Granite has secured a contract valued at approximately $31m from Hydrostor to carry out early site works for the Willow Rock Energy Storage Center project in Kern County, California, US.
The award covers grading and site infrastructure for the planned advanced compressed air energy storage (A-CAES) facility north of Rosamond in the Mojave Desert.
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The Willow Rock Energy Storage Center is designed as a 500MW A-CAES facility, with the capacity to power over 400,000 homes for up to eight hours.
According to Hydrostor, the project will support renewables integration and transmission optimisation. It will aim to address California’s need for large-scale, long-duration energy storage (LDES) as the state expands its renewable generation and addresses increased electricity demand.
Granite’s scope consists of establishing site infrastructure on an 89-acre site. Tasks include creating a nine-acre pad to enable the drilling and excavation of a cavern approximately 2,000ft underground, totalling 1.3 million cubic yards in volume.
The company will also build offsite road improvements, stormwater basins and laydown areas designated for mining materials and equipment needed for the construction of the four-turbine storage facility.
Granite commenced the grading phase in July and expects to finish in March 2027.
Granite area manager Darryl Ebel said: “This award aligns with Granite’s strategic focus on growing specialised private-sector work with clients that value construction expertise, collaboration and problem-solving.”
Hydrostor Project Execution senior vice-president Josh Rowan said: “Hydrostor is thrilled to start pre-construction work on-site in Kern County for our flagship US energy storage facility, which will support thousands of jobs locally and help to ensure a reliable California grid for decades to come.
“Partnering with an organisation like Granite will help us set the stage for successful project delivery, as they bring their industry-leading expertise to the site.”
The Willow Rock Energy Storage Center is currently in late-stage development.
Hydrostor previously received a conditional commitment from the US Department of Energy in January 2025 for a loan guarantee of up to $1.76bn to finance the project.
The development is expected to create around 700 jobs during construction and generate over $500m in direct and indirect economic benefits in the region.
The facility is designed to deliver 4,000MWh of electricity and has a projected operational lifespan of more than 50 years.
