Salt River Project (SRP), a public electricity utility operating in the Phoenix metropolitan area, has announced an agreement with ESS to implement a long-duration energy storage pilot project. The system, with a capacity of five megawatts (MW) and 50 megawatt-hours (MWh), will be installed at the Copper Crossing Energy and Research Center located in Florence, Arizona. The project, named New Horizon, is part of a ten-year capacity storage agreement with SRP.
A full-scale test for non-lithium-ion technologies
This project is part of SRP’s broader initiative to evaluate long-duration storage solutions without relying on lithium-ion. The installation will use ESS’s proprietary Energy Base technology, an iron-based flow battery system. Capable of delivering electricity for ten hours, the system could power 1,125 average homes during that period. The original request for proposals was launched by SRP in 2024 to identify alternative storage technologies.
Currently, SRP manages around 1,300 MW of storage capacity on its network, including eight battery sites totalling 1,100 MW and a 200 MW pumped hydro storage facility. The stated goal is to double generation capacity over the next ten years to keep up with growing energy demand in the Phoenix area.
Deployment expected by end of 2027
ESS plans to begin manufacturing the system in 2026, with commissioning expected by December 2027. The company will work with several industry partners to deliver the project. Additionally, the Electric Power Research Institute (EPRI) will participate in monitoring the project’s performance once operational.
The Copper Crossing site currently includes a 99 MW flexible natural gas plant. A 55 MW solar power plant is under construction at the same location, which will also host another long-duration storage project: Desert Blume, developed by CMBlu Energy, with a 5 MW, ten-hour capacity.
ESS expands its long-duration storage footprint
ESS’s iron flow battery system is composed mainly of iron, salt and water, and promises increased operational safety without thermal risk, while functioning across a wide range of temperatures. ESS claims its solution can achieve a 25-year lifespan with competitive levelised storage costs.
SRP views this partnership as an opportunity to test emerging technologies in Arizona’s climatic conditions. The project complements ongoing efforts to ensure grid reliability and meet sharply increasing regional demand.
