An advanced compressed air energy storage facility proposed in California has won a conditional commitment for a federal loan guarantee of up to $1.76 billion.
The Willow Rock Energy Storage Center is expected to bolster reliability of the California grid with 500 MW/4,000-MWh of long-duration storage.
Parent company Hydrostor of Canada expects to start construction later in 2025 and commission the facility in 2030. The proposal is in permitting review with the California Energy Commission.
The company said in a Jan. 8 news release that if finalized, the loan guarantee would give the U.S. a leadership position in deployment of a novel long-duration energy storage technology.
The Department of Energy’s Loan Programs Office (LPO) said in its Jan. 8 news release that the advanced design of Willow Rock resolves two key shortcomings that have limited conventional compressed air energy storage (CAES) technology to less than 50% round-trip efficiency and therefore limited its commercial appeal.
First, Willow Rock will incorporate a proprietary thermal storage system to capture and reuse heat generated during compression, rather than wasting it and then burning new fuel to create optimal working temperatures during discharge.
Second, water in an above-ground reservoir will maintain constant pressure in the below-ground cavern where the compressed air will be stored, avoiding the fluctuations of air pressure and power generation that otherwise would occur.
Water is in high demand in California’s Central Valley, but Willow Rock is expected to be a net water producer — moisture that condenses during the air compression process will be captured and reused.
Conventional CAES historically has needed to use salt caverns, LPO said, but an estimated 80% of U.S. geology would be suitable for the type of underground air storage proposed by GEN A-CAES, a subsidiary of Hydrostor USA Holdings.
CAES presents other advantages, LPO noted: Facilities use readily available equipment that is not heavily reliant on the critical minerals batteries rely on; generally have lower capital and operating costs; may have operating lifetimes exceeding 50 years with minimal degradation; and can deliver critical grid-supporting ancillary services.
Hydrostor co-founder and CEO Curtis VanWalleghem said in the news release: “We’re thrilled to reach this conditional commitment with the DOE, which is a huge vote of confidence in Hydrostor’s technology, and shows how important energy storage will be as we prioritize the reliability and resiliency of the grid for years to come.”
The project is expected to create 700 construction jobs and up to 40 full-time operational jobs. LPO noted that those operational jobs would entail skillsets similar to the oil and gas jobs that have been an important part of the Kern County economy.
The loan guarantee would involve approximately $1.5 billion of principal and $280 million of capitalized interest and would be offered through the LPO’s Title 17 Clean Energy Financing Program. The project also would benefit from the 48E investment tax credit.
The DOE must complete an environmental review and the company must satisfy technical, legal, commercial, financial and other requirements before DOE decides whether to enter definitive financing.
California Energy Commission records indicate Willow Rock would occupy 87 acres in an agricultural district north of Rosamond. It would consist of four nominal 130-MW air turbine systems outputting a maximum of 500 MW to Southern California Edison’s Whirlwind Substation via a new 19-mile 230-kV generation-tie line.
Hydrostor brought the world’s first commercial advanced CAES — the 2-MW Goderich Energy Storage Centre in Ontario — into service in 2019. It is contracted to the Ontario Independent Electricity System Operator for peaking capacity, ancillary services and full participation in the merchant energy market.
Hydrostor now has three much larger facilities in development in Australia, California and Ontario, plus a pipeline of earlier-stage projects.
