Energy Vault Holdings and Pacific Gas and Electric Company (PG&E), a subsidiary of PG&E Corporation, are partnering to deploy and operate a utility-scale battery plus green hydrogen long-duration energy storage system (BH-ESS) with a minimum of 293 megawatt-hours (MWh) of dispatchable carbon-free energy.

The BH-ESS is designed to power downtown and the surrounding area of the Northern California City of Calistoga for a minimum of 48 hours during planned outages and potential Public Safety Power Shutoffs (PSPS), which is when the powerlines serving the surrounding area must be turned off for safety due to high wildfire risk.

PG&E submitted the project contract for review and approval to the California Public Utilities Commission (CPUC) on December 30, 2022, with a request for the issuance of a final resolution approving the project by May 15, 2023. The energy storage system will be owned, operated and maintained by Energy Vault while providing dispatchable power under a long-term tolling agreement with PG&E. The system’s capacity may be expanded to 700MWh, which would allow it to operate for longer without refueling, enabling further flexibility for PG&E and the City of Calistoga.

Energy Vault’s BH-ESS will replace the typical, mobile diesel generators used to energize PG&E’s Calistoga microgrid during broader grid outages. The project represents a major advance in community-scale microgrid development and a significant step toward realizing the CPUC’s vision of cleaner forms of microgrid generation.

The system is anticipated to provide carbon-free energy for the Calistoga community of more than 2,000 electric customers for a period of 48 hours with a hybrid architecture that will allow for grid forming and black start capabilities, with the potential to further expand the project’s capacity in the future up to 700MWh.

Construction started at the beginning of 2024, with commercial operation expected by the end of second quarter of 2024. Upon completion, this project is expected to be the first-of-its-kind and the largest utility-scale green hydrogen project in the United States.