Pacific Gas & Electric this past weekend performed a 48-hour “islanding” test of its distribution microgrid created to provide uninterrupted power to a high school, water infrastructure, and other customers in a northeastern California community.
The Foresthill microgrid serves slightly more than a dozen PG&E customers in the city of Foresthill in Placer County. Those include Foresthill High School, a wellness center, water agency, church, gas station, market, post office, and bank, among others. The system includes 235 kW in two solar photovoltaic arrays owned separately by the school and the water agency.
The test, which began Friday and ran through Sunday, focused on whether the microgrid could be capable of powering customers in “island mode,” without grid power, for the two-day period. The key differentiator in this islanding test was utilizing solar plus energy storage as an alternative to diesel generators, which remain on-site as a backup if needed.
“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,” PG&E’s Ron Richardson, vice president for electric distribution operations, said in a company statement.
The northern California utility collaborated with Tesla and Vince Segal Electric (VSE) to combine a mobile Tesla Megapack battery storage system with the VSE mobile switchgear technology.
“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,” Richardson added, “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.”
Several years ago, the state of California’s energy grid operators instituted a policy of public safety power shutoffs (PSPS) due to the damage of downed power lines during high winds and significant wildfires. An almost annual barrage of devastating blazes in recent years has caused many deaths and billions of dollars in property damage in the state.
Customers in the Foresthill microgrid receive electricity via underground distribution lines, creating another insulating layer to protect against windy and dry conditions.
The Foresthill Microgrid consists of the 750-kW Tesla Megapack system, a 500-kW diesel generator, step-up and grounding transformers, load bank, 12-kV switchgear and 12-kV line recloser, according to PG&E.
The Foresthill school owns the on-site 175-kW solar PV array, while a local water agency owns its on-site 60-kW solar PV array.
PG&E is incorporating numerous microgrids within its large service territory. Those include the 2,000-customer Calistoga Microgrid. Earlier this year, the utility announced a collaboration with Energy Vault to create and install a hydrogen-plus-battery hybrid energy storage system to further strengthen resiliency on the Calistoga Microgrid.
The Foresthill Microgrid project was first announced in 2021 as the utility ratcheted up its array of microgrids to offset the impact of PSPS events. That project and the Angwin distribution microgrid were designed to be funded with a portion of $10 million in a wildlife settlement fund earmarked for “accelerating commercialization of non-diesel temporary generation,” according to a PG&E document filed with the California Public Utilities Commission in September 2021.
Earlier that year, the CPUC authorized the state's Microgrid Incentive Program allocating close to $200 million to fund clean energy microgrids. In April 2023, the commission rule approval allocated $83.3 million for Southern California Edison, $79.2 million for PG&E and $17.5 million for San Diego Gas & Electric.
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