ESS TECH, INC., 10-Q filed on 5/8/2024
Quarterly Report
v3.24.1.u1
Cover - shares
 3 Months Ended
Mar. 31, 2024
May 03, 2024
Entity Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Mar. 31, 2024  
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   174,918,926
Entity Central Index Key 0001819438  
Document Fiscal Year Focus 2024  
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 $11.50  
Trading Symbol GWH.W  
Security Exchange Name NYSE  
v3.24.1.u1
Condensed Consolidated Balance Sheets (unaudited) - USD ($)
$ in Thousands
Mar. 31, 2024
Dec. 31, 2023
Current assets:    
Cash and cash equivalents $ 36,332 $ 20,165
Restricted cash, current 906 1,373
Accounts receivable, net 1,039 1,990
Short-Term Investments 53,220 87,899
Inventory 3,161 3,366
Prepaid expenses and other current assets 3,588 3,305
Total current assets 98,246 118,098
Property and equipment, net 16,928 16,266
Intangible assets, net 4,857 4,923
Operating lease right-of-use assets 1,841 2,167
Restricted cash, non-current 946 945
Other non-current assets 816 833
Total assets 123,634 143,232
Current liabilities:    
Accounts payable 2,910 2,755
Accrued and other current liabilities 6,552 10,755
Accrued product warranties 3,322 2,129
Operating lease liabilities, current 1,548 1,581
Deferred revenue, current 5,555 2,546
Total current liabilities 19,887 19,766
Operating lease liabilities, non-current 610 957
Deferred revenue, non-current 14,400  
Common stock warrant liabilities 917 917
Total liabilities 35,814 39,875
Commitments and contingencies (Note 8)  
Stockholders’ equity:    
Preferred stock ($0.0001 par value; 200,000,000 shares authorized, none issued and outstanding as of March 31, 2024 and December 31, 2023) 0 0
Common stock ($0.0000 par value; 2,000,000 shares authorized, 174,898,086 and 174,212 shares issued and outstanding as of March 31, 2024 and December 31, 2023, respectively) 18 18
Additional paid-in capital 802,269 799,496
Accumulated deficit (714,467) (696,157)
Total stockholders’ equity 87,820 103,357
Total liabilities and stockholders’ equity 123,634 143,232
Nonrelated party    
Current liabilities:    
Deferred revenue, non-current 0 3,835
Related party    
Current liabilities:    
Deferred revenue, non-current $ 14,400 $ 14,400
v3.24.1.u1
Condensed Consolidated Balance Sheets (unaudited) (Parenthetical) - $ / shares
Mar. 31, 2024
Dec. 31, 2023
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) 174,898,086 174,211,911
Common stock, shares outstanding (in shares) 174,898,086 174,211,911
v3.24.1.u1
Condensed Consolidated Statements of Operations and Comprehensive Loss (unaudited) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Revenue:    
Total revenue $ 2,738 $ 372
Cost of revenue 11,126 0
Gross profit (loss) (8,388) 372
Operating expenses:    
Research and development 3,546 17,732
Sales and marketing 2,034 1,852
General and administrative 5,526 5,287
Total operating expenses 11,106 24,871
Loss from operations (19,494) (24,499)
Other income (expenses), net:    
Interest income, net 1,239 1,252
Gain on revaluation of common stock warrant liabilities 0 688
Other income (expense), net (55) 658
Total other income, net 1,184 2,598
Net loss to common stockholders (18,310) (21,901)
Comprehensive loss to common stockholders $ (18,310) $ (21,901)
Net loss per share - basic (in USD per share) $ (0.10) $ (0.14)
Net loss per share - diluted (in USD per share) $ (0.10) $ (0.14)
Weighted average shares used in per share calculation, basic (in shares) 174,514,538 154,123,911
Weighted average shares used in per share calculation, diluted (in shares) 174,514,538 154,123,911
Nonrelated party    
Revenue:    
Total revenue $ 2,214 $ 371
Related party    
Revenue:    
Total revenue $ 524 $ 1
v3.24.1.u1
Condensed Consolidated Statements of Stockholders' Equity (unaudited) - USD ($)
$ in Thousands
Total
Common Stock
Additional Paid-In Capital
Accumulated Deficit
Balance at beginning of period (in shares) at Dec. 31, 2022   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 stock-based compensation plans, net of stock withheld for taxes (in shares)   523,591    
Issuance of common stock under stock-based compensation plans, net of stock withheld for taxes 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    
Balance at end of period at Mar. 31, 2023 $ 117,236 $ 16 757,700 (640,480)
Balance at beginning of period (in shares) at Dec. 31, 2023 174,211,911 174,211,911    
Balance at beginning of period at Dec. 31, 2023 $ 103,357 $ 18 799,496 (696,157)
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Issuance of common stock under stock-based compensation plans, net of stock withheld for taxes (in shares)   686,175    
Issuance of common stock under stock-based compensation plans, net of stock withheld for taxes (81)   (81)  
Stock-based compensation expense 2,854   2,854  
Net loss $ (18,310)     (18,310)
Balance at end of period (in shares) at Mar. 31, 2024 174,898,086 174,898,086    
Balance at end of period at Mar. 31, 2024 $ 87,820 $ 18 $ 802,269 $ (714,467)
v3.24.1.u1
Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Cash flows from operating activities:    
Net loss $ (18,310) $ (21,901)
Adjustments to reconcile net loss to net cash used in operating activities:    
Depreciation and amortization 1,219 1,077
Non-cash interest income (995) (762)
Non-cash lease expense 326 299
Stock-based compensation expense 2,854 2,059
Inventory write-down and losses on noncancellable purchase commitments (1,979) 0
Change in fair value of common stock warrant liabilities 0 (688)
Other non-cash (income) expenses, net 29 (48)
Changes in operating assets and liabilities:    
Accounts receivable, net 1,309 4,330
Inventory 1,145 0
Prepaid expenses and other current assets (266) 1,731
Accounts payable 153 (529)
Accrued and other current liabilities (4,024) (4,657)
Accrued product warranties 1,193 1,231
Deferred revenue (1,184) (306)
Operating lease liabilities (380) (346)
Net cash used in operating activities (18,910) (18,510)
Cash flows from investing activities:    
Purchases of property and equipment (953) (2,610)
Maturities and purchases of short-term investments, net 35,645 74,668
Net cash provided by investing activities 34,692 72,058
Cash flows from financing activities:    
Payments on notes payable 0 (400)
Proceeds from stock options exercised 0 104
Repurchase of shares from employees for income tax withholding purposes (81) 0
Other, net 0 (7)
Net cash used in financing activities (81) (303)
Net change in cash, cash equivalents and restricted cash 15,701 53,245
Cash, cash equivalents and restricted cash, beginning of period 22,483 36,655
Cash, cash equivalents and restricted cash, end of period 38,184 89,900
Supplemental disclosures of cash flow information:    
Cash paid for operating leases included in cash used in operating activities 449 413
Non-cash investing and financing transactions:    
Purchase of property and equipment included in accounts payable and accrued and other current liabilities 517 623
Transfers between inventory and property and equipment, net 1,051 0
Cash and cash equivalents 36,332 87,811
Restricted cash, current 906 1,413
Restricted cash, non-current 946 676
Total cash, cash equivalents and restricted cash shown in the condensed consolidated statements of cash flows $ 38,184 $ 89,900
v3.24.1.u1
DESCRITPION OF BUSINESS AND BASIS OF PRESENTATION
 3 Months Ended
Mar. 31, 2024
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 predominantly using earth-abundant materials.
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. On March 31, 2024, Legacy ESS merged with ESS Tech, Inc. leaving ESS Tech, Inc. as the sole remaining legal entity. As of April 1, 2024, the Company does not have any subsidiaries.
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, 2024 are not necessarily indicative of the results that may be expected for the year ending December 31, 2024. 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, 2023, as filed with the SEC on March 13, 2024.
Reclassifications—Certain immaterial prior year amounts have been reclassified to conform with current year presentation. These reclassifications had no effect on the reported results of operations.
v3.24.1.u1
SIGNIFICANT ACCOUNTING POLICIES
 3 Months Ended
Mar. 31, 2024
Accounting Policies [Abstract]  
SIGNIFICANT ACCOUNTING POLICIES SIGNIFICANT ACCOUNTING POLICIES
The Company’s significant accounting policies have not changed from those disclosed in the annual audited consolidated financial statements and accompanying notes of the Annual Report on Form 10-K for the fiscal year ended December 31, 2023. As of July 1, 2023 (the “Transition Date”), the Company transitioned out of the research and development phase and into commercial inventory accounting. As a result of the transition, all inventoriable costs incurred are capitalized, net of any lower of cost or net realizable value (“LCNRV”) charges, which are recognized as cost of revenue. Further, unfulfilled noncancellable purchase commitments are recognized as expense for estimated losses in cost of revenue and warranty and fulfillment costs are recorded as a component of cost of revenue rather than research and development expense beginning on the Transition Date. Refer to the accompanying notes of the Annual Report on Form 10-K for the fiscal year ended December 31, 2023 for further details on the accounting policies resulting from the transition.
v3.24.1.u1
INVENTORY
 3 Months Ended
Mar. 31, 2024
Inventory Disclosure [Abstract]  
INVENTORY INVENTORY
Inventory consists of the following (in thousands):
March 31, 2024December 31, 2023
Raw materials$6,778 $7,740 
Work in process2,284 1,236 
Finished goods3,403 5,685 
Inventory, gross$12,465 $14,661 
Net realizable value adjustment(9,304)(11,295)
Inventory$3,161 $3,366 
The balance of the Company’s inventory was written down by $9.3 million and $11.3 million from its cost to its net realizable value as of March 31, 2024 and December 31, 2023, respectively. Additionally, the Company has LCNRV losses related to noncancellable purchase commitments which were $0.7 million and $0.6 million as of March 31, 2024 and December 31, 2023, respectively. These LCNRV losses related to noncancellable purchase commitments are reflected in the materials and related purchases component of accrued and other liabilities on the condensed consolidated balance sheets. For further details, refer to Note 8, Commitments and Contingencies.
v3.24.1.u1
PROPERTY AND EQUIPMENT, NET
 3 Months Ended
Mar. 31, 2024
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, 2024December 31, 2023
Machinery and equipment$19,741 $17,669 
Furniture and fixtures231 184 
Leasehold improvements3,236 3,232 
Software183 183 
Construction in process3,972 4,279 
Total property and equipment27,363 25,547 
Less accumulated depreciation(10,435)(9,281)
Total property and equipment, net$16,928 $16,266 
Depreciation and amortization expense related to property and equipment, net was $1.2 million and $1.1 million for the three months ended March 31, 2024 and 2023, respectively.
v3.24.1.u1
INTANGIBLE ASSETS, NET
 3 Months Ended
Mar. 31, 2024
Goodwill and Intangible Assets Disclosure [Abstract]  
INTANGIBLE ASSETS, NET INTANGIBLE ASSETS, NET
In September 2023, the Company acquired patent rights valued at $5.0 million under a Patent License Agreement with UOP LLC (“UOP”), an affiliate of Honeywell International Inc. (“Honeywell”), a related party. These patent rights were recorded at fair value based on the value of the IP Warrants issued, as defined in Note 9, Common Stock Warrants, and are amortized over an average useful life of 19 years based on the remaining useful lives of the patents acquired. Amortization expense for the three months ended March 31, 2024 was $67 thousand.
Intangible assets, net consisted of the following (in thousands):
March 31, 2024December 31, 2023
CostAccumulated AmortizationNet Carrying AmountCostAccumulated AmortizationNet Carrying Amount
Patents$4,990 $(134)$4,857 $4,990 $(67)$4,923 
v3.24.1.u1
ACCRUED AND OTHER CURRENT LIABILITIES
 3 Months Ended
Mar. 31, 2024
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, 2024December 31, 2023
Payroll and related benefits$2,676 $5,681 
Materials and related purchases1,910 2,083 
Professional and consulting fees910 802 
Amounts due to customers— 545 
Accrued capital purchases52 327 
Noncancellable purchase commitments650 637 
Other354 680 
Total accrued and other current liabilities$6,552 $10,755 
v3.24.1.u1
ACCRUED PRODUCT WARRANTIES
 3 Months Ended
Mar. 31, 2024
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,
20242023
Accrued product warranties - beginning of period$2,129 $1,643 
Accruals for warranties issued 2,583 1,504
Repairs and replacements(1,083)(273)
Adjustments to existing accruals(307)— 
Accrued product warranties - end of period$3,322 $2,874 
v3.24.1.u1
COMMITMENTS AND CONTINGENCIES
 3 Months Ended
Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]  
COMMITMENTS AND CONTINGENCIES COMMITMENTS AND CONTINGENCIES
Legal Proceedings
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 material legal proceedings or other claims, legal actions, or complaints through the date of issuance of these condensed consolidated financial statements.
Letters of Credit
The Company has a standby letter of credit with First Republic Bank for $75 thousand as security for an operating lease of office and manufacturing space in Wilsonville, Oregon secured by a restricted certificate of deposit account totaling $75 thousand. As of March 31, 2024 the letter of credit was recorded as restricted cash, non-current. There were no draws against the letter of credit during the three months ended March 31, 2024 and 2023.
The Company has a standby letter of credit with Bank of America 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 more than a year from the balance sheet date. As of March 31, 2024, $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, 2024 and 2023.
The Company has a standby letter of credit with Bank of America for $200 thousand in support of the Company’s customs and duties due on imported materials. The letter of credit is in effect until May 19, 2024. As of March 31, 2024, $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, 2024 and 2023.
Purchase Commitments
The Company purchases materials from several suppliers and has entered into agreements with various contract manufacturers, which include cancellable and noncancellable purchase commitments. As of March 31, 2024 and December 31, 2023, total unfulfilled noncancellable purchase commitments were $0.7 million and $0.6 million, respectively. In addition, total unfulfilled cancellable purchase commitments amounted to $7.1 million and $7.7 million as of March 31, 2024, and December 31, 2023, respectively.
Joint Development Agreement
In September 2023, the Company entered into a Joint Development Agreement (“JDA”) with UOP, an affiliate of Honeywell, a related party, under which the parties would work collaboratively to engage in certain research and development activities generally related to flow battery technology. Pursuant to the JDA, the Company agreed to reimburse UOP a minimum of $8.0 million for research and development expenses incurred through December 31, 2028. No expenses were incurred under the JDA during the three months ended March 31, 2024.
v3.24.1.u1
COMMON STOCK WARRANTS
 3 Months Ended
Mar. 31, 2024
Equity [Abstract]  
COMMON STOCK WARRANTS COMMON STOCK WARRANTS
Common stock warrant balances consist of the following:
March 31, 2024December 31, 2023
Public Warrants outstanding11,461,227 11,461,227 
SMUD Warrant outstanding12,500 12,500 
Honeywell Warrants outstanding:
Investment Warrant outstanding10,631,633 10,631,633 
IP Warrant outstanding6,269,955 6,269,955 
Performance Warrants outstanding775,760 775,760 
Total common stock warrants29,151,07529,151,075
As part of STWO’s initial public offering, 8,333,287 warrants to purchase common stock (the “Public Warrants”) were sold. The Public Warrants are listed on the New York Stock Exchange (“NYSE”) under the ticker symbol “GWH.W.” 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 expire on October 8, 2026, five years after completion of the Business Combination, 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 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 for any 20 trading days within a 30-trading day period ending on the third trading day prior to the date the Company sends the notice of redemption to the warrant holders provided there is an effective registration statement covering the shares of common stock issuable upon exercise of the warrants.
Simultaneously with STWO’s initial public offering, STWO issued in a private placement 4,666,667 warrants to purchase common stock (the “Private Warrants”) to STWO’s sponsor. In connection with the Business Combination, STWO’s sponsor agreed to forfeit 583,333 Private Warrants. Of the remaining 4,083,334 Private Warrants, 3,500,000 were immediately vested and 583,334 warrants (the “Earnout Warrants”) were vested upon meeting certain earnout milestone events on November 9, 2021. The Private Warrants, including the Earnout Warrants, automatically converted on a 1:1 basis into Public Warrants upon the transfer of such warrants by the initial holder to a third party during the fourth quarter of 2023.
The table below shows the common stock warrant activities during the three months ended March 31, 2024:
December 31, 2023IssuedExercisedMarch 31, 2024
Public Warrants11,461,227 — — 11,461,227
SMUD Warrant12,500 — — 12,500
Investment Warrant10,631,633 — — 10,631,633
IP Warrant6,269,955 — — 6,269,955
Performance Warrants775,760 — — 775,760
Total common stock warrants29,151,075 — — 29,151,075
The table below shows the common stock warrant activities during the three months ended March 31, 2023:
December 31, 2022IssuedExercisedMarch 31, 2023
Earnout Warrants583,334 — — 583,334
Public Warrants7,377,893 — — 7,377,893
Private Warrants (excluding Earnout Warrants)3,500,000 — — 3,500,000
SMUD Warrant12,500 — — 12,500 
Total common stock warrants11,473,727 — — 11,473,727
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 in the condensed consolidated statements of operations and comprehensive loss. For the three months ending March 31, 2024, the Company’s liabilities for Public Warrants remained constant. For the three months ended March 31, 2023, the Company recorded a net decrease to the liabilities for liabilities for Earnout Warrants, Public Warrants and Private Warrants (excluding Earnout Warrants) of $0.7 million.
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, 2024 and December 31, 2023, 12,500 shares underlying the warrant were vested.
Honeywell Warrants
On September 21, 2023, the Company entered into a Common Stock and Warrant Purchase Agreement (the “Purchase Agreement”) with Honeywell ACS Ventures LLC (“Honeywell Ventures”), an affiliate of Honeywell, a related party. Pursuant to the Purchase Agreement, Honeywell invested $27.5 million in the Company and the Company issued 16,491,754 shares of common stock and a warrant to issue up to 10,631,633 shares of common stock (the “Investment Warrant”) to Honeywell Ventures. Pursuant to the Purchase Agreement and also as further consideration for the licensing by UOP, an affiliate of Honeywell, of certain intellectual property to the Company, the Company issued a warrant to issue up to 6,269,955 shares of common stock (the “IP Warrant”) to UOP. The Investment Warrant has an exercise price of $1.89, and the IP Warrant has an exercise price of $2.90. Each warrant will expire on September 21, 2028.
On September 21, 2023, the Company and UOP also entered into a Master Supply Agreement (the “Supply Agreement”), pursuant to which UOP may purchase equipment supplied by the Company. Pursuant to the Supply Agreement, the Company agreed to issue additional warrants to purchase common stock to UOP, consisting of (i) an initial performance warrant to issue up to 775,760 shares of common stock, issued on September 21, 2023 in exchange for a prepayment of equipment by UOP in the amount of $15 million, and (ii) additional performance warrants (not to exceed an aggregate value of $15 million based on target purchase amounts of up to $300 million by 2030) to be issued on an annual basis for the five-year period beginning in 2026, based on UOP’s purchase of additional equipment after execution of the Supply Agreement (the “Performance Warrants”). The initial Performance Warrant has an exercise price of $1.45 and the additional Performance Warrants will have an exercise price equal to the volume-weighted average price of the Company’s common stock for the last fifteen (15) trading days of the relevant
calendar year for which such Performance Warrant is being issued. The initial Performance Warrant will expire on September 21, 2028 and each additional Performance Warrant will have a five-year term from its respective date of issuance.
v3.24.1.u1
STOCK-BASED COMPENSATION
 3 Months Ended
Mar. 31, 2024
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 issued to employees on the Company’s condensed consolidated statements of operations and comprehensive loss (in thousands):
Three Months Ended March 31,
20242023
Cost of revenue$924 $— 
Research and development401 993 
Sales and marketing95 150 
General and administrative1,434 916 
Total stock-based compensation$2,854 $2,059 
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, and Restricted Stock Awards (“RSU”). Only employees are eligible to receive ISO awards. Employees, directors, and consultants who provide continuous service to the Company are eligible to receive stock awards other than ISOs. The number of shares available for issuance under the 2021 Plan will be increased on the first day of each fiscal year beginning with the 2022 fiscal year and ending with the 2031 fiscal year, in an amount equal to the lesser of (i) 15,260,000 shares, (ii) five percent (5%) of the outstanding shares on the last day of the immediately preceding fiscal year, or (iii) such number of shares determined by the Company no later than the last day of the immediately preceding fiscal year. As of January 1, 2024, the number of shares available for issuance under the 2021 Plan was increased by 8,700,000 shares in accordance with the plan and as approved by the Board. Under the 2021 Plan, the Company is authorized to issue 26,310,000 shares of common stock as of March 31, 2024.
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 1/4th at the end of the first year and then vest 1/16th each quarter over the remaining three years. Grants expire 10 years from the date of grant. All other grants vest quarterly over four years.
As of March 31, 2024, there were 6,423,422 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, 2024 are as follows (in thousands, except for share, per share, and contractual term data):
Options OutstandingRSUs
Number of
shares		Weighted
average
exercise price		Weighted
average
remaining
 contractual
term
(years)		Aggregate
intrinsic
values
($'000s)		Number of plan shares outstandingWeighted average
grant date fair value
per Share
Balances as of December 31, 2023
2,598,382 $1.33 6.25$1,422 13,162,368 $2.79 
Options and RSUs granted— — 9,471,453 0.98 
Options exercised and RSUs released— — (779,696)2.92 
Options and RSUs forfeited(9,900)0.54 (1,450,288)1.41 
Balances as of March 31, 2024
2,588,482 $1.34 6.03$648 20,403,837 $2.04 
Options vested and exercisable - December 31, 2023
1,775,256 $1.10 5.62$1,198 
Options vested and exercisable - March 31, 2024
1,881,196 $1.14 5.40$584 
No options were granted during the three months ended March 31, 2024 and 2023.
As of March 31, 2024, there was approximately $30.3 million 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 3.06 years.
Employee Stock Purchase Plan
In May 2022, the Company commenced its first offering period under the ESS Tech, Inc. Employee Stock Purchase Plan (“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. Total ESPP expense for the three months ended March 31, 2024 and 2023 was $84 thousand and $59 thousand, respectively.
v3.24.1.u1
FAIR VALUE MEASUREMENTS
 3 Months Ended
Mar. 31, 2024
Fair Value Disclosures [Abstract]  
FAIR VALUE MEASUREMENTS 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, 2024
Cash Equivalents and Restricted CashShort-Term InvestmentsTotal Assets at Fair Value
Level 1:
Money market funds$10,124 $— $10,124 
U.S. Treasury securities22,532 25,896 48,428 
Total Level 132,656 25,896 58,552 
Level 2:
Certificate of deposit77 — 77 
U.S. agency securities— 4,096 4,096 
Commercial paper— 23,228 23,228 
Total Level 277 27,324 27,401 
Total assets measured at fair value$32,733 $53,220 $85,953 
December 31, 2023
Cash Equivalents and Restricted CashShort-Term InvestmentsTotal Assets at Fair Value
Level 1:
Money market funds$10,126 $— $10,126 
U.S. Treasury securities— 54,681 54,681 
Total Level 110,126 54,681 64,807 
Level 2:
Certificate of deposit77 — 77 
U.S. agency securities— 12,447 12,447 
Commercial paper9,353 20,771 30,124 
Total Level 29,430 33,218 42,648 
Total assets measured at fair value$19,556 $87,899 $107,455 
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, 2024
Level 1Level 2Level 3Total
Liabilities:
Public common stock warrants917 — — 917 
Total liabilities measured at fair value$917 $— $— $917 
December 31, 2023
Level 1Level 2Level 3Total
Liabilities:
Public common stock warrants917 — — 917 
Total liabilities measured at fair value$917 $— $— $917 
There were no transfers among Level 1, Level 2, or Level 3 categories during the periods presented. The carrying amounts of the Company’s 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. 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.
For trading securities held at the reporting date, net losses recorded during the three months ended March 31, 2024 and 2023 were immaterial
v3.24.1.u1
INCOME TAXES
 3 Months Ended
Mar. 31, 2024
Income Tax Disclosure [Abstract]  
INCOME TAXES INCOME TAXESThe Company did not record an income tax provision for the three months ended March 31, 2024 and 2023, 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.
v3.24.1.u1
GOVERNMENT GRANTS
 3 Months Ended
Mar. 31, 2024
Government Assistance [Abstract]  
GOVERNMENT GRANTS GOVERNMENT GRANTS
Inflation Reduction Act of 2022 (“IRA”)
On August 16, 2022, President Biden signed the Inflation Reduction Act of 2022 into law. The IRA has significant economic incentives for both energy storage customers and manufacturers for projects placed in service after December 31, 2022. Starting in 2023, there are Production Tax Credits under Internal Revenue Code 45X (“PTC”), that can be claimed on battery components manufactured in the U.S. and sold to U.S. or foreign customers. The tax
credits available to manufacturers include a credit for ten percent of the cost incurred to make electrode active materials in addition to credits of $35 per kWh of capacity of battery cells and $10 per kWh of capacity of battery modules. The credits are cumulative, meaning that companies will be able to claim each of the available tax credits based on the battery components produced and sold through 2029, after which the PTC will begin to gradually phase down through 2032.
Since the PTC is a refundable credit (i.e., a credit with a direct-pay option available), the PTC is outside the scope of ASC 740, Income Taxes (“ASC 740”). Therefore, the Company accounts for the PTC under a government grant model. GAAP does not address the accounting for government grants received by a business entity that are outside the scope of ASC 740. The Company’s accounting policy is to analogize to IAS 20, Accounting for Government Grants and Disclosure of Government Assistance, under IFRS Accounting Standards. Under IAS 20, once it is reasonably assured that the entity will comply with the conditions of the grant, the grant money should be recognized on a systematic basis over the periods in which the entity recognizes the related expenses or losses for which the grant money is intended to compensate. The Company recognizes grants once it is probable that both of the following conditions will be met: (1) the Company is eligible to receive the grant and (2) the Company is able to comply with the relevant conditions of the grant.
The PTC is recorded as the applicable items are produced and sold. For the three months ended March 31, 2024, the Company recognized PTC of $230 thousand as a reduction of cost of revenue on the condensed consolidated statements of operations and comprehensive loss. As of March 31, 2024, grant receivable related to the PTC in the amount of $1.1 million is recorded in prepaid expenses and other current assets on the condensed consolidated balance sheets.
v3.24.1.u1
REVENUE
 3 Months Ended
Mar. 31, 2024
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,
20242023
Product revenue$2,632 $366 
Service revenue18 6 
Other revenue88 — 
Total revenue$2,738 $372 
The majority of the Company’s revenue is derived from product sales of energy storage systems. During 2024 other revenue included engineering services the Company performed in support of a customer project site and customer reimbursements for freight, travel, and other expenses.
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, 2024December 31, 2023
Contract assets$149 $253 
Deferred revenue19,955 20,781 
Contract assets decreased by $104 thousand during the three months ended March 31, 2024 due to invoicing on contracts for which revenue has previously been recognized. Deferred revenue decreased by $0.8 million during the three months ended March 31, 2024 reflecting $0.1 million in customer advance payments offset by the recognition of $0.9 million of revenue that was included in the deferred revenue balance at the beginning of the period.
Deferred revenue of $5.6 million is expected to be recognized within the next 12 months and non-current deferred revenue of $14.4 million is expected to be recognized thereafter.
v3.24.1.u1
RELATED PARTY TRANSACTIONS
 3 Months Ended
Mar. 31, 2024
Related Party Transactions [Abstract]  
RELATED PARTY TRANSACTIONS RELATED PARTY TRANSACTIONS
During the three months ended March 31, 2024, the Company recognized revenue of $0.5 million for sale of energy storage systems and extended warranty services provided to related parties. During the three months ended March 31, 2023, the Company recognized revenue of $1 thousand for extended warranty services provided to related parties.
As of March 31, 2024, the Company had immaterial deferred revenue for extended warranty services to related parties and $55 thousand of accounts receivable for reimbursable expenses from related parties. As of December 31, 2023, the Company had recorded deferred revenue of $1 thousand for extended warranty services provided to related parties.
As of March 31, 2024 and December 31, 2023, the Company recorded a non-refundable deposit for future equipment purchases by Honeywell of $14.4 million within non-current deferred revenue and an asset of $0.7 million for the value of the initial Performance Warrant issued to Honeywell within other non-current assets on the condensed consolidated balance sheets. The value of the initial Performance Warrant will be recognized as an offset to revenue in the period in which revenue is earned.
v3.24.1.u1
NET LOSS PER SHARE
 3 Months Ended
Mar. 31, 2024
Earnings Per Share [Abstract]  
NET LOSS PER SHARE NET LOSS PER SHARE
The following table presents the calculation of basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data):
Three Months Ended March 31,
20242023
Numerator:
Net loss attributable to common stockholders$(18,310)$(21,901)
Denominator:
Weighted-average shares outstanding – basic and diluted174,514,538 154,123,911 
Net loss per share – basic and diluted$(0.10)$(0.14)
Due to the net losses for the three months ended March 31, 2024 and 2023, basic and diluted net loss per common share were the same, as the effect of potentially dilutive securities would have been anti-dilutive.
The following outstanding balances of common share equivalents have been excluded from the calculation of diluted weighted-average common shares outstanding because the effect is anti-dilutive for the periods presented:
Three Months Ended March 31,
20242023
Stock options2,567,642 2,735,795 
RSUs20,403,837 12,075,979 
Warrants29,151,075 11,473,727 
Total52,122,554 26,285,501 
v3.24.1.u1
Pay vs Performance Disclosure - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Pay vs Performance Disclosure    
Net loss $ (18,310) $ (21,901)
v3.24.1.u1
Insider Trading Arrangements
 3 Months Ended
Mar. 31, 2024
Trading Arrangements, by Individual  
Rule 10b5-1 Arrangement Adopted false
Non-Rule 10b5-1 Arrangement Adopted false
Rule 10b5-1 Arrangement Terminated false
Non-Rule 10b5-1 Arrangement Terminated false
v3.24.1.u1
SIGNIFICANT ACCOUNTING POLICIES (Policies)
 3 Months Ended
Mar. 31, 2024
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 immaterial prior year amounts have been reclassified to conform with current year presentation. These reclassifications had no effect on the reported results of operations.
v3.24.1.u1
INVENTORY (Tables)
 3 Months Ended
Mar. 31, 2024
Inventory Disclosure [Abstract]  
Schedule of Inventory
Inventory consists of the following (in thousands):
March 31, 2024December 31, 2023
Raw materials$6,778 $7,740 
Work in process2,284 1,236 
Finished goods3,403 5,685 
Inventory, gross$12,465 $14,661 
Net realizable value adjustment(9,304)(11,295)
Inventory$3,161 $3,366 
v3.24.1.u1
PROPERTY AND EQUIPMENT, NET (Tables)
 3 Months Ended
Mar. 31, 2024
Property, Plant and Equipment [Abstract]  
Schedule of Property and Equipment, Net
Property and equipment, net consists of the following (in thousands):
March 31, 2024December 31, 2023
Machinery and equipment$19,741 $17,669 
Furniture and fixtures231 184 
Leasehold improvements3,236 3,232 
Software183 183 
Construction in process3,972 4,279 
Total property and equipment27,363 25,547 
Less accumulated depreciation(10,435)(9,281)
Total property and equipment, net$16,928 $16,266 
v3.24.1.u1
INTANGIBLE ASSETS, NET (Tables)
 3 Months Ended
Mar. 31, 2024
Goodwill and Intangible Assets Disclosure [Abstract]  
Schedule of Intangible Assets, Net
Intangible assets, net consisted of the following (in thousands):
March 31, 2024December 31, 2023
CostAccumulated AmortizationNet Carrying AmountCostAccumulated AmortizationNet Carrying Amount
Patents$4,990 $(134)$4,857 $4,990 $(67)$4,923 
v3.24.1.u1
ACCRUED AND OTHER CURRENT LIABILITIES (Tables)
 3 Months Ended
Mar. 31, 2024
Payables and Accruals [Abstract]  
Schedule of Accrued and Other Current Liabilities
Accrued and other current liabilities consist of the following (in thousands):
March 31, 2024December 31, 2023
Payroll and related benefits$2,676 $5,681 
Materials and related purchases1,910 2,083 
Professional and consulting fees910 802 
Amounts due to customers— 545 
Accrued capital purchases52 327 
Noncancellable purchase commitments650 637 
Other354 680 
Total accrued and other current liabilities$6,552 $10,755 
v3.24.1.u1
ACCRUED PRODUCT WARRANTIES (Tables)
 3 Months Ended
Mar. 31, 2024
Guarantees and Product Warranties [Abstract]  
Schedule of Product Warranty Activity
The following table summarizes product warranty activity (in thousands):
Three Months Ended March 31,
20242023
Accrued product warranties - beginning of period$2,129 $1,643 
Accruals for warranties issued 2,583 1,504
Repairs and replacements(1,083)(273)
Adjustments to existing accruals(307)— 
Accrued product warranties - end of period$3,322 $2,874 
v3.24.1.u1
COMMON STOCK WARRANTS (Tables)
 3 Months Ended
Mar. 31, 2024
Equity [Abstract]  
Schedule of Common Stock Warrant Activity
Common stock warrant balances consist of the following:
March 31, 2024December 31, 2023
Public Warrants outstanding11,461,227 11,461,227 
SMUD Warrant outstanding12,500 12,500 
Honeywell Warrants outstanding:
Investment Warrant outstanding10,631,633 10,631,633 
IP Warrant outstanding6,269,955 6,269,955 
Performance Warrants outstanding775,760 775,760 
Total common stock warrants29,151,07529,151,075
The table below shows the common stock warrant activities during the three months ended March 31, 2024:
December 31, 2023IssuedExercisedMarch 31, 2024
Public Warrants11,461,227 — — 11,461,227
SMUD Warrant12,500 — — 12,500
Investment Warrant10,631,633 — — 10,631,633
IP Warrant6,269,955 — — 6,269,955
Performance Warrants775,760 — — 775,760
Total common stock warrants29,151,075 — — 29,151,075
The table below shows the common stock warrant activities during the three months ended March 31, 2023:
December 31, 2022IssuedExercisedMarch 31, 2023
Earnout Warrants583,334 — — 583,334
Public Warrants7,377,893 — — 7,377,893
Private Warrants (excluding Earnout Warrants)3,500,000 — — 3,500,000
SMUD Warrant12,500 — — 12,500 
Total common stock warrants11,473,727 — — 11,473,727
v3.24.1.u1
STOCK-BASED COMPENSATION (Tables)
 3 Months Ended
Mar. 31, 2024
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 issued to employees on the Company’s condensed consolidated statements of operations and comprehensive loss (in thousands):
Three Months Ended March 31,
20242023
Cost of revenue$924 $— 
Research and development401 993 
Sales and marketing95 150 
General and administrative1,434 916 
Total stock-based compensation$2,854 $2,059 
Schedule of Stock Options Activity
Stock option and RSU activity, prices, and values during the three months ended March 31, 2024 are as follows (in thousands, except for share, per share, and contractual term data):
Options OutstandingRSUs
Number of
shares		Weighted
average
exercise price		Weighted
average
remaining
 contractual
term
(years)		Aggregate
intrinsic
values
($'000s)		Number of plan shares outstandingWeighted average
grant date fair value
per Share
Balances as of December 31, 2023
2,598,382 $1.33 6.25$1,422 13,162,368 $2.79 
Options and RSUs granted— — 9,471,453 0.98 
Options exercised and RSUs released— — (779,696)2.92 
Options and RSUs forfeited(9,900)0.54 (1,450,288)1.41 
Balances as of March 31, 2024
2,588,482 $1.34 6.03$648 20,403,837 $2.04 
Options vested and exercisable - December 31, 2023
1,775,256 $1.10 5.62$1,198 
Options vested and exercisable - March 31, 2024
1,881,196 $1.14 5.40$584 
Schedule of Restricted Stock Units Activity
Stock option and RSU activity, prices, and values during the three months ended March 31, 2024 are as follows (in thousands, except for share, per share, and contractual term data):
Options OutstandingRSUs
Number of
shares		Weighted
average
exercise price		Weighted
average
remaining
 contractual
term
(years)		Aggregate
intrinsic
values
($'000s)		Number of plan shares outstandingWeighted average
grant date fair value
per Share
Balances as of December 31, 2023
2,598,382 $1.33 6.25$1,422 13,162,368 $2.79 
Options and RSUs granted— — 9,471,453 0.98 
Options exercised and RSUs released— — (779,696)2.92 
Options and RSUs forfeited(9,900)0.54 (1,450,288)1.41 
Balances as of March 31, 2024
2,588,482 $1.34 6.03$648 20,403,837 $2.04 
Options vested and exercisable - December 31, 2023
1,775,256 $1.10 5.62$1,198 
Options vested and exercisable - March 31, 2024
1,881,196 $1.14 5.40$584 
v3.24.1.u1
FAIR VALUE MEASUREMENTS (Tables)
 3 Months Ended
Mar. 31, 2024
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, 2024
Cash Equivalents and Restricted CashShort-Term InvestmentsTotal Assets at Fair Value
Level 1:
Money market funds$10,124 $— $10,124 
U.S. Treasury securities22,532 25,896 48,428 
Total Level 132,656 25,896 58,552 
Level 2:
Certificate of deposit77 — 77 
U.S. agency securities— 4,096 4,096 
Commercial paper— 23,228 23,228 
Total Level 277 27,324 27,401 
Total assets measured at fair value$32,733 $53,220 $85,953 
December 31, 2023
Cash Equivalents and Restricted CashShort-Term InvestmentsTotal Assets at Fair Value
Level 1:
Money market funds$10,126 $— $10,126 
U.S. Treasury securities— 54,681 54,681 
Total Level 110,126 54,681 64,807 
Level 2:
Certificate of deposit77 — 77 
U.S. agency securities— 12,447 12,447 
Commercial paper9,353 20,771 30,124 
Total Level 29,430 33,218 42,648 
Total assets measured at fair value$19,556 $87,899 $107,455 
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, 2024
Level 1Level 2Level 3Total
Liabilities:
Public common stock warrants917 — — 917 
Total liabilities measured at fair value$917 $— $— $917 
December 31, 2023
Level 1Level 2Level 3Total
Liabilities:
Public common stock warrants917 — — 917 
Total liabilities measured at fair value$917 $— $— $917 
v3.24.1.u1
REVENUE (Tables)
 3 Months Ended
Mar. 31, 2024
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,
20242023
Product revenue$2,632 $366 
Service revenue18 6 
Other revenue88 — 
Total revenue$2,738 $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, 2024December 31, 2023
Contract assets$149 $253 
Deferred revenue19,955 20,781 
v3.24.1.u1
NET LOSS PER SHARE (Tables)
 3 Months Ended
Mar. 31, 2024
Earnings Per Share [Abstract]  
Schedule of Basic and Diluted Net Loss Per Share Attributable to Common Shareholders
The following table presents the calculation of basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data):
Three Months Ended March 31,
20242023
Numerator:
Net loss attributable to common stockholders$(18,310)$(21,901)
Denominator:
Weighted-average shares outstanding – basic and diluted174,514,538 154,123,911 
Net loss per share – basic and diluted$(0.10)$(0.14)
Schedule of Securities Excluded from Calculation of Diluted Weighted-Average Common Shares Outstanding
The following outstanding balances of common share equivalents have been excluded from the calculation of diluted weighted-average common shares outstanding because the effect is anti-dilutive for the periods presented:
Three Months Ended March 31,
20242023
Stock options2,567,642 2,735,795 
RSUs20,403,837 12,075,979 
Warrants29,151,075 11,473,727 
Total52,122,554 26,285,501 
v3.24.1.u1
DESCRITPION OF BUSINESS AND BASIS OF PRESENTATION (Details)
 3 Months Ended
Mar. 31, 2024
h
Organization, Consolidation and Presentation of Financial Statements [Abstract]  
Battery, flexible energy capacity, minimum 4
v3.24.1.u1
INVENTORY - Schedule of Inventory (Details) - USD ($)
$ in Thousands
Mar. 31, 2024
Dec. 31, 2023
Inventory Disclosure [Abstract]    
Raw materials $ 6,778 $ 7,740
Work in process 2,284 1,236
Finished goods 3,403 5,685
Inventory, gross 12,465 14,661
Net realizable value adjustment (9,304) (11,295)
Inventory $ 3,161 $ 3,366
v3.24.1.u1
INVENTORY - Narrative (Details) - USD ($)
$ in Thousands
Mar. 31, 2024
Dec. 31, 2023
Inventory [Line Items]    
Net realizable value adjustment $ 9,304 $ 11,295
Noncancellable Agreement    
Inventory [Line Items]    
Purchase commitments $ 700 $ 600
v3.24.1.u1
PROPERTY AND EQUIPMENT, NET (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Dec. 31, 2023
Property, Plant and Equipment [Line Items]      
Total property and equipment $ 27,363   $ 25,547
Less accumulated depreciation (10,435)   (9,281)
Total property and equipment, net 16,928   16,266
Depreciation expense 1,200 $ 1,100  
Machinery and equipment      
Property, Plant and Equipment [Line Items]      
Total property and equipment 19,741   17,669
Furniture and fixtures      
Property, Plant and Equipment [Line Items]      
Total property and equipment 231   184
Leasehold improvements      
Property, Plant and Equipment [Line Items]      
Total property and equipment 3,236   3,232
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 $ 3,972   $ 4,279
v3.24.1.u1
INTANGIBLE ASSETS, NET (Details) - USD ($)
$ in Thousands
 1 Months Ended 3 Months Ended
Sep. 30, 2023
Mar. 31, 2024
Acquired Finite-Lived Intangible Assets [Line Items]    
Amortization of Intangible Assets   $ 67
Patents    
Acquired Finite-Lived Intangible Assets [Line Items]    
Finite-lived intangible assets acquired $ 5,000  
Intangible asset, useful life (in years)   19 years
v3.24.1.u1
INTANGIBLE ASSETS, NET - Schedule of Intangible Assets, Net (Details) - Patents - USD ($)
$ in Thousands
Mar. 31, 2024
Dec. 31, 2023
Finite-Lived Intangible Assets [Line Items]    
Cost $ 4,990 $ 4,990
Accumulated Amortization (134) (67)
Net Carrying Amount $ 4,857 $ 4,923
v3.24.1.u1
ACCRUED AND OTHER CURRENT LIABILITIES (Details) - USD ($)
$ in Thousands
Mar. 31, 2024
Dec. 31, 2023
Payables and Accruals [Abstract]    
Payroll and related benefits $ 2,676 $ 5,681
Materials and related purchases 1,910 2,083
Professional and consulting fees 0 545
Amounts due to customers 910 802
Accrued capital purchases 52 327
Noncancellable purchase commitments 650 637
Other 354 680
Total accrued and other current liabilities $ 6,552 $ 10,755
v3.24.1.u1
ACCRUED PRODUCT WARRANTIES (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Movement in Standard Product Warranty Accrual [Roll Forward]    
Product warranties at beginning of period $ 2,129 $ 1,643
Accruals for warranties issued 2,583 1,504
Repairs and replacements (1,083) (273)
Adjustments to existing accruals (307) 0
Product warranties at end of period $ 3,322 $ 2,874
v3.24.1.u1
COMMITMENTS AND CONTINGENCIES (Details) - USD ($)
 1 Months Ended 3 Months Ended
Sep. 30, 2023
Mar. 31, 2024
Mar. 31, 2023
Dec. 31, 2023
Other Commitments [Line Items]        
Restricted certificate of deposit   $ 75,000    
Research and development   3,546,000 $ 17,732,000  
Joint Development Agreement | UOP        
Other Commitments [Line Items]        
Research and development $ 8,000,000 0    
Noncancellable Agreement        
Other Commitments [Line Items]        
Purchase commitments   700,000   $ 600,000
Cancellable Agreement        
Other Commitments [Line Items]        
Purchase commitments   7,100,000   7,700,000
Letter of Credit | First Republic Bank        
Other Commitments [Line Items]        
Standby letter of credit       75,000
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    
v3.24.1.u1
COMMON STOCK WARRANTS - Schedule of Common Stock Warrant Balances (Details) - shares
Mar. 31, 2024
Dec. 31, 2023
Mar. 31, 2023
Dec. 31, 2022
Class of Warrant or Right [Line Items]        
Warrants (in shares) 29,151,075 29,151,075 11,473,727 11,473,727
Public Warrants outstanding        
Class of Warrant or Right [Line Items]        
Warrants (in shares) 11,461,227 11,461,227 7,377,893 7,377,893
SMUD Warrant outstanding        
Class of Warrant or Right [Line Items]        
Warrants (in shares) 12,500 12,500 12,500 12,500
Investment Warrant outstanding        
Class of Warrant or Right [Line Items]        
Warrants (in shares) 10,631,633 10,631,633    
IP Warrant outstanding        
Class of Warrant or Right [Line Items]        
Warrants (in shares) 6,269,955 6,269,955    
Performance Warrants outstanding        
Class of Warrant or Right [Line Items]        
Warrants (in shares) 775,760 775,760    
v3.24.1.u1
COMMON STOCK WARRANTS - Narrative (Details)
$ / shares in Units, $ in Thousands
 3 Months Ended
Sep. 21, 2023
USD ($)
tradingDay
$ / shares
shares
Oct. 08, 2021
$ / shares
shares
Sep. 21, 2020
shares
Mar. 31, 2024
USD ($)
$ / shares
shares
Mar. 31, 2023
USD ($)
shares
Dec. 31, 2023
shares
Dec. 31, 2022
shares
Sep. 16, 2022
$ / shares
shares
Nov. 09, 2021
shares
Class of Warrant or Right [Line Items]                  
Warrants issued (in shares)       0 0        
Warrants (in shares)       29,151,075 11,473,727 29,151,075 11,473,727    
Net decrease to warrant liabilities | $       $ 0 $ 688        
Number of shares with vesting conditions met (in shares)       12,500   12,500      
Scenario two                  
Class of Warrant or Right [Line Items]                  
Price of common stock triggering redemption of warrants (in USD per share) | $ / shares       $ 10.00          
Trading days triggering redemption of warrants       20 days          
Consecutive trading day period       30 days          
STWO | Common Stock                  
Class of Warrant or Right [Line Items]                  
Price per share (in USD per share) | $ / shares   $ 11.50              
STWO | Private 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 common stock warrants                  
Class of Warrant or Right [Line Items]                  
Warrants issued (in shares)       0 0        
Warrants (in shares)       11,461,227 7,377,893 11,461,227 7,377,893    
Net decrease to warrant liabilities | $         $ 700        
Public common stock warrants | Scenario one                  
Class of Warrant or Right [Line Items]                  
Redemption price per share (in USD per share) | $ / shares       $ 0.01          
Price of common stock triggering redemption of warrants (in USD per share) | $ / shares       $ 18.00          
Trading days triggering redemption of warrants       20 days          
Consecutive trading day period       30 days          
Public common stock warrants | Scenario two                  
Class of Warrant or Right [Line Items]                  
Redemption price per share (in USD per share) | $ / shares       $ 0.10          
Public common stock warrants | STWO                  
Class of Warrant or Right [Line Items]                  
Warrants issued (in shares)   8,333,287              
Warrants term (in years)   5 years              
Private Warrants                  
Class of Warrant or Right [Line Items]                  
Warrants issued (in shares)         0        
Warrants (in shares)   4,083,334     3,500,000   3,500,000    
Warrants vested (in shares)   3,500,000              
Private 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        
Warrants (in shares)         583,334   583,334    
Warrants vested (in shares)                 583,334
SMUD Warrant outstanding                  
Class of Warrant or Right [Line Items]                  
Warrants issued (in shares)       0 0        
Warrants (in shares)       12,500 12,500 12,500 12,500    
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) | $ / shares               $ 4.296  
Honeywell Warrants                  
Class of Warrant or Right [Line Items]                  
Shares issued (in shares) 16,491,754                
Proceeds from issuance of common stock and common stock warrants, net of issuance costs | $ $ 27,500                
Honeywell Warrants | IP Warrant outstanding                  
Class of Warrant or Right [Line Items]                  
Warrants (in shares) 6,269,955                
Class of warrant or right, exercise price of warrants or rights (in dollars per share) | $ / shares $ 2.90                
Honeywell Warrants | Investment Warrant outstanding                  
Class of Warrant or Right [Line Items]                  
Warrants (in shares) 10,631,633                
Class of warrant or right, exercise price of warrants or rights (in dollars per share) | $ / shares $ 1.89                
Performance Warrant                  
Class of Warrant or Right [Line Items]                  
Warrants term (in years) 5 years                
Class of warrant or right, exercise price of warrants or rights (in dollars per share) | $ / shares $ 1.45                
Proceeds from issuance of common stock and common stock warrants, net of issuance costs | $ $ 300,000                
Additional performance warrants | $ $ 15,000                
Number of trading days | tradingDay 15                
Performance Warrant | UOP LLC | Related party                  
Class of Warrant or Right [Line Items]                  
Warrants term (in years) 5 years                
Class of warrant or right, number of securities called by each warrant or right (in shares) 775,760                
Exchange for pre-payment of equipment | $ $ 15,000                
v3.24.1.u1
COMMON STOCK WARRANTS - Schedule of Common Stock Warrant Activity (Details) - shares
 3 Months Ended
Oct. 08, 2021
Mar. 31, 2024
Mar. 31, 2023
Class of Warrant or Right [Roll Forward]      
Warrants or rights at beginning of period (in shares)   29,151,075 11,473,727
Warrants issued (in shares)   0 0
Warrants exercised (in shares)   0 0
Warrants or rights at end of period (in shares)   29,151,075 11,473,727
Public Warrants      
Class of Warrant or Right [Roll Forward]      
Warrants or rights at beginning of period (in shares)   11,461,227 7,377,893
Warrants issued (in shares)   0 0
Warrants exercised (in shares)   0 0
Warrants or rights at end of period (in shares)   11,461,227 7,377,893
Earnout Warrants      
Class of Warrant or Right [Roll Forward]      
Warrants or rights at beginning of period (in shares)     583,334
Warrants issued (in shares)     0
Warrants exercised (in shares)     0
Warrants or rights at end of period (in shares)     583,334
Private Warrants (excluding Earnout Warrants)      
Class of Warrant or Right [Roll Forward]      
Warrants or rights at beginning of period (in shares)     3,500,000
Warrants issued (in shares)     0
Warrants exercised (in shares)     0
Warrants or rights at end of period (in shares) 4,083,334   3,500,000
SMUD Warrant outstanding      
Class of Warrant or Right [Roll Forward]      
Warrants or rights at beginning of period (in shares)   12,500 12,500
Warrants issued (in shares)   0 0
Warrants exercised (in shares)   0 0
Warrants or rights at end of period (in shares)   12,500 12,500
Investment Warrant outstanding      
Class of Warrant or Right [Roll Forward]      
Warrants or rights at beginning of period (in shares)   10,631,633  
Warrants issued (in shares)   0  
Warrants exercised (in shares)   0  
Warrants or rights at end of period (in shares)   10,631,633  
IP Warrant outstanding      
Class of Warrant or Right [Roll Forward]      
Warrants or rights at beginning of period (in shares)   6,269,955  
Warrants issued (in shares)   0  
Warrants exercised (in shares)   0  
Warrants or rights at end of period (in shares)   6,269,955  
Performance Warrants outstanding      
Class of Warrant or Right [Roll Forward]      
Warrants or rights at beginning of period (in shares)   775,760  
Warrants issued (in shares)   0  
Warrants exercised (in shares)   0  
Warrants or rights at end of period (in shares)   775,760  
v3.24.1.u1
STOCK-BASED COMPENSATION - Schedule of Stock-Based Compensation (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]    
Total stock-based compensation $ 2,854 $ 2,059
Cost of revenue    
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]    
Total stock-based compensation 924 0
Research and development    
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]    
Total stock-based compensation 401 993
Sales and marketing    
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]    
Total stock-based compensation 95 150
General and administrative    
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]    
Total stock-based compensation $ 1,434 $ 916
v3.24.1.u1
STOCK-BASED COMPENSATION - Narrative (Details) - USD ($)
$ in Thousands
 3 Months Ended
Jan. 01, 2022
Mar. 31, 2024
Mar. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of potential increase of shares authorized   5.00%  
Award vesting period   3 years  
Unamortized stock-based compensation costs   $ 30,300  
Weighted average period of recognition for unamortized stock-based compensation costs   3 years 21 days  
Total stock-based compensation   $ 2,854 $ 2,059
Tranche one      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting rights, percentage   25.00%  
Tranche two      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting rights, percentage   6.25%  
2021 Equity Incentive Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Potential increase of shares authorized (in shares)   15,260,000  
Increase in shares authorized for issuance (in shares) 8,700,000    
Shares authorized for issuance (in shares)   26,310,000  
Shares available for future grant (in shares)   6,423,422,000  
Stock options | 2021 Equity Incentive Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period   4 years  
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   85.00%  
Total stock-based compensation   $ 84 $ 59
v3.24.1.u1
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, 2024
Dec. 31, 2023
Options Outstanding    
Options outstanding at beginning of period (in shares) 2,598,382  
Options granted (in shares) 0  
Options released (in shares) 0  
Options forfeited (in shares) (9,900)  
Options outstanding at end of period (in shares) 2,588,482 2,598,382
Options vested and exercisable (in shares) 1,881,196 1,775,256
Weighted average exercise price    
Weighted average exercise price of options outstanding at beginning of period (in USD per share) $ 1.33  
Weighted average exercise price of options granted (in USD per share) 0  
Weighted average exercise price of options released (in USD per share) 0  
Weighted average exercise price of options forfeited (in USD per share) 0.54  
Weighted average exercise price of options outstanding at end of period (in USD per share) 1.34 $ 1.33
Weighted average exercise price of options vested and exercisable (in USD per share) $ 1.14 $ 1.10
Options, Additional Disclosures    
Weighted average remaining contractual term of options outstanding 6 years 10 days 6 years 3 months
Weighted average remaining contractual term of options vested and exercisable 5 years 4 months 24 days 5 years 7 months 13 days
Aggregate intrinsic value of options outstanding $ 648 $ 1,422
Aggregate intrinsic value of options vested and exercisable $ 584 $ 1,198
RSUs    
RSUs    
Units outstanding at beginning of period (in shares) 13,162,368  
Units granted (in shares) 9,471,453  
Units released (in shares) (779,696)  
Units forfeited (in shares) (1,450,288)  
Units outstanding at end of period (in shares) 20,403,837 13,162,368
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) $ 2.79  
Weighted average grant date fair value per share of units granted (in USD per share) 0.98  
Weighted average grant date fair value per share of units released (in USD per share) 2.92  
Weighted average grant date fair value per share of units forfeited (in USD per share) 1.41  
Weighted average grant date fair value per share of units outstanding at end of period (in USD per share) $ 2.04 $ 2.79
v3.24.1.u1
FAIR VALUE MEASUREMENTS - Schedule of Assets and Liabilities on Recurring Basis (Details) - USD ($)
$ in Thousands
Mar. 31, 2024
Dec. 31, 2023
Assets, Fair Value Disclosure [Abstract]    
Short-Term Investments $ 53,220 $ 87,899
Recurring    
Assets, Fair Value Disclosure [Abstract]    
Cash Equivalents and Restricted Cash 32,733 19,556
Short-Term Investments 53,220 87,899
Total Assets at Fair Value 85,953 107,455
Liabilities, Fair Value Disclosure [Abstract]    
Total liabilities measured at fair value 917 917
Recurring | Public common stock warrants    
Liabilities, Fair Value Disclosure [Abstract]    
Public common stock warrants 917 917
Recurring | Level 1    
Assets, Fair Value Disclosure [Abstract]    
Cash Equivalents and Restricted Cash 32,656 10,126
Short-Term Investments 25,896 54,681
Total Assets at Fair Value 58,552 64,807
Liabilities, Fair Value Disclosure [Abstract]    
Total liabilities measured at fair value 917 917
Recurring | Level 1 | Public common stock warrants    
Liabilities, Fair Value Disclosure [Abstract]    
Public common stock warrants 917 917
Recurring | Level 1 | Money market funds    
Assets, Fair Value Disclosure [Abstract]    
Cash Equivalents and Restricted Cash 10,124 10,126
Short-Term Investments 0 0
Total Assets at Fair Value 10,124 10,126
Recurring | Level 1 | U.S. Treasury securities    
Assets, Fair Value Disclosure [Abstract]    
Cash Equivalents and Restricted Cash 22,532 0
Short-Term Investments 25,896 54,681
Total Assets at Fair Value 48,428 54,681
Recurring | Level 2    
Assets, Fair Value Disclosure [Abstract]    
Cash Equivalents and Restricted Cash 77 9,430
Short-Term Investments 27,324 33,218
Total Assets at Fair Value 27,401 42,648
Liabilities, Fair Value Disclosure [Abstract]    
Total liabilities measured at fair value 0 0
Recurring | Level 2 | Public common stock warrants    
Liabilities, Fair Value Disclosure [Abstract]    
Public common stock warrants 0 0
Recurring | Level 2 | Certificate of deposit    
Assets, Fair Value Disclosure [Abstract]    
Cash Equivalents and Restricted Cash 77 77
Short-Term Investments 0 0
Total Assets at Fair Value 77 77
Recurring | Level 2 | U.S. agency securities    
Assets, Fair Value Disclosure [Abstract]    
Cash Equivalents and Restricted Cash 0 0
Short-Term Investments 4,096 12,447
Total Assets at Fair Value 4,096 12,447
Recurring | Level 2 | Commercial paper    
Assets, Fair Value Disclosure [Abstract]    
Cash Equivalents and Restricted Cash 0 9,353
Short-Term Investments 23,228 20,771
Total Assets at Fair Value 23,228 30,124
Recurring | Level 3    
Liabilities, Fair Value Disclosure [Abstract]    
Total liabilities measured at fair value 0 0
Recurring | Level 3 | Public common stock warrants    
Liabilities, Fair Value Disclosure [Abstract]    
Public common stock warrants $ 0 $ 0
v3.24.1.u1
INCOME TAXES (Details) - USD ($)
 3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Income Tax Disclosure [Abstract]    
Income tax expense provision $ 0 $ 0
v3.24.1.u1
GOVERNMENT GRANTS (Details)
$ in Thousands
 3 Months Ended
Mar. 31, 2024
USD ($)
Government Assistance [Line Items]  
Government Assistance, Current, Statement of Financial Position [Extensible Enumeration] Prepaid expenses and other current assets
Production Tax Credits  
Government Assistance [Line Items]  
Government assistance amount $ 230
Current grants receivable $ 1,100
v3.24.1.u1
REVENUE - Schedule of Revenue Disaggregated by Source (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Disaggregation of Revenue [Line Items]    
Revenue $ 2,738 $ 372
Product revenue    
Disaggregation of Revenue [Line Items]    
Revenue 2,632 366
Service revenue    
Disaggregation of Revenue [Line Items]    
Revenue 18 6
Other revenue    
Disaggregation of Revenue [Line Items]    
Revenue $ 88 $ 0
v3.24.1.u1
REVENUE - Schedule of Revenue Contract Assets and Deferred Revenue (Details) - USD ($)
$ in Thousands
Mar. 31, 2024
Dec. 31, 2023
Revenue from Contract with Customer [Abstract]    
Contract assets $ 149 $ 253
Deferred revenue $ 19,955 $ 20,781
v3.24.1.u1
REVENUE - Narrative (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2024
Dec. 31, 2023
Revenue from Contract with Customer [Abstract]    
Contract assets increased $ 104  
Increase in deferred revenue 800  
Advance payment 100  
Revenue recognized 900  
Deferred revenue, current 5,555 $ 2,546
Deferred revenue, non-current $ 14,400  
v3.24.1.u1
RELATED PARTY TRANSACTIONS (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Dec. 31, 2023
Related Party Transaction [Line Items]      
Revenue $ 2,738 $ 372  
Deferred revenue, current 5,555   $ 2,546
Accounts receivable, net 1,039   1,990
Related party      
Related Party Transaction [Line Items]      
Revenue 524 1  
Energy Warehouse Sales | Related party      
Related Party Transaction [Line Items]      
Revenue 500    
Deferred revenue, current 0   $ 1
Accounts receivable, net 55    
Energy Storage Systems Sales | Related party      
Related Party Transaction [Line Items]      
Revenue   $ 1  
Honeywell ACS Ventures LLC | Related party      
Related Party Transaction [Line Items]      
Prepayment of equipment 14,400    
Deferred revenue, non-current - related parties $ 700    
v3.24.1.u1
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, 2024
Mar. 31, 2023
Numerator:    
Net loss to common stockholders, basic $ (18,310) $ (21,901)
Net loss to common stockholders, diluted $ (18,310) $ (21,901)
Denominator:    
Weighted-average shares outstanding – basic (in shares) 174,514,538 154,123,911
Weighted-average shares outstanding – diluted (in shares) 174,514,538 154,123,911
Net loss per share - basic (in USD per share) $ (0.10) $ (0.14)
Net loss per share - diluted (in USD per share) $ (0.10) $ (0.14)
v3.24.1.u1
NET LOSS PER SHARE - Schedule Antidilutive Securities (Details) - shares
 3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Number of securities excluded (in shares) 52,122,554 26,285,501
Stock options    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Number of securities excluded (in shares) 2,567,642 2,735,795
RSUs    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Number of securities excluded (in shares) 20,403,837 12,075,979
Warrants    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Number of securities excluded (in shares) 29,151,075 11,473,727