Borrego Springs, California, sits less than 100 miles from San Diego, but in terms of electric reliability the two places were once worlds apart.

San Diego Gas & Electric serves 3.4 million consumers with 1.4 million electric meters in its territory. And last year – for the ninth consecutive year – it was named the most reliable Western utility by PA Consulting Group.  But if you lived in Borrego Springs, an isolated desert community surrounded by a state park, your utility experience was markedly different.

“That area has seen outages over the years, some lasting days on end,” according to Jim Avery, SDG&E’s chief development officer. “Borrego Springs is served by one radial transmission line traversing 60 miles of exposure. It is susceptible to wildfires, windstorms, flooding and hail.”

That's the Colorado Desert – where record highs can top 120 degrees Fahrenheit, and the coldest temperature readings are below zero.

After wildfires knocked out power to the area in 2007 for two days, the utility took a hard look at how to better supply residents and businesses. About 2,800 people live in the community, which is entirely surrounded by Anza-Borrego State Park, the largest park in California.

“As a result of the wildfires, we decided we were going to rethink the way we served communities such as Borrego Springs,” Avery said. “We started our quest for designing a fully-integrated microgrid, one that could integrate conventional sources of generation, renewable sources, such as rooftop solar, as well as substation and utility-scale solar.” The system also includes distributed energy storage and batteries located at substations.

With the help of $8 million from the U.S. Department of Energy, “we've gone through an evolution in the last seven years towards building that ultimate microgrid,” Avery said. “And we've had some opportunities to test it under different conditions.”

A real-world test

The grid was used to avoid some smaller outages, and then earlier this year the California Energy Commission awarded the utility a $5 million grant to expand, allowing it to interconnect with the nearby 26-MW Borrego Springs solar facility. That turned out to be a prescient investment.

In late spring, major flooding did damage to SDG&E's transmission corridor – potentially leaving customers in the dark again. Historically, that would have meant a 10-hour outage as the utility rebuilt the poles. And if it was something that could be scheduled, the work would have been done over a weekend.

“We would have had customers out of service for almost an entire day,” Avery said. “But because the microgrid was up and running we were able to switch over all of our customers to be fed by the rooftop solar systems scattered out in the community, in addition the large-scale solar, and it was all balanced by the batteries located on the distribution line and at our substations.”

Borrego Springs' peak load is about 14 MW, and rooftop plus utility-scale solar give the community about 30 MW of generation. The batteries can store about 1.5 MW.

Microgrids are popping up everywhere

Borrego Springs isn't the only microgrid out there, of course. It's not even the only one operated by SDG&E, which has a few other grids in place for voltage regulation. But, according to Avery, it is the first of its kind to power an entire community with renewable energy.

“That in itself is a major accomplishment,” he said. 

The technology is set to take off, it appears. GTM Research's analysis has microgrid capacity more than doubling by 2020, rising from 1,283 MW this year up to 2,855 MW. And the generation mix is expected to evolve as well.

Right now diesel generators account for 90% of microgrid capacity, with renewables at just 6%. But green energy capacity on microgrids is also expected to quadruple by 2020, as the cost of integration declines.

New York is incorporating microgrids into its Reforming the Energy Vision process, and utilities are announcing demonstration projects this week. Central Hudson Gas & Electric wants to build, own and operate microgrids for customers with a total or aggregated load of at least 500 kW. National Grid will reportedly bring its own project to the table.

In New York City, one of the largest housing developments in the world — Co-Cop City — is run on a combined heat and power microgrid serving 50,000 residents in 35 high rise buildings. The grid made news in the wake of Superstorm Sandy, when it kept the lights on for residents.

Texas utility Oncor developed an innovative microgrid to showcase the integration of distributed generation and storage technologies in the Lone Star State. Constructed near Lancaster, it is made up of four interconnected microgrids and utilizes nine different distributed generation sources.

The future of Borrego Springs

Despite the grid's ability to power the entire community through the day, SDG&E is still looking for ways to make it more effective. The difficult weather and extreme temperature swings mean system planning is difficult, however.

“Because this portion of our system is out in the desert, the temperatures change drastically through the season – and as a result, the loads change drastically as well,” Avery said. “While we have ample solar in the middle of the day to serve the entire community,  in the evening times at different times of the year we may not have enough energy storage in the batteries to hold the entire community through the evening hours.”

During milder weather, in the spring, the microgrid's batteries can store enough power to get Borrego Springs residents through the night. But Avery said when temperatures soar and air conditioners run all night, the community's load rises as much as 700%, meaning batteries can't keep up except for the most important customers.

Under the most extreme conditions, Avery said the grid would seamlessly shift power only to essential services. And if there is enough power left, the grid could rotate to service some customers.

The utility is looking to upgrade the grid, allowing operators to isolate discrete loads to maintain power to critical services like police, fire prevention and medical care. They also power “cool zones” in schools and libraries. The next evolution of the microgrid will also allow seamless switching. Right now, customers still drop power before being switched over to local generation – but Avery said the ultimate goal is to be able to switch back and forth without customers ever noticing.

“We want to make some improvements so customers can be switched without any interruption of service, not even for a moment,” Avery said.