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Cover - USD ($)
 12 Months Ended
Dec. 31, 2021
Feb. 28, 2022
Jun. 30, 2021
Entity Information [Line Items]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2021    
Current Fiscal Year End Date --12-31    
Document Transition Report false    
Entity File Number 001-39525    
Entity Registrant Name ESS Tech, Inc.    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 98-1550150    
Entity Address, Address Line One 26440 SW Parkway Ave.    
Entity Address, Address Line Two Bldg. 83    
Entity Address, City or Town Wilsonville    
Entity Address, State or Province OR    
Entity Address, Postal Zip Code 97070    
City Area Code 855    
Local Phone Number 423-9920    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Non-accelerated Filer    
Entity Small Business true    
Entity Emerging Growth Company true    
Entity Ex Transition Period false    
Entity Shell Company false    
Entity Public Float     $ 261,000,000
Entity Common Stock, Shares Outstanding (in shares)   152,556,734  
Entity Central Index Key 0001819438    
Document Fiscal Year Focus 2021    
Document Fiscal Period Focus FY    
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    
Common Stock Warrants      
Entity Information [Line Items]      
Title of 12(b) Security Warrants, each whole warrant exercisable for one share of common stock at an exercise price of $11.50    
Trading Symbol GWH.W    
Security Exchange Name NYSE