ESS Tech (GWH) 10-Q 9 May 23 2023 Q1 Quarterly report Financial data

Cover

Cover - shares	3 Months Ended
	Mar. 31, 2023	May 03, 2023
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2023
Document Transition Report	false
Entity File Number	001-39525
Entity Registrant Name	ESS Tech, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	98-1550150
Entity Address, Address Line One	26440 SW Parkway Ave.
Entity Address, Address Line Two	Bldg. 83
Entity Address, City or Town	Wilsonville
Entity Address, State or Province	OR
Entity Address, Postal Zip Code	97070
City Area Code	855
Local Phone Number	423-9920
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		154,366,717
Entity Central Index Key	0001819438
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Amendment Flag	false
Common Stock
Entity Information [Line Items]
Title of 12(b) Security	Common stock, $0.0001 par value per share
Trading Symbol	GWH
Security Exchange Name	NYSE
Warrants
Entity Information [Line Items]
Title of 12(b) Security	Warrants, each whole warrant exercisable for one share of common stock at an exercise price of $11.50
Trading Symbol	GWH.W
Security Exchange Name	NYSE

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 87,811	$ 34,767
Restricted cash, current	1,413	1,213
Accounts receivable, net	689	4,952
Short-term investments	31,196	105,047
Prepaid expenses and other current assets	3,952	5,657
Total current assets	125,061	151,636
Property and equipment, net	18,373	17,570
Operating lease right-of-use assets	3,102	3,401
Restricted cash, non-current	676	675
Other non-current assets	239	271
Total assets	147,451	173,553
Current liabilities:
Accounts payable	2,699	3,036
Accrued and other current liabilities	8,533	14,125
Accrued product warranties	2,874	1,643
Operating lease liabilities, current	1,464	1,421
Deferred revenue	5,929	6,168
Notes payable, current	1,522	1,600
Total current liabilities	23,021	27,993
Notes payable, non-current	0	315
Operating lease liabilities, non-current	2,151	2,535
Deferred revenue, non-current	2,442	2,442
Common stock warrant liabilities	2,521	3,209
Other non-current liabilities	80	85
Total liabilities	30,215	36,579
Commitments and contingencies (Note 9)
Stockholders’ equity:
Preferred stock ($0.0001 par value; 200,000,000 shares authorized, none issued and outstanding as of March 31, 2023 and December 31, 2022)	0	0
Common stock ($0.0001 par value; 2,000,000,000 shares authorized, 154,344,930 and 153,821,339 shares issued and outstanding as of March 31, 2023 and December 31, 2022, respectively)	16	16
Additional paid-in capital	757,700	755,537
Accumulated deficit	(640,480)	(618,579)
Total stockholders’ equity	117,236	136,974
Total liabilities and stockholders’ equity	$ 147,451	$ 173,553

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2023	Dec. 31, 2022
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)	154,344,930	153,821,339
Common stock, shares outstanding (in shares)	154,344,930	153,821,339

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Revenue:
Total revenue	$ 372	$ 0
Operating expenses:
Research and development	17,732	12,898
Sales and marketing	1,852	1,501
General and administrative	5,287	7,789
Total operating expenses	24,871	22,188
Loss from operations	(24,499)	(22,188)
Other income (expenses), net:
Interest income (expense), net	1,252	(29)
Gain on revaluation of common stock warrant liabilities	688	16,504
Other income, net	658	4
Total other income (expenses), net	2,598	16,479
Net loss to common stockholders	(21,901)	(5,709)
Comprehensive loss to common stockholders	$ (21,901)	$ (5,709)
Net loss per share, basic (in USD per share)	$ (0.14)	$ (0.04)
Net loss per share, diluted (in USD per share)	$ (0.14)	$ (0.04)
Weighted average shares used in per share calculation, basic (in shares)	154,123,911	151,683,819
Weighted average shares used in per share calculation, diluted (in shares)	154,123,911	151,683,819
Revenue
Revenue:
Total revenue	$ 371	$ 0
Revenue - related parties
Revenue:
Total revenue	$ 1	$ 0

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit
Balance at beginning of period (in shares) at Dec. 31, 2021	0
Balance at beginning of period at Dec. 31, 2021	$ 0
Balance at end of period (in shares) at Mar. 31, 2022	0
Balance at end of period at Mar. 31, 2022	$ 0
Balance at beginning of period (in shares) at Dec. 31, 2021		151,839,058
Balance at beginning of period at Dec. 31, 2021	205,159	$ 16	$ 745,753	$ (540,610)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock plans (in shares)		1,011,687
Issuance of common stock under employee stock plans	47		47
Cancellation of shares used to settle payroll tax withholding (in shares)		(244,202)
Cancellation of shares used to settle payroll tax withholding	(2,808)		(2,808)
Warrants exercised (in shares)		20
Stock-based compensation expense	2,760		2,760
Net loss	(5,709)			(5,709)
Balance at end of period (in shares) at Mar. 31, 2022		152,606,563
Balance at end of period at Mar. 31, 2022	$ 199,449	$ 16	745,752	(546,319)
Balance at beginning of period (in shares) at Dec. 31, 2022	0
Balance at beginning of period at Dec. 31, 2022	$ 0
Balance at end of period (in shares) at Mar. 31, 2023	0
Balance at end of period at Mar. 31, 2023	$ 0
Balance at beginning of period (in shares) at Dec. 31, 2022	153,821,339	153,821,339
Balance at beginning of period at Dec. 31, 2022	$ 136,974	$ 16	755,537	(618,579)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock plans (in shares)		523,591
Issuance of common stock under employee stock plans	104		104
Stock-based compensation expense	2,059		2,059
Net loss	$ (21,901)			(21,901)
Balance at end of period (in shares) at Mar. 31, 2023	154,344,930	154,344,930
Balance at end of period at Mar. 31, 2023	$ 117,236	$ 16	$ 757,700	$ (640,480)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Cash flows from operating activities:
Net loss	$ (21,901)	$ (5,709)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,077	196
Non-cash interest (income) expense	(762)	14
Non-cash lease expense	299	275
Stock-based compensation expense	2,059	2,760
Change in fair value of common stock warrant liabilities	(688)	(16,504)
Other non-cash income and expenses, net	(48)	0
Changes in operating assets and liabilities:
Accounts receivable	4,330	785
Prepaid expenses and other assets	1,731	405
Accounts payable	(529)	(1,852)
Accrued and other current liabilities	(4,657)	421
Accrued product warranties	1,231	0
Deferred revenue	(306)	0
Operating lease liabilities	(346)	(165)
Net cash used in operating activities	(18,510)	(19,374)
Cash flows from investing activities:
Purchases of property and equipment	(2,610)	(4,041)
Maturities and purchases of short-term investments, net	74,668	0
Net cash provided by (used in) investing activities	72,058	(4,041)
Cash flows from financing activities:
Payments on notes payable	(400)	(483)
Proceeds from stock options exercised	104	47
Repurchase of shares from employees for income tax withholding purposes	0	(2,808)
Other, net	(7)	0
Net cash used in financing activities	(303)	(3,244)
Net change in cash, cash equivalents and restricted cash	53,245	(26,659)
Cash, cash equivalents and restricted cash, beginning of period	36,655	240,232
Cash, cash equivalents and restricted cash, end of period	89,900	213,573
Supplemental disclosures of cash flow information:
Cash paid for operating leases included in cash used in operating activities	413	403
Non-cash investing and financing transactions:
Purchase of property and equipment included in accounts payable and accrued and other current liabilities	623	2,235
Right-of-use operating lease assets obtained in exchange for lease obligations	0	4,534
Right-of-use finance lease assets obtained in exchange for lease obligations	0	123
Cash and cash equivalents	87,811	212,331
Restricted cash, current	1,413	1,167
Restricted cash, non-current	676	75
Total cash, cash equivalents and restricted cash shown in the condensed consolidated statements of cash flows	$ 89,900	$ 213,573

DESCRITPION OF BUSINESS AND BAS

DESCRITPION OF BUSINESS AND BASIS OF PRESENTATION	3 Months Ended
	Mar. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
DESCRITPION OF BUSINESS AND BASIS OF PRESENTATION	DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION Description of Business —ESS Tech, Inc. (“ESS” or the “Company”) is a long-duration energy storage company specializing in iron flow battery technology. ESS develops long-duration iron flow batteries for commercial and utility-scale energy storage applications requiring four or more hours of flexible energy capacity. The Company designs and produces long-duration batteries predominantly using earth-abundant materials that the Company believes can be cycled over 20,000 times without capacity fade. The Company continues to be in the research and development phase. The Company was originally incorporated as a Cayman Islands exempted company on July 21, 2020 as a publicly traded special purpose acquisition company under the name ACON S2 Acquisition Corp. (“STWO”) for the purpose of effecting a business combination. On October 8, 2021 (the “Closing Date”), the Company consummated a business combination (the “Business Combination”) pursuant to the merger agreement, dated May 6, 2021, by and among STWO, SCharge Merger Sub, Inc., a Delaware corporation and wholly owned direct subsidiary of STWO (“Merger Sub”), and ESS Tech, Inc., a Delaware corporation (“Legacy ESS”), wherein Merger Sub merged with and into Legacy ESS, with Legacy ESS surviving as a wholly owned subsidiary of STWO. On the Closing Date, STWO changed its name from “ACON S2 Acquisition Corp.” to “ESS Tech, Inc.”, and its shares of common stock and warrants for shares of common stock commenced trading on the New York Stock Exchange under the ticker symbols “GWH” and “GWH.W”, respectively Basis of Presentation —The accompanying condensed 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”). Condensed Consolidated Financial Statements —The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. GAAP for interim financial information and in accordance with the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) for interim financial reporting. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. The condensed consolidated financial statements reflect all normal and recurring adjustments that are, in the opinion of the Company’s management, necessary in order to make the condensed consolidated financial statements not misleading. Operating results for the three months ended March 31, 2023 are not necessarily indicative of the results that may be expected for the year ending December 31, 2023. These condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and related notes included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2022, as filed with the SEC on March 2, 2023. Reclassifications —Certain prior year amounts have been reclassified to conform with current year presentation. These reclassifications had no effect on the reported results of operations.

SIGNIFICANT ACCOUNTING POLICIES

SIGNIFICANT ACCOUNTING POLICIES	3 Months Ended
	Mar. 31, 2023
Accounting Policies [Abstract]
SIGNIFICANT ACCOUNTING POLICIES	SIGNIFICANT ACCOUNTING POLICIES Use of Estimates —The preparation of the condensed 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 condensed consolidated financial statements and the reported amounts of expenses during the reporting periods. Such estimates relate to, among others, the useful lives and assessment of recoverability of property and equipment, deferred tax assets valuation, determination of the fair value of the Company’s investments, earnout warrant liabilities, public warrants and private warrants and the determination of variable consideration, standalone selling prices, product warranty liabilities, as well as other accruals. These estimates are based on historical trends, market pricing, current events and other relevant assumptions and data points. Actual results could differ from those estimates and such differences may be material to the condensed consolidated financial statements. Net Loss Per Share —The Company will use the two-class method when computing net loss per common share when shares are issued that meet the definition of participating securities. Under this method, net earnings are reduced by the amount of dividends declared in the current period for common stockholders and participating security holders. The remaining earnings or “undistributed earnings” are allocated between common stock and participating securities to the extent that each security may share in earnings as if all the earnings for the period had been distributed. Once calculated, the loss per common share is computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding during each year presented. Diluted loss attributable to common stockholders per common share has been computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding plus the dilutive effect of outstanding options, warrants, and restricted stock units (“RSUs”) during the respective periods. In cases where the Company has a net loss, no dilutive effect is shown as options, warrants, and RSUs become anti-dilutive. Cash and Cash Equivalents —Cash and cash equivalents include cash in bank accounts, money market funds, and investments with a maturity of three months or less at the date of purchase. Cash equivalents are recorded at carrying value, which approximates fair value. Restricted Cash — Restricted cash is required as collateral for certain of the Company’s lease agreements and contractual supply and service arrangements. Restricted cash includes a certificate of deposit for the Company’s lease agreements, collateral associated with a standby letter of credit issued to a customer, and a performance and payment bond for the Company’s supply and service arrangements. The certificate of deposit and bond are recorded at carrying value, which approximates fair value. Restricted cash amounts are reported in the condensed consolidated balance sheets as current or non-current depending on when the cash will be contractually released. Accounts Receivable, Net —The Company evaluates the creditworthiness of its customers. If the collection of any specific receivable is doubtful, an allowance is recorded in the allowance for expected credit losses which is included in accounts receivable, net in the condensed consolidated balance sheets. The Company had no allowance for expected credit losses recorded at either March 31, 2023 or December 31, 2022. Investments —Investments consist primarily of U.S. Treasury securities, U.S. agency securities, and commercial paper and are classified as trading securities as they are bought and held principally for the purpose of selling them in the near term. Trading securities are carried on the condensed consolidated balance sheets at fair value. Unrealized gains and losses on trading securities are included in other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. For trading securities still held at the reporting date, the Company recorded net gains of $5 thousand and zero for the three month periods ended March 31, 2023 and 2022, respectively. Revenue Recognition —Revenue is earned from the sale, installation and commissioning of energy storage systems and is derived from customer contracts. Revenue is recognized in an amount that reflects the consideration to which the Company expects to be entitled in exchange for transferring the promised goods and/or services to the customer, when or as the Company’s performance obligations are satisfied which includes estimates for variable consideration (e.g., liquidated damages). For product sales of energy storage systems, the Company’s performance obligations are satisfied at the point in time when the customer obtains control of the system, based primarily on shipping terms within individual customer contracts, unless specific customer acceptance criteria must be met, in which case revenue is deferred until customer acceptance has been received. No right of return exists on sales of energy storage systems. Performance obligations for services, including the optional Ironclad Services Plan (“ISP”) extended warranty and ongoing operations and maintenance program provided to customers, are satisfied over time as the respective services are performed. The transaction price of the underlying customer agreement is allocated to each performance obligation based on its relative standalone selling price. When the standalone selling price is not directly observable, revenue is determined based on an estimate of selling price using the observable market price that the good or service sells for separately in similar circumstances and to similar customers, and/or an expected cost plus margin approach when the observable selling price of a good or services is not known and is either highly variable or uncertain. Costs to obtain a contract relate primarily to commissions paid to the Company’s sales personnel related to the sale of energy storage systems. The Company expenses costs associated with obtaining new contracts as incurred if the amortization period of the asset recognized by the Company is one year or less. The Company invoices customers in accordance with customer agreements and in advance of recognizing revenue as the Company has not satisfied certain performance obligations that transfer control to the customer. Payment terms generally include advance payments to reserve capacity and/or upon issuance of the customer’s purchase order with the remainder due upon the achievement of various milestones including but not limited to shipment readiness, delivery, commissioning of the system, and completion of final site testing. Advanced customer payments and unsatisfied performance obligations are recognized as deferred revenue in the condensed consolidated balance sheets. Sales tax collected from customers is recorded on a net basis and therefore, not included in revenue. Sales tax is recorded as a liability until remitted to governmental authorities. Shipping and handling, freight costs and other reimbursable costs are accounted for as fulfillment activities and included in revenue. Related costs are included in research and development expenses while the Company is in the research and development phase. Product Warranties —Warranty obligations are incurred in connection with the sale of the Company’s products. The Company generally provides a standard warranty for a period of one year and an extended warranty through the optional ISP. The standard warranty is accounted for as an assurance-type warranty, which provides customers with assurance that the product complies with agreed-upon specifications and does not represent a separate performance obligation. The ISP warranty is considered a service-type warranty which is a distinct service and a portion of the transaction price is allocated to that performance obligation. Costs to provide for standard warranty obligations are estimated and recorded as a liability at the time revenue is recognized on the sale of the energy storage system. Warranty reserves include management’s best estimate of the projected costs to repair or to replace any items under warranty, which is based on various factors, including the use of actual claim data to date. Initial accruals and adjustments to warranty reserves are recorded to research and development expenses while the Company is in the research and development phase. Stock-Based Compensation —The Company accounts for stock-based compensation in accordance with ASC 718, Compensation – Stock Compensation (“ASC 718”) . The Company measures and recognizes compensation expense for all stock-based awards based on estimated fair values on the date of the grant, recognized over the requisite service period. For awards that vest solely based on a service condition, the Company recognizes stock-based compensation expense on a straight-line basis over the requisite service period. The compensation expense related to stock-based awards with performance conditions is recognized over the requisite service period when achievement of the performance conditions is probable. The compensation expense related to stock-based awards with market conditions is recognized on an accelerated attribution basis over the requisite service period, identified as the derived service period over which the market conditions are expected to be achieved, and is not reversed if the market condition is not satisfied. The Company accounts for forfeitures as they occur. Stock-based awards granted to employees are primarily stock options and RSUs. The fair value of each stock option granted is estimated using the Black-Scholes Merton option-pricing model using the single-option award approach. The following assumptions are used in the Black-Scholes Merton option-pricing model: Risk-Free Interest Rate —The risk-free interest rate is based on the implied yield available on the date of grant on U.S. Treasury zero-coupon bonds issued with a term that is equal to the option’s expected term at the grant date. Expected Volatility —The Company estimates the volatility for option grants by evaluating the average historical volatility of a peer group of companies for the period immediately preceding the option grant for a term that is approximately equal to the option’s expected term. Expected Term —The expected term for employees represents the period over which options granted are expected to be outstanding using the simplified method, as the Company’s historical share option exercise experience does not provide a reasonable basis upon which to estimate the expected term. The simplified method deems the term to be the average of the time-to-vesting and contractual life of the stock-based awards. Dividend Yield —The Company has not declared or paid dividends to date and does not anticipate declaring dividends. As such, the dividend yield has been estimated to be zero. 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 disclosures 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 condensed consolidated financial statements may not be comparable to the financial statements of issuers who are required to comply with the effective date for new or revised accounting standards that are applicable to public companies. The Company also intends to continue to take advantage of some of the reduced regulatory and reporting requirements of emerging growth companies pursuant to the JOBS Act so long as the Company qualifies as an emerging growth company. Recently Adopted Accounting Pronouncements —On January 1, 2023, the Company adopted ASU 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. The adoption did not result in a material impact to the Company’s condensed consolidated financial statements or related disclosures. In future periods, as revenue and accounts receivable increase, ASU 2016-13 could have a material impact on its condensed consolidated financial statements.

NET LOSS PER SHARE

NET LOSS PER SHARE	3 Months Ended
	Mar. 31, 2023
Earnings Per Share [Abstract]
NET LOSS PER SHARE	NET LOSS PER SHARE The following table presents the calculation of basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data): Three Months Ended March 31, 2023 2022 Net loss attributable to common stockholders $ (21,901) $ (5,709) Weighted-average shares outstanding – basic and diluted 154,123,911 151,683,819 Net loss per share – basic and diluted $ (0.14) $ (0.04) Due to the net losses for the three months ended March 31, 2023 and 2022, 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: Three Months Ended March 31, 2023 2022 Stock options 2,735,795 3,707,113 RSUs 12,075,979 4,633,968 Warrants 11,473,727 11,461,227 Number of securities excluded 26,285,501 19,802,308

PREPAID EXPENSES AND OTHER CURR

PREPAID EXPENSES AND OTHER CURRENT ASSETS	3 Months Ended
	Mar. 31, 2023
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
PREPAID EXPENSES AND OTHER CURRENT ASSETS	PREPAID EXPENSES AND OTHER CURRENT ASSETS Prepaid expenses and other current assets consist of the following (in thousands): March 31, 2023 December 31, 2022 Insurance $ 1,669 $ 2,033 Vendor advances 1,716 3,147 Other 567 477 Total prepaid expenses and other current assets $ 3,952 $ 5,657

PROPERTY AND EQUIPMENT, NET

PROPERTY AND EQUIPMENT, NET	3 Months Ended
	Mar. 31, 2023
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT, NET	PROPERTY AND EQUIPMENT, NET Property and equipment, net consists of the following (in thousands): March 31, 2023 December 31, 2022 Machinery and equipment $ 14,417 $ 13,699 Furniture and fixtures 184 184 Leasehold improvements 3,175 3,115 Software 183 183 Construction in process 4,326 3,230 Total property and equipment 22,285 20,411 Less accumulated depreciation (3,912) (2,841) Total property and equipment, net $ 18,373 $ 17,570

ACCRUED AND OTHER CURRENT LIABI

ACCRUED AND OTHER CURRENT LIABILITIES	3 Months Ended
	Mar. 31, 2023
Payables and Accruals [Abstract]
ACCRUED AND OTHER CURRENT LIABILITIES	ACCRUED AND OTHER CURRENT LIABILITIES Accrued and other current liabilities consist of the following (in thousands): March 31, 2023 December 31, 2022 Payroll and related benefits $ 2,580 $ 2,948 Materials and related purchases 3,515 6,892 Amounts due to customers 1,014 770 Professional and consulting fees 935 1,011 Accrued capital purchases 190 1,093 Other 299 1,411 Total accrued and other current liabilities $ 8,533 $ 14,125

ACCRUED PRODUCT WARRANTIES

ACCRUED PRODUCT WARRANTIES	3 Months Ended
	Mar. 31, 2023
Guarantees and Product Warranties [Abstract]
ACCRUED PRODUCT WARRANTIES	ACCRUED PRODUCT WARRANTIES The following table summarizes product warranty activity (in thousands): Three Months Ended March 31, 2023 2022 Accrued product warranties - beginning of period $ 1,643 $ — Accruals for warranties issued 1,504 — Repairs and replacements (273) — Accrued product warranties - end of period $ 2,874 $ —

BORROWINGS

BORROWINGS	3 Months Ended
	Mar. 31, 2023
Debt Disclosure [Abstract]
BORROWINGS	BORROWINGS Borrowings consist of the following (in thousands): March 31, 2023 December 31, 2022 Total notes payable $ 1,522 $ 1,915 Less current portion of notes payable 1,522 1,600 Notes payable, non-current $ — $ 315 Notes Payable In 2018, the Company entered into a $1,000 thousand note payable with Silicon Valley Bank (“SVB”) 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, 2022. The Company’s notes payable to SVB were recorded at fair value as part of the extinguishment. The $4,000 thousand note payable’s original maturity date was January 1, 2023. In April 2020, the Company entered into a deferral agreement (“Deferral Agreement”) to extend the maturity date of the original $1,000 thousand note payable to September 1, 2022 and extend the maturity date of the additional $4,000 thousand note payable to January 1, 2024. The Company accounted for the Deferral Agreement as a debt modification based on an analysis of cash flows before and after the debt modification. The original $1,000 thousand note payable was fully repaid in September 2022, pursuant to the terms of the Deferral Agreement. The notes payable bear interest at 0.50% below the bank’s prime rate (7.50% on March 31, 2023). The Company makes monthly interest and principal payments on the notes payable based on the schedule defined in the agreement. In connection with the closure of SVB on March 10, 2023, the notes payable have been assumed by First Citizens BancShares. The notes payable retained the same existing terms and covenants that were in place with SVB. At March 31, 2023 and subsequently, the notes payable were in default due to lower than required cash balances held by the Company at SVB; however, no event of default has been declared nor has acceleration of indebtedness been triggered by the bank. Should the bank trigger acceleration of indebtedness, the Company has sufficient cash on hand to meet the obligation. The notes payable are classified within notes payable, current as of March 31, 2023.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 2023
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 condensed consolidated financial statements. As of December 31, 2022, 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. In March 2023, the letter of credit was reduced to $75 thousand. As of March 31, 2023 the letter of credit was secured by a restricted certificate of deposit account totaling $75 thousand. There were no draws against the letter of credit during the three months ended March 31, 2023 and 2022. On September 1, 2022, the Company executed a standby letter of credit with CitiBank, N.A., for $600 thousand as security for the performance and payment of the Company’s obligations under a customer agreement. The letter of credit is in effect until the date on which the warranty period under the agreement expires, which is anticipated to be in 2025. As of March 31, 2023, $600 thousand was pledged as collateral for the letter of credit and recorded as restricted cash, non-current. There were no draws against the letter of credit during the three months ended March 31, 2023. On March 9, 2023, the Company executed a standby letter of credit with SVB (subsequently assumed by First Citizens BancShares) for $200 thousand in support of the Company’s customs and duties due on imported materials. The letter of credit is in effect until March 9, 2024. As of March 31, 2023, $200 thousand was pledged as collateral for the letter of credit and recorded as restricted cash, current. There were no draws against the letter of credit during the three months ended March 31, 2023.

COMMON STOCK WARRANTS

COMMON STOCK WARRANTS	3 Months Ended
	Mar. 31, 2023
Equity [Abstract]
COMMON STOCK WARRANTS	COMMON STOCK WARRANTS Common stock warrant balances consist of the following: March 31, 2023 December 31, 2022 Public Warrants outstanding 7,377,893 7,377,893 Private Warrants outstanding: Other Private Warrants outstanding 3,500,000 3,500,000 Earnout Warrants outstanding 583,334 583,334 Total common stock warrants 11,461,227 11,461,227 As part of STWO’s initial public offering, 8,333,287 warrants to purchase common stock listed on the New York Stock Exchange (“NYSE”) under the ticker symbol “GWH.W” (the “Public Warrants”) were sold. The Public Warrants entitle the holder thereof to purchase one share of common stock at a price of $11.50 per share, subject to adjustments. The Public Warrants may be exercised only for a whole number of shares of common stock. No fractional shares will be issued upon exercise of the warrants. The Public Warrants will expire five years after completion of the Business Combination, on October 8, 2026, or earlier upon redemption or liquidation. The Company may call the Public Warrants for redemption starting any time, in whole and not in part, at a price of $0.01 per warrant, so long as the Company provides no 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 any time, in whole and not in part, at a price of $0.10 per warrant, so long as the Company provides no less than 30 days prior written notice of redemption to each warrant holder; provided that holders will be able to exercise their warrants on a cashless basis prior to redemption and receive a number of shares determined based on the redemption date fair market value of the shares, and if, and only if, the reported last sale price of common stock equals or exceeds $10.00 per share or $10.00 per share for any 20 trading days within a 30-trading day period ending on the third trading day prior to the date the Company sends the notice of redemption to the warrant holders provided there is an effective registration statement covering the shares of common stock issuable upon exercise of the warrants. Simultaneously with STWO’s initial public offering, STWO issued in a private placement of 4,666,667 warrants to purchase common stock (the “Private Warrants”) to STWO’s sponsor. In connection with the Business Combination, STWO’s sponsor agreed to forfeit 583,333 Private Warrants. Of the remaining 4,083,334 Private Warrants, 3,500,000 were immediately vested and 583,334 warrants (the “Earnout Warrants”) were vested upon meeting certain earnout milestone events on November 9, 2021. Each Private Warrant and Earnout Warrant is exercisable for one share of common stock at a price of $11.50 per share, subject to adjustment. The Private Warrants and Earnout Warrants, post vesting on November 9, 2021, are identical to the Public Warrants, except that the Private Warrants and Earnout Warrants and the shares of common stock issuable upon exercise of the Private Warrants were not transferable, assignable or salable until 30 days after the completion of the 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 three months ended March 31, 2023: December 31, 2022 Issued Exercised March 31, 2023 Earnout Warrants 583,334 — — 583,334 Public Warrants 7,377,893 — — 7,377,893 Private Warrants (excluding Earnout Warrants) 3,500,000 — — 3,500,000 Total common stock warrants 11,461,227 — — 11,461,227 The table below shows the common stock warrant activities during the three months ended March 31, 2022: December 31, 2021 Issued Exercised March 31, 2022 Earnout Warrants 583,334 — — 583,334 Public Warrants 7,377,913 — 20 7,377,893 Private Warrants (excluding Earnout Warrants) 3,500,000 — — 3,500,000 Total common stock warrants 11,461,247 — 20 11,461,227 The 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 condensed consolidated statements of operations and comprehensive loss. For the three months ending March 31, 2023, the Company recorded a net decrease to the liabilities for Earnout Warrants, Public Warrants and Private Warrants (excluding Earnout Warrants) of $35 thousand, $443 thousand and $210 thousand, respectively. For the three months ended March 31, 2022, the Company recorded a net decrease to the liabilities for the for Earnout Warrants, Public Warrants and Private Warrants (excluding Earnout Warrants) of $840 thousand, $10,624 thousand and $5,040 thousand, respectively. SMUD Warrant On September 16, 2022, the Company entered into a warrant agreement with the Sacramento Municipal Utility District (“SMUD”), whereby the Company agreed to issue a warrant for up to 500,000 shares of the Company’s common stock at an exercise price of $4.296 per share. The vesting of the shares underlying the warrant will be subject to the achievement of certain commercial milestones through December 31, 2030 pursuant to a related commercial agreement. As of March 31, 2023 and December 31, 2022, 12,500 shares underlying the warrant were vested.

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	3 Months Ended
	Mar. 31, 2023
Share-Based Payment Arrangement [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION Stock-based compensation expense is allocated on a departmental basis based on the classification of the award holder. The following table presents the amount of stock-based compensation related to stock-based awards to employees on the Company’s condensed consolidated statements of operations and comprehensive loss (in thousands): Three Months Ended March 31, 2023 2022 Research and development $ 993 $ 587 Sales and marketing 150 54 General and administrative 916 2,119 Total stock-based compensation $ 2,059 $ 2,760 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. Stock awards under the plan may be issued as Incentive Stock Options (“ISO”), Non-statutory Stock Options (“NSO”), Stock Appreciation Rights, Restricted Stock Awards, or RSU Awards. Only employees are eligible to receive ISO awards. Employees, directors, and consultants who are providing continuous service to the Company are eligible to receive stock awards other than ISOs. The number of shares available for issuance under the 2021 Plan will be increased on the first day of each fiscal year beginning with the 2022 fiscal year and ending with the 2031 fiscal year, in an amount equal to the lesser of (i) 15,260,000 Shares, (ii) five percent (5%) of the outstanding shares on the last day of the immediately preceding fiscal year, or (iii) such number of shares determined by the Company no later than the last day of the immediately preceding fiscal year. Under the 2021 Plan, the Company is authorized to issue 22,224,640 shares of common stock as of March 31, 2023. Option prices for incentive stock options are set at the fair market value of the Company’s common stock at the date of grant. The fair market value of RSUs is set at the closing sales price of the Company’s common stock at the date of grant. Employee new hire grants generally cliff vest at the end of the first year and then 1/48 th of the original grant ratably over the remaining three years. Grants expire 10 years from the date of grant. As of March 31, 2023, there were 9,530,520 shares available for future grant under the 2021 Plan. Stock Options and Restricted Stock Units Stock option and RSU activity, prices, and values during the three months ended March 31, 2023 are as follows (in thousands, except for share, per share, and contractual term data): Options Outstanding RSUs Number of Weighted Weighted Aggregate Number of plan shares outstanding Weighted average Balances as of December 31, 2022 3,223,109 $ 1.01 7.39 $ 4,583 6,346,955 $ 6.10 Options and RSUs granted — — 6,471,697 1.18 Options exercised and RSUs released (300,501) 2.17 (223,090) 2.05 Options and RSUs forfeited (186,813) 0.51 (519,583) 4.38 Balances as of March 31, 2023 2,735,795 $ 1.12 7.08 $ 2,428 12,075,979 $ 3.53 Options vested and exercisable - December 31, 2022 1,947,123 $ 0.76 7.06 $ 3,244 Options vested and exercisable - March 31, 2023 1,811,938 $ 0.86 6.77 $ 1,710 No options were granted during the three months ended March 31, 2023. The weighted average assumptions used to determine the fair value of options granted in the three months ended March 31, 2022 were as follows: 2022 Risk-free rate 1.64 % Expected volatility 73.95 % Expected term 6 years Expected dividends — As of March 31, 2023, there was approximately $31,014 thousand of unamortized stock-based compensation expense related to unvested stock options and RSUs, which is expected to be recognized over a weighted-average period of 3.22 years. Employee Stock Purchase Plan In May 2022, the Company commenced its first offering period under the ESS Tech, Inc. Employee Stock Purchase Plan (the “ESPP”), which assists employees in acquiring a stock ownership interest in the Company. The ESPP permits eligible employees to purchase common stock at a discount through payroll deductions during specified offering periods. No employee may purchase more than $25,000 worth of stock in any calendar year. The price of shares purchased under the ESPP is equal to 85% of the fair market value of the common stock on the first or last day of the offering period, whichever is lower. The total ESPP expense for the three months ended March 31, 2023 was $59 thousand.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	3 Months Ended
	Mar. 31, 2023
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS The Company follows ASC 820, which establishes a common definition of fair value to be applied when U.S. GAAP requires the use of fair value, establishes a framework for measuring fair value, and requires certain disclosures about such fair value measurements. The following tables present the Company’s fair value hierarchy for its financial assets measured at fair value on a recurring basis (in thousands): March 31, 2023 Total Assets at Fair Value Cash Equivalents and Restricted Cash Short-Term Investments Level 1: Money market funds $ 69,243 $ 69,243 $ — U.S. Treasury securities 8,404 — 8,404 Total Level 1 77,647 69,243 8,404 Level 2: Certificate of deposit 76 76 — U.S. agency securities 25,358 13,488 11,870 Commercial paper 14,901 3,979 10,922 Total Level 2 40,335 17,543 22,792 Total assets measured at fair value $ 117,982 $ 86,786 $ 31,196 December 31, 2022 Total Assets at Fair Value Cash Equivalents and Restricted Cash Short-Term Investments Level 1: Money market funds $ 27,993 $ 27,993 $ — U.S. Treasury securities 19,944 — 19,944 Total Level 1 47,937 27,993 19,944 Level 2: Certificate of deposit 75 75 — U.S. agency securities 55,319 — 55,319 Commercial paper 35,756 5,972 29,784 Total Level 2 91,150 6,047 85,103 Total assets measured at fair value $ 139,087 $ 34,040 $ 105,047 The following tables present the Company’s fair value hierarchy for its financial liabilities measured at fair value on a recurring basis (in thousands): March 31, 2023 Level 1 Level 2 Level 3 Total Liabilities: Earnout Warrants $ — $ 128 $ — $ 128 Public Warrants 1,623 — — 1,623 Private Warrants (excluding Earnout Warrants) — 770 — 770 Total liabilities measured at fair value $ 1,623 $ 898 $ — $ 2,521 December 31, 2022 Level 1 Level 2 Level 3 Total Liabilities: Earnout Warrants $ — $ 163 $ — $ 163 Public Warrants 2,066 — — 2,066 Private Warrants (excluding Earnout Warrants) — 980 — 980 Total liabilities measured at fair value $ 2,066 $ 1,143 $ — $ 3,209 There were no transfers among Level 1, Level 2, or Level 3 categories during the periods presented. The carrying amounts of the Company’s notes payable and accounts payable approximate their fair values due to their short maturities. Level 1 Assets: The Company invests in money market funds and U.S Treasury securities that have maturities of 90 days or less. These assets are valued using observable inputs that reflect quoted prices for securities with identical characteristics. Level 2 Assets: The Company invests in a certificate of deposit, U.S. agency securities, and commercial paper. These assets are valued using observable inputs that reflect quoted prices for securities with similar characteristics and other observable inputs (such as interest rates that are observable at commonly quoted intervals). Level 1 Liabilities: The Company values its public common stock warrants based on the market price of the warrants. Level 2 Liabilities: The Company values its earnout warrant liabilities and private common stock warrants based on the market price of the Company’s public common stock warrants.

INCOME TAXES

INCOME TAXES	3 Months Ended
	Mar. 31, 2023
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXESThe Company did not record an income tax provision for the three month periods ended March 31, 2023 and 2022, respectively, due to the Company’s history of losses, and accordingly, has recorded a valuation allowance against substantially all of the Company’s net deferred tax assets. The Company records a valuation allowance when it is more likely than not that some portion, or all, of the Company’s deferred tax assets will not be realized.

REVENUE

REVENUE	3 Months Ended
	Mar. 31, 2023
Revenue from Contract with Customer [Abstract]
REVENUE	REVENUE Disaggregated Revenue The following table presents the Company’s revenue, disaggregated by source (in thousands): Three Months Ended March 31, 2023 2022 Product revenue $ 366 $ — Service and other revenue 6 — Total revenue $ 372 $ — The majority of the Company’s revenue is derived from the product sales of energy storage systems. See Note 2, Significant Accounting Policies , for further information regarding revenue recognition. Contract Balances Contract assets relate to unbilled amounts resulting from contract arrangements in which the related revenue recognition performance obligations have been satisfied, however invoicing to the customer has not yet occurred. Deferred revenue (or contract liabilities) relates to consideration received from customers in advance of the Company satisfying the revenue recognition performance obligations under the related contractual arrangements. Contract balances are reported in a net contract asset or deferred revenue liability position on a contract-by-contract basis at the end of each reporting period. Contract assets are included in prepaid expenses and other current assets and deferred revenue is presented separately on the condensed consolidated balance sheets. The following table provides information about contract assets and deferred revenue from contracts with customers (in thousands): March 31, 2023 December 31, 2022 Contract assets $ 76 $ 11 Deferred revenue 8,371 8,610 Contract assets increased by $65 thousand during the three months ended March 31, 2023 due to the recognition of revenues for which invoicing had not yet occurred. Deferred revenue decreased by $239 thousand during the three months ended March 31, 2023, reflecting $370 thousand in customer advance payments, offset by the recognition of $372 thousand of revenue that was included in the deferred revenue balance at the beginning of the period, $58 thousand of deposits returned to customers, and $244 thousand of reclassifications to accrued and other current liabilities due to changes in the estimation of variable consideration. Deferred revenue of $5,929 thousand is expected to be recognized within the next twelve months and non-current deferred revenue of $2,442 thousand is expected to be recognized in the subsequent twelve months.

RELATED PARTY TRANSACTIONS

RELATED PARTY TRANSACTIONS	3 Months Ended
	Mar. 31, 2023
Related Party Transactions [Abstract]
RELATED PARTY TRANSACTIONS	RELATED PARTY TRANSACTIONS During the year ended December 31, 2022, the Company recognized revenue of $284 thousand for sales of energy storage systems and extended warranty services to related parties. As of December 31, 2022, the Company had recorded deferred revenue of $5 thousand for sales of extended warranty services to related parties. During the three months ended March 31, 2023, the Company recognized revenue of $1 thousand for sales of extended warranty services to related parties. As of March 31, 2023, the Company had recorded deferred revenue of $4 thousand for sales of extended warranty services to related parties.

SIGNIFICANT ACCOUNTING POLICI_2

SIGNIFICANT ACCOUNTING POLICIES (Policies)	3 Months Ended
	Mar. 31, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation—The accompanying condensed 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”).
Reclassifications	Reclassifications —Certain prior year amounts have been reclassified to conform with current year presentation. These reclassifications had no effect on the reported results of operations.
Use of Estimates	Use of Estimates—The preparation of the condensed 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 condensed consolidated financial statements and the reported amounts of expenses during the reporting periods. Such estimates relate to, among others, the useful lives and assessment of recoverability of property and equipment, deferred tax assets valuation, determination of the fair value of the Company’s investments, earnout warrant liabilities, public warrants and private warrants and the determination of variable consideration, standalone selling prices, product warranty liabilities, as well as other accruals. These estimates are based on historical trends, market pricing, current events and other relevant assumptions and data points. Actual results could differ from those estimates and such differences may be material to the condensed consolidated financial statements.
Net Loss Per Share	Net Loss Per Share —The Company will use the two-class method when computing net loss per common share when shares are issued that meet the definition of participating securities. Under this method, net earnings are reduced by the amount of dividends declared in the current period for common stockholders and participating security holders. The remaining earnings or “undistributed earnings” are allocated between common stock and participating securities to the extent that each security may share in earnings as if all the earnings for the period had been distributed. Once calculated, the loss per common share is computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding during each year presented. Diluted loss attributable to
Cash, Cash Equivalents, and Restricted Cash	Cash and Cash Equivalents —Cash and cash equivalents include cash in bank accounts, money market funds, and investments with a maturity of three months or less at the date of purchase. Cash equivalents are recorded at carrying value, which approximates fair value. Restricted Cash — Restricted cash is required as collateral for certain of the Company’s lease agreements and contractual supply and service arrangements. Restricted cash includes a certificate of deposit for the Company’s lease agreements, collateral associated with a standby letter of credit issued to a customer, and a performance and payment bond for the Company’s supply and service arrangements. The certificate of deposit and bond are recorded at carrying value, which approximates fair value. Restricted cash amounts are reported in the condensed consolidated balance sheets as current or non-current depending on when the cash will be contractually released.
Accounts Receivable, Net	Accounts Receivable, Net —The Company evaluates the creditworthiness of its customers. If the collection of any specific receivable is doubtful, an allowance is recorded in the allowance for expected credit losses which is included in accounts receivable, net in the condensed consolidated balance sheets. The Company had no allowance for expected credit losses recorded at either March 31, 2023 or December 31, 2022.
Investments	Investments —Investments consist primarily of U.S. Treasury securities, U.S. agency securities, and commercial paper and are classified as trading securities as they are bought and held principally for the purpose of selling them in the near term. Trading securities are carried on the condensed consolidated balance sheets at fair value. Unrealized gains and losses on trading securities are included in other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. For trading securities still held at the reporting date, the Company recorded net gains of $5 thousand and zero for the three month periods ended March 31, 2023 and 2022, respectively.
Revenue Recognition	Revenue Recognition —Revenue is earned from the sale, installation and commissioning of energy storage systems and is derived from customer contracts. Revenue is recognized in an amount that reflects the consideration to which the Company expects to be entitled in exchange for transferring the promised goods and/or services to the customer, when or as the Company’s performance obligations are satisfied which includes estimates for variable consideration (e.g., liquidated damages). For product sales of energy storage systems, the Company’s performance obligations are satisfied at the point in time when the customer obtains control of the system, based primarily on shipping terms within individual customer contracts, unless specific customer acceptance criteria must be met, in which case revenue is deferred until customer acceptance has been received. No right of return exists on sales of energy storage systems. Performance obligations for services, including the optional Ironclad Services Plan (“ISP”) extended warranty and ongoing operations and maintenance program provided to customers, are satisfied over time as the respective services are performed. The transaction price of the underlying customer agreement is allocated to each performance obligation based on its relative standalone selling price. When the standalone selling price is not directly observable, revenue is determined based on an estimate of selling price using the observable market price that the good or service sells for separately in similar circumstances and to similar customers, and/or an expected cost plus margin approach when the observable selling price of a good or services is not known and is either highly variable or uncertain. Costs to obtain a contract relate primarily to commissions paid to the Company’s sales personnel related to the sale of energy storage systems. The Company expenses costs associated with obtaining new contracts as incurred if the amortization period of the asset recognized by the Company is one year or less. The Company invoices customers in accordance with customer agreements and in advance of recognizing revenue as the Company has not satisfied certain performance obligations that transfer control to the customer. Payment terms generally include advance payments to reserve capacity and/or upon issuance of the customer’s purchase order with the remainder due upon the achievement of various milestones including but not limited to shipment readiness, delivery, commissioning of the system, and completion of final site testing. Advanced customer payments and unsatisfied performance obligations are recognized as deferred revenue in the condensed consolidated balance sheets. Sales tax collected from customers is recorded on a net basis and therefore, not included in revenue. Sales tax is recorded as a liability until remitted to governmental authorities. Shipping and handling, freight costs and other reimbursable costs are accounted for as fulfillment activities and included in revenue. Related costs are included in research and development expenses while the Company is in the research and development phase.
Product Warranties	Product Warranties —Warranty obligations are incurred in connection with the sale of the Company’s products. The Company generally provides a standard warranty for a period of one year and an extended warranty through the optional ISP. The standard warranty is accounted for as an assurance-type warranty, which provides customers with assurance that the product complies with agreed-upon specifications and does not represent a separate performance obligation. The ISP warranty is considered a service-type warranty which is a distinct service and a portion of the transaction price is allocated to that performance obligation. Costs to provide for standard warranty obligations are estimated and recorded as a liability at the time revenue is recognized on the sale of the energy storage system. Warranty reserves include management’s best estimate of the projected costs to repair or to replace any items under warranty, which is based on various factors, including the use of actual claim data to date. Initial accruals and adjustments to warranty reserves are recorded to research and development expenses while the Company is in the research and development phase.
Stock-Based Compensation	Stock-Based Compensation —The Company accounts for stock-based compensation in accordance with ASC 718, Compensation – Stock Compensation (“ASC 718”) . The Company measures and recognizes compensation expense for all stock-based awards based on estimated fair values on the date of the grant, recognized over the requisite service period. For awards that vest solely based on a service condition, the Company recognizes stock-based compensation expense on a straight-line basis over the requisite service period. The compensation expense related to stock-based awards with performance conditions is recognized over the requisite service period when achievement of the performance conditions is probable. The compensation expense related to stock-based awards with market conditions is recognized on an accelerated attribution basis over the requisite service period, identified as the derived service period over which the market conditions are expected to be achieved, and is not reversed if the market condition is not satisfied. The Company accounts for forfeitures as they occur. Stock-based awards granted to employees are primarily stock options and RSUs. The fair value of each stock option granted is estimated using the Black-Scholes Merton option-pricing model using the single-option award approach. The following assumptions are used in the Black-Scholes Merton option-pricing model: Risk-Free Interest Rate —The risk-free interest rate is based on the implied yield available on the date of grant on U.S. Treasury zero-coupon bonds 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.
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 disclosures about such fair value measurements. ASC 820 establishes a hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that observable inputs be used when available. Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about what market participants would use in pricing the asset or liability based on the best information available in the circumstances. The hierarchy is broken down into three levels based on the reliability of inputs as follows: Level 1: Observable inputs such as quoted prices in active markets for identical assets or liabilities to which the Company has access at a measurement date. Level 2: Observable inputs other than Level 1 quoted prices that are observable for the asset or liability, either directly or indirectly; these include quoted prices for similar assets or liabilities in an active market, quoted prices for identical assets and liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3: Unobservable inputs for which little or no market data exists and for which the Company must develop its own assumptions regarding the assumptions that market participants would use in pricing the asset or liability, including assumptions regarding risk. Because of the uncertainties inherent in the valuation of assets or liabilities for which there are no observable inputs, those estimated fair values may differ significantly from the values that may have been used had a ready market for the assets or liabilities existed.
Recent Accounting Pronouncements and Recently Adopted Accounting Pronouncements	Recent Accounting Pronouncements —Pursuant to the Jumpstart Our Business Startups Act (“JOBS Act”), an emerging growth company is provided the option to adopt new or revised accounting standards that may be issued by the FASB or the SEC either (i) within the same periods as those otherwise applicable to non-emerging growth companies or (ii) within the same time periods as private companies. The Company has elected to use the extended transition period for complying with any new or revised financial accounting standards. As a result, the Company’s condensed consolidated financial statements may not be comparable to the financial statements of issuers who are required to comply with the effective date for new or revised accounting standards that are applicable to public companies. The Company also intends to continue to take advantage of some of the reduced regulatory and reporting requirements of emerging growth companies pursuant to the JOBS Act so long as the Company qualifies as an emerging growth company. Recently Adopted Accounting Pronouncements —On January 1, 2023, the Company adopted ASU 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. The adoption did not result in a material impact to the Company’s condensed consolidated financial statements or related disclosures. In future periods, as revenue and accounts receivable increase, ASU 2016-13 could have a material impact on its condensed consolidated financial statements.

NET LOSS PER SHARE (Tables)

NET LOSS PER SHARE (Tables)	3 Months Ended
	Mar. 31, 2023
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 stockholders (in thousands, except share and per share data): Three Months Ended March 31, 2023 2022 Net loss attributable to common stockholders $ (21,901) $ (5,709) Weighted-average shares outstanding – basic and diluted 154,123,911 151,683,819 Net loss per share – basic and diluted $ (0.14) $ (0.04)
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: Three Months Ended March 31, 2023 2022 Stock options 2,735,795 3,707,113 RSUs 12,075,979 4,633,968 Warrants 11,473,727 11,461,227 Number of securities excluded 26,285,501 19,802,308

PREPAID EXPENSES AND OTHER CU_2

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Tables)	3 Months Ended
	Mar. 31, 2023
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consist of the following (in thousands): March 31, 2023 December 31, 2022 Insurance $ 1,669 $ 2,033 Vendor advances 1,716 3,147 Other 567 477 Total prepaid expenses and other current assets $ 3,952 $ 5,657

PROPERTY AND EQUIPMENT, NET (Ta

PROPERTY AND EQUIPMENT, NET (Tables)	3 Months Ended
	Mar. 31, 2023
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, net	Property and equipment, net consists of the following (in thousands): March 31, 2023 December 31, 2022 Machinery and equipment $ 14,417 $ 13,699 Furniture and fixtures 184 184 Leasehold improvements 3,175 3,115 Software 183 183 Construction in process 4,326 3,230 Total property and equipment 22,285 20,411 Less accumulated depreciation (3,912) (2,841) Total property and equipment, net $ 18,373 $ 17,570

ACCRUED AND OTHER CURRENT LIA_2

ACCRUED AND OTHER CURRENT LIABILITIES (Tables)	3 Months Ended
	Mar. 31, 2023
Payables and Accruals [Abstract]
Schedule of Accrued and Other Current Liabilities	Accrued and other current liabilities consist of the following (in thousands): March 31, 2023 December 31, 2022 Payroll and related benefits $ 2,580 $ 2,948 Materials and related purchases 3,515 6,892 Amounts due to customers 1,014 770 Professional and consulting fees 935 1,011 Accrued capital purchases 190 1,093 Other 299 1,411 Total accrued and other current liabilities $ 8,533 $ 14,125

ACCRUED PRODUCT WARRANTIES (Tab

ACCRUED PRODUCT WARRANTIES (Tables)	3 Months Ended
	Mar. 31, 2023
Guarantees and Product Warranties [Abstract]
Schedule of Product Warranty Activity	The following table summarizes product warranty activity (in thousands): Three Months Ended March 31, 2023 2022 Accrued product warranties - beginning of period $ 1,643 $ — Accruals for warranties issued 1,504 — Repairs and replacements (273) — Accrued product warranties - end of period $ 2,874 $ —

BORROWINGS (Tables)

BORROWINGS (Tables)	3 Months Ended
	Mar. 31, 2023
Debt Disclosure [Abstract]
Schedule of Borrowings	Borrowings consist of the following (in thousands): March 31, 2023 December 31, 2022 Total notes payable $ 1,522 $ 1,915 Less current portion of notes payable 1,522 1,600 Notes payable, non-current $ — $ 315

COMMON STOCK WARRANTS (Tables)

COMMON STOCK WARRANTS (Tables)	3 Months Ended
	Mar. 31, 2023
Equity [Abstract]
Schedule of Common Stock Warrant Activity	Common stock warrant balances consist of the following: March 31, 2023 December 31, 2022 Public Warrants outstanding 7,377,893 7,377,893 Private Warrants outstanding: Other Private Warrants outstanding 3,500,000 3,500,000 Earnout Warrants outstanding 583,334 583,334 Total common stock warrants 11,461,227 11,461,227 The table below shows the common stock warrant activities during the three months ended March 31, 2023: December 31, 2022 Issued Exercised March 31, 2023 Earnout Warrants 583,334 — — 583,334 Public Warrants 7,377,893 — — 7,377,893 Private Warrants (excluding Earnout Warrants) 3,500,000 — — 3,500,000 Total common stock warrants 11,461,227 — — 11,461,227 The table below shows the common stock warrant activities during the three months ended March 31, 2022: December 31, 2021 Issued Exercised March 31, 2022 Earnout Warrants 583,334 — — 583,334 Public Warrants 7,377,913 — 20 7,377,893 Private Warrants (excluding Earnout Warrants) 3,500,000 — — 3,500,000 Total common stock warrants 11,461,247 — 20 11,461,227

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	3 Months Ended
	Mar. 31, 2023
Share-Based Payment Arrangement [Abstract]
Schedule of Stock-Based Compensation	The following table presents the amount of stock-based compensation related to stock-based awards to employees on the Company’s condensed consolidated statements of operations and comprehensive loss (in thousands): Three Months Ended March 31, 2023 2022 Research and development $ 993 $ 587 Sales and marketing 150 54 General and administrative 916 2,119 Total stock-based compensation $ 2,059 $ 2,760
Schedule of Share-based Payment Arrangement, Option, Activity	Stock option and RSU activity, prices, and values during the three months ended March 31, 2023 are as follows (in thousands, except for share, per share, and contractual term data): Options Outstanding RSUs Number of Weighted Weighted Aggregate Number of plan shares outstanding Weighted average Balances as of December 31, 2022 3,223,109 $ 1.01 7.39 $ 4,583 6,346,955 $ 6.10 Options and RSUs granted — — 6,471,697 1.18 Options exercised and RSUs released (300,501) 2.17 (223,090) 2.05 Options and RSUs forfeited (186,813) 0.51 (519,583) 4.38 Balances as of March 31, 2023 2,735,795 $ 1.12 7.08 $ 2,428 12,075,979 $ 3.53 Options vested and exercisable - December 31, 2022 1,947,123 $ 0.76 7.06 $ 3,244 Options vested and exercisable - March 31, 2023 1,811,938 $ 0.86 6.77 $ 1,710
Schedule of Share-based Payment Arrangement, Restricted Stock Unit, Activity	Stock option and RSU activity, prices, and values during the three months ended March 31, 2023 are as follows (in thousands, except for share, per share, and contractual term data): Options Outstanding RSUs Number of Weighted Weighted Aggregate Number of plan shares outstanding Weighted average Balances as of December 31, 2022 3,223,109 $ 1.01 7.39 $ 4,583 6,346,955 $ 6.10 Options and RSUs granted — — 6,471,697 1.18 Options exercised and RSUs released (300,501) 2.17 (223,090) 2.05 Options and RSUs forfeited (186,813) 0.51 (519,583) 4.38 Balances as of March 31, 2023 2,735,795 $ 1.12 7.08 $ 2,428 12,075,979 $ 3.53 Options vested and exercisable - December 31, 2022 1,947,123 $ 0.76 7.06 $ 3,244 Options vested and exercisable - March 31, 2023 1,811,938 $ 0.86 6.77 $ 1,710
Schedule of Valuation Assumptions	The weighted average assumptions used to determine the fair value of options granted in the three months ended March 31, 2022 were as follows: 2022 Risk-free rate 1.64 % Expected volatility 73.95 % Expected term 6 years Expected dividends —

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	3 Months Ended
	Mar. 31, 2023
Fair Value Disclosures [Abstract]
Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis	The following tables present the Company’s fair value hierarchy for its financial assets measured at fair value on a recurring basis (in thousands): March 31, 2023 Total Assets at Fair Value Cash Equivalents and Restricted Cash Short-Term Investments Level 1: Money market funds $ 69,243 $ 69,243 $ — U.S. Treasury securities 8,404 — 8,404 Total Level 1 77,647 69,243 8,404 Level 2: Certificate of deposit 76 76 — U.S. agency securities 25,358 13,488 11,870 Commercial paper 14,901 3,979 10,922 Total Level 2 40,335 17,543 22,792 Total assets measured at fair value $ 117,982 $ 86,786 $ 31,196 December 31, 2022 Total Assets at Fair Value Cash Equivalents and Restricted Cash Short-Term Investments Level 1: Money market funds $ 27,993 $ 27,993 $ — U.S. Treasury securities 19,944 — 19,944 Total Level 1 47,937 27,993 19,944 Level 2: Certificate of deposit 75 75 — U.S. agency securities 55,319 — 55,319 Commercial paper 35,756 5,972 29,784 Total Level 2 91,150 6,047 85,103 Total assets measured at fair value $ 139,087 $ 34,040 $ 105,047 The following tables present the Company’s fair value hierarchy for its financial liabilities measured at fair value on a recurring basis (in thousands): March 31, 2023 Level 1 Level 2 Level 3 Total Liabilities: Earnout Warrants $ — $ 128 $ — $ 128 Public Warrants 1,623 — — 1,623 Private Warrants (excluding Earnout Warrants) — 770 — 770 Total liabilities measured at fair value $ 1,623 $ 898 $ — $ 2,521 December 31, 2022 Level 1 Level 2 Level 3 Total Liabilities: Earnout Warrants $ — $ 163 $ — $ 163 Public Warrants 2,066 — — 2,066 Private Warrants (excluding Earnout Warrants) — 980 — 980 Total liabilities measured at fair value $ 2,066 $ 1,143 $ — $ 3,209

REVENUE (Tables)

REVENUE (Tables)	3 Months Ended
	Mar. 31, 2023
Revenue from Contract with Customer [Abstract]
Schedule of Revenue Disaggregated by Source	The following table presents the Company’s revenue, disaggregated by source (in thousands): Three Months Ended March 31, 2023 2022 Product revenue $ 366 $ — Service and other revenue 6 — Total revenue $ 372 $ —
Schedule of Contract Asset and Deferred Revenue	The following table provides information about contract assets and deferred revenue from contracts with customers (in thousands): March 31, 2023 December 31, 2022 Contract assets $ 76 $ 11 Deferred revenue 8,371 8,610

DESCRITPION OF BUSINESS AND B_2

DESCRITPION OF BUSINESS AND BASIS OF PRESENTATION (Details) cycle in Thousands	3 Months Ended
	Mar. 31, 2023 cycle h
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Battery, flexible energy capacity, minimum | h	4
Battery lifespan, number of cycles | cycle	20

SIGNIFICANT ACCOUNTING POLICI_3

SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Significant Accounting Policies [Line Items]
Net gains on trading securities	$ 5	$ 0
Stock options
Significant Accounting Policies [Line Items]
Expected dividends	0%	0%

NET LOSS PER SHARE - Schedule o

NET LOSS PER SHARE - Schedule of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Earnings Per Share [Abstract]
Net loss to common stockholders, basic	$ (21,901)	$ (5,709)
Net loss to common stockholders, diluted	$ (21,901)	$ (5,709)
Weighted-average shares outstanding – basic (in shares)	154,123,911	151,683,819
Weighted-average shares outstanding – diluted (in shares)	154,123,911	151,683,819
Net loss per share, basic (in USD per share)	$ (0.14)	$ (0.04)
Net loss per share, diluted (in USD per share)	$ (0.14)	$ (0.04)

NET LOSS PER SHARE - Schedule A

NET LOSS PER SHARE - Schedule Antidilutive Securities (Details) - shares	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of securities excluded (in shares)	26,285,501	19,802,308
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of securities excluded (in shares)	2,735,795	3,707,113
RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of securities excluded (in shares)	12,075,979	4,633,968
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of securities excluded (in shares)	11,473,727	11,461,227

PREPAID EXPENSES AND OTHER CU_3

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Insurance	$ 1,669	$ 2,033
Vendor advances	1,716	3,147
Other	567	477
Total prepaid expenses and other current assets	$ 3,952	$ 5,657

PROPERTY AND EQUIPMENT, NET (De

PROPERTY AND EQUIPMENT, NET (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 22,285		$ 20,411
Less accumulated depreciation	(3,912)		(2,841)
Total property and equipment, net	18,373		17,570
Depreciation expense	1,071	$ 196
Machinery and equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	14,417		13,699
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment	184		184
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	3,175		3,115
Software
Property, Plant and Equipment [Line Items]
Total property and equipment	183		183
Construction in process
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 4,326		$ 3,230

ACCRUED AND OTHER CURRENT LIA_3

ACCRUED AND OTHER CURRENT LIABILITIES (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Payroll and related benefits	$ 2,580	$ 2,948
Materials and related purchases	3,515	6,892
Amounts due to customers	1,014	770
Professional and consulting fees	935	1,011
Accrued capital purchases	190	1,093
Other	299	1,411
Total accrued and other current liabilities	$ 8,533	$ 14,125

ACCRUED PRODUCT WARRANTIES (Det

ACCRUED PRODUCT WARRANTIES (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Movement in Standard Product Warranty Accrual [Roll Forward]
Product warranties at beginning of period	$ 1,643	$ 0
Accruals for warranties issued	1,504	0
Repairs and replacements	(273)	0
Product warranties at end of period	$ 2,874	$ 0

BORROWINGS - Schedule of Borrow

BORROWINGS - Schedule of Borrowings (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Debt Disclosure [Abstract]
Total notes payable	$ 1,522	$ 1,915
Less current portion of notes payable	1,522	1,600
Notes payable, non-current	$ 0	$ 315

BORROWINGS - Narrative (Details

BORROWINGS - Narrative (Details) - Notes Payable	1 Months Ended	3 Months Ended	12 Months Ended
	Sep. 30, 2022 USD ($)	Mar. 31, 2023	Dec. 31, 2022 USD ($)	Sep. 30, 2020	Mar. 31, 2020 USD ($)	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Debt amount					$ 4,000,000	$ 1,000,000
Percent change in present value of cash flows				0.10
Loss on extinguishment of debt			$ 62,000
Repayments of debt	$ 1,000,000
Effective interest rate		7.50%
Prime
Debt Instrument [Line Items]
Spread on interest rate		0.50%

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details) - USD ($)	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 09, 2023	Dec. 31, 2022	Sep. 01, 2022
Other Commitments [Line Items]
Restricted certificate of deposit	$ 75,000
Noncancellable Agreement
Other Commitments [Line Items]
Noncancelable purchase commitments	17,497,000			$ 21,540,000
Cancellable Agreement
Other Commitments [Line Items]
Noncancelable purchase commitments	5,275,000			5,663,000
Letter of Credit | First Republic Bank
Other Commitments [Line Items]
Standby letter of credit	75,000			$ 725,000
Draws against letter of credit	0	$ 0
Letter of Credit | CitiBank N.A
Other Commitments [Line Items]
Standby letter of credit					$ 600,000
Draws against letter of credit	0
Letter of Credit | CitiBank N.A | Asset Pledged as Collateral
Other Commitments [Line Items]
Amounts pledged as collateral	600,000
Letter of Credit | First Citizens BancShares
Other Commitments [Line Items]
Standby letter of credit			$ 200,000
Draws against letter of credit	0
Letter of Credit | First Citizens BancShares | Asset Pledged as Collateral
Other Commitments [Line Items]
Amounts pledged as collateral	$ 200,000

COMMON STOCK WARRANTS - Schedul

COMMON STOCK WARRANTS - Schedule of Common Stock Warrant Balances (Details) - shares	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021	Oct. 08, 2021
Class of Warrant or Right [Line Items]
Warrants (in shares)	11,461,227	11,461,227	11,461,227	11,461,247
Public Warrants
Class of Warrant or Right [Line Items]
Warrants (in shares)	7,377,893	7,377,893	7,377,893	7,377,913
Private Warrants (excluding Earnout Warrants)
Class of Warrant or Right [Line Items]
Warrants (in shares)	3,500,000	3,500,000	3,500,000	3,500,000	4,083,334
Earnout Warrants
Class of Warrant or Right [Line Items]
Warrants (in shares)	583,334	583,334	583,334	583,334

COMMON STOCK WARRANTS - Narrati

COMMON STOCK WARRANTS - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended
	Oct. 08, 2021	Sep. 21, 2020	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022	Sep. 16, 2022	Dec. 31, 2021	Nov. 09, 2021
Class of Warrant or Right [Line Items]
Warrants issued (in shares)			0	0
Warrants (in shares)			11,461,227	11,461,227	11,461,227		11,461,247
Gain on revaluation of common stock warrant liabilities			$ 688	$ 16,504
Number of shares with vesting conditions met (in shares)			12,500		12,500
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
Earnout Warrant Holders | Common Stock
Class of Warrant or Right [Line Items]
Class of warrant or right, number of securities called by each warrant or right (in shares)	1
STWO | Common Stock
Class of Warrant or Right [Line Items]
Price per share (in USD per share)	$ 11.50
STWO | Private Warrants (excluding Earnout Warrants) | ACON S2 Acquisition Corp. Sponsor | Private Placement
Class of Warrant or Right [Line Items]
Shares issued (in shares)		4,666,667
STWO | Public Warrant Holders | Common Stock
Class of Warrant or Right [Line Items]
Issuance of shares (in shares)	1
Public Warrants
Class of Warrant or Right [Line Items]
Warrants issued (in shares)			0	0
Warrants (in shares)			7,377,893	7,377,893	7,377,893		7,377,913
Gain on revaluation of common stock warrant liabilities			$ 443	$ 10,624
Public 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 Warrants | Redemption Scenario, Two
Class of Warrant or Right [Line Items]
Redemption price per share (in USD per share)			$ 0.10
Public 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
Public Warrants | STWO
Class of Warrant or Right [Line Items]
Warrants issued (in shares)	8,333,287
Warrants term (in years)	5 years
Private Warrants (excluding Earnout Warrants)
Class of Warrant or Right [Line Items]
Warrants issued (in shares)			0	0
Warrants (in shares)	4,083,334		3,500,000	3,500,000	3,500,000		3,500,000
Warrants vested (in shares)	3,500,000
Gain on revaluation of common stock warrant liabilities			$ 210	$ 5,040
Private Warrants (excluding Earnout Warrants) | ACON S2 Acquisition Corp. Sponsor
Class of Warrant or Right [Line Items]
Warrants forfeited (in shares)	583,333
Earnout Warrants
Class of Warrant or Right [Line Items]
Warrants issued (in shares)			0	0
Warrants (in shares)			583,334	583,334	583,334		583,334
Warrants vested (in shares)								583,334
Gain on revaluation of common stock warrant liabilities			$ 35	$ 840
SMUD Warrant
Class of Warrant or Right [Line Items]
Class of warrant or right, number of securities called by each warrant or right (in shares)						500,000
Class of warrant or right, exercise price of warrants or rights (in dollars per share)						$ 4.296

COMMON STOCK WARRANTS - Sched_2

COMMON STOCK WARRANTS - Schedule of Common Stock Warrant Activity (Details) - shares		3 Months Ended
	Oct. 08, 2021	Mar. 31, 2023	Mar. 31, 2022
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		11,461,227	11,461,247
Warrants issued (in shares)		0	0
Warrants exercised (in shares)		0	20
Warrants or rights at end of period (in shares)		11,461,227	11,461,227
Earnout Warrants
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		583,334	583,334
Warrants issued (in shares)		0	0
Warrants exercised (in shares)		0	0
Warrants or rights at end of period (in shares)		583,334	583,334
Public Warrants
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		7,377,893	7,377,913
Warrants issued (in shares)		0	0
Warrants exercised (in shares)		0	20
Warrants or rights at end of period (in shares)		7,377,893	7,377,893
Private Warrants (excluding Earnout Warrants)
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		3,500,000	3,500,000
Warrants issued (in shares)		0	0
Warrants exercised (in shares)		0	0
Warrants or rights at end of period (in shares)	4,083,334	3,500,000	3,500,000

STOCK-BASED COMPENSATION - Sche

STOCK-BASED COMPENSATION - Schedule of Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	$ 2,059	$ 2,760
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	993	587
Sales and marketing
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	150	54
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	$ 916	$ 2,119

STOCK-BASED COMPENSATION - Narr

STOCK-BASED COMPENSATION - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of potential increase of shares authorized	5%
Award vesting period	3 years
Options granted (in shares)	0
Unamortized stock-based compensation costs	$ 31,014
Weighted average period of recognition for unamortized stock-based compensation costs	3 years 2 months 19 days
Total stock-based compensation	$ 2,059	$ 2,760
2021 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential increase of shares authorized (in shares)	15,260,000
Shares authorized for issuance (in shares)	22,224,640
Shares available for future grant (in shares)	9,530,520
Stock options | 2021 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share expiration period	10 years
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum employee stock purchase amount	$ 25
ESPP purchase price of common stock, percent of fair market value	85%
Total stock-based compensation	$ 59

STOCK-BASED COMPENSATION - Sc_2

STOCK-BASED COMPENSATION - Schedule of Share-based Payment Arrangement, Option and RSU Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2022
Options Outstanding
Options outstanding at beginning of period (in shares)	3,223,109
Options granted (in shares)	0
Options released (in shares)	(300,501)
Options forfeited (in shares)	(186,813)
Options outstanding at end of period (in shares)	2,735,795	3,223,109
Options vested and exercisable (in shares)	1,811,938	1,947,123
Weighted average exercise price
Weighted average exercise price of options outstanding at beginning of period (in USD per share)	$ 1.01
Weighted average exercise price of options granted (in USD per share)	0
Weighted average exercise price of options released (in USD per share)	2.17
Weighted average exercise price of options forfeited (in USD per share)	0.51
Weighted average exercise price of options outstanding at end of period (in USD per share)	1.12	$ 1.01
Weighted average exercise price of options vested and exercisable (in USD per share)	$ 0.86	$ 0.76
Options, Additional Disclosures
Weighted average remaining contractual term of options outstanding	7 years 29 days	7 years 4 months 20 days
Weighted average remaining contractual term of options vested and exercisable	6 years 9 months 7 days	7 years 21 days
Aggregate intrinsic value of options outstanding	$ 2,428	$ 4,583
Aggregate intrinsic value of options vested and exercisable	$ 1,710	$ 3,244
RSUs
RSUs
Units outstanding at beginning of period (in shares)	6,346,955
Units granted (in shares)	6,471,697
Units released (in shares)	(223,090)
Units forfeited (in shares)	(519,583)
Units outstanding at end of period (in shares)	12,075,979	6,346,955
Weighted average grant date fair value per Share
Weighted average grant date fair value per share of units outstanding at beginning of period (in USD per share)	$ 6.10
Weighted average grant date fair value per share of units granted (in USD per share)	1.18
Weighted average grant date fair value per share of units released (in USD per share)	2.05
Weighted average grant date fair value per share of units forfeited (in USD per share)	4.38
Weighted average grant date fair value per share of units outstanding at end of period (in USD per share)	$ 3.53	$ 6.10

STOCK-BASED COMPENSATION - Sc_3

STOCK-BASED COMPENSATION - Schedule of Valuation Assumptions (Details) - Stock options	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free rate		1.64%
Expected volatility		73.95%
Expected term		6 years
Expected dividends	0%	0%

FAIR VALUE MEASUREMENTS - Sched

FAIR VALUE MEASUREMENTS - Schedule of Assets and Liabilities on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Assets, Fair Value Disclosure [Abstract]
Short-term investments	$ 31,196	$ 105,047
Fair Value, Recurring
Assets, Fair Value Disclosure [Abstract]
Total Assets at Fair Value	117,982	139,087
Cash Equivalents and Restricted Cash	86,786	34,040
Short-term investments	31,196	105,047
Liabilities, Fair Value Disclosure [Abstract]
Earnout Warrants	128	163
Total liabilities measured at fair value	2,521	3,209
Fair Value, Recurring | Public Warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	1,623	2,066
Fair Value, Recurring | Private Warrants (excluding Earnout Warrants)
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	770	980
Fair Value, Recurring | Level 1
Assets, Fair Value Disclosure [Abstract]
Total Assets at Fair Value	77,647	47,937
Cash Equivalents and Restricted Cash	69,243	27,993
Short-term investments	8,404	19,944
Liabilities, Fair Value Disclosure [Abstract]
Earnout Warrants	0	0
Total liabilities measured at fair value	1,623	2,066
Fair Value, Recurring | Level 1 | Public Warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	1,623	2,066
Fair Value, Recurring | Level 1 | Private Warrants (excluding Earnout Warrants)
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	0	0
Fair Value, Recurring | Level 1 | Money market funds
Assets, Fair Value Disclosure [Abstract]
Total Assets at Fair Value	69,243	27,993
Cash Equivalents and Restricted Cash	69,243	27,993
Short-term investments	0	0
Fair Value, Recurring | Level 1 | U.S. Treasury securities
Assets, Fair Value Disclosure [Abstract]
Total Assets at Fair Value	8,404	19,944
Cash Equivalents and Restricted Cash	0	0
Short-term investments	8,404	19,944
Fair Value, Recurring | Level 2
Assets, Fair Value Disclosure [Abstract]
Total Assets at Fair Value	40,335	91,150
Cash Equivalents and Restricted Cash	17,543	6,047
Short-term investments	22,792	85,103
Liabilities, Fair Value Disclosure [Abstract]
Earnout Warrants	128	163
Total liabilities measured at fair value	898	1,143
Fair Value, Recurring | Level 2 | Public Warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	0	0
Fair Value, Recurring | Level 2 | Private Warrants (excluding Earnout Warrants)
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	770	980
Fair Value, Recurring | Level 2 | Certificate of deposit
Assets, Fair Value Disclosure [Abstract]
Total Assets at Fair Value	76	75
Cash Equivalents and Restricted Cash	76	75
Short-term investments	0	0
Fair Value, Recurring | Level 2 | U.S. agency securities
Assets, Fair Value Disclosure [Abstract]
Total Assets at Fair Value	25,358	55,319
Cash Equivalents and Restricted Cash	13,488	0
Short-term investments	11,870	55,319
Fair Value, Recurring | Level 2 | Commercial paper
Assets, Fair Value Disclosure [Abstract]
Total Assets at Fair Value	14,901	35,756
Cash Equivalents and Restricted Cash	3,979	5,972
Short-term investments	10,922	29,784
Fair Value, Recurring | Level 3
Liabilities, Fair Value Disclosure [Abstract]
Earnout Warrants	0	0
Total liabilities measured at fair value	0	0
Fair Value, Recurring | Level 3 | Public Warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	0	0
Fair Value, Recurring | Level 3 | Private Warrants (excluding Earnout Warrants)
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	$ 0	$ 0

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Income Tax Disclosure [Abstract]
Income tax expense provision	$ 0	$ 0

REVENUE - Schedule of Revenue D

REVENUE - Schedule of Revenue Disaggregated by Source (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Disaggregation of Revenue [Line Items]
Revenue	$ 372	$ 0
Product revenue
Disaggregation of Revenue [Line Items]
Revenue	366	0
Service and other revenue
Disaggregation of Revenue [Line Items]
Revenue	$ 6	$ 0

REVENUE - Schedule of Revenue C

REVENUE - Schedule of Revenue Contract Assets and Deferred Revenue (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Revenue from Contract with Customer [Abstract]
Contract assets	$ 76	$ 11
Deferred revenue	$ 8,371	$ 8,610

REVENUE - Narrative (Details)

REVENUE - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Dec. 31, 2022
Revenue from Contract with Customer [Abstract]
Contract assets	$ 65
Decrease in deferred revenue	239
Advance payment	370
Revenue recognized	372
Deposits returned to customers	58
Change in estimate of variable consideration	244
Deferred revenue, current	5,929	$ 6,168
Deferred revenue, non-current	$ 2,442	$ 2,442

RELATED PARTY TRANSACTIONS (Det

RELATED PARTY TRANSACTIONS (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2022
Related Party Transaction [Line Items]
Deferred revenue	$ 5,929	$ 6,168
Energy Storage Systems Sales
Related Party Transaction [Line Items]
Revenue - related parties		284
Energy Warehouse Sales
Related Party Transaction [Line Items]
Revenue - related parties	1
Deferred revenue	$ 4	$ 5