Inside the Calistoga Resiliency Center, One of Only a Few Community Microgrids in California
The Calistoga Resiliency Center, a community microgrid in wildfire-prone Pacific Gas & Electric (PG&E) territory, is now operational, following years of non-utility stakeholder complaints about the difficulty of deploying community microgrids to provide resilience during outages and public safety power shutoffs (PSPS).
Owned by energy-storage project developer Energy Vault, the Calistoga Resiliency Center is one of only a few community microgrids in PG&E territory–and across California–and can serve 1,600 customers during the utility’s PSPS.
The project is unique in many ways. It consists of batteries and hydrogen fuel cells, will participate in the California Independent System Operator (CAISO) market and will also sell power to PG&E. Also unusual is the 293-MWh system’s ability to supply 48 hours of continuous energy. The microgrid has a peak power output of 8.5 MW during PSPS.
Microgrid provides resilience only during planned outages
The microgrid will only operate during PSPS, not during unplanned outages, which is surprising, given the potential for outages in California.
“We essentially were buying the nugget and allowing the third party to do whatever the rest of the year. So that's why we structured the deal that way,” said Jeremy Donnell, senior manager, microgrid strategy and implementation at PG&E.
The project aims to provide clean power to PG&E as an alternative to diesel generators that have been used by PG&E during PSPS.
Will the California microgrid tariff lead to more community microgrids?
Community microgrids haven’t been deployed rapidly in California,in spite of wildfire threats to resilience. Non-utility stakeholders argue that the state’s multi-property microgrid tariff doesn’t help solve this challenge.
The stakeholders expressed frustration over the California Public Utility Commission’s (CPUC) efforts to create a multi-property microgrid tariff, which was finalized in December 2024. They complained that the tariff is based on a PG&E program that has only yielded one microgrid, the Redwood Coast Airport Microgrid, which received financial help in the form of a $5 million grant from the California Energy Commission and a $6.5 million loan from the U.S. Department of Agriculture.
PG&E is also building remote community microgrids to ensure resilience in wildfire-prone areas.
The CPUC’s goal of avoiding diesel generators during PSPS
The Calistoga Resiliency Center’s deployment has its roots in a Jan. 21, 2021 CPUC order. The decision outlined guidelines for utilities that reserve diesel generators for providing resilience during PSPS. The CPUC asked utilities to begin transitioning toward clean generation and required utilities that reserve temporary diesel generators to pursue at least one clean microgrid to provide resilience during PSPS.
In response to that order, PG&E chose Calistoga as the site of a clean microgrid because the town had experienced numerous PSPS, said Jeremy Donnell, senior manager, microgrid strategy and implementation at PG&E.
“PG&E was seeking to procure quite a lot of diesel generation to provide resilience during PSPS events,” said Donnell. “But PG&E and stakeholders all preferred a cleaner solution.”
The search for clean microgrids costing less than twice the cost of diesel units
The CPUC said that clean microgrids deployed as alternatives to diesel should cost PG&E less than twice the cost of diesel generators, explained Donnell. Under this project, Energy Vault covered the cost of the microgrid, while PG&E covered the necessary infrastructure upgrades for its deployment. PG&E’s costs also include its payments to Energy Vault for the microgrid power.
But some argue that the microgrid is not as clean as it could be because of how Plug Power–which provided the fuel cells–produces hydrogen.
How clean is the hydrogen used in the project?
The hydrogen for the microgrid apparently is not produced locally from clean electricity. Instead, it’s transported from Plug Power’s electrolyser in Georgia, which draws some power from the grid, according to CleanTechnica. Both Georgia’s grid and the hydrogen transportation yield carbon emissions.
Electrolyzers use electricity to split water into hydrogen and oxygen, and are an important technology for producing low-emission hydrogen from renewable or nuclear electricity, according to the International Energy Agency.
Plug Power is moving toward 100% green hydrogen, according to its website.
“Hydrogen can be produced by renewable sources like wind and solar energy. We’re projecting using more than 80 tons of hydrogen in 2024, and have made a commitment to achieve 50% green content,” the company said on its website.
When asked whether the fuel cell technology is truly green, Craig Horne, senior vice president of advanced energy solutions at Energy Vault, said, “We are using clean hydrogen that meets the project’s technical and contractual requirements.”
The advantages of fuel cells
The Plug Power fuel cells are attractive to PG&E because they can ramp up quickly and have a high power density and small footprint, Donnell said.
“They can tolerate being on standby for long periods of time and then can ramp up very quickly, well within the time periods that we have for PSPS events,” Donnell said. “The rating of 1 ⅓ MW in a 40-foot footprint was very attractive and really unique for products available at the time of design,” he said.
Horne added, “The footprint or the area that you occupy with the fuel cell units and the liquid hydrogen tank sized for delivering 293 MWh was smaller than you would have with batteries.”
With its many unique features, the Calistoga Resiliency Center is an important component of PG&E’s innovation efforts, Donnell said.
Calistoga Resiliency Center helps move PG&E’s resilience efforts forward
“This has helped us continue on our innovation journey, both in terms of understanding how technologies perform, as well as building operational capabilities to deploy microgrids within our system,” he said. PG&E is still working to find innovative ways to provide resilience to customers, he added.
That innovation journey led to much-needed resiliency, said Craig Lewis, executive director at Clean Coalition.
"The Calistoga Resiliency Center is one of the few community microgrids in any California utility service territory," he said.
About the Author
Lisa Cohn
Contributing Editor
I focus on the West Coast and Midwest. Email me at [email protected]
I’ve been writing about energy for more than 20 years, and my stories have appeared in EnergyBiz, SNL Financial, Mother Earth News, Natural Home Magazine, Horizon Air Magazine, Oregon Business, Open Spaces, the Portland Tribune, The Oregonian, Renewable Energy World, Windpower Monthly and other publications. I’m also a former stringer for the Platts/McGraw-Hill energy publications. I began my career covering energy and environment for The Cape Cod Times, where Elisa Wood also was a reporter. I’ve received numerous writing awards from national, regional and local organizations, including Pacific Northwest Writers Association, Willamette Writers, Associated Oregon Industries, and the Voice of Youth Advocates. I first became interested in energy as a student at Wesleyan University, Middletown, Connecticut, where I helped design and build a solar house.
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