ESS Tech GWHT

ESS Tech, Inc. is a long‑duration energy storage company that designs and manufactures iron flow battery systems for stationary applications. The firm’s core technology stores energy in liquid electrolytes made primarily of iron, salt and water, which enables a non‑flammable chemistry and a wide operating temperature range from ‑15 °C to 50 °C. ESS aims to provide batteries that can be cycled over 20,000 times without capacity loss, offering a durable alternative to lithium‑ion systems for durations exceeding eight hours. The iron‑flow battery stores energy by changing the oxidation state of iron in two separate electrolyte tanks, which are pumped through a cell stack where the electrochemical reaction occurs. A proprietary Proton Pacifier recycles hydrogen generated at the negative electrode back into protons, maintaining stable pH and preventing the formation of performance‑degrading hydroxides. This design enables the battery to deliver both high power and long duration independently, because power is set by the membrane size while duration is determined by the tank volume and electrolyte amount. ESS’s manufacturing process emphasizes the use of commercially available pumps, tanks and enclosures, allowing the system to be assembled close to the point of use. The company was founded in 2011 and became publicly traded through a business combination with ACON S2 Acquisition Corp., which later renamed itself ESS Tech, Inc.

ESS generates revenue mainly from the sale of its energy storage hardware, including the flagship Energy Base system and the associated power‑train modules that can be assembled on site with tanks, pumps and other balance‑of‑system components. The company also provides warranty and maintenance services for its earlier Energy Warehouse and Energy Center products that remain under contract in the field. Sales are made to utilities, independent power producers and commercial‑and‑industrial customers, both behind‑the‑meter and front‑of‑the‑meter. In addition, ESS earns income from engineering and project‑development fees related to custom storage solutions and from licensing its patented Proton Pacifier technology to partners. The firm’s revenue model relies on long‑term contracts that often include multi‑year service agreements. For the year ended December 31 2025, ESS reported revenue of $1.6 million, down from $6.3 million in the prior year, reflecting the early stage of commercialization and limited volume shipments.

Within the emerging long‑duration energy storage market, ESS positions itself as an early mover with a proprietary iron‑flow chemistry that addresses the duration and cost gaps of lithium‑ion batteries for applications longer than eight hours. Its competitive advantages stem from the use of low‑cost, abundant materials, a non‑flammable design, and the patented Proton Pacifier that eliminates hydroxide buildup and enables up to 20,000 cycles without degradation. The company faces competition from established lithium‑ion suppliers such as Contemporary Amperex Technology Co. Limited, LG Chem, Ltd., Samsung Electronics Co., Ltd., Sungrow Power Supply Co., Ltd. and Tesla, Inc., as well as from alternative flow‑battery firms like Form Energy, Eos Energy Enterprises, Inc., Invinity Energy Systems and CellCube. ESS also competes with other storage technologies including sodium‑sulfur, vanadium‑redox, compressed‑air and pumped‑hydro systems. Despite having fewer financial resources than many rivals, ESS believes its technology’s safety, longevity and recyclability give it a differentiated edge in markets that value sustainability and long‑duration performance. The company’s strategy is to leverage its cost advantage at longer durations, where the levelized cost of storage is expected to fall below that of lithium‑ion solutions, thereby targeting utilities and renewable‑energy developers that need multi‑hour to multi‑day discharge capabilities.

ESS serves a broad range of customers that includes utilities seeking grid‑scale storage to balance renewable generation, independent power producers looking to enhance the economics of wind and solar projects, and commercial‑and‑industrial operators such as data centers, microgrids and critical‑facility owners who need behind‑the‑meter resilience. The company has undertaken pilot projects with the Sacramento Municipal Utility District (SMUD) for its Energy Warehouse system and has reported sales in Australia, where government incentives support renewable‑energy storage. While the filing does not disclose the full list of end‑users, it notes that ESS targets customers in both the United States and international markets who require safe, long‑duration batteries that can operate in harsh environments and provide multi‑hour to multi‑day discharge capabilities. ESS also works with partners such as OneBeacon Insurance for surety bonds and the Export‑Import Bank of the United States for financing options, which help facilitate project execution for its clients.