Placer County: PG&E Piloting Novel, Mobile Battery Energy Storage System at Foresthill Microgrid

Test to determine capability of powering customers within islanded microgrid for up to 48 hours using solar plus storage solution as alternative to diesel generators

By Paul Doherty

FOREST HILL — As part of ongoing efforts to build a more resilient grid and minimize impacts of Public Safety Power Shutoffs on customers, PG&E is testing the use and integration of alternative temporary generation solutions. This includes piloting a Mainspring Linear generator, collaborating with Energy Vault to build and operate the largest green hydrogen long-duration energy storage system in the U.S., and — as of today (Aug. 21) — deploying and testing a first-of-its-kind solution utilizing a mobile battery energy storage system (a Tesla Megapack) paired with existing, locally sited solar at PG&E’s Foresthill, Calif. distribution microgrid.

The Foresthill microgrid includes 14 PG&E customers in the general vicinity of Foresthill Road (extending between Baltimore Mine Road and Racetrack Street). This includes Foresthill High School (which also owns the onsite 175 Kw solar PV array), a water agency (which also owns the onsite 60 Kw solar PV array), a wellness center, church, gas station, market, post office, bank, and some other businesses, facilities and community services that can continue to have power during potential PSPS events impacting the area in 2023. The customers within the microgrid receive electric distribution service via underground powerlines, considered safe to energize when the surrounding area — with overhead lines — may need to be turned off for safety.

PG&E conducted a 48-hour test of the system commencing on Friday, August 18 to determine the capability to powering customers within the islanded microgrid for up to 48 hours using the solar plus storage solution as alternative to diesel generators, which will also be on hand as a backup.

PG&E collaborated with Tesla and Santa Rosa-based Vince Segal Electric (VSE) to develop the new solution, which combines a mobile Tesla Megapack with VSE’s mobile switchgear technology.

“PG&E is working with our vendor partners to develop and test workable, cost-effective solutions that accelerate the integration of clean energy technologies that have the potential for reducing our reliance on backup diesel generators, resulting in lower emissions and greater societal benefit,” said Ron Richardson, Vice President, Electric Distribution Operations at PG&E. “Together, with Tesla and Vince Segal Electric, we’ve created a one-stop solution: a trailer-mounted transportable battery energy storage system that can be quickly deployed and rapidly interconnected for immediate customer benefit, and we are proud to be pioneering the use of existing solar infrastructure that has significant promise for the integration of clean energy to support community resiliency as a new grid architecture.”

Historically, PG&E will strategically reserve and deploy mobile generators across its service area for use during emergencies and PSPS events to keep the power on for customers. These generators are connected to the grid at community resource centers, critical facilities, distribution microgrid sites, and at other locations in other instances, as needed and available.

A PG&E distribution microgrid is a grouping of electric lines and infrastructure that PG&E can quickly isolate, or island, from the larger electric grid. PG&E can safely provide electricity to customers within the microgrid when the surrounding lines need to be turned off for safety. This means residents in the area without power can still utilize services for gas, food and other necessities without having to travel to another area. Though each distribution microgrid will vary in size and capability, they all include:

• Devices that can disconnect the microgrid from the larger electrical grid
• Pre-determined space and connection equipment for a backup generator or alternative

Specifically, the Foresthill microgrid consists of:

• A Tesla Megapack BESS, 750 kW
• Diesel Generator, 500 kW
• Step-up transformer and Grounding transformer
• Load Bank
• 12 kV Switch Gear and 12 kV Line Recloser

Based on the testing, PG&E will determine opportunities to leverage the solution at the site during potential PSPS events in 2023.