ESS Tech (GWH) S-1 4 Mar 22 IPO registration Financial data

Cover

Cover	12 Months Ended
	Dec. 31, 2021
Cover [Abstract]
Document Type	S-1
Entity Registrant Name	ESS TECH, INC.
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Central Index Key	0001819438
Amendment Flag	false
Amendment Description	On November 2, 2021, ESS filed a registration statement with the Securities and Exchange Commission (the “SEC”), on Form S-1 (File No. 333-260693) (the “Prior Registration Statement”), to initially register for resale by the selling stockholders named therein or their permitted transferees (i) 25,000,000 shares of our common stock, par value $0.0001 per share (the “Common Stock”) purchased or owned by the PIPE Investors; and (ii) 100,952,180 shares of Common Stock consisting of (a) 86,477,462 shares of Common Stock beneficially owned by certain former stockholders of ESS Tech Subsidiary, Inc. (f/k/a ESS Tech, Inc.), (b) up to 13,638,114 to be issued to eligible ESS securityholders representing shares of earnout stock under the Merger Agreement, (c) up to 824,998 shares underlying restricted stock units issued to certain Legacy ESS stockholders and (d) 11,606 shares of restricted Common Stock held by Legacy ESS securityholders that were issued pursuant to the exercise of options issued pursuant to the ESS 2014 Equity Incentive Plan that were assumed by us pursuant to the Merger Agreement. The Prior Registration Statement was declared effective by the SEC on November 10, 2021. Subsequently, we issued a Current Report on Form 8-K on November 22, 2021 notifying investors that they should not rely on certain previously issued financial statements. On December 9, 2021, we filed the Post-Effective Amendment No. 1 to the Prior Registration Statement with the SEC to include restated financial statements and to update certain other information, which was declared effective by the SEC on December 13, 2021. Pursuant to Rule 429 this registration statement shall constitute Post-Effective Amendment No. 2 to the Prior Registration Statement with respect to the offering of any unsold shares thereunder and is being filed (i) to include information from our Annual Report on Form 10-K for the year ended December 31, 2021 that was filed on March 3, 2022 (the “Annual Report”); and (ii) to update certain other information in the Prior Registration Statement. No additional securities are being registered under this Post-Effective Amendment No. 2. All applicable registration fees were paid at the time of the original filing of the Registration Statement.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
CURRENT ASSETS:
Cash and cash equivalents	$ 238,940	$ 4,901
Restricted cash	1,217	1,167
Prepaid expenses and other current assets	5,361	793
Total current assets	245,518	6,861
Property and equipment, net	4,501	1,836
Restricted cash	75	326
Other non-current assets	105	0
TOTAL ASSETS	250,199	9,023
CURRENT LIABILITIES:
Accounts payable	1,572	522
Accrued and other current liabilities	6,487	2,194
Deferred revenue	3,663	0
Notes payable	1,900	5,678
Total current liabilities	13,622	8,394
Notes payable	1,869	19
Warrant liabilities	0	3,329
Derivative liabilities	0	22,911
Earnout warrant liabilities	1,476	0
Public warrant liabilities	18,666	0
Private warrant liabilities	8,855	0
Other non-current liabilities	552	2,258
TOTAL LIABILITIES	45,040	36,911
COMMITMENTS AND CONTINGENCIES (NOTE 11)
STOCKHOLDERS' EQUITY (DEFICIT):
Preferred stock, $0.0001 par value, 200,000,000 shares authorized, none issued and outstanding as of December 31, 2021 and 2020	0	0
Common stock ($0.0001 par value; 2,000,000,000 shares authorized, 151,839,058 and 58,919,345 shares issued and outstanding as of December 31, 2021 and 2020, respectively)	16	6
Common stock warrants	0	153
Additional paid-in capital	745,753	35,446
Accumulated deficit	(540,610)	(63,493)
Total stockholders' equity (deficit)	205,159	(27,888)
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY (DEFICIT)	$ 250,199	$ 9,023

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
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)	151,839,058	58,919,345
Common stock, shares outstanding (in shares)	151,839,058	58,919,345

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating expenses
Research and development	$ 30,275	$ 12,896
Sales and marketing	3,041	1,158
General and administrative	27,286	3,338
Total operating expenses	60,602	17,392
Loss from operations	(60,602)	(17,392)
Other income (expenses)
Interest expense, net	(1,886)	(132)
Loss on revaluation of warrant liabilities	(37,584)	(1,296)
Loss on revaluation of derivative liabilities	(223,165)	(11,532)
Loss on revaluation of earnout liabilities	(154,806)	0
Other income (expense), net	926	(67)
Total other income (expenses)	(416,515)	(13,027)
Net loss to common stockholders	(477,117)	(30,419)
Comprehensive loss to common stockholders	$ (477,117)	$ (30,419)
Net loss per share, basic (in USD per share)	$ (5.73)	$ (0.52)
Net loss per share, diluted (in USD per share)	$ (5.73)	$ (0.52)
Weighted average shares used in per share calculation, basic (in shares)	83,256,431	58,880,742
Weighted average shares used in per share calculation, diluted (in shares)	83,256,431	58,880,742

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 StockLegacy ESS Common Stock	Common StockSeries C-2 Redeemable Convertible Preferred Stock	Common Stock Warrants	Common Stock WarrantsLegacy ESS Common Stock	Additional Paid-In Capital	Additional Paid-In CapitalLegacy ESS Common Stock	Additional Paid-In CapitalSeries C-2 Redeemable Convertible Preferred Stock	Accumulated Deficit	Previously Reported	Previously ReportedCommon Stock	Previously ReportedCommon Stock Warrants	Previously ReportedAdditional Paid-In Capital	Previously ReportedAccumulated Deficit	Retroactive application of recapitalization	Retroactive application of recapitalizationCommon Stock	Retroactive application of recapitalizationCommon Stock Warrants	Retroactive application of recapitalizationAdditional Paid-In Capital	Retroactive application of recapitalizationAccumulated Deficit
Balance at beginning of period (in shares) at Dec. 31, 2019	0												32,865,949					(32,865,949)
Balance at beginning of period at Dec. 31, 2019	$ 0												$ 34,372					$ (34,372)
Balance at end of period (in shares) at Dec. 31, 2020	0
Balance at end of period at Dec. 31, 2020	$ 0
Balance at beginning of period (in shares) at Dec. 31, 2019				58,810,346,000										7,060,668,000					51,749,678,000
Balance at beginning of period at Dec. 31, 2019	$ 2,214			$ 6			$ 153		$ 35,129			$ (33,074)	$ (32,158)	$ 1	$ 153	$ 762	$ (33,074)	$ 34,372	$ 5	$ 0	$ 34,367	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options (in shares)	108,999			108,999,000
Issuance of common stock upon exercise of options	$ 7								7
Stock-based compensation expense	310								310
Net loss	(30,419)											(30,419)
Balance at end of period (in shares) at Dec. 31, 2020				58,919,345,000
Balance at end of period at Dec. 31, 2020	$ (27,888)			$ 6			153		35,446			(63,493)
Balance at end of period (in shares) at Dec. 31, 2021	0
Balance at end of period at Dec. 31, 2021	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options (in shares)	2,496,070			13,112,000	2,482,958,000
Issuance of common stock upon exercise of options	$ 7	$ 664							7	$ 664
Shares issued (in shares)				5,746,003,000
Value of share issued	29,516			$ 1					29,515
Issuance of common stock upon exercise of warrants (in shares)				955,374,000	3,398,214,000
Issuance of 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)						29,153,806,000
Issuance of Legacy ESS Series C-2 Redeemable Convertible Preferred Stock upon exercise of C-2 Purchase Right and warrant			$ 238,483			$ 3					$ 238,480
Net business Combination and PIPE Financing (in shares)				35,495,281,000
Net Business Combination and PIPE Financing	128,917			$ 4					128,913
Issuance of common stock upon achievement of earnout (in shares)				15,674,965,000
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				151,839,058,000
Balance at end of period at Dec. 31, 2021	$ 205,159			$ 16			$ 0		$ 745,753			$ (540,610)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (477,117)	$ (30,419)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	572	436
Non-cash interest expense	80	91
Stock-based compensation expense	7,922	310
Loss on extinguishment of debt	0	62
Change in fair value of warrant liabilities	37,584	1,296
Loss on revaluation of derivative liabilities	223,165	11,532
Change in earnout liabilities	154,806	0
PPP loan forgiveness	(948)	0
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(4,673)	(135)
Accounts payable	886	(221)
Deferred revenue, current	3,663	0
Accrued and other liabilities	2,211	403
Net cash used in operating activities	(51,849)	(16,645)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(2,767)	(502)
Net cash used in investing activities	(2,767)	(502)
CASH FLOWS FROM FINANCING ACTIVITIES:
Borrowings on notes payable	20,000	4,936
Principal payments on notes payable	(21,067)	(221)
Proceeds from stock options exercised	671	7
Net cash contributions from Business Combination and PIPE Financing	258,730	0
Payments made towards offering costs	(7,895)	0
Proceeds from warrants exercised	10,995	0
Proceeds from exercise of Legacy ESS Series C-2 redeemable convertible preferred stock purchase rights and C-2 warrants upon Business Combination	15,559	0
Proceeds from sale of Legacy ESS Series C-2 redeemable convertible preferred stock, net of issuance costs	11,461	0
Net cash provided by financing activities	288,454	4,722
NET CHANGE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	233,838	(12,425)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH, BEGINNING OF YEAR	6,394	18,819
CASH, CASH EQUIVALENTS AND RESTRICTED CASH, END OF YEAR	240,232	6,394
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Interest	1,799	111
Non-cash investing and financing transactions:
Property and equipment purchases financed with term loan	0	52
Purchase of property and equipment included in accounts payable and accrued and other current liabilities	526	55
Extinguishment of derivative liabilities upon sale of Legacy ESS Series C-2 redeemable convertible preferred stock, net of amount allocated to warrants	18,055	0
Extinguishment of warrant liabilities upon exercise of Legacy ESS Series B, Series C-1 and Series C-2 redeemable convertible preferred stock warrants	26,178	0
Assumption of accrued expenses upon Business Combination	75	0
Assumption of private and public warrant liabilities upon Business Combination	11,833	0
Assumption of earnout warrant liabilities upon Business Combination	502	0
Assumption of earnout liability upon Business Combination	109,507	0
Extinguishment of earnout liability upon achievement of earnout and issuance of shares	263,338	0
Extinguishment of derivative liability upon exercise of Legacy ESS Series C-2 purchase right and related Series C-2 warrant liability upon Business Combination	222,924	0
Extinguishment of public warrant liability upon exercise of warrants	4,143	0
Cash and cash equivalents	238,940	4,901
Restricted cash, current	1,217	1,167
Restricted cash, non-current	75	326
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	$ 240,232	$ 6,394

DESCRITPION OF BUSINESS, BASIS

DESCRITPION OF BUSINESS, BASIS OF PRESENTATION AND RISKS AND UNCERTAINTIES	12 Months Ended
	Dec. 31, 2021
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 —On October 8, 2021 (the “Closing Date”), ACON S2 Acquisition Corp. (“STWO”), a publicly traded special purpose acquisition company, consummated a merger pursuant to the Agreement and Plan of Merger, dated May 6, 2021 (the “Merger Agreement”), 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”) following the approval at a special meeting of the stockholders of STWO held on October 5, 2021. 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 (the “Domestication”), 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.” (the “Company” or “ESS”), and its common shares of stock and warrants for shares of ESS common stock commenced trading on the New York Stock Exchange under the new ticker symbols “GWH” and “GWH.W”, respectively. ESS 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’s products are designed for a 25-year operating life without performance degradation, and with minimal annual operations and maintenance requirements. The Company is in the research and development phase. Its products are still being developed and do not yet meet standard specifications to be sold (“Commercially Available”). 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’s existing stockholders had the greatest voting interest in the Company; • Legacy ESS’s directors represented all of the new board of directors of the Company; • Legacy ESS’s 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 (“CODM”). 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, 2021 and 2020. 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 Bridge Loan, warrant liabilities, Series C-2 Convertible Preferred Stock Issuance Right, earnout liabilities, earnout warrant liabilities, public warrants, private warrants, 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 and money market accounts. The Company’s restricted cash includes a certificate of deposit and performance and payment bond. Deposits held with banks may exceed the amount of insurance provided on such deposits.

SIGNIFICANT ACCOUNTING POLICIES

SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
SIGNIFICANT ACCOUNTING POLICIES	SIGNIFICANT ACCOUNTING POLICIES Net Loss Per Share — The Company follows the two-class method when computing net income (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 shareholders 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 income (loss) attributable to common shareholders by the weighted average number of common shares outstanding during each year presented. Diluted income (loss) attributable to common shareholders per common share has been computed by dividing the net income (loss) attributable to common shareholders by the weighted average number of common shares outstanding plus the dilutive effect of outstanding options, warrants, restricted stock units (“RSU”), and earnout shares pending satisfaction of a regulatory holding period during the respective periods computed using the treasury method. In cases where the Company has a net loss, no dilutive effect is shown as options, warrants, RSU, and earnout shares pending satisfaction of a regulatory holding period become anti-dilutive. Cash and Cash Equivalents —The Company considers all highly liquid investments with an original maturity of three months or less when purchased to be cash equivalents. Cash equivalents are recorded at carrying value, which approximates fair value. Cash and cash equivalents include cash in bank accounts and money market funds. 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 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 balance sheets as current or non-current depending on when the cash will be contractually released. Property and Equipment —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, 2021 and 2020. Revenue Recognition —The Company did not recognize any revenue in fiscal years 2021 and 2020. The Company will recognize revenue in compliance with the requirements of, and the guidance provided by Accounting Standards Codification (“ASC”) 606 - Revenue from Contracts with Customers (Topic 606) . Sales and Marketing —Sales and marketing costs consist of compensation costs and employee benefits of marketing and sales personnel and related support teams, stock-based compensation, depreciation as well as travel, trade show sponsorships and events, conferences, and internet advertising costs. Advertising costs are expensed as incurred. The Company incurred advertising costs of $45 thousand and $8 thousand for the years ended December 31, 2021 and 2020, respectively. Research and Development —The Company is in the research and development phase. The Company’s product offering relies heavily on new technology currently undergoing development and does not yet meet standard specifications to be sold commercially. Research and development costs are expensed as incurred and consist primarily of product development material costs, consumables, maintenance spare parts, raw materials, components, scrap, freight costs, compensation costs and employee benefits, stock-based compensation, depreciation charges, consulting services, and other direct expenses, net of government grants. 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 monetizes the results of the activities funded by the grantor. The portion of such funding that the Company may be required to repay in certain circumstances is recorded in accrued and other liabilities and was $452 thousand and $186 thousand as of December 31, 2021 and 2020, respectively. General and Administrative —General and administrative costs include executive and administrative compensation costs and employee benefits, stock-based compensation, depreciation charges, professional services fees, insurance costs, bad debt, other allocated costs, such as facility-related expenses, supplies, and other fixed costs. Stock-Based Compensation —The Company accounts for stock-based compensation in accordance with ASC 718, Compensation – Stock Compensation (“ASC 718”) . The Company measures compensation expense for all stock-based awards for stock options granted to employees and non-employees based on the estimated fair values on the date of the grant. 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 Rat e—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. A such, the dividend yield has been estimated to be zero. In accordance with ASU 2016-09, Improvements to Employee Share-Based Payment Accounting, the Company may account for forfeitures as they occur or use estimated forfeitures. The Company elected to use actual forfeitures. The share-based compensation expense is recognized using a straight-line basis over the requisite service periods of the awards. The requisite service period is generally the vesting period of such options, and the stock-based compensation expense is presented as a component of operating expenses within the statements of operations. The Company recognizes all excess tax benefits and deficiencies for share-based awards as an income tax expense or benefit in the statements of operations. Excess tax benefits are classified with other income tax in the Consolidated Statement of Cash Flows as an operating activity. 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 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, 2021 and 2020, the Company has recorded a full valuation allowance against its deferred tax assets. ASC 740, Accounting for Income Taxes , 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 fiscal years 2021 and 2020. The Company recognizes accrued interest and penalties related to unrecognized tax benefits as income tax expense. No amounts were accrued for the payment of interest and penalties as of December 31, 2021 and 2020 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 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 February 2016, the FASB issued No. ASU 2016-02, Leases (ASC 842) which superseded previous guidance related to accounting for leases. This new guidance requires lessees to recognize most leases on their balance sheets as right-of-use (“ROU”) assets with corresponding lease liabilities and eliminates certain real estate-specific provisions. Accounting for lessors is substantially unchanged from current accounting principles. Lessees will be required to classify leases as either finance leases or operation leases. Initial balance sheet measurement is similar for both types of leases; however, expense recognition and amortization of right-of-use assets will differ. The new standard provides optional practical expedients in transition including a package of practical expedients that will allow the Company to carry forward its historical classification of existing leases. In addition, the new standard also provides practical expedients for an entity’s ongoing accounting. The Company elected the short-term lease recognition exemption for all leases that qualify, which means leases with initial terms of 12 months or less will not be recorded on the balance sheet. The new standard is effective for fiscal years beginning after December 15, 2021. The Company adopted ASC 842 effective January 1, 2022. The most significant effect of the adoption resulted in the recognition of an ROU asset and liability of approximately $5,000 thousand. The adoption of this standard did not have a material impact on the Company’s results of operations, cash flows or liquidity measures. 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 is currently evaluating the impact that the standard will have on its financial statements and related disclosures. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which simplifies the accounting for income taxes. ASU 2019-12 is effective for emerging-growth companies for fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022. The Company is currently evaluating the impact that the standard will have on its financial statements and related disclosures. In August 2020, the FASB issued ASU 2020-06 , Debt— Debt with Conversion and Other Options (Subtopic470-20) and Derivatives and Hedging— Contracts in Entity’s Own Equity (Subtopic 815-40) —Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (“ASU 2020-06”). ASU 2020-06 reduces the number of accounting models for convertible debt instruments and redeemable convertible preferred stock. For convertible instruments with conversion features that are not required to be accounted for as derivatives under Topic 815, Derivatives and Hedging , or that do not result in substantial premiums accounted for as paid-in capital, the embedded conversion features no longer are separated from the host contract. ASU 2020-06 also removes certain conditions that should be considered in the derivatives scope exception evaluation under Subtopic 815-40, Derivatives and Hedging—Contracts in Entity’s Own Equity

BUSINESS COMBINATION

BUSINESS COMBINATION	12 Months Ended
	Dec. 31, 2021
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’s 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 (see below for definition)), 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 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 5. 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 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

DEFERRED REVENUE

DEFERRED REVENUE	12 Months Ended
	Dec. 31, 2021
Contract with Customer, Liability [Abstract]
DEFERRED REVENUE	DEFERRED REVENUE As of December 31, 2021, the Company has entered into contracts with customers for which sales have not been recognized as the Company has not yet met revenue recognition criteria. As per customer arrangements, the Company invoices customers in advance of recognizing the sale of units and records advance deposits as deferred revenue, as reported in current liabilities. The following table summarizes the balances of the Company’s deferred revenue as of December 31, 2021 and 2020 for contracts that are expected to be completed and revenue recognized in the subsequent twelve month period (in thousands): 2021 2020 Deferred revenue - units shipped in August 2021 $ 383 $ — Deferred revenue - units shipped in September 2021 171 — Other deferred revenue 3,109 — Total deferred revenue $ 3,663 $ —

LOSS PER SHARE

LOSS PER SHARE	12 Months Ended
	Dec. 31, 2021
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, 2021 and 2020 (in thousands, except per share data): 2021 2020 Net Loss attributable to common stockholders $ (477,117) $ (30,419) Weighted-average shares outstanding – Basic and Diluted 83,256,431 58,880,742 Net loss per share – Basic and Diluted $ (5.73) $ (0.52) Due to the net losses for the years ended December 31, 2021 and 2020, 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: 2021 2020 Stock options 3,796,530 5,732,422 Restricted stock units 3,392,153 — Warrants 11,461,247 450,153 Earnout shares pending satisfaction of regulatory holding period 6,707,318 — 25,357,248 6,182,575

PREPAID EXPENSES AND OTHER CURR

PREPAID EXPENSES AND OTHER CURRENT ASSETS	12 Months Ended
	Dec. 31, 2021
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 as of December 31, 2021 and 2020 (in thousands): 2021 2020 Insurance $ 3,482 $ 107 Vendor advances 1,103 473 Accounts receivable 517 — Other 259 213 Total prepaid expenses and other current assets $ 5,361 $ 793

PROPERTY AND EQUIPMENT, NET

PROPERTY AND EQUIPMENT, NET	12 Months Ended
	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT, NET	PROPERTY AND EQUIPMENT, NET Property and equipment, net consist of the following as of December 31, 2021 and 2020 (in thousands): 2021 2020 Machinery and equipment $ 2,868 $ 2,217 Furniture and fixtures 90 90 Leasehold improvements 746 677 Construction in process 2,517 — Total property and equipment 6,221 2,984 Less accumulated depreciation (1,720) (1,148) Total property and equipment, net $ 4,501 $ 1,836

ACCRUED AND OTHER CURRENT LIABI

ACCRUED AND OTHER CURRENT LIABILITIES	12 Months Ended
	Dec. 31, 2021
Payables and Accruals [Abstract]
ACCRUED AND OTHER CURRENT LIABILITIES	ACCRUED AND OTHER CURRENT LIABILITIES Accrued and other current liabilities consist of the following as of December 31, 2021 and 2020 (in thousands): 2021 2020 Payroll and related benefits $ 1,876 $ 777 Materials and related purchases 2,108 464 Deferred rent 142 462 Professional and consulting fees 1,820 248 Other 541 243 Total accrued and other current liabilities $ 6,487 $ 2,194

LEASES

LEASES	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
LEASES	LEASES The Company leases office and manufacturing space in Wilsonville, Oregon under operating leases that expire in 2025. Future minimum lease payments 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 aggregated $1,491 thousand and $837 thousand in 2021 and 2020, respectively. Each of these leases provides the Company an option to renew the lease for an additional 60 months, exercisable upon notice to renew ranging from 60 days to 12 months prior to the end of the initial lease term. As of the date of issuance of these financial statements, the Company has not provided such notice.

BORROWINGS

BORROWINGS	12 Months Ended
	Dec. 31, 2021
Debt Disclosure [Abstract]
BORROWINGS	BORROWINGS Long term debt consists of the following as of December 31, 2021 and 2020 (in thousands): 2021 2020 Notes payable $ 3,769 $ 4,761 PPP loan — 936 Total notes payable 3,769 5,697 Less current portion of notes payable 1,900 5,678 Long-term notes payable, net of current portion $ 1,869 $ 19 Payroll Protection Program Loan On April 19, 2020, the Company entered into an unsecured promissory note under the Payroll Protection Program (“the PPP Loan”), with a bank under the PPP administered by the United States Small Business Administration (“SBA”) and authorized by the Keeping American Workers Employed and Paid Act, which is part of the CARES Act, enacted on March 27, 2020. The principal amount of the PPP Loan was $936 thousand. The PPP Loan bore interest of 1.0% per annum and was disbursed to the Company on April 20, 2020. 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 year ended December 31, 2021. Bridge Loan In July 2021, the Company entered into a six-month $20,000 thousand bridge loan (the “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. 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. 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 January 1, 2023 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 notes payable bear interest at 0.50% below the bank’s prime rate (2.75% on December 31, 2021). The Company makes monthly interest and principal payments on the note payable based on the schedule defined in the agreement. In conjunction with the notes payable, Legacy ESS issued warrants to purchase 100,161 shares of Series B redeemable convertible preferred stock and 103,107 shares of Series C redeemable convertible preferred stock in July 2018 and March 2020, respectively. The Series B redeemable convertible preferred stock warrants and Series C redeemable convertible preferred stock warrants have exercise prices of $0.96 and $1.25 per share, respectively and expire 10 years after issuance. The fair value of Series B redeemable convertible preferred stock warrants and Series C redeemable convertible preferred stock warrants were $55 thousand and $44 thousand, respectively, at the time of issuance. The fair value of the Series B redeemable convertible preferred stock warrants was initially recorded as a reduction of the value of the notes payable and were amortized over the term of the loan as interest expense using the effective interest rate method. Unamortized Series B redeemable convertible preferred stock warrants were treated as a component of loss on extinguishment of debt. The Series C redeemable convertible preferred stock warrants were issued in conjunction with the additional $4,000 thousand borrowing and were a component of the loss on extinguishment of debt. All outstanding shares of Legacy ESS’s redeemable convertible preferred stock were converted to shares of common stock immediately prior to the completion of the Business Combination. See Note 12. Interest expense of $0 and $4 thousand were recognized related to the amortization of warrants issued in conjunction with the notes payable for the years ended December 31, 2021 and December 31, 2020, respectively. The audit opinion as of and for the year ended December 31, 2020 financial statements contained a going concern explanatory paragraph. Under the notes payable loan agreement, a going concern opinion with respect to the Company’s audited financial statements is a material adverse change resulting in an event of default. In accordance with a subjective acceleration clause, the Lender had an option to elect to accelerate $4,583 thousand of the Company’s existing indebtedness as of December 31, 2020 to be immediately due and payable. As of December 31, 2020, the event of default would have also accelerated the $943 thousand in principal and interest due on the PPP Loan because of the cross-default provisions. The Company had classified the notes payable and PPP loan as current liabilities as of December 31, 2020 due to the considerations discussed above and the assessment that the material adverse change clause under the notes payable and PPP Loan agreements was not within the Company’s control. As of December 31, 2021, the Company has concluded that the Business Combination alleviated the risk related to going concern, as well as that related to the subjective acceleration clause. Annual maturities on notes payable outstanding at December 31, 2021 are as follows (in thousands): 2022 $ 1,900 2023 1,600 2024 333 Total maturities 3,833 Less: unamortized debt premium (64) Total notes payable $ 3,769

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2021
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 financial statements. As of December 31, 2021, and 2020, 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, 2021 the letter of credit was secured by a restricted certificate of deposit account totaling $125 thousand. There were no draws against the letter of credit during the years ended December 31, 2021 and 2020. 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, 2021 and 2020, total unfulfilled noncancelable purchase commitments were $10,160 thousand and $3,410 thousand, respectively. In addition, total unfulfilled cancellable purchase commitments amounted to $10,446 thousand and $787 thousand as of December 31, 2021, and 2020, respectively. These purchase commitments were not recorded in the financial statements.

LEGACY ESS REDEEMABLE CONVERTIB

LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK	12 Months Ended
	Dec. 31, 2021
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’s redeemable convertible preferred stock converted into an aggregate 57,104,332 shares of common stock. Legacy ESS Rights to Purchase Series C-2 Convertible Preferred Stock Legacy ESS’s 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’s 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 and expense in the Consolidated Statement of Operations. The Series C-2 Redeemable Convertible Preferred Stock Issuance Right was initially scheduled to expire in August 2021 and was classified as a noncurrent 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 C-2 Purchase 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’s 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 Purchase 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 C-2 Convertible Redeemable Preferred Stock required to be issued by Legacy ESS and purchased by investors under the C-2 Redeemable Convertible Preferred Stock Purchase Right were adjusted, and Legacy ESS issued Series C-2 warrants. The Series C-2 warrants were exercisable at a price of $.00007 per share upon a successful Business Combination with STWO. The investors were permitted to purchase shares subject to the C-2 Redeemable Convertible Preferred Stock Purchase 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 C-2 Redeemable Convertible Preferred Stock Purchase Agreement and related C-2 Warrants were as follows: As of May 7, 2021 Upon Completion of SPAC merger Quantity Price Series C-2 Redeemable Convertible Preferred Stock Purchase Right 7,994,442 $ 2.00 Series C-2 Warrant exercisable upon SPAC merger 21,159,364 $ 0.00007 Total Proceeds Upon Exercise The C-2 warrants and Purchase Rights were exercised in conjunction with the Business Combination which closed on October 8, 2021 and the Company received proceeds of $15,559 thousand, which were net of $439 thousand in issuance costs, see Note 3. The table below summarizes the shares subject to C-2 Purchase Right activity during the year ended December 31, 2021: December 31, Extinguished Exercised December 31, Series C-2 Purchase Right 39,971,716 26,231,295 13,740,421 — The Company recorded net increases in the derivative liability of $223,165 thousand and $11,532 thousand for the years ended December 31, 2021 and 2020, respectively, for changes in the estimated fair value of the Series C-2 Redeemable Convertible Preferred Stock Purchase Right and C-2 Warrant exercisable upon completion of the Business Combination. As of December 31, 2021 and 2020, the derivative liability associated with the C-2 Purchase Right was zero and $22,911 thousand, respectively. Legacy ESS Warrants Legacy ESS periodically issued warrants (“Legacy ESS warrants”) in conjunction with the issuance of preferred stock or debt. As of December 31, 2021 and 2020, the following Legacy ESS warrants were outstanding: 2021 2020 Common Stock Warrants — 450,153 Series B Preferred Warrants — 2,007,308 Series C-1 Preferred Warrants — 103,107 Total Warrants — 2,560,568 Legacy ESS outstanding warrants as of December 31, 2020 include awards issued in conjunction with stock and debt issuances discussed within Note 10. Legacy ESS Series B redeemable convertible preferred stock warrants and Series C redeemable convertible preferred stock warrants were liability awards. Refer to Note 16. 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 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. The table below shows the Legacy ESS warrant activities during the year ended December 31, 2021: December 31, Issued Exercised December 31, Common Stock Warrants 450,153 — 450,153 — Series B Preferred Stock Warrants 2,007,308 — 2,007,308 — Series C-1 Preferred Stock Warrants 103,107 — 103,107 — Series C-2 Preferred Stock Warrants — 22,021,284 22,021,284 — Total Warrants 2,560,568 22,021,284 24,581,852 — The warrants were valued using the following assumptions: For the year ended December 31, 2021 Preferred B warrants Preferred C warrants Expected volatility 80 % 60% - 80% Expected term (in years) 2.00 2.00 Risk‑free interest rate 0.16% - 0.28% 0.16% - 0.32% Dividend yield 0 % 0 % As of December 31, 2020 Preferred B Preferred C Expected volatility 80 % 80 % Expected term (in years) 2.00 2.00 Risk‑free interest rate 0.13 % 0.13 % Dividend yield 0 % 0 % 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, 2021
Equity [Abstract]
COMMON STOCK WARRANTS	COMMON STOCK WARRANTS ESS assumed all warrants issued by STWO upon completion of the Business Combination (see Note 3). As of December 31, 2021, the Company had 7,377,913 Public Warrants, 3,500,000 Private Warrants and 583,334 Earnout Warrants outstanding. As part of STWO’s initial public offering, 8,333,287 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 Public Warrants are listed on the NYSE under the symbol “GWH.W.” 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 consummated a private placement of 4,666,667 Private Warrants with 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, 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 — 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, 2021, the Company recorded a net increase to the liabilities for Earnout Warrants, Public Warrants and Private Warrants of $974 thousand, $14,476 thousand and $5,355 thousand, respectively. The Company received proceeds of $10,987 thousand related to the exercise of 955,374 Public Warrants during the year ending December 31, 2021.

EMPLOYEE STOCK PURCHASE PLAN

EMPLOYEE STOCK PURCHASE PLAN	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
EMPLOYEE STOCK PURCHASE PLAN	EMPLOYEE STOCK PURCHASE PLANThe Company adopted an Employee Stock Purchase Plan (the “ESPP Plan”) in connection with the consummation of the Business Combination on October 8, 2021. All qualified employees may voluntarily enroll to purchase the Company’s common stock through payroll deductions at a price equal to 85% of the lower of the fair market values of the stock as of the beginning or the end of the offering periods. An employee’s payroll deductions under the ESPP Plan are limited to 15% of the employee’s compensation. As of December 31, 2021, 3,060,000 shares were reserved for future issuance under the ESPP Plan.

STOCK-BASED COMPENSATION PLAN

STOCK-BASED COMPENSATION PLAN	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
STOCK-BASED COMPENSATION PLAN	STOCK-BASED COMPENSATION PLAN 2014 Equity Incentive Plan The Company has a stock-based compensation plan called the 2014 Equity Incentive Plan (“2014 Plan”). Under the 2014 Plan, the Company is authorized to issue 15,482,675 shares of common stock. 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. No Stock Appreciation Rights, Restricted Stock Awards, or Restricted Stock Unit Awards are outstanding as of December 31, 2021 and 2020. Option prices for incentive stock options are normally set at not less than the fair market value of the Company’s common stock at the date of grant. Employee options generally cliff vest at the end of the first year and then 1/48th of the original grant over the remaining three years; however, some vesting dates granted under the 2014 Plan began prior to the grant date, which accelerated the vesting period for the related options. The Board has the power to accelerate the vesting of options granted. There were no accelerations during fiscal years 2020 and 2021. Options were contingent on continued employment with the Company. Grants expired 10 years from the date of grant. Each Legacy ESS option from the 2014 Plan that was outstanding immediately prior to the Business Combination, whether vested or unvested, was converted into an option to acquire a number of shares of the Company’s common stock (each such option, an "Exchanged Option") equal to the product (rounded down to the nearest whole number) of (i) the number of shares of Legacy ESS common stock subject to such Legacy ESS option immediately prior to the Business Combination and (ii) the Per Share Consideration, at an exercise price per share (rounded up to the nearest whole cent) equal to (A) the exercise price per share of such Legacy ESS option immediately prior to the consummation of the Business Combination, divided by (B) the Per Share Consideration. Except as specifically provided in the Merger Agreement, following the Business Combination, each Exchanged Option will continue to be governed by the same terms and conditions (including vesting and exercisability terms) as were applicable to the corresponding former Legacy ESS option immediately prior to the consummation of the Business Combination. All stock option activities were retroactively restated to reflect the Exchanged Options. 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 . Under the 2021 Plan, the Company is authorized to issue 12,210,000 shares of common stock. The stock awards may be issued as ISO, NSO, Stock Appreciation Rights, Restricted Stock Awards, or Restricted Stock Unit Awards. 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 least 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, 2022, the number of Shares available for issuance under the 2021 Plan was increased by 5,400,000 in accordance with the plan and as approved by the Board. The stock awards may be issued as ISO, 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. Option prices for incentive stock options are set at the fair market value of the Company’s common stock at the date of grant. Employee options generally cliff vest at the end of the first year and then 1/48th of the original grant over the remaining three years. Grants expire 10 years from the date of grant. No ISOs, NSOs, Restricted Stock Awards, nor Stock Appreciation Rights are outstanding as of December 31, 2021. Shares Available for Future Grant As of December 31, 2021, shares available for future grant under the Company’s 2021 Plan was 9,785,574 shares, which includes shares assumed from the Company’s 2014 Plan. Stock option and RSU activity, prices, and values adjusted by the Per Share Consideration, during the year ended December 31, 2021 is as follows (in thousands, except for share, per share, and contractual term data): Options Outstanding Restricted Stock Units Number of Weighted Weighted Aggregate Number of plan shares outstanding Weighted average Balances as of December 31, 2019 2,104,223 $ 0.37 7.82 $ 821 Recapitalization Impact 995,215 (0.12) Balances at December 31, 2019 3,099,438 $ 0.25 7.82 821 Granted 3,271,856 0.33 Exercised (108,999) 0.06 Forfeited (529,873) 0.29 Balances as of December 31, 2020 5,732,422 $ 0.30 8.23 4,333 Granted 1,454,549 1.75 3,392,153 $ 10.69 Exercised (2,496,070) 0.27 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 vested and exercisable - December 31, 2020 2,825,238 $ 0.26 7.21 2,215 Options vested and exercisable - December 31, 2021 1,827,374 $ 0.31 7.20 20,337 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 $6,244 thousand and $48 thousand during the years ended December 31, 2021 and 2020, 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, 2021, and 2020, respectively, the weighted average estimated fair value using the Black-Scholes Merton option pricing model was $5.63 and $0.65 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: 2021 2020 Risk-free rate 1.01 % 0.93 % Expected dividends — — Expected term 6 years 6 years Expected volatility 75.14 % 71.06 % The 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, 2021 and 2020 (in thousands): 2021 2020 Research and development $ 2,233 $ 79 Sales and marketing 213 47 General and administrative 5,476 184 Total stock-based compensation $ 7,922 $ 310

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS The Company follows ASC 820, Fair Value Measurements , 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, 2021 Level 1 Level 2 Level 3 Total Assets: Cash equivalents and restricted cash: Money market funds $ 237,897 $ — $ — $ 237,897 Certificate of deposit — 125 — 125 Total assets $ 237,897 $ 125 $ — $ 238,022 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 $ 18,666 $ 10,331 $ — $ 28,997 December 31, 2020 Level 1 Level 2 Level 3 Total Assets: Cash equivalents and restricted cash: Money market funds $ 3,046 $ — $ — $ 3,046 Certificate of deposit — 326 — 326 Total assets $ 3,046 $ 326 $ — $ 3,372 Liabilities: Derivative liabilities $ — $ — $ 22,911 $ 22,911 Warrant liabilities — — 3,329 3,329 Total liabilities $ — $ — $ 26,240 $ 26,240 For fiscal year 2020 and 2021, there were no transfers among Level 1, Level 2, or Level 3 categories. 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 that have maturities of 90 days or less. Money market funds are classified as cash equivalents and are recorded at their carrying value, which approximates fair value. Level 2 Assets: The Company invests in a certificate of deposit with a maturity of one year from purchase date. The certificate of deposit is classified as restricted cash and is recorded at its carrying value, which approximates fair value. Level 1 Liabilities: The Company values its Public Common Stock warrants based on the market price of the warrant. 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: 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 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 Statement of Operations and Other Comprehensive Income. 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 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’s 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. 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 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 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, 2021 and 2020 (in thousands): 2021 2020 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 — — Warrant liabilities: Beginning balance January 1 3,329 1,989 Change in fair value 17,753 1,296 Fair value of warrants issued 5,096 44 Fair value of warrants exercised (26,178) — Ending balance December 31 — 3,329 Series C-2 Convertible Preferred Stock Issuance Right liability: Beginning balance January 1 22,911 11,379 Change in fair value 223,165 11,532 Fair value of derivatives extinguished (23,152) — Fair value of Series C-2 Convertible Preferred Stock Issuance Right exercised (222,924) — Ending balance December 31 — 22,911 Total $ — $ 26,240

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2021
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, 2021 2020 Deferred Tax Assets: Net operating losses $ 24,655 $ 11,566 Tax credit carryforward 292 47 Non-qualifying stock options 1,143 — Other 1,231 837 Deferred tax assets 27,321 12,450 Valuation allowance (27,321) (12,450) Deferred tax assets, net of valuation allowance $ — $ — ASC Topic 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 2021 and 2020. The valuation allowance increased by $14,871 thousand during the year ended December 31, 2021. As of December 31, 2021, the Company has federal and state net operating loss carryforwards of $94,058 thousand and $94,023 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 research and development tax credit carryforwards totaling $584 thousand. The federal research and development credit carryforwards begin to expire in 2039, unless previously utilized. The effective tax rate of the Company’s provision for income taxes differs from the federal statutory rate as follows: Years Ended December 31, 2021 2020 Tax computed at federal statutory rate 21.0 % 21.0 % State tax, net of federal tax benefit 0.6 3.0 Stock compensation (0.1) (0.2) Transaction costs related to the Business Combination (0.2) — Warrant liabilities revaluation (1.7) (8.9) Derivative liabilities revaluation (9.8) — Earnout shares liabilities revaluation (6.8) — R&D tax credits — 0.1 Other 0.1 — Valuation allowance (3.1) (15.0) Income tax expense (benefit) — % — % The changes in the Company's uncertain tax positions are summarized as follows (in thousands): Balance as of December 31, 2019 $ 12 Additions in 2020 35 Balance as of December 31, 2020 $ 47 Additions in 2021 245 Balance as of December 31, 2021 $ 292 During the years ended December 31, 2021 and 2020, the Company recognized uncertain tax positions of $245 thousand and $35 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 2021 and 2020. 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.

DEFINED CONTRIBUTION PLAN

DEFINED CONTRIBUTION PLAN	12 Months Ended
	Dec. 31, 2021
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 fully always vested. For the years ended December 31, 2021 and 2020, the Company contributed $292 thousand and $173 thousand, respectively.

RELATED PARTY TRANSACTIONS

RELATED PARTY TRANSACTIONS	12 Months Ended
	Dec. 31, 2021
Related Party Transactions [Abstract]
RELATED PARTY TRANSACTIONS	RELATED PARTY TRANSACTIONS During the year ended December 31, 2020, the Company hired consultants through one of its Board members to review its technology. The Company paid $31 thousand to the consultants. In December 2020, the Company also entered into a sales agreement for the purchase and installation of one Energy Warehouse with a related party. 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 our 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. These related parties were also issued 6,707,318 of the Earnout Shares discussed in Note 3. As of December 31, 2021, the Company had recorded accounts receivable of $66 thousand and deferred revenue of $171 thousand for sales of Energy Warehouse products to related parties based on the December 2020 sales agreement above.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	12 Months Ended
	Dec. 31, 2021
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTSIn February 2022, the Compensation Committee of the Board of Directors granted various employees RSU awards under which the holders have the right to receive an aggregate of approximately 2,100,000 shares of the Company’s common stock. These awards vest in sixteen equal quarterly installments beginning on May 20, 2022.

SIGNIFICANT ACCOUNTING POLICI_2

SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2021
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’s existing stockholders had the greatest voting interest in the Company; • Legacy ESS’s directors represented all of the new board of directors of the Company; • Legacy ESS’s 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	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 (“CODM”). 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, 2021 and 2020.
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 Bridge Loan, warrant liabilities, Series C-2 Convertible Preferred Stock Issuance Right, earnout liabilities, earnout warrant liabilities, public warrants, private warrants, 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 and money market accounts. The Company’s restricted cash includes a certificate of deposit and performance and payment bond. Deposits held with banks may exceed the amount of insurance provided on such deposits.
Net Loss per Share	Net Loss Per Share — The Company follows the two-class method when computing net income (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 shareholders 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 income (loss) attributable to common shareholders by the weighted average number of common shares outstanding during each year presented. Diluted income (loss) attributable to common shareholders per common share has been computed by dividing the net income (loss) attributable to common shareholders by the weighted average number of common shares outstanding plus the dilutive effect of outstanding options, warrants, restricted stock units (“RSU”), and earnout shares pending satisfaction of a regulatory holding period during the respective periods computed using the treasury method. In cases where the Company has a net loss, no dilutive effect is shown as options, warrants, RSU, and earnout shares pending satisfaction of a regulatory holding period become anti-dilutive.
Cash, Cash Equivalents, and Restricted Cash	Cash and Cash Equivalents —The Company considers all highly liquid investments with an original maturity of three months or less when purchased to be cash equivalents. Cash equivalents are recorded at carrying value, which approximates fair value. Cash and cash equivalents include cash in bank accounts and money market funds. 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
Property and Equipment	Property and Equipment —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, 2021 and 2020.
Revenue Recognition	Revenue Recognition —The Company did not recognize any revenue in fiscal years 2021 and 2020. The Company will recognize revenue in compliance with the requirements of, and the guidance provided by Accounting Standards Codification (“ASC”) 606 - Revenue from Contracts with Customers (Topic 606)
Sales and Marketing	Sales and Marketing —Sales and marketing costs consist of compensation costs and employee benefits of marketing and sales personnel and related support teams, stock-based compensation, depreciation as well as travel, trade show sponsorships and events, conferences, and internet advertising costs. Advertising costs are expensed as incurred. The Company incurred advertising costs of $45 thousand and $8 thousand for the years ended December 31, 2021 and 2020, respectively.
Research and Development	Research and Development —The Company is in the research and development phase. The Company’s product offering relies heavily on new technology currently undergoing development and does not yet meet standard specifications to be sold commercially. Research and development costs are expensed as incurred and consist primarily of product development material costs, consumables, maintenance spare parts, raw materials, components, scrap, freight costs, compensation costs and employee benefits, stock-based compensation, depreciation charges, consulting services, and other direct expenses, net of government grants. 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 monetizes the results of the activities funded by the grantor.
General and Administrative	General and Administrative —General and administrative costs include executive and administrative compensation costs and employee benefits, stock-based compensation, depreciation charges, professional services fees, insurance costs, bad debt, other allocated costs, such as facility-related expenses, supplies, and other fixed costs.
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 compensation expense for all stock-based awards for stock options granted to employees and non-employees based on the estimated fair values on the date of the grant. 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 Rat e—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. A such, the dividend yield has been estimated to be zero. In accordance with ASU 2016-09, Improvements to Employee Share-Based Payment Accounting, the Company may account for forfeitures as they occur or use estimated forfeitures. The Company elected to use actual forfeitures. The share-based compensation expense is recognized using a straight-line basis over the requisite service periods of the awards. The requisite service period is generally the vesting period of such options, and the stock-based compensation expense is presented as a component of operating expenses within the statements of operations. The Company recognizes all excess tax benefits and deficiencies for share-based awards as an income tax expense or benefit in the statements of operations. Excess tax benefits are classified with other income tax in the Consolidated Statement of Cash Flows as an operating activity.
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 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, 2021 and 2020, the Company has recorded a full valuation allowance against its deferred tax assets. ASC 740, Accounting for Income Taxes , 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 fiscal years 2021 and 2020. The Company recognizes accrued interest and penalties related to unrecognized tax benefits as income tax expense. No amounts were accrued for the payment of interest and penalties as of December 31, 2021 and 2020 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	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 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 February 2016, the FASB issued No. ASU 2016-02, Leases (ASC 842) which superseded previous guidance related to accounting for leases. This new guidance requires lessees to recognize most leases on their balance sheets as right-of-use (“ROU”) assets with corresponding lease liabilities and eliminates certain real estate-specific provisions. Accounting for lessors is substantially unchanged from current accounting principles. Lessees will be required to classify leases as either finance leases or operation leases. Initial balance sheet measurement is similar for both types of leases; however, expense recognition and amortization of right-of-use assets will differ. The new standard provides optional practical expedients in transition including a package of practical expedients that will allow the Company to carry forward its historical classification of existing leases. In addition, the new standard also provides practical expedients for an entity’s ongoing accounting. The Company elected the short-term lease recognition exemption for all leases that qualify, which means leases with initial terms of 12 months or less will not be recorded on the balance sheet. The new standard is effective for fiscal years beginning after December 15, 2021. The Company adopted ASC 842 effective January 1, 2022. The most significant effect of the adoption resulted in the recognition of an ROU asset and liability of approximately $5,000 thousand. The adoption of this standard did not have a material impact on the Company’s results of operations, cash flows or liquidity measures. 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 is currently evaluating the impact that the standard will have on its financial statements and related disclosures. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which simplifies the accounting for income taxes. ASU 2019-12 is effective for emerging-growth companies for fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022. The Company is currently evaluating the impact that the standard will have on its financial statements and related disclosures. In August 2020, the FASB issued ASU 2020-06 , Debt— Debt with Conversion and Other Options (Subtopic470-20) and Derivatives and Hedging— Contracts in Entity’s Own Equity (Subtopic 815-40) —Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (“ASU 2020-06”). ASU 2020-06 reduces the number of accounting models for convertible debt instruments and redeemable convertible preferred stock. For convertible instruments with conversion features that are not required to be accounted for as derivatives under Topic 815, Derivatives and Hedging , or that do not result in substantial premiums accounted for as paid-in capital, the embedded conversion features no longer are separated from the host contract. ASU 2020-06 also removes certain conditions that should be considered in the derivatives scope exception evaluation under Subtopic 815-40, Derivatives and Hedging—Contracts in Entity’s Own Equity

BUSINESS COMBINATION (Tables)

BUSINESS COMBINATION (Tables)	12 Months Ended
	Dec. 31, 2021
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 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

DEFERRED REVENUE (Tables)

DEFERRED REVENUE (Tables)	12 Months Ended
	Dec. 31, 2021
Contract with Customer, Liability [Abstract]
Schedule of Deferred Revenue	The following table summarizes the balances of the Company’s deferred revenue as of December 31, 2021 and 2020 for contracts that are expected to be completed and revenue recognized in the subsequent twelve month period (in thousands): 2021 2020 Deferred revenue - units shipped in August 2021 $ 383 $ — Deferred revenue - units shipped in September 2021 171 — Other deferred revenue 3,109 — Total deferred revenue $ 3,663 $ —

LOSS PER SHARE (Tables)

LOSS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2021
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, 2021 and 2020 (in thousands, except per share data): 2021 2020 Net Loss attributable to common stockholders $ (477,117) $ (30,419) Weighted-average shares outstanding – Basic and Diluted 83,256,431 58,880,742 Net loss per share – Basic and Diluted $ (5.73) $ (0.52)
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: 2021 2020 Stock options 3,796,530 5,732,422 Restricted stock units 3,392,153 — Warrants 11,461,247 450,153 Earnout shares pending satisfaction of regulatory holding period 6,707,318 — 25,357,248 6,182,575

PREPAID EXPENSES AND OTHER CU_2

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Tables)	12 Months Ended
	Dec. 31, 2021
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 as of December 31, 2021 and 2020 (in thousands): 2021 2020 Insurance $ 3,482 $ 107 Vendor advances 1,103 473 Accounts receivable 517 — Other 259 213 Total prepaid expenses and other current assets $ 5,361 $ 793

PROPERTY AND EQUIPMENT, NET (Ta

PROPERTY AND EQUIPMENT, NET (Tables)	12 Months Ended
	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, net	Property and equipment, net consist of the following as of December 31, 2021 and 2020 (in thousands): 2021 2020 Machinery and equipment $ 2,868 $ 2,217 Furniture and fixtures 90 90 Leasehold improvements 746 677 Construction in process 2,517 — Total property and equipment 6,221 2,984 Less accumulated depreciation (1,720) (1,148) Total property and equipment, net $ 4,501 $ 1,836

ACCRUED AND OTHER CURRENT LIA_2

ACCRUED AND OTHER CURRENT LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2021
Payables and Accruals [Abstract]
Schedule of Accrued and Other Current Liabilities	Accrued and other current liabilities consist of the following as of December 31, 2021 and 2020 (in thousands): 2021 2020 Payroll and related benefits $ 1,876 $ 777 Materials and related purchases 2,108 464 Deferred rent 142 462 Professional and consulting fees 1,820 248 Other 541 243 Total accrued and other current liabilities $ 6,487 $ 2,194

LEASES (Tables)

LEASES (Tables)	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Schedule of Future Minimum Lease Payments	Future minimum lease payments 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, 2021
Debt Disclosure [Abstract]
Schedule of Long Term Debt	Long term debt consists of the following as of December 31, 2021 and 2020 (in thousands): 2021 2020 Notes payable $ 3,769 $ 4,761 PPP loan — 936 Total notes payable 3,769 5,697 Less current portion of notes payable 1,900 5,678 Long-term notes payable, net of current portion $ 1,869 $ 19
Schedule of Annual Maturities on Notes Payable	Annual maturities on notes payable outstanding at December 31, 2021 are as follows (in thousands): 2022 $ 1,900 2023 1,600 2024 333 Total maturities 3,833 Less: unamortized debt premium (64) Total notes payable $ 3,769

LEGACY ESS REDEEMABLE CONVERT_2

LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK (Tables)	12 Months Ended
	Dec. 31, 2021
Temporary Equity Disclosure [Abstract]
Schedule of Warrants	The number of shares subject to and potential proceeds from the C-2 Redeemable Convertible Preferred Stock Purchase Agreement and related C-2 Warrants were as follows: As of May 7, 2021 Upon Completion of SPAC merger Quantity Price Series C-2 Redeemable Convertible Preferred Stock Purchase Right 7,994,442 $ 2.00 Series C-2 Warrant exercisable upon SPAC merger 21,159,364 $ 0.00007 Total Proceeds Upon Exercise The table below summarizes the shares subject to C-2 Purchase Right activity during the year ended December 31, 2021: December 31, Extinguished Exercised December 31, Series C-2 Purchase Right 39,971,716 26,231,295 13,740,421 — Legacy ESS periodically issued warrants (“Legacy ESS warrants”) in conjunction with the issuance of preferred stock or debt. As of December 31, 2021 and 2020, the following Legacy ESS warrants were outstanding: 2021 2020 Common Stock Warrants — 450,153 Series B Preferred Warrants — 2,007,308 Series C-1 Preferred Warrants — 103,107 Total Warrants — 2,560,568 The table below shows the Legacy ESS warrant activities during the year ended December 31, 2021: December 31, Issued Exercised December 31, Common Stock Warrants 450,153 — 450,153 — Series B Preferred Stock Warrants 2,007,308 — 2,007,308 — Series C-1 Preferred Stock Warrants 103,107 — 103,107 — Series C-2 Preferred Stock Warrants — 22,021,284 22,021,284 — Total Warrants 2,560,568 22,021,284 24,581,852 — 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 — 3,500,000 — 3,500,000 Total Common Stock Warrants — 12,416,621 955,374 11,461,247
Schedule of Warrant Valuation Assumptions	The warrants were valued using the following assumptions: For the year ended December 31, 2021 Preferred B warrants Preferred C warrants Expected volatility 80 % 60% - 80% Expected term (in years) 2.00 2.00 Risk‑free interest rate 0.16% - 0.28% 0.16% - 0.32% Dividend yield 0 % 0 % As of December 31, 2020 Preferred B Preferred C Expected volatility 80 % 80 % Expected term (in years) 2.00 2.00 Risk‑free interest rate 0.13 % 0.13 % Dividend yield 0 % 0 %

COMMON STOCK WARRANTS (Tables)

COMMON STOCK WARRANTS (Tables)	12 Months Ended
	Dec. 31, 2021
Equity [Abstract]
Schedule of Common Stock Warrant Activity	The number of shares subject to and potential proceeds from the C-2 Redeemable Convertible Preferred Stock Purchase Agreement and related C-2 Warrants were as follows: As of May 7, 2021 Upon Completion of SPAC merger Quantity Price Series C-2 Redeemable Convertible Preferred Stock Purchase Right 7,994,442 $ 2.00 Series C-2 Warrant exercisable upon SPAC merger 21,159,364 $ 0.00007 Total Proceeds Upon Exercise The table below summarizes the shares subject to C-2 Purchase Right activity during the year ended December 31, 2021: December 31, Extinguished Exercised December 31, Series C-2 Purchase Right 39,971,716 26,231,295 13,740,421 — Legacy ESS periodically issued warrants (“Legacy ESS warrants”) in conjunction with the issuance of preferred stock or debt. As of December 31, 2021 and 2020, the following Legacy ESS warrants were outstanding: 2021 2020 Common Stock Warrants — 450,153 Series B Preferred Warrants — 2,007,308 Series C-1 Preferred Warrants — 103,107 Total Warrants — 2,560,568 The table below shows the Legacy ESS warrant activities during the year ended December 31, 2021: December 31, Issued Exercised December 31, Common Stock Warrants 450,153 — 450,153 — Series B Preferred Stock Warrants 2,007,308 — 2,007,308 — Series C-1 Preferred Stock Warrants 103,107 — 103,107 — Series C-2 Preferred Stock Warrants — 22,021,284 22,021,284 — Total Warrants 2,560,568 22,021,284 24,581,852 — 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 — 3,500,000 — 3,500,000 Total Common Stock Warrants — 12,416,621 955,374 11,461,247

STOCK-BASED COMPENSATION PLAN (

STOCK-BASED COMPENSATION PLAN (Tables)	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
Schedule of Share-based Payment Arrangement, Option, Activity	Stock option and RSU activity, prices, and values adjusted by the Per Share Consideration, during the year ended December 31, 2021 is as follows (in thousands, except for share, per share, and contractual term data): Options Outstanding Restricted Stock Units Number of Weighted Weighted Aggregate Number of plan shares outstanding Weighted average Balances as of December 31, 2019 2,104,223 $ 0.37 7.82 $ 821 Recapitalization Impact 995,215 (0.12) Balances at December 31, 2019 3,099,438 $ 0.25 7.82 821 Granted 3,271,856 0.33 Exercised (108,999) 0.06 Forfeited (529,873) 0.29 Balances as of December 31, 2020 5,732,422 $ 0.30 8.23 4,333 Granted 1,454,549 1.75 3,392,153 $ 10.69 Exercised (2,496,070) 0.27 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 vested and exercisable - December 31, 2020 2,825,238 $ 0.26 7.21 2,215 Options vested and exercisable - December 31, 2021 1,827,374 $ 0.31 7.20 20,337
Schedule of Share-based Payment Arrangement, Restricted Stock Unit, Activity	Stock option and RSU activity, prices, and values adjusted by the Per Share Consideration, during the year ended December 31, 2021 is as follows (in thousands, except for share, per share, and contractual term data): Options Outstanding Restricted Stock Units Number of Weighted Weighted Aggregate Number of plan shares outstanding Weighted average Balances as of December 31, 2019 2,104,223 $ 0.37 7.82 $ 821 Recapitalization Impact 995,215 (0.12) Balances at December 31, 2019 3,099,438 $ 0.25 7.82 821 Granted 3,271,856 0.33 Exercised (108,999) 0.06 Forfeited (529,873) 0.29 Balances as of December 31, 2020 5,732,422 $ 0.30 8.23 4,333 Granted 1,454,549 1.75 3,392,153 $ 10.69 Exercised (2,496,070) 0.27 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 vested and exercisable - December 31, 2020 2,825,238 $ 0.26 7.21 2,215 Options vested and exercisable - December 31, 2021 1,827,374 $ 0.31 7.20 20,337
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: 2021 2020 Risk-free rate 1.01 % 0.93 % Expected dividends — — Expected term 6 years 6 years Expected volatility 75.14 % 71.06 %
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, 2021 and 2020 (in thousands): 2021 2020 Research and development $ 2,233 $ 79 Sales and marketing 213 47 General and administrative 5,476 184 Total stock-based compensation $ 7,922 $ 310

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2021
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, 2021 Level 1 Level 2 Level 3 Total Assets: Cash equivalents and restricted cash: Money market funds $ 237,897 $ — $ — $ 237,897 Certificate of deposit — 125 — 125 Total assets $ 237,897 $ 125 $ — $ 238,022 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 $ 18,666 $ 10,331 $ — $ 28,997 December 31, 2020 Level 1 Level 2 Level 3 Total Assets: Cash equivalents and restricted cash: Money market funds $ 3,046 $ — $ — $ 3,046 Certificate of deposit — 326 — 326 Total assets $ 3,046 $ 326 $ — $ 3,372 Liabilities: Derivative liabilities $ — $ — $ 22,911 $ 22,911 Warrant liabilities — — 3,329 3,329 Total liabilities $ — $ — $ 26,240 $ 26,240
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, 2021 and 2020 (in thousands): 2021 2020 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 — — Warrant liabilities: Beginning balance January 1 3,329 1,989 Change in fair value 17,753 1,296 Fair value of warrants issued 5,096 44 Fair value of warrants exercised (26,178) — Ending balance December 31 — 3,329 Series C-2 Convertible Preferred Stock Issuance Right liability: Beginning balance January 1 22,911 11,379 Change in fair value 223,165 11,532 Fair value of derivatives extinguished (23,152) — Fair value of Series C-2 Convertible Preferred Stock Issuance Right exercised (222,924) — Ending balance December 31 — 22,911 Total $ — $ 26,240

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2021
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, 2021 2020 Deferred Tax Assets: Net operating losses $ 24,655 $ 11,566 Tax credit carryforward 292 47 Non-qualifying stock options 1,143 — Other 1,231 837 Deferred tax assets 27,321 12,450 Valuation allowance (27,321) (12,450) Deferred tax assets, net of valuation allowance $ — $ —
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, 2021 2020 Tax computed at federal statutory rate 21.0 % 21.0 % State tax, net of federal tax benefit 0.6 3.0 Stock compensation (0.1) (0.2) Transaction costs related to the Business Combination (0.2) — Warrant liabilities revaluation (1.7) (8.9) Derivative liabilities revaluation (9.8) — Earnout shares liabilities revaluation (6.8) — R&D tax credits — 0.1 Other 0.1 — Valuation allowance (3.1) (15.0) Income tax expense (benefit) — % — %
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, 2019 $ 12 Additions in 2020 35 Balance as of December 31, 2020 $ 47 Additions in 2021 245 Balance as of December 31, 2021 $ 292

DESCRITPION OF BUSINESS, BASI_2

DESCRITPION OF BUSINESS, BASIS OF PRESENTATION AND RISKS AND UNCERTAINTIES (Details)	12 Months Ended
	Dec. 31, 2021segment	Oct. 08, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Recapitalization exchange ratio		0.0147
Number of reportable segments	1

SIGNIFICANT ACCOUNTING POLICI_3

SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Jan. 01, 2022
Significant Accounting Policies [Line Items]
Impairment recognized	$ 0	$ 0
Revenue recognized	0	0
Advertising costs	45,000	8,000
Repayable research and development funding arrangement	452,000	186,000
Accrued interest and penalties related to uncertain tax positions	$ 0	$ 0
Subsequent Event | Accounting Standards Update 2016-02
Significant Accounting Policies [Line Items]
Right of use asset recognized			$ 5,000,000
Operating lease liability recognized			$ 5,000,000
Stock options
Significant Accounting Policies [Line Items]
Expected dividends	0.00%	0.00%
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)	Nov. 09, 2021shares	Oct. 08, 2021USD ($)tranche$ / sharesshares	Oct. 07, 2021$ / sharesshares	May 07, 2021$ / sharesshares	Mar. 03, 2022shares	Dec. 31, 2021$ / sharesshares	Dec. 31, 2020$ / sharesshares
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 pending satisfaction of regulatory holding period | Subsequent Event
Business Acquisition [Line Items]
Shares delivered (in shares)					6,707,318
Restricted Stock Units
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
Shares issued (in shares)
Price per share (in USD per share) | $ / shares
Legacy ESS | Common Stock
Business Acquisition [Line Items]
Shares issued upon completion of milestones (in shares)	15,674,965
STWO
Business Acquisition [Line Items]
Shares repurchased (in shares)			20,754,719
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	Oct. 08, 2021	Oct. 07, 2021	Dec. 31, 2021	Dec. 31, 2020
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		151,839,058	58,919,345
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	57,104,322
Common Stock
Schedule of Reverse Recapitalization [Line Items]
Legacy ESS stock converted to ESS common stock	13,442,198

DEFERRED REVENUE (Details)

DEFERRED REVENUE (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Contract With Customer, Liability [Line Items]
Total deferred revenue	$ 3,663	$ 0
Customer deposits	552	2,258
Deferred revenue - units shipped in August 2021
Contract With Customer, Liability [Line Items]
Total deferred revenue	383	0
Deferred revenue - units shipped in September 2021
Contract With Customer, Liability [Line Items]
Total deferred revenue	171	0
Other deferred revenue
Contract With Customer, Liability [Line Items]
Total deferred revenue	$ 3,109	$ 0

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, 2021	Dec. 31, 2020
Earnings Per Share [Abstract]
Net loss to common stockholders, diluted	$ (477,117)	$ (30,419)
Net loss to common stockholders, basic	$ (477,117)	$ (30,419)
Weighted average shares used in per share calculation, basic (in shares)	83,256,431	58,880,742
Weighted average shares used in per share calculation, diluted (in shares)	83,256,431	58,880,742
Net loss per share, diluted (in USD per share)	$ (5.73)	$ (0.52)
Net loss per share, basic (in USD per share)	$ (5.73)	$ (0.52)

LOSS PER SHARE - Schedule Antid

LOSS PER SHARE - Schedule Antidilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	25,357,248	6,182,575,000
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	3,796,530	5,732,422,000
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	3,392,153	0
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	11,461,247	450,153,000
Earnout shares pending satisfaction of regulatory holding period
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	6,707,318	0

PREPAID EXPENSES AND OTHER CU_3

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Insurance	$ 3,482	$ 107
Vendor advances	1,103	473
Accounts receivable	517	0
Other	259	213
Total prepaid expenses and other current assets	$ 5,361	$ 793

PROPERTY AND EQUIPMENT, NET (De

PROPERTY AND EQUIPMENT, NET (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 6,221	$ 2,984
Less accumulated depreciation	(1,720)	(1,148)
Total property and equipment, net	4,501	1,836
Depreciation expense	572	436
Machinery and equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	2,868	2,217
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment	90	90
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	746	677
Construction in process
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 2,517	$ 0

ACCRUED AND OTHER CURRENT LIA_3

ACCRUED AND OTHER CURRENT LIABILITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Payroll and related benefits	$ 1,876	$ 777
Materials and related purchases	2,108	464
Deferred rent	142	462
Professional and consulting fees	1,820	248
Other	541	243
Total accrued and other current liabilities	$ 6,487	$ 2,194

LEASES - Schedule of Future Min

LEASES - Schedule of Future Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2021USD ($)
Leases [Abstract]
2022	$ 1,625
2023	1,670
2024	1,720
2025	983
Total	$ 5,998

LEASES - Narrative (Details)

LEASES - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Leases [Abstract]
Rent expense	$ 1,491	$ 837
Renewal term	60 months

BORROWINGS - Schedule of Long T

BORROWINGS - Schedule of Long Term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Total notes payable	$ 3,769	$ 5,697
Less current portion of notes payable	1,900	5,678
Long-term notes payable, net of current portion	1,869	19
Notes payable
Debt Instrument [Line Items]
Total notes payable	3,769	4,761
PPP loan
Debt Instrument [Line Items]
Total notes payable	$ 0	$ 936

BORROWINGS - Narrative (Details

BORROWINGS - Narrative (Details)	1 Months Ended		12 Months Ended
	Jul. 31, 2021USD ($)	Mar. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Oct. 08, 2021USD ($)	Apr. 30, 2020USD ($)	Apr. 19, 2020USD ($)	Dec. 31, 2018USD ($)	Jul. 31, 2018USD ($)$ / sharesshares
Debt Instrument [Line Items]
Gain (loss) on extinguishment of debt			$ 0	$ (62,000)
Fair value of warrants			0	26,240,000
Interest expense			1,886,000	132,000
Acceleration of existing indebtedness payable				4,583,000
Series B Preferred Warrants
Debt Instrument [Line Items]
Warrants issued (in shares) | shares									100,161
Warrant exercise price (in USD per share) | $ / shares									$ 0.96
Warrants term									10 years
Series B Preferred Warrants | Common Stock Warrants
Debt Instrument [Line Items]
Fair value of warrants									$ 55,000
Preferred C warrants
Debt Instrument [Line Items]
Warrants issued (in shares) | shares		103,107
Warrant exercise price (in USD per share) | $ / shares		$ 1.25
Warrants term		10 years
Interest expense			0	4,000
Preferred C warrants | Common Stock Warrants
Debt Instrument [Line Items]
Fair value of warrants		$ 44,000
PPP loan
Debt Instrument [Line Items]
Debt amount							$ 936,000
Interest rate							1.00%
Debt forgiveness	$ 936,000
Accrued interest	12,000
Gain (loss) on extinguishment of debt			948,000
Acceleration of existing indebtedness payable				943,000
Bridge loan:
Debt Instrument [Line Items]
Debt amount	$ 20,000,000
Interest rate	9.00%
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
Notes payable
Debt Instrument [Line Items]
Debt amount		$ 4,000,000				$ 4,000,000		$ 1,000,000
Gain (loss) on extinguishment of debt				$ (62,000)
Percent change in present value of cash flows		0.10
Effective interest rate			2.75%
Notes payable | Prime
Debt Instrument [Line Items]
Spread on interest rate		0.50%

BORROWINGS - Schedule of Annual

BORROWINGS - Schedule of Annual Maturities on Notes Payable (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Debt Disclosure [Abstract]
2022	$ 1,900
2023	1,600
2024	333
Total maturities	3,833
Less: unamortized debt premium	(64)
Total notes payable	$ 3,769	$ 5,697

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Other Commitments [Line Items]
Restricted certificate of deposit	$ 125
Noncancellable Agreement
Other Commitments [Line Items]
Noncancelable purchase commitments	10,160	$ 3,410
Cancellable Agreement
Other Commitments [Line Items]
Noncancelable purchase commitments	10,446	787
Letter of Credit | First Republic Bank
Other Commitments [Line Items]
Standby letter of credit	725	725
Draws against letter of credit	$ 0	$ 0

LEGACY ESS REDEEMABLE CONVERT_3

LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK - Narrative (Details) $ / shares in Units, $ in Thousands	Oct. 08, 2021USD ($)$ / sharesshares	Oct. 07, 2021$ / sharesshares	Mar. 31, 2021USD ($)$ / sharesshares	Dec. 31, 2021USD ($)shares	Dec. 31, 2020USD ($)$ / sharesshares	May 07, 2021$ / shares	Dec. 31, 2019USD ($)	Jul. 31, 2018$ / shares
Temporary Equity [Line Items]
Recapitalization exchange ratio	0.0147
Fair value of temporary equity | $				$ 0	$ 0		$ 0
Shares issued (in shares)	25,000,000
Value of share issued | $				29,516
Stock issuance costs | $				$ 7,895	0
Warrants issued (in shares)				12,416,621
Warrants exercised (in shares)				955,374
Transaction value | $				$ 0	153
Increase in derivative liability | $				(223,165)	(11,532)
Derivative liabilities | $				$ 0	$ 22,911
Warrants (in shares)				11,461,247	0
Series B Preferred Warrants
Temporary Equity [Line Items]
Warrant exercise price (in USD per share) | $ / shares								$ 0.96
Warrants term								10 years
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]
Warrants issued (in shares)				22,021,284
Warrants exercised (in shares)				24,581,852
Transaction value | $			$ 34,613
Warrants (in shares)				0	2,560,568
Warrants term		10 years
Legacy ESS | Series C-2 Redeemable Convertible Preferred Stock Purchase Rights
Temporary Equity [Line Items]
Fair value of temporary equity | $					$ 11,379
Warrants issued (in shares)			861,896
Warrants exercised (in shares)			5,746,003	13,740,421
Warrant exercise price (in USD per share) | $ / shares			$ 0.0001
Warrants (in shares)				0	39,971,716
Legacy ESS | Series C-2 Redeemable Convertible Preferred Stock Warrants
Temporary Equity [Line Items]
Warrants issued (in shares)				22,021,284
Warrants exercised (in shares)				22,021,284
Warrant exercise price (in USD per share) | $ / shares						$ 0.00007
Warrants (in shares)					0
Warrants term		10 years
Legacy ESS | Series C-2 Redeemable Convertible Preferred Stock Warrants | Minimum
Temporary Equity [Line Items]
Warrant exercise price (in USD per share) | $ / shares		$ 0.00007
Legacy ESS | Series C-2 Redeemable Convertible Preferred Stock Warrants | Maximum
Temporary Equity [Line Items]
Warrant exercise price (in USD per share) | $ / shares		$ 1.25
Legacy ESS | Series B Preferred Warrants
Temporary Equity [Line Items]
Warrants issued (in shares)				0
Warrants exercised (in shares)				2,007,308
Warrants (in shares)		100,161		0	2,007,308
Legacy ESS | Series B Preferred Warrants | Minimum
Temporary Equity [Line Items]
Warrant exercise price (in USD per share) | $ / shares		$ 0.0007
Legacy ESS | Series B Preferred Warrants | Maximum
Temporary Equity [Line Items]
Warrant exercise price (in USD per share) | $ / shares		$ 0.83
Legacy ESS | Series C-1 Preferred Warrants
Temporary Equity [Line Items]
Warrants issued (in shares)				0
Warrants exercised (in shares)				103,107
Warrants (in shares)				0	103,107
Warrants term		10 years
Legacy ESS | Series C-1 Preferred Warrants | Minimum
Temporary Equity [Line Items]
Warrant exercise price (in USD per share) | $ / shares		$ 0.00007
Legacy ESS | Series C-1 Preferred Warrants | Maximum
Temporary Equity [Line Items]
Warrant exercise price (in USD per share) | $ / shares		1.25
Legacy ESS | Common Stock Warrants
Temporary Equity [Line Items]
Warrants issued (in shares)				0
Warrants exercised (in shares)				450,153
Warrant exercise price (in USD per share) | $ / shares		$ 0.0007
Warrants (in shares)				0	450,153
Common Stock
Temporary Equity [Line Items]
Conversion of convertible shares (in 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
Committed purchase of shares (in shares)					39,971,716
Committed price per share (in USD per share) | $ / shares					$ 2
Shares issued (in shares)			5,746,003
Price per share (in USD per share) | $ / shares			$ 2
Value of share issued | $			$ 11,500
Stock issuance costs | $			39
Derivative liabilities | $			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$ / sharesshares
Class of Warrant or Right [Line Items]
Shares issued (in shares) | shares
Price per share (in USD per share) | $ / shares
Series C-2 Redeemable Convertible Preferred Stock Purchase Rights
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 Preferred Stock Warrants
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

LEGACY ESS REDEEMABLE CONVERT_5

LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK - Schedule of Purchase Rights Activity (Details) - shares	1 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2021
Class of Warrant or Right [Line Items]
Warrants or rights at beginning of period (in shares)		0
Rights exercised (in shares)		955,374
Warrants or rights at end of period (in shares)		11,461,247
Legacy ESS
Class of Warrant or Right [Line Items]
Warrants or rights at beginning of period (in shares)		2,560,568
Rights exercised (in shares)		24,581,852
Warrants or rights at end of period (in shares)		0
Legacy ESS | Series C-2 Redeemable Convertible Preferred Stock Purchase Rights
Class of Warrant or Right [Line Items]
Warrants or rights at beginning of period (in shares)		39,971,716
Rights forfeited (in shares)		26,231,295
Rights exercised (in shares)	5,746,003	13,740,421
Warrants or rights at end of period (in shares)		0

LEGACY ESS REDEEMABLE CONVERT_6

LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK - Schedule of Warrants Outstanding (Details) - shares	Dec. 31, 2021	Oct. 07, 2021	Dec. 31, 2020
Class of Warrant or Right [Line Items]
Warrants (in shares)	11,461,247		0
Legacy ESS
Class of Warrant or Right [Line Items]
Warrants (in shares)	0		2,560,568
Common Stock Warrants | Legacy ESS
Class of Warrant or Right [Line Items]
Warrants (in shares)	0		450,153
Series B Preferred Warrants | Legacy ESS
Class of Warrant or Right [Line Items]
Warrants (in shares)	0	100,161	2,007,308
Series C-1 Preferred Warrants | Legacy ESS
Class of Warrant or Right [Line Items]
Warrants (in shares)	0		103,107

LEGACY ESS REDEEMABLE CONVERT_7

LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK - Schedule of Warrant Activity (Details) - shares	Oct. 08, 2021	Dec. 31, 2021
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		0
Warrants issued (in shares)		12,416,621
Warrants exercised (in shares)		955,374
Warrants or rights at end of period (in shares)		11,461,247
Legacy ESS
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		2,560,568
Warrants issued (in shares)		22,021,284
Warrants exercised (in shares)		24,581,852
Warrants or rights at end of period (in shares)		0
Common Stock Warrants | Legacy ESS
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		450,153
Warrants issued (in shares)		0
Warrants exercised (in shares)		450,153
Warrants or rights at end of period (in shares)		0
Series B Preferred Warrants | Legacy ESS
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)	100,161	2,007,308
Warrants issued (in shares)		0
Warrants exercised (in shares)		2,007,308
Warrants or rights at end of period (in shares)		0
Series C-1 Preferred Warrants | Legacy ESS
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		103,107
Warrants issued (in shares)		0
Warrants exercised (in shares)		103,107
Warrants or rights at end of period (in shares)		0
Series C-2 Preferred Stock Warrants | Legacy ESS
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		0
Warrants issued (in shares)		22,021,284
Warrants exercised (in shares)		22,021,284

LEGACY ESS REDEEMABLE CONVERT_8

LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK - Schedule of Warrant Valuation Assumptions (Details) - Legacy ESS	Dec. 31, 2021yr	Dec. 31, 2020yr
Expected volatility | Series B Preferred Warrants
Class of Warrant or Right [Line Items]
Warrant valuation assumption	0.80	0.80
Expected volatility | Series B Preferred Warrants | Minimum
Class of Warrant or Right [Line Items]
Warrant valuation assumption	0.60
Expected volatility | Series B Preferred Warrants | Maximum
Class of Warrant or Right [Line Items]
Warrant valuation assumption	0.80
Expected volatility | Preferred C warrants
Class of Warrant or Right [Line Items]
Warrant valuation assumption		0.80
Expected term (in years) | Series B Preferred Warrants
Class of Warrant or Right [Line Items]
Warrant valuation assumption	2	2
Expected term (in years) | Preferred C warrants
Class of Warrant or Right [Line Items]
Warrant valuation assumption	2	2
Risk‑free interest rate | Series B Preferred Warrants
Class of Warrant or Right [Line Items]
Warrant valuation assumption		0.0013
Risk‑free interest rate | Series B Preferred Warrants | Minimum
Class of Warrant or Right [Line Items]
Warrant valuation assumption	0.0016
Risk‑free interest rate | Series B Preferred Warrants | Maximum
Class of Warrant or Right [Line Items]
Warrant valuation assumption	0.0028
Risk‑free interest rate | Preferred C warrants
Class of Warrant or Right [Line Items]
Warrant valuation assumption		0.0013
Risk‑free interest rate | Preferred C warrants | Minimum
Class of Warrant or Right [Line Items]
Warrant valuation assumption	0.0016
Risk‑free interest rate | Preferred C warrants | Maximum
Class of Warrant or Right [Line Items]
Warrant valuation assumption	0.0032
Dividend yield | Series B Preferred Warrants
Class of Warrant or Right [Line Items]
Warrant valuation assumption	0	0
Dividend yield | Preferred C warrants
Class of Warrant or Right [Line Items]
Warrant valuation assumption	0	0

COMMON STOCK WARRANTS - Narrati

COMMON STOCK WARRANTS - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	Oct. 08, 2021	Sep. 21, 2020	Dec. 31, 2021	Dec. 31, 2020	Nov. 09, 2021
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)			11,461,247	0
Warrants issued (in shares)			12,416,621
Warrants exercised (in shares)			955,374
Net increase to warrant liabilities			$ (37,584)	$ (1,296)
Proceeds from warrants exercised			$ 10,995	$ 0
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)			7,377,913	0
Warrants issued (in shares)			8,333,287
Warrants exercised (in shares)			955,374
Net increase to warrant liabilities			$ 14,476
Proceeds from warrants exercised			$ 10,987
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	0
Warrants issued (in shares)			3,500,000
Warrants vested (in shares)	3,500,000
Warrants exercised (in shares)			0
Net increase to warrant liabilities			$ 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	0
Warrants issued (in shares)			583,334
Warrants vested (in shares)					583,334
Warrants exercised (in shares)			0
Net increase to warrant liabilities			$ 974

COMMON STOCK WARRANTS - Schedul

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

EMPLOYEE STOCK PURCHASE PLAN (D

EMPLOYEE STOCK PURCHASE PLAN (Details) - Employee Stock	12 Months Ended
	Dec. 31, 2021shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
ESPP purchase price of common stock, percent of market price	85.00%
Fixed contribution rate	15.00%
Number of shares reserved for future issuance (in shares)	3,060,000

STOCK-BASED COMPENSATION PLAN -

STOCK-BASED COMPENSATION PLAN - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	Jan. 01, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value of options exercised		$ 6,244	$ 48
Unamortized stock-based compensation costs		$ 16,949
Weighted average period of recognition for unamortized stock-based compensation costs		2 years 1 month 24 days
Percentage of potential increase of shares authorized		5.00%
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)		3,392,153
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)		$ 5.63	$ 0.65
2014 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for issuance (in shares)		15,482,675
2014 Equity Incentive Plan | Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)		0	0
2014 Equity Incentive Plan | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)		0	0
2014 Equity Incentive Plan | Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)		0	0
2014 Equity Incentive Plan | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Accelerated vesting of shares (in shares)		0	0
Share expiration period		10 years
Award vesting period		4 years
2021 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for issuance (in shares)		12,210,000
Shares available for future grant (in shares)		9,785,574
Potential increase of shares authorized (in shares)		15,260,000
2021 Equity Incentive Plan | Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in shares authorized for issuance (in shares)	5,400,000
2021 Equity Incentive Plan | Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)		0
2021 Equity Incentive Plan | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)		0
2021 Equity Incentive Plan | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share expiration period		10 years
Award vesting period		4 years
2021 Equity Incentive Plan | Non-qualified Stock Options (NSOs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)		0
2021 Equity Incentive Plan | Incentive Stock Options (ISOs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)		0

STOCK-BASED COMPENSATION PLAN_2

STOCK-BASED COMPENSATION PLAN - Schedule of Share-based Payment Arrangement, Option and RSU Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Options Outstanding
Options outstanding at beginning of period (in shares)	5,732,422	3,099,438
Options granted (in shares)	1,454,549	3,271,856
Options exercised (in shares)	(2,496,070)	(108,999)
Options forfeited (in shares)	(894,371)	(529,873)
Options outstanding at end of period (in shares)	3,796,530	5,732,422	3,099,438
Options vested and exercisable (in shares)	1,827,374	2,825,238
Weighted average exercise price
Weighted average exercise price of options outstanding at beginning of period (in USD per share)	$ 0.30	$ 0.25
Weighted average exercise price of options granted (in USD per share)	1.75	0.33
Weighted average exercise price of options exercised (in USD per share)	0.27	0.06
Weighted average exercise price of options forfeited (in USD per share)	0.46	0.29
Weighted average exercise price of options outstanding at end of period (in USD per share)	0.83	0.30	$ 0.25
Weighted average exercise price of options vested and exercisable (in USD per share)	$ 0.31	$ 0.26
Options, Additional Disclosures
Weighted average remaining contractual term of options outstanding	8 years 29 days	8 years 2 months 23 days	7 years 9 months 25 days
Weighted average remaining contractual term of options vested and exercisable	7 years 2 months 12 days	7 years 2 months 15 days
Aggregate intrinsic value of options outstanding	$ 40,274	$ 4,333	$ 821
Aggregate intrinsic value of options vested and exercisable	$ 20,337	$ 2,215
Previously Reported
Options Outstanding
Options outstanding at beginning of period (in shares)		2,104,223
Options outstanding at end of period (in shares)			2,104,223
Weighted average exercise price
Weighted average exercise price of options outstanding at beginning of period (in USD per share)		$ 0.37
Weighted average exercise price of options outstanding at end of period (in USD per share)			$ 0.37
Options, Additional Disclosures
Weighted average remaining contractual term of options outstanding			7 years 9 months 25 days
Aggregate intrinsic value of options outstanding			$ 821
Retroactive application of recapitalization
Options Outstanding
Options outstanding at beginning of period (in shares)		995,215
Options outstanding at end of period (in shares)			995,215
Weighted average exercise price
Weighted average exercise price of options outstanding at beginning of period (in USD per share)		$ (0.12)
Weighted average exercise price of options outstanding at end of period (in USD per share)			$ (0.12)
Restricted Stock Units
Restricted Stock Units
Units granted (in shares)	3,392,153
Units outstanding at end of period (in shares)	3,392,153
Weighted average grant date fair value per Share
Weighted average grant date fair value per share of units granted (in USD per share)	$ 10.69
Weighted average grant date fair value per share of units outstanding at end of period (in USD per share)	$ 10.69

STOCK-BASED COMPENSATION PLAN_3

STOCK-BASED COMPENSATION PLAN - Schedule of Valuation Assumptions (Details) - Stock options	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free rate	1.01%	0.93%
Expected dividends	0.00%	0.00%
Expected term	6 years	6 years
Expected volatility	75.14%	71.06%

STOCK-BASED COMPENSATION PLAN_4

STOCK-BASED COMPENSATION PLAN - Schedule of Stock-Based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	$ 7,922	$ 310
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	2,233	79
Sales and marketing
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	213	47
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	$ 5,476	$ 184

FAIR VALUE MEASUREMENTS - Sched

FAIR VALUE MEASUREMENTS - Schedule of Assets and Liabilities on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Public common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	$ 18,666
Private common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	8,855
Level 1 | Public common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	18,666
Level 1 | Private common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	0
Level 2 | Public common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	0
Level 2 | Private common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	8,855
Level 3 | Public common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	0
Level 3 | Private common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	0
Fair Value, Recurring
Assets, Fair Value Disclosure [Abstract]
Total assets	238,022	$ 3,372
Liabilities, Fair Value Disclosure [Abstract]
Earnout warrant liabilities	1,476
Derivative liabilities		22,911
Warrant liabilities		3,329
Total liabilities	28,997	26,240
Fair Value, Recurring | Money market funds
Assets, Fair Value Disclosure [Abstract]
Cash equivalents and restricted cash:	237,897	3,046
Fair Value, Recurring | Certificate of deposit
Assets, Fair Value Disclosure [Abstract]
Cash equivalents and restricted cash:	125	326
Fair Value, Recurring | Level 1
Assets, Fair Value Disclosure [Abstract]
Total assets	237,897	3,046
Liabilities, Fair Value Disclosure [Abstract]
Earnout warrant liabilities	0
Derivative liabilities		0
Warrant liabilities		0
Total liabilities	18,666	0
Fair Value, Recurring | Level 1 | Money market funds
Assets, Fair Value Disclosure [Abstract]
Cash equivalents and restricted cash:	237,897	3,046
Fair Value, Recurring | Level 1 | Certificate of deposit
Assets, Fair Value Disclosure [Abstract]
Cash equivalents and restricted cash:	0	0
Fair Value, Recurring | Level 2
Assets, Fair Value Disclosure [Abstract]
Total assets	125	326
Liabilities, Fair Value Disclosure [Abstract]
Earnout warrant liabilities	1,476
Derivative liabilities		0
Warrant liabilities		0
Total liabilities	10,331	0
Fair Value, Recurring | Level 2 | Money market funds
Assets, Fair Value Disclosure [Abstract]
Cash equivalents and restricted cash:	0	0
Fair Value, Recurring | Level 2 | Certificate of deposit
Assets, Fair Value Disclosure [Abstract]
Cash equivalents and restricted cash:	125	326
Fair Value, Recurring | Level 3
Assets, Fair Value Disclosure [Abstract]
Total assets	0	0
Liabilities, Fair Value Disclosure [Abstract]
Earnout warrant liabilities	0
Derivative liabilities		22,911
Warrant liabilities		3,329
Total liabilities	0	26,240
Fair Value, Recurring | Level 3 | Money market funds
Assets, Fair Value Disclosure [Abstract]
Cash equivalents and restricted cash:	0	0
Fair Value, Recurring | Level 3 | Certificate of deposit
Assets, Fair Value Disclosure [Abstract]
Cash equivalents and restricted cash:	$ 0	$ 0

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, 2021	Dec. 31, 2020
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 26,240
Balance at end of period	0	$ 26,240
Total	0	26,240
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	20,000	0
Accrued interest	1,578	0
Change in fair value	0	0
Fair value settled	(21,578)	0
Balance at end of period	0	0
Total	0	0
Warrant liabilities:
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	3,329	1,989
Fair value issued	5,096	44
Change in fair value	17,753	1,296
Fair value settled	(26,178)	0
Balance at end of period	0	3,329
Total	0	3,329
Redeemable Convertible Preferred Stock
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	22,911	11,379
Change in fair value	223,165	11,532
Fair value of derivatives extinguished	(23,152)	0
Fair value settled	(222,924)	0
Balance at end of period	0	22,911
Total	$ 0	$ 22,911

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Increase in valuation allowance	$ 14,871,000
Addition to uncertain tax position related to reduction of research and development credit	245,000	$ 35,000
Accrued interest and penalties related to uncertain tax positions	0	$ 0
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	94,058,000
Research and development credits	584,000
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 94,023,000

INCOME TAXES - Schedule of Defe

INCOME TAXES - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred Tax Assets:
Net operating losses	$ 24,655	$ 11,566
Tax credit carryforward	292	47
Non-qualifying stock options	1,143	0
Other	1,231	837
Deferred tax assets	27,321	12,450
Valuation allowance	(27,321)	(12,450)
Deferred tax assets, net of valuation allowance	$ 0	$ 0

INCOME TAXES - Schedule of Prov

INCOME TAXES - Schedule of Provision for Income Taxes (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Tax computed at federal statutory rate	21.00%	21.00%
State tax, net of federal tax benefit	0.60%	3.00%
Stock compensation	(0.10%)	(0.20%)
Transaction costs related to the Business Combination	(0.002)	0
Warrant liabilities revaluation	(0.017)	(0.089)
Derivative liabilities revaluation	(0.098)	0
Earnout shares liabilities revaluation	(0.068)	0
R&D tax credits	0.00%	0.10%
Other	0.10%	0.00%
Valuation allowance	(3.10%)	(15.00%)
Income tax expense (benefit)	0.00%	0.00%

INCOME TAXES - Schedule of Unce

INCOME TAXES - Schedule of Uncertain Tax Positions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 47	$ 12
Additions	245	35
Balance at end of period	$ 292	$ 47

DEFINED CONTRIBUTION PLAN (Deta

DEFINED CONTRIBUTION PLAN (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Retirement Benefits [Abstract]
Employer contributions	$ 292	$ 173

RELATED PARTY TRANSACTIONS (Det

RELATED PARTY TRANSACTIONS (Details) - USD ($) $ in Thousands	Nov. 09, 2021	Dec. 31, 2020	Dec. 31, 2021
Related Party Transaction [Line Items]
Deferred revenue		$ 0	$ 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
Technology Consulting
Related Party Transaction [Line Items]
Related party transaction amount		$ 31
Energy Warehouse Sales
Related Party Transaction [Line Items]
Accounts receivable from related party			66
Deferred revenue			$ 171

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) - Restricted Stock Units - shares	1 Months Ended	12 Months Ended
	Feb. 28, 2022	Dec. 31, 2021
Subsequent Event [Line Items]
Units granted (in shares)		3,392,153
Subsequent Event
Subsequent Event [Line Items]
Units granted (in shares)	2,100,000