California regulators voted to approve an innovative long-duration energy storage microgrid project that pairs batteries with green hydrogen in a bid to mitigate outages.

The California Public Utilities Commission approved the project between Pacific Gas & Electric, the state’s largest utility, and energy storage provider Energy Vault on April 27.

PG&E and Energy Vault sought to use the battery plus green hydrogen long-duration energy storage system (BH-ESS) to 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 aims to 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.

PG&E and Energy Vault expect the project to operate for 10.5 years starting in 2024. The project is expected to cost no more than $46.3 million. No parties in the CPUC proceeding objected to PG&E’s cost recovery and cost allocation plan.

PG&E selected Calistoga because, according to PG&E’s 10-year Lookback Analysis, the Calistoga substation has one of the highest frequencies of modeled direct impacts with safe-to-energize customers. PG&E noted eight direct transmission-level impacts in the 2021 update of the historic lookback analysis submitted to the CPUC.

The CPUC acknowledged, but rejected, objections from the Public Advisor’s Office within the commission that PG&E’s plan leaned too heavily on emerging technologies and a provider in Energy Vault that does not have sufficient experience.

California rules, however, allow for projects that are novel or not commercially tested. The onus is on PG&E to reject projects that it deems technologically infeasible.

In approving the PG&E application, the CPUC directed the utility to report on cost, performance, and learnings from the pilot project. The commission also said PG&E and Energy Vault should utilize the project, namely the battery storage system, to support typical grid operations when not in use as a microgrid.

“Energy Vault is pleased with the CPUC’s approval of our innovative microgrid project with PG&E in Calistoga,” Marco Terruzzin, Energy Vault’s chief commercial and product officer, said in a statement. “We are committed to supporting local communities to have access to resilient and clean power.”

Who is Energy Vault?

grid scale renewable energy storage
Energy Vault’s energy storage systems use gravity to store and release renewable energy on demand, giving grid-scale reliability to clean energy sources in place of fossil fuels. (Courtesy: Energy Vault)

Energy Vault was founded by serial clean energy entrepreneur Bill Gross, who tapped Robert Piconi to lead the energy storage solution provider as its CEO and co-founder in 2017.

Energy Vault made its splash with an unconventional long-duration energy storage system that used a set of linked six tower cranes to lift and lower composite blocks. By 2020, Energy Vault had built and grid-connected a 5 MW/35 MWh commercial demonstration unit operating in Switzerland.

The company announced a Series B round of $110 million from the Softbank Vision Fund in 2019, which was followed by a $100 million Series C round in 2021. Energy Vault began listing on the New York Stock Exchange in 2022.

Energy Vault’s first commercial gravity storage system, a 25 MW/100 MWh facility in Rudong, China, is 75% complete. (Courtesy: Energy Vault)

Today, Energy Vault’s first commercial gravity storage system is 75% complete. The 25 MW/100 MWh facility in Rudong, China. This facility ditches the cranes in favor of a standard building construction that protects against outside elements and simplifies the lifting system to improve round-trip efficiency. At around 80-85% RTE, the facility will be one of the most efficient energy storage systems in the world.

The principles for energy storage, however, remain the same. Composite blocks are moved vertically and horizontally to store energy, guided by advanced software.

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