Late last October, when Pacific Gas & Electric (PG&E) shut off power to vast swaths of its service territory in anticipation of heightened fire conditions, four towns in Northern California managed to keep the lights on, in part.

The towns — Angwin, Calistoga, Placerville and Grass Valley —​ are part of PG&E's effort to build a network of "resilience zones" and temporary microgrids in portions of its service territory that are especially vulnerable to fire-related outages. PG&E deployed 23 MW of temporary generation in the four towns, the utility reported, powering fire stations, medical centers and business districts and keeping more than 4,800 customers energized during the public safety power shut-off (PSPS).

PG&E is aiming to "support community normalcy by providing power continuity," using the temporary microgrids, utility spokesperson Paul Doherty told Utility Dive.

"I would say this was definitely a bright spot in the PSPS —​ I saw some folks internally talk about light in a sea of darkness," he added.

As California grapples with increased fire risk from a drier climate and aging utility infrastructure, industry experts have been eyeing microgrids as a potential way forward for the state's electrical service. PG&E, meanwhile, is betting heavily on distributed generation. In December, the utility issued a request for offers for distributed generation-enabled microgrid services that could power targeted locations during future safety shut-offs, as well as provide broader reliability to its electric system. Last week, the utility filed testimony with the California Public Utilities Commission outlining plans to set up 300 MW of temporary generation for the 2020 wildfire season —​ a majority of which would comprise microgrids.​

But environmental advocates have raised concerns about the proposal's potential carbon impacts. So far, PG&E has relied exclusively on diesel to power its temporary microgrids.

The utility is aware that diesel isn't the preferred fuel mix to meet California's clean energy requirements, but it was the only option that met its shut-off requirements in 2019, Doherty said.

"We definitely recognize that the current generation source that we utilize is fossil diesel generation, but that's due to the current widespread availability as well as its functional capability," he said.

"We see there being tremendous value in the flexibility that these sort of temporary microgrids provide." Paul Doherty Spokesperson, PG&E

PG&E is looking out for the right fuel mix in the market, Doherty said —​ "if it's natural gas, if it's something else, that would be the preference to diesel generation."

Environmentalists, meanwhile, are wary of fossil fuel generation, especially as PG&E plans to scale up its microgrid activity to combat the shut-offs that could continue for the next half-decade.

"When we got involved with this proceeding, we weren't really expecting to have to talk about microgrids as it relates to gas or biomass," Luis Amezcua, senior campaign representative with Sierra Club, told Utility Dive.

PG&E sees 'tremendous value' in temporary microgrids

PG&E's first resilience zone was set up in Angwin, where it used a pre-installed interconnection hub (PIH) to power up critical facilities —​ a gas station, medical facility and student housing —​ during the shut-offs. When the power goes out, the utility can simply plug into the system, isolate the microgrid and turn on generation, according to Jon Stallman, strategic projects manager of grid innovation and integration at PG&E.

In Calistoga, Placerville and Grass Valley, however, the utility has a different set-up. During the 2019 wildfire season, PG&E brought in temporary generators connected directly to substations.

"We see there being tremendous value in the flexibility that these sort of temporary microgrids provide," Doherty said. "This allows us to be able to bring in the generation when needed and where needed."

Now, the utility is looking to expand on this concept, with the overarching goal of reducing the number of customers affected by safety shut-offs in 2020 by around one-third and halving the time it takes to restore power. The strategy involves three components, the first of which is to create permanent microgrids around high-priority substations.

PG&E received responses to its RFO on Jan. 17 and is currently in the process of reviewing them. It will accept offers for all generation resource types that can effectively power communities affected by shut-offs, according to the RFO, and expects to submit the final agreements to the CPUC and bankruptcy court for approval by Feb. 21.

In the meantime, the utility is focusing on a "temporary generation program" for the upcoming wildfire season, which would involve procuring 260 MW of mobile generation to power microgrids. The third element of PG&E's proposed strategy is a "community microgrid enablement program," which will provide communities with technical and financial support.

"[P]eople in the industry trust that diesel will operate. When we need it to show up, it works." Jon Stallman Strategic projects manager of grid innovation and integration, PG&E

In an effort to move away from the current model of diesel generation, PG&E also issued a request-for-information in late December, looking for generation technologies that could meet its requirements without the same level of emissions. If it is not able to find non-fossil fuel temporary generation, the utility will look into options like biogas and biodiesel, Doherty said in an email.

"Diesel is such a lightning rod for issues, and so I will say that diesel is tried, it's true. We know it functions and the people in the industry trust that diesel will operate. When we need it to show up, it works," Stallman said.

The ultimate goal, he added, is to get to a point where solar, battery storage and other clean technologies can be used as a grid resource. But that comes with its own challenges. Battery and solar systems are well proven as behind-the-meter resources for microgrids, but most of those systems have a third type of back-up energy resource like propane, diesel or natural gas, Stallman said. The utility would have to deploy a very large PV array to meet demands during shut-offs.

"The surface area required for a mobile PV array and the amount of time it would take to set that up —​ we haven't seen that from the industry," he said.

It's really important to find cleaner forms of energy, but "we are going to likely need to use diesel as a bridge between what is available on the market today, and what is coming on the market or can be proven to work as effectively as diesel," he said.

‘Not all microgrids are created equal'

Environmental advocates see the effort as an opportunity to deploy clean distributed generation across Northern California, but the requirements associated with a prolonged shut-off could make that difficult. PG&E is looking for projects that can meet the full microgrid load —​ which ranges between 4 MW and 69.9 MW —​ for four or five consecutive days without any load drop, "and be able to meet peak and minimum customer demand" throughout that period.

"A microgrid developer once told me that not all microgrids are created equal and none of them are created the same. They're all developed uniquely for the type of load they're serving and what their purpose is," Aaron Kressig, flexible grid analyst with the Western Resource Advocates, told Utility Dive.

PG&E's requirements call for "pretty substantial" microgrids, he added. A solar-plus-storage system might be able to power a single building for a small amount of time, but the kind of generation PG&E is looking for would need to have a dispatchable load associated with it, according to Kressig.

"I don't think it's possible to meet these requirements with 100% solar-plus-storage," he said, adding, "I do think you could have an integrated system, which has significant solar-plus-storage, but also has some type of back-up power," whether that's diesel or natural gas.

PG&E's "three, four, five-day requirement makes the solar and storage alternative for resiliency untenable." Allan Schurr Chief Commercial Officer, Enchanted Rock

One of the vendors that's interested in PG&E's RFO is Enchanted Rock, a developer of natural gas-powered generators. The company has had numerous conversations with PG&E over the last many months, Chief Commercial Officer Allan Schurr told Utility Dive.

He said the requirements in the RFO — generation to serve multiple days of outages —​ are too cost prohibitive for solar and storage alone.

"I just think that the three, four, five-day requirement makes the solar and storage alternative for resiliency untenable. It's by our calculation between 50 to 80 times more expensive to do it with solar plus storage," he said.

But environmentalists are staunchly opposed to using gas generation to power the microgrids.

"We think you could do clean energy —​ it's a mix of generation, batteries and demand response," Sierra Club's Amezcua said, adding that PG&E's plans for its resilience zones needs to be consistent with the state's air quality and greenhouse gas emission reduction goals.

California should not have a tradeoff between grid resilience and clean energy technologies, Michael Colvin, California energy director with the Environmental Defense Fund, told Utility Dive in an email. Installing fossil fuel-powered back-up creates air pollution problems and new demands on the gas pipeline system, making the system more expensive in the long run, he said.