Hydrostor’s 4 GWh compressed air storage project signs offtake agreement with California Community Power

Canadian long-duration energy storage (LDES) developer Hydrostor has signed a 50 MW/400 MWh offtake agreement with California Community Power (CC Power) for its Willow Rock Energy Storage Center project. The agreement secures storage capacity for six of CC Power’s community choice aggregator members.

The 500 MW/4,000 MWh advanced compressed air energy storage (A-CAES) facility is designed to deliver eight hours of continuous discharge to the grid. It will provide firm, long-duration capacity to six CC Power members: CleanPowerSF, Peninsula Clean Energy, Redwood Coast Energy Authority, San José Clean Energy, Silicon Valley Clean Energy Authority, and Valley Clean Energy Authority.

“Hydrostor’s Willow Rock project brings much-needed grid benefits to California by providing reliable long-duration energy storage capacity using domestic content, off-the-shelf turbomachinery, and only air and water to store energy,” said Alexander Morris, CC Power’s general manager.

The Willow Rock project received its California Energy Commission permit in December last year, secured a franchise agreement from the Kern County Board of Supervisors the same month, and obtained a conditional letter of support from the board in April 2025. The facility is expected to come online in 2030.

Willow Rock will deploy Hydrostor’s A-CAES technology, which the company says addresses longstanding efficiency and scalability challenges associated with conventional compressed air energy storage. Traditional CAES systems typically recover less than 50% of input energy. Hydrostor’s approach integrates a proprietary thermal storage system that captures and stores heat generated during compression, then reuses it during discharge instead of releasing it as waste.

The A-CAES tech also aims to resolve another limitation of conventional CAES: variable power output caused by fluctuating underground air pressure. Hydrostor maintains constant cavern pressure by using water from an above-ground reservoir. Water condensed during compression is captured and reused. This design enables deployment across a broader range of underground conditions, whereas traditional CAES has often relied on salt caverns to withstand pressure fluctuations.

“Through this agreement with CC Power, we’re demonstrating how A‑CAES can be deployed at meaningful scale to meet emerging reliability needs while offering a cost‑competitive, infrastructure‑ready solution for utilities navigating rapid load growth,” added Jordan Cole, Hydrostor’s Chief Commercial Officer. “Willow Rock is a strong example of how our commercial strategy translates into real projects delivering significant value for customers and communities.”

Willow Rock marks Hydrostor’s first utility-scale project under development in the United States, building on its operational project in Ontario, Canada. The company is also advancing a late-stage project in New South Wales, Australia, and reports a global pipeline of 7 GW spanning the US, Australia, Canada, and the UK.

According to a recent long-duration energy storage market analysis by Sightline Climate, which focuses on technologies capable of at least eight hours of discharge, Hydrostor ranks as the fifth-largest provider globally, behind lithium-ion battery manufacturers Tesla and Chint Power.

A recent analysis of the long-duration energy storage scene, focusing on technologies with at least eight-hour durations, provided by Sightline Climate shows Hydrostor as the fifth leading provider globally with lithium-ion battery manufacturers Tesla and Chint Power occupying the top two positions.