ESS Tech

ESS Tech was founded in 2011 in Wilsonville, Oregon by Craig Evans (President & CEO) and Dr. Julia Song (Chief Technology Officer), who are married partners who met while working together at ClearEdge Power, a fuel cell company. Evans is an aerospace and mechanical engineer; Song is an electrochemist. Working from their garage — until the DEA began investigating why a residential address was receiving such large chemical shipments — they built the earliest prototypes of what would become the iron flow battery. The company incorporated and moved to Portland State University's business accelerator before establishing its current headquarters and manufacturing facility in Wilsonville, Oregon. ESS is publicly traded on the NYSE under the ticker GWH.

ESS was founded on a specific technical observation: the power grid needed a storage technology that could provide 4–12 hours of storage at costs far below lithium-ion, using earth-abundant, non-toxic materials, and with a battery capable of lasting 25+ years without significant degradation. Evans and Song converged on iron flow batteries — a chemistry with roots in 1970s DOE research — because iron, salt, and water are the cheapest imaginable storage materials, with no fire risk, no toxic heavy metals, and no supply chain dependence on lithium or cobalt. Their key technical breakthrough was the "proton pump" — a fuel cell-like unit that prevents the two electrolyte halves of the battery from drifting out of balance, solving the main problem that had prevented iron flow batteries from cycling indefinitely.

ESS went public via a SPAC merger in October 2021 and has raised over $398 million including a DOE Loan Programs Office loan guarantee. Prior investors include Breakthrough Energy Ventures, SoftBank, Honeywell, and BASF Venture Capital. The company publishes a mission statement focused on accelerating global decarbonization safely and sustainably through longer-lasting energy storage.

ESS commercialized its first products — the Energy Warehouse (shipping container scale) and Energy Center (building scale) — beginning in 2015 and has deployed systems at solar farms, utilities, airports, and water utilities globally. The company has received UL 1973 certification and in 2025 announced a major strategic pivot to focus on AI and data center customers requiring firm, long-duration power. ESS's iron flow batteries are among the few truly non-lithium grid-scale storage technologies in active commercial production.

Publicly traded (NYSE: GWH). IPO via SPAC merger (Oct 2021). Key pre-IPO investors: Breakthrough Energy Ventures, ACES (a JV with Ascend Elements), SoftBank. $398M DOE Loan Programs Office loan guarantee.