Toronto-based long-duration energy storage company Hydrostor has received a major regulatory milestone as the California Energy Commission (CEC) issued its final permit for the Willow Rock Energy Storage Center, a 500 MW / 4 GWh project in Kern County, California. The approval clears the way for one of the world’s largest compressed air energy storage facilities, capable of delivering electricity at full power for up to eight hours.
The Willow Rock project will deploy Hydrostor’s proprietary underwater compressed air energy storage (UWCAES) technology, positioning it as a first-of-its-kind commercial-scale deployment in the United States. Hydrostor plans to break ground in mid-2026, with the facility designed for an operational lifespan of up to 50 years, significantly longer than conventional battery-based storage systems.
Technology Overview
Hydrostor’s UWCAES system stores energy by using electricity to compress air, which is then held underwater in specially designed accumulators at a fixed depth. The compressed air displaces water within the accumulators and remains stored until electricity is required. When demand rises, water pressure forces the air back to the surface, where it drives a turbine-generator system to produce electricity.
This reversible process enables large-scale, long-duration energy storage with minimal degradation over time, making it well-suited to support grid reliability and the integration of variable renewable energy sources such as wind and solar.
Company Background and Global Presence
Founded in 2010 by Curtis Vanwalleghem, Cameron Lewis, Yannick Beaudoin, and Esther Pinto, Hydrostor specializes in long-duration energy storage solutions aimed at strengthening grid resilience. The company operates a commercial utility-scale facility contracted with Ontario’s Independent Electricity System Operator (IESO) in Goderich, Canada.
In addition to Willow Rock, Hydrostor has another advanced-stage project under development in New South Wales, Australia, and maintains an early-stage development pipeline exceeding 6 GW across renewables-rich regions, including Australia, the United Kingdom, the southwestern United States, and parts of Europe. The company has offices in Toronto, Melbourne, and Denver.
Funding and Investors
Hydrostor has raised a total of USD 615 million across 11 funding rounds since 2016. Its most recent Series D round in February 2025 brought in USD 200 million, led by investors such as CPP Investments, Goldman Sachs, BDC, and Sustainable Development Technology Canada.
The company’s investor base includes 18 institutional backers, notably Goldman Sachs Asset Management, the Canada Pension Plan Investment Board (CPPIB), and the Canada Growth Fund (CGF).
With the final permit now in hand, the Willow Rock Energy Storage Center marks a significant step forward for long-duration energy storage in California, reinforcing Hydrostor’s position as a key player in next-generation grid-scale energy solutions.
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