SRP and ESS Announce New 50 MWh Long Duration Energy Storage Pilot Project

Salt River Project (SRP), a not-for-profit public power utility serving the greater Phoenix metropolitan area, and ESS (NYSE:GWH), a leading manufacturer of iron flow long-duration energy storage (LDES) systems, today announced an agreement to add Project New Horizon, a five megawatt (MW), 50 megawatt-hour (MWh) battery system, to the grid. The pilot project will be installed at SRP’s Copper Crossing Energy and Research Center in Florence, Arizona and sell capacity to SRP under a ten-year energy storage agreement.

The ESS Iron Flow Battery (IFB) project will be part of SRP’s effort to evaluate emerging, non-lithium ion LDES technologies and support SRP’s reliability and sustainability goals. The system, which will utilize ESS’ Energy Base technology, will store enough energy to power 1,125 average-size homes for 10 hours. This project is the result of an RFP issued by SRP in 2024 for LDES pilots.

SRP is working to at least double the number of generating resources on its power system in the next 10 years to meet increasing energy demand in the Phoenix metropolitan area. SRP has nearly 1,300 MW of energy storage currently supporting its grid, which includes 1,100 MW of battery storage— spanning eight facilities— and 200 MW of pumped hydro storage.

“As the Valley continues to see rapid commercial and residential growth, projects like this allow us to better understand the efficacy and impact of different kinds of LDES technologies as they mature,” said Chico Hunter, SRP Manager of Innovation and Development. “This is another opportunity for SRP to evaluate the real-world performance of emergent technologies on our grid and in the Arizona climate.”

ESS’ technology uses a combination consisting mainly of iron, salt and water to store and discharge energy. The Energy Base will be designed to deliver 10 hours of discharge with “fast charging” of 10 hours or less. ESS’s products are safe and sustainable with no risk of thermal runaway, operate in a wide range of temperature environments and are Made in America with over 90% domestic content. They further offer a competitive levelized storage cost with a 25-year life expectancy.

“SRP once again demonstrates its leadership with its commitment to non-lithium, long duration energy storage,” said Kelly Goodman, Interim Chief Executive Officer of ESS. “This project is a significant validation in both the LDES industry and ESS as a technology provider. We are thrilled to be working with SRP to deliver more hours of clean energy to its customers.”

The Copper Crossing Energy and Research Center currently includes a 99-MW flexible natural gas facility. A 55-MW utility scale solar project is currently under construction at the site. The site will also host CMBlu Energy's “Desert Blume”, a 5 MW, 10-hour LDES project.

ESS will be partnering with industry leaders to deliver the project by December of 2027. Design is already underway, and manufacturing will begin in 2026. SRP and ESS will work with the Electric Power Research Institute (EPRI) to monitor performance data of the project.

About ESS Tech, Inc.

At ESS (NYSE: GWH), we deliver safe, sustainable, long-duration energy storage to ensure energy abundance and security. As energy demand continues to grow, our solutions provide essential reliability and resilience to people, communities, and businesses in the United States and throughout the world. Our technology uses earth-abundant iron, salt and water to deliver environmentally safe solutions capable of providing 10+ hours of flexible energy capacity for commercial and utility-scale energy storage applications. Established in 2011, ESS enables project developers, independent power producers, utilities and other large energy users to deploy reliable, sustainable long-duration energy storage solutions. For more information visit www.essinc.com.

About SRP

SRP is a community-based, not-for-profit public power utility and the largest electricity provider in the greater Phoenix metropolitan area, serving about 1.1 million customers. SRP provides water to about 2.5 million Valley residents, delivering more than 244 billion gallons of water (750,000 acre-feet) each year, and manages a 13,000-square-mile watershed that includes an extensive system of reservoirs, wells, irrigation laterals, and 131 miles of canals.

This release contains certain forward-looking statements, including statements regarding the Company and its management team’s expectations, hopes, beliefs, intentions or strategies regarding the future. The words “anticipate”, “believe”, “continue”, “could”, “estimate”, “expect”, “intends”, “may”, “might”, “plan”, “possible”, “potential”, “predict”, “project”, “should”, “will” and “would” and similar expressions may identify forward-looking statements, but the absence of these words does not mean that a statement is not forward-looking. Examples of forward-looking statements include, among others, statements regarding the Company’s productization, manufacturing and delivery of the Energy Base and relationships with customers, including Salt River Project. These forward-looking statements are based on the Company’s current expectations and beliefs concerning future developments and their potential effects on the Company and involve a number of risks, uncertainties (some of which are beyond the Company’s control) or other assumptions that may cause actual results or performance to be materially different from those expressed or implied by these forward-looking statements, which include, but are not limited to, delays, disruptions, or quality control problems in the Company’s manufacturing operations; issues related to the development and launch of the Energy Base product; failure to raise additional capital on acceptable terms or at all; and other risks and uncertainties described more fully in the section titled “Risk Factors” in the Company’s Quarterly Report on Form 10-Q filed on August 14, 2025, and the Company’s other filings with the U.S. Securities and Exchange Commission. Except as required by law, the Company is not undertaking any obligation to update or revise any forward-looking statements whether as a result of new information, future events or otherwise.

Source: ESS Inc.

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