Did the Calistoga Microgrid Fail September 8? Nope.

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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.


By Antonio Guillem/Shutterstock.com

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. 

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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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  1. Any where else and one might think, yeah, O.K.. When you mention PG&E in the next breath, I hear, the squirrel ate the micro-grid connection. I wouldn’t trust PG&E to run a competent and comprehensive grid any further than I could throw them.

  2. This is a case in point as to why substation level microgrids powered by diesel (or other) gensets are NOT the best path forward. It is a replication, on a smaller scale, of the vulnerable centralized grid model. The best system is a renewable DER solution utilizing multiple customers and their interconnected assets in a community microgrid. This results in no SINGLE POINT OF FAILURE. A squirrel then can take out one or even a few of the connected homes or businesses, but the others remain functional and powering the community.
    PG&E has shown they can isolate that section of the grid, why not power it with multiple site based DER assets owned by both PG&E and private owners?

    • I believe the answer there is PG&E doesn’t want to aggregate or even partner with individual residential solar PV and energy storage systems. I believe you’ll find most IOU electric utilities want to own, operate and distribute energy on a uni-directional grid, that way the common practice of cost bundling helps hide glitches in their operations from weather driven events to simple rote incompetence in O&M and grid hardening programs.

    • Large weather driven events have a threshold which above they can be excluded from SAIDI and SAIFI. Solarman is projecting his incompetence of utility operations onto PG&E O&M with zero basis. I wonder if he would like some troll to do the same to his business?
      As for the article, “…intermittent squirrel outages may become a thing of the past”. That’s nonsense. During a PSPS the smart grid computer (FLISR) feature for the adjacent circuits, which relies on recloser load calcs and substation breaker positions would be cutout/disabled. Plus, in High and Very High fire adjective indexes, the circuit line test feature is cutout at the substation feeder and a patrol is mandated before testing a line after fault. 3 hours is not bad for patrolling, engineers interrogating impedance or overcurrent relays to find fault distance, finding the squirrel and restoring which could be cutting a pole top transformer in the clear (me speculating). If there had been damage to a pothead riser leaving the substation, then it would have been an 8 hour plus outage. If the squirrel had gone cross-phase on a recloser or substation circuit breaker (which should already have silicon guards installed) either would have to be bypassed and that would have been about 3 to 4 hours for discovery, to create switching and execute field switching. My suggestion is to embed a diagram showing the fault area between the substation source and customer loads in these type of articles rather than vague facts referencing another vague news article from another periodical.

  3. Wow: Scott M, says: “Large weather driven events have a threshold which above they can be excluded from SAIDI and SAIFI. Solarman is projecting his incompetence of utility operations onto PG&E O&M with zero basis. I wonder if he would like some troll to do the same to his business?”

    Well Scotty, its called the PSPS and I would venture your animus here, you are part of the problem, not part of the solution. I can understand your “ire” as it is becoming more irrelevant your tomes of past rules and regulations and test procedures are falling by the wayside to individual residential solar PV and smart ESS. I get it Scott, your paycheck, benefits, and probably retirement are all tied to what you have done so far. The “chain” of your career has been tied to the anchor of the past and is weighting you down more each day. Troll, yeah right a weak argument from the elitist who created the problem in the first place. Good luck with that.

    • PSPS is a weather driven event, ie wind, humidity, heat, CalFire Fire Adjective Indexes….Control room operators are forbidden by FERC Rule 717 to know what generation is bid into the system. If grid operators find out inadvertently about generation availability it’s a federal requirement to report the awareness on OASIS. The difference here is I know the FERC generation & NERC cyber security CIP rules, grid operating variables and you can only speculate with incomplete behind the meter only knowledge. Thanks for elevating me to “elitist”. I haven’t felt that empowered since passing my nuke SRO 3-day test battery in 1983. Sorry to everyone else reading, but I try to impart my significant operating and investigation knowledge for context on these vague articles.

  4. “Thanks for elevating me to “elitist”. I haven’t felt that empowered since passing my nuke SRO 3-day test battery in 1983. Sorry to everyone else reading, but I try to impart my significant operating and investigation knowledge for context on these vague articles.”
    Yeah, its the governments fault, the squirrel fried the fault circuit, my SRO-3 is bigger than your SRO-3. My tomes of classifications are more comprehensive than the arduous articles and of course your ‘significant operating and investigation knowledge…’ You’ve “certified” yourself up and speak of operation and investigation. Perhaps YOU should spend some of YOUR valuable time investigating your coming irrelevance in the (operations) of residential solar PV and smart ESS. Can your pension, benefits and paycheck also become irrelevant in the future? In allllllll of your ‘context’, perhaps the ratepayer really doesn’t care if you’re (there) and competent or not.