Did the Calistoga Microgrid Fail September 8? Nope.

Sept. 21, 2020
Although it has a fully-ready microgrid, Calistoga, California experienced a series of unfortunate events that led to loss of power for more than 2,000 utility customers, a side effect of a preventative power shutoff in neighboring regions.

Although it has a fully-ready microgrid, Calistoga, California experienced a series of unfortunate events that led to loss of power for more than 2,000 utility customers, a side effect of a preventative power shutoff in neighboring regions.

On September 8 dangerous wildfire conditions caused Pacific Gas & Electric (PG&E) to trigger their first public safety power shutoff (PSPS) of the year, intended to impact about 172,000 customers in Northern California, not initially including Calistoga. But subsequently, an errant squirrel found its way into distribution grid equipment, and the lights went out throughout the town despite the means to mitigate it.

Calistoga was the recent recipient of a temporary microgrid, installed in collaboration with PG&E to provide resilience for the wildfire-prone community in the event of PSPS shutoffs.

In this case, the microgrid performed exactly as designed — unfortunately, that meant not turning on at all.

Purpose-built systems

The Calistoga community microgrid was built to keep the community’s lights on in the event of a PSPS, and is meant as a temporary solution until permanent resilience infrastructure is deployed. Earlier in the month, PG&E had installed new generators for the microgrid to replace those used during last year’s wildfire season for anticipated PSPS events.

When the shutoff commenced “the temporary microgrid in Calistoga was ready, but was out of operational scope for this PSPS event,” a PG&E spokesperson told the Napa Valley Register.

Since the town was not intended to be a part of the PSPS event and the main substation was to remain active, the microgrid was not called upon by the grid operator.

Microgrids can be designed to respond instantly to grid signals and outages, but the temporary microgrids deployed by PG&E (more than 70 in total so far) are not configured that way. Instead, they are intended for the very specific use of community resilience during PSPS outages. 

PG&E’s temporary microgrids are powered by mobile diesel generators, so any deviation from their primary usage — keeping the lights on during a PSPS — is not allowed due to their noxious emissions and certain utility regulations. California utilities had to request special dispensation from regulators to use these mobile generators when heatwaves plagued the state in late August, though constrained energy supplies still resulted in rolling blackouts.

Since deviation from their primary directive is not allowed, when the PSPS was initiated and Calistoga was excluded; come what may, the microgrid remained in standby.

Enter the squirrel

Squirrels are an ever-present challenge for the electric grid, and one nimble rodent seeking shelter or trying to hide an acorn can cause havoc for the entire system. With thousands of squirrel related outages across the US every year, utilities and grid operators are typically well prepared to address the challenge and mitigate any impacts.

When a squirrel found its way into the Calistoga system around 10 am and subsequently short circuited the area grid, it severed the link between the still energized substation and the townsfolk. 

At any other time, PG&E would have an array of tools at its disposal to address minor events like this, but the broader PSPS active in the region limited capabilities. There was no redundancy available, and neighboring circuits were deenergized and couldn’t be called upon for support. As confirmed by a PG&E spokesman, the PSPS created abnormal grid architecture in an instant, and what otherwise may have been a momentary disturbance lasted for the better part of the day.

Local new outlets quickly began asking why the oft-touted backup power system designed to keep the lights on during wildfire season was ‘missing in action’ during the PSPS event. 

Collateral damage

Microgrid or not, in these circumstances the squirrel most likely would have caused a temporary outage either way. But with the backdrop of wildfire-related power outages and the shiny new microgrid built for what would appear to be this very purpose, residents and officials were confused and disappointed.

When PSPS outages take some customers offline, those that remain energized are also left with an incrementally less resilient grid. They no longer have a neighbor to share the burden of reliability with, the traditional hub-and-spoke grid design is more vulnerable to incursions with less redundancy, and even minor disruptions are amplified when there are fewer customers to spread any impacts out over.

Calistoga’s microgrid could have responded near instantly to keep residents illuminated, but that wasn’t what it was designed to do, and in this case the community was left wanting. But as California transitions from temporary microgrids to mitigate PSPS events to permanent resilience infrastructure for communities, intermittent squirrel outages may become a thing of the past.

Until then, California utilities’ temporary microgrids may in certain instances sit idle while residents sit in the dark.

Matt Roberts is the director of strategic growth & government affairs at Microgrid Knowledge.

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About the Author

Matt Roberts

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