Hydrostor has secured final permitting approval from the California Energy Commission (CEC) for the 500 MW / 4,000 MWh Willow Rock BESS Center in Kern County, designed to provide up to eight hours of discharge through advanced compressed air storage. It will connect to existing transmission infrastructure and is intended to support rising electricity demand in Southern California. The project is expected to be construction-ready in 2026 and represents Hydrostor’s first planned utility-scale energy storage development in the United States.
DATA SNAPSHOT
| Field | Value | |
|---|---|---|
| Project name | Willow Rock Energy Storage Center | |
| Developer / Operator | Hydrostor | |
| Installed capacity | 500 MW | |
| Energy storage duration | 4 | 000 MWh (8-hour discharge) |
| Location | Kern County, California, U.S. | |
| Technology | Advanced Compressed Air Energy Storage (A-CAES) |
Canada -based long duration energy storage (LDES) developer and operator, Hydrostor has received final permitting approval from the California Energy Commission (CEC) for the 500 MW / 4,000 MWh Willow Rock Energy Storage Center in Kern County, California, enabling the project to advance toward shovel-ready status in 2026.
The Willow Rock project has been designed for eight-hour continuous discharge, using advanced compressed air storage to deliver firm, dispatchable utility-scale capacity without conventional battery chemistries. The facility has been planned to connect with existing transmission networks, supporting Southern California load centers as electricity demand increases from data centers and broader electrification.
Hydrostor’s A-CAES system stores compressed air in underground caverns, using water for pressure control during charging and discharge cycles. The Willow Rock Energy Storage Center has been planned to deliver electricity equivalent to the needs of more than 400,000 homes for over eight hours, subject to operating conditions. The facility has been designed for an operating life of about 50 years, positioning it as long-term grid infrastructure in the region.
According to the company, the Willow Rock project is expected to involve more than USD 500 million in development and construction investment. The project is anticipated to support thousands of jobs during construction, with approximately 40 permanent positions planned for the operational phase.
In addition to the approval from CEC, the project has secured a franchise agreement from the Kern County Board of Supervisors, along with a conditional letter of support issued earlier in the year. These local actions align with the state-level permitting process and reflect coordination between county and state authorities.
Willow Rock represents Hydrostor’s first utility-scale energy storage project planned for construction in the United States. Beyond California, the company is advancing a late-stage project in New South Wales, Australia, and maintains a global development pipeline of approximately 7 GW across the U.S., Australia, Canada, and the UK. The Willow Rock Energy Storage Center is expected to serve as a reference project for Hydrostor’s A-CAES technology within the U.S. market.
Curtis VanWalleghem, Co-Founder and CEO of Hydrostor, said that approval from the California Energy Commission moved the Willow Rock project forward and supported development across the company’s North American portfolio, with A-CAES technology intended to address rising electricity demand.
Jon Norman, President of Hydrostor, said that the permitting process required coordination with the California Energy Commission and local stakeholders, and that the project is expected to contribute to economic activity and grid reliability in Kern County.