First-of-a-Kind, Triple-Tasking, Front-of-Meter Microgrid in Sonoma, California

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A front-of-meter microgrid located at the Sonoma Valley Unified School District has set out to become the first to achieve three goals: help bring more solar online, participate in wholesale markets and charge electric school buses.

“This has never been done successfully,” said Nick Tumilowicz, principal manager, grid integration of distributed energy resources for the Electric Power Research Institute (EPRI).

There are no other examples of multi-use applications involving a utility customer, the distribution system operator and the transmission system operator, he said. In this case, the school district and EPRI are working with Pacific Gas & Electric (PG&E) and the California Independent System Operator (CAISO).

Inside the front-of meter microgrid
front-of-meter microgrid

Image courtesy EPRI

The three year, $2 million research project was funded with $1 million from the California Energy Commission (CEC) through its Electric Program Investment Charge (EPIC), which invests in research that aims to transform the electricity sector to meet energy and climate goals.

An additional $1 million came from the school district.

The microgrid consists of a 710 kW/510 kWh, one hour battery tied to an existing 200 kW of PV located at the school district. The battery is unusual in that it is situated at the front-of-the-meter, but still on the school premises.

Increase the grid’s PV hosting capacity

The project’s first goal is to use the microgrid to increase the grid’s PV hosting capacity, which would benefit the school district, the local community, the grid and the environment, said Tumilowicz.

“We are investigating any thermal and voltage violations that come with high penetration PV. The battery will mitigate challenges that come with high penetration PV, usually voltage violations.”

The project will help the school district, the community and the grid by allowing the community to install cleaner and more cost-effective generation, he said.

With high penetrations of PV, voltage issues at the distribution level can cause lights to flicker and other challenges, he said. It’s best to keep voltage within a given range, and the project intends to show how energy storage can do that when renewables penetration is high.

This is especially important given that cities and states are aiming for 100% renewable energy. In addition, installations of solar plus storage are skyrocketing in the San Francisco area in the wake of recent public safety power shut offs by PG&E

“For every new PV system installed in San Francisco, 60% are now including some form of storage,” he said.

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Microgrid participates in wholesale markets

A second goal is for the front-of-meter microgrid to participate in wholesale markets. The battery would be offered to the energy market and for grid services. Earning income from the market would help pay for the cost of the microgrid.

“We’re working with CAISO on participating in wholesale markets. This will help accelerate the payback on the microgrid,” said Tumilowicz.

Numerous parties benefit if the microgrid can participate in markets, he added.

“PG&E gets value, the customer gets value, CAISO gets value.”

Provide resilience, charge buses

A third goal of the project is to provide resilience for the Sonoma school district if the grid goes down and also to charge electric buses as the district continues to electrify them.

As Bruce Abbott, associate superintendent of the school district, pointed out: “With PG&E, we could lose power at any time (because of public safety power shutoffs). With electric buses, we wouldn’t have any way to get kids to school when the power is out. It’s a major issue for us.”

The Sonoma school district now has three electric buses and plans to convert to nine soon.

When the three year project ends, the district may decide to move the battery to behind the meter, he said. The district also wants to install a microgrid in each of its schools.

front-of-meter microgrid

By David Prahl/

“We already have PV; we will add batteries so we don’t have to cancel school during outages. The microgrids can also be resources for the community,” he added.

Interconnection process slow

Two years into the three year project, EPRI has not yet interconnected with PG&E, said Tumilowicz.

“The biggest learning has been about design and interconnection,” he said. “We’re working closely with the tariff department at PG&E’s interconnection office.” EPRI wants to make sure that its microgrid project aligns with CEC rules for multi-use applications. Those rules and regulations are always evolving, which has slowed the interconnection process.

In addition, the project has been slowed by the fact that this type of microgrid application has never been done before.

Overall, EPRI’s goal is to create a system that can be duplicated.

“At a very high level, what this project is trying to do in Sonoma is streamline the deployment of customer sided distribution level storage. How can we find a product that we can plug and play, drop it in to resolve issues quickly and reliably?”

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  1. Shunsuke Amanai says:

    Very fascinating. . Where can I locate the Architecture diagram in the article?


  1. […] school districts in California also are turning to microgrids, among them the Sonoma Valley Unified School District and the Santa Barbara Unified School District, as the state grapples with […]