Canadian compressed air energy storage (CAES) developer Hydrostor has signed an offtake agreement for its 500 MW/4,000 MWh project in Kern County, California.
Hydrostor and local power provider Clean Energy Alliance have signed an agreement covering 60 MW, providing a level of revenue certainty for the under-construction Willow Rock Energy Storage Center.
On-site work at the Willow Rock project began in July 2026, after securing a permit from the California Energy Commission in December 2025. Willow Rock Energy Storage Center is Hydrostor’s first utility-scale project in the United States. The CAES developer has an operational 2 MW demonstration project deployed in 2020 in Ontario, Canada.
Hydrostor’s CAES works by mining underground caverns using established hard-rock mining techniques. The company then floods the caverns and when air is compressed in, it displaces water to the surface. This creates constant pressure, making the system space efficient.
Jon Norman, president of Hydrostor, told pv magazine in May that the company’s CAES system can achieve around 60% to 65% round-trip efficiency.
In a press release, Hydrostor chief commercial officer Jordan Cole described the offtake agreement for Willow Rock as a “key milestone” for the project, as the company begins significant works on the project site.
Greg Wade, CEO of CEA, said investing in long-duration energy storage would allow the provider to capture excess solar energy during peak production for discharge when demand is high.
“This innovative facility in Kern County will play a vital role in helping CEA meet both state reliability mandates and our customers’ growing energy needs with clean, dependable capacity,” Wade said.
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