, and values during the years ended December 31, 2022 and 2021 are as follows (in thousands, except for share, per share, and contractual term data): Options Outstanding RSUs Number of Weighted Weighted Aggregate Number of plan shares outstanding Weighted average Balances at December 31, 2020 5,732,422 $ 0.30 8.23 $ 4,333 — $ — Options and RSUs granted 1,454,549 1.75 3,392,153 10.69 Options exercised and RSUs released (2,496,070) 0.27 — — Options and RSUs forfeited (894,371) 0.46 — — Balances as of December 31, 2021 3,796,530 $ 0.83 8.08 $ 40,274 3,392,153 $ 10.69 Options and RSUs granted 65,717 8.00 5,602,206 4.68 Options exercised and RSUs released (529,832) 4.28 (1,526,784) 8.02 Options and RSUs forfeited (109,306) 2.53 (1,120,620) 10.46 Balances as of December 31, 2022 3,223,109 $ 1.01 7.39 $ 4,583 6,346,955 $ 6.10 Options vested and exercisable - December 31, 2021 1,827,374 $ 0.31 7.20 $ 20,337 Options vested and exercisable - December 31, 2022 1,947,123 $ 0.76 7.06 $ 3,244
Schedule of Share-based Payment Arrangement, Restricted Stock Unit, Activity	Stock option and RSU activity, prices, and values during the years ended December 31, 2022 and 2021 are as follows (in thousands, except for share, per share, and contractual term data): Options Outstanding RSUs Number of Weighted Weighted Aggregate Number of plan shares outstanding Weighted average Balances at December 31, 2020 5,732,422 $ 0.30 8.23 $ 4,333 — $ — Options and RSUs granted 1,454,549 1.75 3,392,153 10.69 Options exercised and RSUs released (2,496,070) 0.27 — — Options and RSUs forfeited (894,371) 0.46 — — Balances as of December 31, 2021 3,796,530 $ 0.83 8.08 $ 40,274 3,392,153 $ 10.69 Options and RSUs granted 65,717 8.00 5,602,206 4.68 Options exercised and RSUs released (529,832) 4.28 (1,526,784) 8.02 Options and RSUs forfeited (109,306) 2.53 (1,120,620) 10.46 Balances as of December 31, 2022 3,223,109 $ 1.01 7.39 $ 4,583 6,346,955 $ 6.10 Options vested and exercisable - December 31, 2021 1,827,374 $ 0.31 7.20 $ 20,337 Options vested and exercisable - December 31, 2022 1,947,123 $ 0.76 7.06 $ 3,244
Schedule of Valuation Assumptions	In accordance with ASC 718, the fair value of each option grant has been estimated as of the date of grant using the following weighted average assumptions: 2022 2021 Risk-free rate 1.64 % 1.01 % Expected volatility 73.95 % 75.14 % Expected term 6 years 6 years Expected dividends — —

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis	The following table presents the Company’s fair value hierarchy for its financial assets and liabilities measured at fair value on a recurring basis (in thousands): December 31, 2022 Total Assets at Fair Value Cash Equivalents and Restricted Cash Short-Term Investments Level 1: Money market funds $ 27,993 $ 27,993 $ — U.S. Treasury securities 19,944 — 19,944 Total Level 1 47,937 27,993 19,944 Level 2: Certificate of deposit 75 75 — U.S. agency securities 55,319 — 55,319 Commercial paper 35,756 5,972 29,784 Total Level 2 91,150 6,047 85,103 Total assets measured at fair value $ 139,087 $ 34,040 $ 105,047 December 31, 2021 Total Assets at Fair Value Cash Equivalents and Restricted Cash Short-Term Investments Level 1: Money market funds $ 237,897 $ 237,897 $ — Level 2: Certificate of deposit 125 125 — Total assets measured at fair value $ 238,022 $ 238,022 $ — The following tables present the Company’s fair value hierarchy for its financial liabilities measured at fair value on a recurring basis (in thousands): December 31, 2022 Level 1 Level 2 Level 3 Total Liabilities: Earnout warrant liabilities $ — $ 163 $ — $ 163 Public common stock warrants 2,066 — — 2,066 Private common stock warrants — 980 — 980 Total liabilities measured at fair value $ 2,066 $ 1,143 $ — $ 3,209 December 31, 2021 Level 1 Level 2 Level 3 Total Liabilities: Earnout warrant liabilities $ — $ 1,476 $ — $ 1,476 Public common stock warrants 18,666 — — 18,666 Private common stock warrants — 8,855 — 8,855 Total liabilities measured at fair value $ 18,666 $ 10,331 $ — $ 28,997
Schedule of Changes in Fair Value Liabilities on Recurring Basis	The following table sets forth a summary of changes in the fair value of the Company’s Level 3 liabilities at fair value on a recurring basis for the years ended December 31, 2022 and 2021 (in thousands): 2022 2021 Bridge loan: Beginning balance January 1 $ — $ — Fair value of Bridge loan funded — 20,000 Accrued interest — 1,578 Change in fair value — — Repayment of loan principal and interest — (21,578) Ending balance December 31 — — Legacy ESS Warrant liabilities: Beginning balance January 1 — 3,329 Change in fair value — 17,753 Fair value of warrants issued — 5,096 Fair value of warrants exercised — (26,178) Ending balance December 31 — — Series C-2 Redeemable Convertible Preferred Stock Issuance Right liability: Beginning balance January 1 — 22,911 Change in fair value — 223,165 Fair value of derivatives extinguished — (23,152) Fair value of Series C-2 Redeemable Convertible Preferred Stock Issuance Right exercised — (222,924) Ending balance December 31 — — Total $ — $ —

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Schedule of Deferred Tax Assets and Liabilities	The significant components of deferred tax assets and liabilities are as follows (in thousands): As of December 31, 2022 2021 Deferred tax assets: Net operating losses $ 34,454 $ 24,655 Tax credit carryforward 909 292 Equity compensation 737 1,143 Capitalized research and development expenses 16,946 — Other 2,153 1,231 Total deferred tax assets 55,199 27,321 Valuation allowance (54,261) (27,321) Deferred tax assets, net of valuation allowance 938 — Deferred tax liabilities: Right-of-use assets (938) — Net deferred tax $ — $ —
Schedule of Provision for Income Taxes	The effective tax rate of the Company’s provision for income taxes differs from the federal statutory rate as follows: Years Ended December 31, 2022 2021 Federal statutory tax rate 21.0 % 21.0 % State tax, net of federal tax benefit 7.2 0.6 Stock compensation (0.2) 0.0 Non-deductible officer compensation (1.4) (0.1) Transaction costs related to the Business Combination — (0.2) Warrant liabilities revaluation 6.6 (1.7) Derivative liabilities revaluation — (9.8) Earnout Shares liabilities revaluation 0.4 (6.8) Permanent differences 0.1 0.0 R&D tax credits 0.8 0.0 Other 0.1 0.1 Valuation allowance (34.6) (3.1) Effective tax rate — % — %
Schedule of Uncertain Tax Positions	The changes in the Company's uncertain tax positions are summarized as follows (in thousands): Balance as of December 31, 2020 $ 47 Additions in 2021 245 Balance as of December 31, 2021 292 Additions in 2022 613 Balance as of December 31, 2022 $ 905

REVENUE (Tables)

REVENUE (Tables)	12 Months Ended
	Dec. 31, 2022
Revenue from Contract with Customer [Abstract]
Schedule of Revenue Disaggregated by Source	The following table presents the Company’s revenue, disaggregated by source (in thousands): Year Ended December 31, 2022 2021 Product revenue $ 803 $ — Service and other revenue 91 — Total revenue $ 894 $ —
Schedule of Deferred Revenue	The following table summarizes deferred revenue activity (in thousands): Year Ended December 31, 2022 2021 Deferred revenue - beginning of period $ 3,663 2,258 Deferral of revenue 7,704 1,405 Recognition of previously unearned revenue (830) — Deposits returned to customers (1,157) — Reclassification to accrued liabilities due to estimation of variable consideration (770) — Deferred revenue - ending of period $ 8,610 $ 3,663

DESCRITPION OF BUSINESS, BASI_2

DESCRITPION OF BUSINESS, BASIS OF PRESENTATION AND RISKS AND UNCERTAINTIES (Details)	12 Months Ended
	Dec. 31, 2022 cycle segment h	Oct. 08, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Battery, flexible energy capacity, minimum | h	4
Battery lifespan, number of cycles | cycle	20,000
Recapitalization exchange ratio		0.0147
Number of reportable segments | segment	1

SIGNIFICANT ACCOUNTING POLICI_3

SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Jan. 01, 2022
Significant Accounting Policies [Line Items]
Impairment recognized	$ 0	$ 0
Net losses on trading securities	45,000	0
Advertising costs	173,000	45,000
Research and development grant refund liability	452,000	452,000
Accrued interest and penalties related to uncertain tax positions	0	0
Operating lease right-of-use assets	3,401,000	$ 0
Operating lease liabilities	$ 3,956,000
Accounting Standards Update 2016-02
Significant Accounting Policies [Line Items]
Operating lease right-of-use assets			$ 4,534,000
Operating lease liabilities			$ 5,229,000
Stock options
Significant Accounting Policies [Line Items]
Expected dividends	0%	0%
Minimum
Significant Accounting Policies [Line Items]
Estimated useful live of assets	3 years
Maximum
Significant Accounting Policies [Line Items]
Estimated useful live of assets		7 years

BUSINESS COMBINATION - Narrativ

BUSINESS COMBINATION - Narrative (Details)			12 Months Ended
	Nov. 09, 2021 shares	Oct. 08, 2021 USD ($) tranche $ / shares shares	Dec. 31, 2022 $ / shares shares	Dec. 31, 2021 $ / shares shares	Oct. 07, 2021 $ / shares
Business Acquisition [Line Items]
Common stock, par value (in USD per share) | $ / shares		$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock, par value (in USD per share) | $ / shares		$ 0.0001	$ 0.0001	$ 0.0001
Common and preferred stock authorized (in shares)		2,200,000,000
Common stock, shares authorized (in shares)		2,000,000,000	2,000,000,000	2,000,000,000
Preferred stock, shares authorized (in shares)		200,000,000	200,000,000	200,000,000
Number of tranches under contingent consideration | tranche		2
Common Stock
Business Acquisition [Line Items]
Shares issuable under contingent consideration (in shares)		16,500,000
Earnout Shares
Business Acquisition [Line Items]
Shares delivered (in shares)			6,707,318
RSUs
Business Acquisition [Line Items]
Awards issued (in shares)		824,998
Awards vested (in shares)	757,448
Awards cancelled (in shares)	67,550
Legacy ESS
Business Acquisition [Line Items]
Common stock, par value (in USD per share) | $ / shares					$ 0.0001
Preferred stock, par value (in USD per share) | $ / shares					$ 0.0001
Legacy ESS | Common Stock
Business Acquisition [Line Items]
Shares issued upon completion of milestones (in shares)	15,674,965
STWO
Business Acquisition [Line Items]
Goodwill and intangible assets | $		$ 0
Legacy ESS Shareholders
Business Acquisition [Line Items]
Shares issued (in shares)		99,700,326
Legacy ESS Shareholders | Transaction Expense Adjustment
Business Acquisition [Line Items]
Shares issued (in shares)		125,958
Private Placement | STWO
Business Acquisition [Line Items]
Shares issued (in shares)		25,000,000
Price per share (in USD per share) | $ / shares		$ 10
Proceeds from transaction | $		$ 250,000,000

BUSINESS COMBINATION - Schedule

BUSINESS COMBINATION - Schedule of Reverse Recapitalization (Details) - USD ($) $ in Thousands			12 Months Ended
	Oct. 08, 2021	Oct. 07, 2021	Dec. 31, 2022	Dec. 31, 2021
Schedule of Reverse Recapitalization [Line Items]
Cash contributions from Business Combination and PIPE Financing, net of redemptions			$ 258,730
Less: transaction costs paid by ESS			(7,895)
Net cash contributions from Business Combination and PIPE Financing			250,835
Less: non-cash fair value of Public and Private Common Stock Warrants			(11,833)
Less: non-cash fair value of Earnout Shares and Warrants			(110,010)
Less: liabilities assumed from STWO			(75)
Net Business Combination and PIPE Financing			$ 128,917
Common stock, shares outstanding (in shares)	135,195,607		153,821,339	151,839,058
Common stock of STWO (in shares)	10,495,281
ESS common stock issued upon exercise of C-2 Right and Warrant (in shares)	29,153,806
Shares issued in Private Placement Financing (in shares)	25,000,000
Business Combination and Private Placement Financing shares - common stock (in shares)	64,649,087
STWO
Schedule of Reverse Recapitalization [Line Items]
Less: redemption of STWO shares (in shares)		(20,754,719)
Common Class A | STWO
Schedule of Reverse Recapitalization [Line Items]
Common stock, shares outstanding (in shares)		25,000,000
Common Class B | STWO
Schedule of Reverse Recapitalization [Line Items]
Common stock, shares outstanding (in shares)		6,250,000
Redeemable Convertible Preferred Stock
Schedule of Reverse Recapitalization [Line Items]
Legacy ESS stock converted to ESS common stock (in shares)	57,104,322
Common Stock
Schedule of Reverse Recapitalization [Line Items]
Legacy ESS stock converted to ESS common stock (in shares)	13,442,198

LOSS PER SHARE - Schedule of Ba

LOSS PER SHARE - Schedule of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Earnings Per Share [Abstract]
Net loss to common stockholders, basic	$ (77,969)	$ (477,177)
Net loss to common stockholders, diluted	$ (77,969)	$ (477,177)
Weighted average shares used in per share calculation, basic (in shares)	152,676,155	83,256,431
Weighted average shares used in per share calculation, diluted (in shares)	152,676,155	83,256,431
Net loss per share, diluted (in USD per share)	$ (0.51)	$ (5.73)
Net loss per share, basic (in USD per share)	$ (0.51)	$ (5.73)

LOSS PER SHARE - Schedule Antid

LOSS PER SHARE - Schedule Antidilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	21,043,791	25,357,248
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	3,223,109	3,796,530
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	6,346,955	3,392,153
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	11,473,727	11,461,247
Earnout shares pending satisfaction of regulatory holding period
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	0	6,707,318

PREPAID EXPENSES AND OTHER CU_3

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Insurance	$ 2,033	$ 3,482
Vendor advances	3,147	1,103
Other	477	259
Total prepaid expenses and other current assets	$ 5,657	$ 4,844

PROPERTY AND EQUIPMENT, NET (De

PROPERTY AND EQUIPMENT, NET (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 20,411	$ 6,221
Less accumulated depreciation	(2,841)	(1,720)
Total property and equipment, net	17,570	4,501
Depreciation expense	1,506	572
Machinery and equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	13,699	2,868
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment	184	90
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	3,115	746
Software
Property, Plant and Equipment [Line Items]
Total property and equipment	183	0
Construction in process
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 3,230	$ 2,517

ACCRUED AND OTHER CURRENT LIA_3

ACCRUED AND OTHER CURRENT LIABILITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Payables and Accruals [Abstract]
Payroll and related benefits	$ 2,948	$ 1,876
Materials and related purchases	6,892	2,108
Amounts due to customers	770	0
Deferred rent	0	142
Professional and consulting fees	1,011	1,820
Accrued capital purchases	1,093	0
Other	1,411	541
Total accrued and other current liabilities	$ 14,125	$ 6,487

ACCRUED PRODUCT WARRANTIES (Det

ACCRUED PRODUCT WARRANTIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Movement in Standard Product Warranty Accrual [Roll Forward]
Product warranties at beginning of period	$ 0	$ 0
Accruals for warranties issued	2,612	0
Repairs and replacements	(969)	0
Product warranties at end of period	$ 1,643	$ 0

LEASES - Narrative (Details)

LEASES - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Renewal term	60 months
Operating lease cost	$ 1,483
Operating lease, weighted average remaining term	2 years 7 months 6 days
Operating lease, weighted average discount rate	7.50%
Finance lease, weighted average remaining term	4 years 3 months 18 days
Operating lease, weighted average discount rate	7.50%
Rent expense		$ 1,491
Finance Lease, Liability, Statement of Financial Position [Extensible Enumeration]	Accrued and other current liabilities, Other non-current liabilities

LEASES- Maturities of Operating

LEASES- Maturities of Operating and Financing Lease Liabilities (Details) $ in Thousands	Dec. 31, 2022 USD ($)
Operating Leases
2023	$ 1,670
2024	1,720
2025	986
2026	0
2027	0
Thereafter	0
Total minimum lease payments	4,376
Less imputed interest	(420)
Total	3,956
Finance Leases
2023	30
2024	30
2025	30
2026	30
2027	6
Thereafter	0
Total minimum lease payments	126
Less imputed interest	(19)
Total	$ 107

LEASES - Schedule of Future Min

LEASES - Schedule of Future Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2022 USD ($)
Leases [Abstract]
2022	$ 1,625
2023	1,670
2024	1,720
2025	983
Total	$ 5,998

BORROWINGS - Schedule of Borrow

BORROWINGS - Schedule of Borrowings (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Debt Disclosure [Abstract]
Total notes payable	$ 1,915	$ 3,769
Less current portion of notes payable	1,600	1,900
Notes payable, non-current	$ 315	$ 1,869

BORROWINGS - Narrative (Details

BORROWINGS - Narrative (Details)	1 Months Ended		12 Months Ended
	Sep. 30, 2022 USD ($)	Jul. 31, 2021 USD ($)	Dec. 31, 2022	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Apr. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2018 USD ($)
Notes Payable
Debt Instrument [Line Items]
Debt amount						$ 4,000,000	$ 4,000,000	$ 1,000,000
Percent change in present value of cash flows							0.10
Gain (loss) on extinguishment of debt					$ 62,000
Repayments of debt	$ 1,000
Effective interest rate			7.50%
Notes Payable | Prime
Debt Instrument [Line Items]
Spread on interest rate			0.50%
Payroll Protection Program Loans
Debt Instrument [Line Items]
Debt amount						$ 936,000
Gain (loss) on extinguishment of debt				$ (948,000)
Interest rate						1%
Debt forgiveness		$ 936,000
Accrued interest		12,000
Bridge loan:
Debt Instrument [Line Items]
Debt amount		$ 20,000,000
Interest rate		9%
Debt instrument, term		6 months
Monthly interest rate		0.0225
PIK interest rate		0.0675
Final payment		$ 1,250,000
Fair value of loan at issuance				20,000,000
Interest expense on loan				$ 1,578,000

BORROWINGS - Schedule of Annual

BORROWINGS - Schedule of Annual Maturities on Notes Payable (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Debt Disclosure [Abstract]
2023	$ 1,600
2024	333
Total maturities	1,933
Less unamortized debt premium	(18)
Total notes payable	$ 1,915	$ 3,769

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Sep. 01, 2022
Other Commitments [Line Items]
Restricted certificate of deposit	$ 75,000
Noncancellable Agreement
Other Commitments [Line Items]
Noncancelable purchase commitments	21,540,000	$ 10,160,000
Cancellable Agreement
Other Commitments [Line Items]
Noncancelable purchase commitments	5,663,000	10,446,000
Letter of Credit | First Republic Bank
Other Commitments [Line Items]
Standby letter of credit	725,000	725,000
Draws against letter of credit	0	$ 0
Letter of Credit | CitiBank N.A
Other Commitments [Line Items]
Standby letter of credit			$ 600,000
Draws against letter of credit	0
Letter of Credit | CitiBank N.A | Asset Pledged as Collateral
Other Commitments [Line Items]
Amounts pledged as collateral	$ 600,000

LEGACY ESS REDEEMABLE CONVERT_3

LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK - Narrative (Details) $ / shares in Units, $ in Thousands			1 Months Ended	12 Months Ended
	Oct. 08, 2021 USD ($) $ / shares shares	Oct. 07, 2021 USD ($) $ / shares shares	Mar. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2022 USD ($) shares	Dec. 31, 2021 USD ($) shares	Mar. 31, 2022 $ / shares	May 07, 2021 $ / shares	Dec. 31, 2020 USD ($) shares
Temporary Equity [Line Items]
Recapitalization exchange ratio	0.0147
Fair value of temporary equity				$ 0	$ 0			$ 0
Shares issued (in shares) | shares	25,000,000
Issuance of Legacy ESS Redeemable Convertible Preferred Stock					29,516
Stock issuance costs				$ 0	$ 7,895
Warrants issued (in shares) | shares				0	12,416,621
Warrants exercised (in shares) | shares				20	955,374
Increase in derivative liability				$ 0	$ (223,165)
Warrants (in shares) | shares				11,461,227	11,461,247			0
Series C-2 Redeemable Convertible Preferred Stock Purchase Rights And Warrants
Temporary Equity [Line Items]
Stock issuance costs	$ 439
Proceeds from transaction	$ 15,559
Legacy ESS
Temporary Equity [Line Items]
Transaction value			$ 34,613
Warrants term		10 years
Legacy ESS | Series C-2 Redeemable Convertible Preferred Stock Issuance Right
Temporary Equity [Line Items]
Fair value of temporary equity		$ 11,379
Warrants issued (in shares) | shares			861,896
Warrants exercised (in shares) | shares			5,746,003
Class of warrant or right, exercise price of warrants or rights (in dollars per share) | $ / shares			$ 0.0001
Legacy ESS | Series C-2 Redeemable Convertible Preferred Stock Warrants
Temporary Equity [Line Items]
Class of warrant or right, exercise price of warrants or rights (in dollars per share) | $ / shares							$ 0.00007
Warrants term		10 years
Legacy ESS | Series C-2 Redeemable Convertible Preferred Stock Warrants | Minimum
Temporary Equity [Line Items]
Class of warrant or right, exercise price of warrants or rights (in dollars per share) | $ / shares		$ 0.00007
Legacy ESS | Series C-2 Redeemable Convertible Preferred Stock Warrants | Maximum
Temporary Equity [Line Items]
Class of warrant or right, exercise price of warrants or rights (in dollars per share) | $ / shares		$ 1.25
Legacy ESS | Series B Redeemable Convertible Preferred Stock Warrants
Temporary Equity [Line Items]
Warrants (in shares) | shares		100,161
Legacy ESS | Series B Redeemable Convertible Preferred Stock Warrants | Minimum
Temporary Equity [Line Items]
Class of warrant or right, exercise price of warrants or rights (in dollars per share) | $ / shares		$ 0.0007
Legacy ESS | Series B Redeemable Convertible Preferred Stock Warrants | Maximum
Temporary Equity [Line Items]
Class of warrant or right, exercise price of warrants or rights (in dollars per share) | $ / shares		$ 0.83
Legacy ESS | Series C-1 Redeemable Convertible Preferred Stock Warrants
Temporary Equity [Line Items]
Warrants term		10 years
Legacy ESS | Series C-1 Redeemable Convertible Preferred Stock Warrants | Minimum
Temporary Equity [Line Items]
Class of warrant or right, exercise price of warrants or rights (in dollars per share) | $ / shares		$ 0.00007
Legacy ESS | Series C-1 Redeemable Convertible Preferred Stock Warrants | Maximum
Temporary Equity [Line Items]
Class of warrant or right, exercise price of warrants or rights (in dollars per share) | $ / shares		1.25
Legacy ESS | Common Stock Warrants
Temporary Equity [Line Items]
Class of warrant or right, exercise price of warrants or rights (in dollars per share) | $ / shares		$ 0.0007
Common Stock
Temporary Equity [Line Items]
Conversion of convertible shares (in shares) | shares		57,104,332
Price per share (in USD per share) | $ / shares	$ 11.50
Series C-2 Redeemable Convertible Preferred Stock | Legacy ESS
Temporary Equity [Line Items]
Committed funding amount	$ 79,999	$ 79,999
Committed purchase of shares (in shares) | shares	39,971,716	39,971,716
Committed price per share (in USD per share) | $ / shares	$ 2	$ 2
Shares issued (in shares) | shares			5,746,003
Price per share (in USD per share) | $ / shares						$ 2
Issuance of Legacy ESS Redeemable Convertible Preferred Stock			$ 11,500
Stock issuance costs			39
Extinguishment of preferred stock issuance right			23,152
Transaction value			29,516
Warrants | Legacy ESS
Temporary Equity [Line Items]
Transaction value			$ 5,096

LEGACY ESS REDEEMABLE CONVERT_4

LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK - Schedule of Rights and Warrants (Details) - Legacy ESS	May 07, 2021 $ / shares shares
Series C-2 Redeemable Convertible Preferred Stock Issuance Right
Class of Warrant or Right [Line Items]
Shares issued (in shares) | shares	7,994,442
Price per share (in USD per share) | $ / shares	$ 2
Series C-2 Warrant exercisable upon completion of the Business Combination
Class of Warrant or Right [Line Items]
Shares issued (in shares) | shares	21,159,364
Price per share (in USD per share) | $ / shares	$ 0.00007

COMMON STOCK WARRANTS - Schedul

COMMON STOCK WARRANTS - Schedule of Common Stock Warrant Balances (Details) - shares	Dec. 31, 2022	Dec. 31, 2021	Oct. 08, 2021	Dec. 31, 2020
Class of Warrant or Right [Line Items]
Warrants (in shares)	11,461,227	11,461,247		0
Public common stock warrants
Class of Warrant or Right [Line Items]
Warrants (in shares)	7,377,893	7,377,913		0
Private common stock warrants
Class of Warrant or Right [Line Items]
Warrants (in shares)	3,500,000	3,500,000	4,083,334	0
Earnout Warrants
Class of Warrant or Right [Line Items]
Warrants (in shares)	583,334	583,334		0

COMMON STOCK WARRANTS - Narrati

COMMON STOCK WARRANTS - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Oct. 08, 2021	Sep. 21, 2020	Dec. 31, 2022	Dec. 31, 2021	Sep. 16, 2022	Nov. 09, 2021	Dec. 31, 2020
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)			11,461,227	11,461,247			0
Warrants issued (in shares)			0	12,416,621
Net decrease (increase) to warrant liabilities			$ (24,475)	$ 37,584
Number of shares with vesting conditions met (in shares)			12,500
Private Placement | STWO
Class of Warrant or Right [Line Items]
Shares issued (in shares)	25,000,000
Redemption Scenario, Two
Class of Warrant or Right [Line Items]
Price of common stock triggering redemption of warrants (in USD per share)			$ 10
Price of common stock with trading days threshold, triggering redemption of warrants (in USD per share)			$ 10
Trading days triggering redemption of warrants			20 days
Consecutive trading day period			30 days
Common Stock
Class of Warrant or Right [Line Items]
Price per share (in USD per share)	$ 11.50
Common Stock | STWO
Class of Warrant or Right [Line Items]
Price per share (in USD per share)		$ 11.50
Common Stock | Public Warrant Holders | STWO
Class of Warrant or Right [Line Items]
Issuance of shares (in shares)		1
Common Stock | Private Warrant Holders
Class of Warrant or Right [Line Items]
Issuance of shares (in shares)	1
Common Stock | Earnout Warrant Holders
Class of Warrant or Right [Line Items]
Issuance of shares (in shares)	1
Private common stock warrants | Private Placement | STWO | STWO's Sponsor
Class of Warrant or Right [Line Items]
Shares issued (in shares)		4,666,667
Public common stock warrants
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)			7,377,893	7,377,913			0
Warrants issued (in shares)			0	8,333,287
Net decrease (increase) to warrant liabilities			$ 16,600	$ 14,476
Public common stock warrants | STWO
Class of Warrant or Right [Line Items]
Warrants issued (in shares)	8,333,287
Warrants term		5 years
Public common stock warrants | Redemption Scenario, One
Class of Warrant or Right [Line Items]
Redemption price per share (in USD per share)			$ 0.01
Price of common stock triggering redemption of warrants (in USD per share)			18
Price of common stock with trading days threshold, triggering redemption of warrants (in USD per share)			$ 10
Trading days triggering redemption of warrants			20 days
Consecutive trading day period			30 days
Public common stock warrants | Redemption Scenario, Two
Class of Warrant or Right [Line Items]
Redemption price per share (in USD per share)			$ 0.10
Public common stock warrants | Redemption Scenario, Three
Class of Warrant or Right [Line Items]
Price of common stock triggering redemption of warrants (in USD per share)			18
Price of common stock with trading days threshold, triggering redemption of warrants (in USD per share)			$ 10
Trading days triggering redemption of warrants			20 days
Consecutive trading day period			30 days
Private common stock warrants
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)	4,083,334		3,500,000	3,500,000			0
Warrants issued (in shares)			0	3,500,000
Warrants vested (in shares)	3,500,000
Net decrease (increase) to warrant liabilities			$ 7,875	$ 5,355
Private common stock warrants | STWO's Sponsor
Class of Warrant or Right [Line Items]
Warrants forfeited (in shares)	583,333
Earnout Warrants
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)			583,334	583,334			0
Warrants issued (in shares)			0	583,334
Warrants vested (in shares)						583,334
Net decrease (increase) to warrant liabilities			$ 1,313	$ 974
SMUD Warrant
Class of Warrant or Right [Line Items]
Class of warrant or right, number of securities called by each warrant or right (in shares)					500,000
Class of warrant or right, exercise price of warrants or rights (in dollars per share)					$ 4.296

COMMON STOCK WARRANTS - Sched_2

COMMON STOCK WARRANTS - Schedule of Common Stock Warrant Activity (Details) - shares		12 Months Ended
	Oct. 08, 2021	Dec. 31, 2022	Dec. 31, 2021
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		11,461,247	0
Warrants issued (in shares)		0	12,416,621
Warrants exercised (in shares)		20	955,374
Warrants or rights at end of period (in shares)		11,461,227	11,461,247
Earnout Warrants
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		583,334	0
Warrants issued (in shares)		0	583,334
Warrants exercised (in shares)		0	0
Warrants or rights at end of period (in shares)		583,334	583,334
Public Warrants
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		7,377,913	0
Warrants issued (in shares)		0	8,333,287
Warrants exercised (in shares)		20	955,374
Warrants or rights at end of period (in shares)		7,377,893	7,377,913
Private Warrants (excluding Earnout Warrants)
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		3,500,000	0
Warrants issued (in shares)		0	3,500,000
Warrants exercised (in shares)		0	0
Warrants or rights at end of period (in shares)	4,083,334	3,500,000	3,500,000

STOCK-BASED COMPENSATION - Sche

STOCK-BASED COMPENSATION - Schedule of Stock-Based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	$ 11,889	$ 7,922
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	2,856	2,233
Sales and marketing
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	456	213
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	$ 8,577	$ 5,476

STOCK-BASED COMPENSATION - Narr

STOCK-BASED COMPENSATION - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Jan. 01, 2022	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of potential increase of shares authorized		5%
Aggregate intrinsic value of options exercised		$ 2,107	$ 6,244
Unamortized stock-based compensation costs		$ 28,129
Weighted average period of recognition for unamortized stock-based compensation costs		2 years 9 months 21 days
Total stock-based compensation		$ 11,889	$ 7,922
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average estimated fair value of options granted using Black-Scholes options pricing model (in USD per share)		$ 5.23	$ 5.63
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum employee stock purchase amount		$ 25
ESPP purchase price of common stock, percent of market price		85%
Total stock-based compensation		$ 270
2021 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential increase of shares authorized (in shares)		15,260,000
Increase in shares authorized for issuance (in shares)	4,614,640
Shares authorized for issuance (in shares)		17,610,000
Shares available for future grant (in shares)		10,626,299
2021 Equity Incentive Plan | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share expiration period		10 years

STOCK-BASED COMPENSATION - Sc_2

STOCK-BASED COMPENSATION - Schedule of Share-based Payment Arrangement, Option and RSU Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Options Outstanding
Options outstanding at beginning of period (in shares)	3,796,530	5,732,422
Options granted (in shares)	65,717	1,454,549
Options exercised (in shares)	(529,832)	(2,496,070)
Options forfeited (in shares)	(109,306)	(894,371)
Options outstanding at end of period (in shares)	3,223,109	3,796,530	5,732,422
Options vested and exercisable (in shares)	1,947,123	1,827,374
Weighted average exercise price
Weighted average exercise price of options outstanding at beginning of period (in USD per share)	$ 0.83	$ 0.30
Weighted average exercise price of options granted (in USD per share)	8	1.75
Weighted average exercise price of options exercised (in USD per share)	4.28	0.27
Weighted average exercise price of options forfeited (in USD per share)	2.53	0.46
Weighted average exercise price of options outstanding at end of period (in USD per share)	1.01	0.83	$ 0.30
Weighted average exercise price of options vested and exercisable (in USD per share)	$ 0.76	$ 0.31
Options, Additional Disclosures
Weighted average remaining contractual term of options outstanding	7 years 4 months 20 days	8 years 29 days	8 years 2 months 23 days
Weighted average remaining contractual term of options vested and exercisable	7 years 21 days	7 years 2 months 12 days
Aggregate intrinsic value of options outstanding	$ 4,583	$ 40,274	$ 4,333
Aggregate intrinsic value of options vested and exercisable	$ 3,244	$ 20,337
RSUs
RSUs
Units outstanding at beginning of period (in shares)	3,392,153	0
Units granted (in shares)	5,602,206	3,392,153
Units released (in shares)	(1,526,784)	0
Units forfeited (in shares)	(1,120,620)	0
Units outstanding at end of period (in shares)	6,346,955	3,392,153	0
Weighted average grant date fair value per share
Weighted average grant date fair value per share of units outstanding at beginning of period (in USD per share)	$ 10.69	$ 0
Weighted average grant date fair value per share of units granted (in USD per share)	4.68	10.69
Weighted average grant date fair value per share of units exercised (in USD per share)	8.02	0
Weighted average grant date fair value per share of units forfeited (in USD per share)	10.46	0
Weighted average grant date fair value per share of units outstanding at end of period (in USD per share)	$ 6.10	$ 10.69	$ 0

STOCK-BASED COMPENSATION - Sc_3

STOCK-BASED COMPENSATION - Schedule of Valuation Assumptions (Details) - Stock options	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free rate	1.64%	1.01%
Expected volatility	73.95%	75.14%
Expected term	6 years	6 years
Expected dividends	0%	0%

FAIR VALUE MEASUREMENTS - Sched

FAIR VALUE MEASUREMENTS - Schedule of Assets and Liabilities on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Assets, Fair Value Disclosure [Abstract]
Short-Term Investments	$ 105,047	$ 0
Fair Value, Recurring
Assets, Fair Value Disclosure [Abstract]
Total Assets at Fair Value	139,087	238,022
Cash Equivalents and Restricted Cash	34,040	238,022
Short-Term Investments	105,047	0
Liabilities, Fair Value Disclosure [Abstract]
Earnout warrant liabilities	163
Earnout warrant liabilities		1,476
Liabilities, Fair Value Disclosure, Total	3,209	28,997
Fair Value, Recurring | Public common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	2,066	18,666
Fair Value, Recurring | Private common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	980	8,855
Fair Value, Recurring | Level 1
Assets, Fair Value Disclosure [Abstract]
Total Assets at Fair Value	47,937
Cash Equivalents and Restricted Cash	27,993
Short-Term Investments	19,944
Liabilities, Fair Value Disclosure [Abstract]
Earnout warrant liabilities	0
Earnout warrant liabilities		0
Liabilities, Fair Value Disclosure, Total	2,066	18,666
Fair Value, Recurring | Level 1 | Public common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	2,066	18,666
Fair Value, Recurring | Level 1 | Private common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	0	0
Fair Value, Recurring | Level 1 | Money market funds
Assets, Fair Value Disclosure [Abstract]
Total Assets at Fair Value	27,993	237,897
Cash Equivalents and Restricted Cash	27,993	237,897
Short-Term Investments	0	0
Fair Value, Recurring | Level 1 | U.S. Treasury securities
Assets, Fair Value Disclosure [Abstract]
Total Assets at Fair Value	19,944
Cash Equivalents and Restricted Cash	0
Short-Term Investments	19,944
Fair Value, Recurring | Level 2
Assets, Fair Value Disclosure [Abstract]
Total Assets at Fair Value	91,150
Cash Equivalents and Restricted Cash	6,047
Short-Term Investments	85,103
Liabilities, Fair Value Disclosure [Abstract]
Earnout warrant liabilities	163
Earnout warrant liabilities		1,476
Liabilities, Fair Value Disclosure, Total	1,143	10,331
Fair Value, Recurring | Level 2 | Public common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	0	0
Fair Value, Recurring | Level 2 | Private common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	980	8,855
Fair Value, Recurring | Level 2 | Certificate of deposit
Assets, Fair Value Disclosure [Abstract]
Total Assets at Fair Value	75	125
Cash Equivalents and Restricted Cash	75	125
Short-Term Investments	0	0
Fair Value, Recurring | Level 2 | U.S. agency securities
Assets, Fair Value Disclosure [Abstract]
Total Assets at Fair Value	55,319
Cash Equivalents and Restricted Cash	0
Short-Term Investments	55,319
Fair Value, Recurring | Level 2 | Commercial paper
Assets, Fair Value Disclosure [Abstract]
Total Assets at Fair Value	35,756
Cash Equivalents and Restricted Cash	5,972
Short-Term Investments	29,784
Fair Value, Recurring | Level 3
Liabilities, Fair Value Disclosure [Abstract]
Earnout warrant liabilities	0
Earnout warrant liabilities		0
Liabilities, Fair Value Disclosure, Total	0	0
Fair Value, Recurring | Level 3 | Public common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	0	0
Fair Value, Recurring | Level 3 | Private common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	$ 0	$ 0

FAIR VALUE MEASUREMENTS - Narra

FAIR VALUE MEASUREMENTS - Narrative (Details) - Series C-2 Redeemable Convertible Preferred Stock Rights - Legacy ESS - USD ($) $ / shares in Units, $ in Thousands	Oct. 08, 2021	Oct. 07, 2021
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Committed funding amount	$ 79,999	$ 79,999
Committed purchase of shares (in shares)	39,971,716	39,971,716
Committed price per share (in USD per share)	$ 2	$ 2

FAIR VALUE MEASUREMENTS - Sch_2

FAIR VALUE MEASUREMENTS - Schedule of Changes in Fair Value Liabilities on Recurring Basis (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 0
Balance at end of period	0	$ 0
Total	0	0
Bridge loan:
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	0	0
Fair value issued	0	20,000
Accrued interest	0	1,578
Change in fair value	0	0
Fair value settled	0	(21,578)
Balance at end of period	0	0
Total	0	0
Legacy ESS Warrant liabilities:
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	0	3,329
Fair value issued	0	5,096
Change in fair value	0	17,753
Fair value settled	0	(26,178)
Balance at end of period	0	0
Total	0	0
Redeemable Convertible Preferred Stock
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	0	22,911
Change in fair value	0	223,165
Fair value of derivatives extinguished	0	(23,152)
Fair value settled	0	(222,924)
Balance at end of period	0	0
Total	$ 0	$ 0

INCOME TAXES - Schedule of Defe

INCOME TAXES - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets:
Net operating losses	$ 34,454	$ 24,655
Tax credit carryforward	909	292
Equity compensation	737	1,143
Capitalized research and development expenses	16,946	0
Other	2,153	1,231
Total deferred tax assets	55,199	27,321
Valuation allowance	(54,261)	(27,321)
Deferred tax assets, net of valuation allowance	938	0
Deferred tax liabilities:
Right-of-use assets	(938)	0
Net deferred tax	$ 0	$ 0

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Operating Loss Carryforwards [Line Items]
Capitalized research and development expenses	$ 16,946,000	$ 0
Increase in valuation allowance	26,940,000
Addition to uncertain tax position related to reduction of research and development credit	613,000	245,000
Accrued interest and penalties related to uncertain tax positions	0	$ 0
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	130,708,000
Research and development credits	1,795,000
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	130,578,000
Research and development credits	$ 28,000

INCOME TAXES - Schedule of Prov

INCOME TAXES - Schedule of Provision for Income Taxes (Details)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Federal statutory tax rate	21%	21%
State tax, net of federal tax benefit	7.20%	0.60%
Stock compensation	(0.20%)	0%
Non-deductible officer compensation	(0.014)	(0.001)
Transaction costs related to the Business Combination	0	(0.002)
Warrant liabilities revaluation	0.066	(0.017)
Derivative liabilities revaluation	0	(0.098)
Earnout Shares liabilities revaluation	0.004	(0.068)
Permanent differences	0.001	0
R&D tax credits	0.80%	0%
Other	0.10%	0.10%
Valuation allowance	(34.60%)	(3.10%)
Effective tax rate	0%	0%

INCOME TAXES - Schedule of Unce

INCOME TAXES - Schedule of Uncertain Tax Positions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 292	$ 47
Additions	613	245
Balance at end of period	$ 905	$ 292

REVENUE - Schedule of Revenue D

REVENUE - Schedule of Revenue Disaggregated by Source (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Total revenue	$ 894	$ 0
Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	803	0
Service and other revenue
Disaggregation of Revenue [Line Items]
Total revenue	$ 91	$ 0

REVENUE - Schedule of Changes i

REVENUE - Schedule of Changes in Deferred Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Revenue from Contract with Customer [Roll Forward]
Deferred revenue at beginning of period	$ 3,663	$ 2,258
Deferral of revenue	7,704	1,405
Recognition of previously unearned revenue	(830)	0
Deposits returned to customers	(1,157)	0
Reclassification to accrued liabilities due to estimation of variable consideration	(770)	0
Deferred revenue at end of period	$ 8,610	$ 3,663

DEFINED CONTRIBUTION PLAN (Deta

DEFINED CONTRIBUTION PLAN (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Retirement Benefits [Abstract]
Employer contributions	$ 674	$ 292

RELATED PARTY TRANSACTIONS (Det

RELATED PARTY TRANSACTIONS (Details) - USD ($) $ in Thousands		12 Months Ended
	Nov. 09, 2021	Dec. 31, 2022	Dec. 31, 2021
Related Party Transaction [Line Items]
Deferred revenue		$ 6,168	$ 3,663
Common Stock | Legacy ESS
Related Party Transaction [Line Items]
Shares issued to related parties (in shares)	15,674,965
Related parties | Common Stock | Legacy ESS
Related Party Transaction [Line Items]
Shares issued to related parties (in shares)	6,707,318
Energy Storage Systems Sales
Related Party Transaction [Line Items]
Accounts receivable from related party			66
Deferred revenue			$ 171
Revenue recognized from sales to related parties		284
Energy Warehouse Sales
Related Party Transaction [Line Items]
Deferred revenue		$ 5