ESS Tech, Inc. (NYSE: GWH) is a Portland, Oregon-based long-duration energy storage company that completed its business combination with ACON S2 Acquisition Corp. in October 2021, bringing the iron flow battery developer to public markets under the energy storage and clean-technology sector. The SPAC was sponsored by ACON Investments, a Washington, D.C.-based private equity firm. ESS Tech filed an S-1 registration statement with the SEC on December 27, 2021, accession number 0001193125-21-367045, following the close of the merger. The company develops iron flow battery systems designed for commercial and utility-scale grid storage applications. Sign up at SpacDesk for full filing history, sponsor profiles, and deal-level analytics on GWH and hundreds of other SPAC transactions.