Storage developer Energy Vault and utility Pacific Gas and Electric Company (PG&E) have proposed a partnership to deploy and operate a grid-scale battery plus green hydrogen long-duration energy storage system (BH-ESS).

The BH-ESS would power the downtown and surrounding area of Calistoga, a city in Northern California, for a minimum of 48 hours during planned outages and shutoffs due to high wildfire risk. The system would provide a minimum of 293 MWh of dispatchable energy. Capacity could eventually be expanded to 700 MWh, which would allow it to operate for longer without refueling.

The project is still pending regulatory approval. PG&E submitted the project contract for review to the California Public Utilities Commission (CPUC) on Dec. 30, with a request for a final approval by May 15.

If approved, construction could begin in the fourth quarter, with commercial operation expected by the end of second quarter of 2024. Energy Vault called the project a “first-of-its-kind” and the largest utility-scale green hydrogen project in the U.S.

The storage system will be owned, operated and maintained by Energy Vault while providing dispatchable power under a 10+ year agreement with California’s largest utility.

Energy Vault’s BH-ESS would replace the diesel generators used in PG&E’s Calistoga microgrid during grid outages. The system would integrate a short duration battery system, for grid forming and black start capabilities, with a long duration fuel cell plus green liquid hydrogen storage system. The fuel cell would be powered by electrolytic hydrogen from renewable energy sources.

PG&E would use and upgrade its existing distribution infrastructure to establish the microgrid. The entire system would be developed on less than one acre of land and is expected to serve as a model for Energy Vault’s future utility-scale hybrid storage system deployments.

A June 2020 CPUC Decision required large electric investor-owned utilities to accelerate deployment of microgrids and resiliency projects to minimize the impacts of power outages. In 2021, CPUC directed PG&E to implement a microgrid program to support the resiliency of local governments.

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