Granite Secures $31 Million Early Works Package for Willow Rock Energy Storage Center in California
Granite, a leading infrastructure contractor and construction company, has been awarded an approximately $31 million Early Works Grading Package by Hydrostor for the Willow Rock Energy Storage Center (WRESC) Project in Kern County, California. The project, located north of Rosamond in the Mojave Desert, represents a major step forward in the development of large-scale, long-duration energy storage infrastructure designed to strengthen California’s electricity grid.
The award is expected to be included in Granite’s third-quarter 2026 Construction Awards Program (CAP). The contract brings Granite’s site development and heavy civil construction expertise to a major energy infrastructure project that is expected to play an important role in supporting California’s growing need for reliable energy storage.
The Willow Rock Energy Storage Center is planned as a 500-megawatt Advanced Compressed Air Energy Storage (A-CAES) facility. Once completed, the facility is expected to have the capacity to provide electricity to more than 400,000 homes for up to eight hours. Its long-duration storage capabilities are intended to help balance electricity supply and demand while supporting the reliability of California’s power system.
Unlike conventional battery storage projects, A-CAES technology stores energy by compressing air and using underground storage infrastructure. The Willow Rock facility will use a large underground cavern as part of its energy storage system. The project is therefore designed to combine large-scale underground construction with above-ground energy generation and supporting infrastructure.
Granite’s initial assignment focuses on preparing the site for the next stages of construction. The company will carry out early site infrastructure and grading activities across the project’s approximately 89-acre site. One of the most significant elements of Granite’s scope will be the construction of a nine-acre pad that will support the work of the subsurface contractor.
The subsurface construction phase will involve drilling and excavating a cavern approximately 2,000 feet below ground. The cavern is expected to involve roughly 1.3 million cubic yards of excavation, making the underground works one of the defining engineering components of the Willow Rock project.
Preparing the site for such a complex underground operation requires extensive grading, access improvements and supporting infrastructure. Granite’s early works package is intended to establish the physical foundation needed for the subsurface and subsequent energy facility construction activities.
In addition to the main grading work, Granite will undertake improvements to roads outside the project site. These improvements are expected to support construction access and the movement of equipment, materials and personnel throughout the project’s development.
The company will also construct onsite stormwater basins as part of the early infrastructure program. Proper stormwater management will be essential during construction, particularly as extensive grading and excavation activities take place across the site.
Granite’s responsibilities further include developing laydown areas for materials and equipment associated with the underground mining operations. Additional staging areas will be prepared for the topside engineering, procurement, construction management (EPCM) contractors. These areas will provide space for contractors to organize construction materials and equipment as work progresses toward development of the facility’s four-turbine energy storage system.
The early works package demonstrates the importance of site preparation in delivering large-scale energy infrastructure. By completing the necessary grading, access, drainage and staging infrastructure ahead of major construction activities, Granite will help establish the conditions required for the project’s subsequent phases.
Darryl Ebel, Granite Area Manager, said the project supports the company’s strategic objective of expanding specialized private-sector construction work with clients that value technical expertise, collaboration and problem-solving. He also highlighted the experience of Granite’s Bakersfield team in site development and its ability to contribute to a project focused on California’s long-term energy storage requirements.
The Willow Rock project also represents an important opportunity for Hydrostor as the company advances its flagship U.S. energy storage development. The project is expected to contribute to local economic activity and create construction-related employment opportunities in Kern County as development moves forward.
Josh Rowan, Senior Vice President of Project Execution at Hydrostor, said the company is pleased to begin pre-construction activities at the Kern County site. He emphasized the project’s potential to support local employment while contributing to a more reliable California power grid over the long term.
Hydrostor’s partnership with Granite is expected to provide the project with significant construction and site-development expertise during its initial phase. Granite’s involvement will help prepare the site for the complex underground and above-ground construction activities that will follow.
The Willow Rock Energy Storage Center comes at a time when California is seeking additional energy storage capacity to support a changing electricity system. As renewable energy generation expands, long-duration storage technologies can help retain energy when production exceeds demand and make that energy available when it is needed.
With its planned 500 MW capacity and eight-hour storage duration, Willow Rock is designed to operate at a scale capable of making a significant contribution to grid reliability. The project’s combination of advanced compressed-air technology, underground cavern storage and a four-turbine generation system represents a different approach to long-duration energy storage compared with conventional battery facilities.
Granite’s $31 million early works contract marks an important milestone in bringing the project closer to full construction. Through grading, infrastructure development, road improvements, stormwater management and construction staging, the company will help establish the foundation for one of California’s significant planned long-duration energy storage facilities.
As work progresses, the Willow Rock Energy Storage Center is positioned to become a major energy infrastructure asset in Kern County and an important component of California’s efforts to develop a more resilient and flexible electricity grid. Granite’s early involvement provides the project with specialized construction capabilities while establishing the groundwork for the next stages of development.
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