ESS Tech stock soars after securing long-duration battery deal with SRP

Published 09/10/2025, 21:26
© Reuters.

Investing.com -- ESS Tech Inc (NYSE:GWH) stock surged 13.4% Thursday after the iron flow battery manufacturer announced a significant agreement with Salt River Project (SRP), a Phoenix-area public power utility, to deploy a large-scale energy storage system.

The deal involves installing a five megawatt (MW), 50 megawatt-hour (MWh) battery system called Project New Horizon at SRP’s Copper Crossing Energy and Research Center in Florence, Arizona. Under the ten-year energy storage agreement, ESS will provide capacity to SRP using its Iron Flow Battery technology.

The system will store enough energy to power approximately 1,125 homes for 10 hours and represents a major validation for ESS’s long-duration energy storage technology. The project resulted from an RFP issued by SRP earlier this year specifically seeking long-duration energy storage pilots.

"This project is a significant validation in both the LDES industry and ESS as a technology provider," said Kelly Goodman, Interim Chief Executive Officer of ESS. "We are thrilled to be working with SRP to deliver more hours of clean energy to its customers."

SRP is expanding its energy storage capacity as part of efforts to meet increasing power demand in the Phoenix metropolitan area. The utility currently has nearly 1,300 MW of energy storage supporting its grid, including 1,100 MW of battery storage across eight facilities.

The ESS system will be designed to deliver 10 hours of discharge with charging times of 10 hours or less. According to the company, its iron flow batteries offer advantages over lithium-ion alternatives, including no risk of thermal runaway, operation across wide temperature ranges, and over 90% domestic content.

Design work for the project is already underway, with manufacturing scheduled to begin in 2026 and completion expected by December 2027.

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