Exhibit 99.1 ESS Tech, Inc. Announces First Quarter 2024 Financial Results Q1 Revenue of $2.7 Million Partnered with Sapele Power to Supply LDES in Africa Completed Testing of First Energy Center for Portland General Electric Ordered Second Power Module Automation Line with 40% Greater Production Capacity Exited Q1 with Cash and Short-Term Investments over $89 million; Expected to Carry ESS Well Into H1’25 WILSONVILLE, Ore. – May 7, 2024 – ESS Tech, Inc. (“ESS,” “ESS, Inc.” or the “Company”) (NYSE: GWH), a ...