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Calistoga microgrid rollout leaves parts of Mora and Riverly excluded; PG&E, Energy Vault to follow up
Summary
PG&E and Energy Vault briefed the Calistoga City Council on the town'scale microgrid, explaining that a recent HFRA map update placed parts of Mora in a high-fire area and that those sections cannot be energized without risking the entire microgrid; PG&E said it will provide documentation and explore engineering options to add isolation points.
PG&E and Energy Vault told the Calistoga City Council on Oct. 1 that a recent change to the High Fire Risk Area (HFRA) map means parts of Mora cannot be energized by the city's new microgrid and therefore must be isolated when the system is activated during public safety power shutoffs.
"I apologize" for a communications gap that left city staff and residents without an updated coverage map, Mark Van Gorder, PG&E local government affairs representative, told the council and attendees. Van Gorder said the map only matters when the microgrid is actually turned on during extreme events and that the company should have shared the updated map first with city staff and the media.
Jeremy Donnell, PG&E senior manager for microgrid strategy and implementation, told the council the HFRA map "was updated last year" and that including the aquamarine (high-fire-threat) portion of Mora would make it unsafe to energize that area. "It would be unsafe to energize that area, which would require us to shut down the entire microgrid," Donnell said, explaining PG&E moved the isolation point up the line to protect the rest of Calistoga.
Councilmembers pressed for more detail about who updated the map, when that happened, and how many residents are affected. Councilmember Gibbs said the change could affect roughly 57 properties and said many residents rely on air conditioning and refrigeration during PSPS events. Mayor Williams asked specifically whether the adjacent Riverly neighborhood (about 100 homes) could be powered; Donnell said he could not answer immediately and committed to written follow-up once PG&E's circuitry maps are reviewed.
Craig Horn, senior vice president for advanced energy solutions at Energy Vault, which is building the Calistoga resiliency center, said construction is active, mechanical completion is targeted by the end of the month, and commissioning would begin the following month. Horn said the project needs a permanent easement so a short PG&E extension line can be undergrounded and connected to the project; Energy Vault expects easement documents to be provided to the city within one to two weeks for review.
PG&E representatives committed to better communications going forward, said the microgrid is intended to provide power only when a transmission substation is shut down during high-risk weather (PG&E cited wind speeds in the neighborhood of 50'to'70 mph as potential triggers), and acknowledged that engineering changes such as additional isolation points or undergrounding could alter the coverage map over time.
Next steps: PG&E committed to provide the HFRA/mapping documentation, investigate whether new isolation points or undergrounding could include more of Mora or Riverly, and return to the council with written follow-up on circuitry and the map update.
