Microgrids Keep These Cities Running When the Power Goes Out

Resiliency is one of the main reasons the market in microgrids is booming, with installed capacity in the United States projected to more than double between 2017 and 2022, according to a new report on microgrids from GTM Research.

Another is that microgrids can ease the entry of intermittent renewable energy sources, like wind and solar, into the modern grid. Utilities are also interested in microgrids because of the money they can save by deferring the need to build new transmission lines.

Microgrids have long been used in remote areas to power off-grid villages, military operations or industrial projects. But increasingly they're being used in cities or towns, in urban centers, on university or corporate campuses, in hospitals or at data centers.

These microgrids run in parallel with the main grid. When severe weather knocks out power lines, a microgrid can separate itself like an island from the main grid and continue to serve its customers. But when it's connected, it's an island with a causeway, funneling electrical traffic to and from the big grid. Because the microgrid consolidates electricity generation and battery storage, it offers the big grid a larger resource to help it maintain its balance, which can be complicated with wind and solar, demand response and other factors.

Set up in the city's core, the microgrid can unplug from the main grid in an emergency and keep power flowing to critical resources, including a health center, a school, a grocery store and a gas station.

While older microgrids were typically powered by diesel, these newer microgrids can be powered by fuel cells, solar, wind, combined heat and power, and batteries instead of or in addition to diesel.

The Borrego Springs microgrid is powered by diesel and local residents' rooftop solar. And in 2015, the California Energy Commission awarded San Diego Gas & Electric a $5 million grant to connect it with a nearby 26-megawatt NRG solar farm, making it the largest microgrid in the country that can operate solely on renewable energy.

As solar and wind prices have dropped, use of these renewable sources has expanded in microgrids, says Asmus, generally as an add-on to existing diesel power.

Renewable energy has the added benefit of reliability because it will not run out, as fossil fuels might, during an emergency. The Borrego Springs microgrid expansion was one of three awarded by the state agency because it had a high penetration of renewables, Gravely says. An additional four were chosen because they supported critical resources like a hospital, a military base or an emergency command center.

In August the California Energy Commission issued a new, $45 million request for proposals for advanced microgrids that can help the state transition to using more distributed energy resources. A winning bid must demonstrate at least a 20 percent reduction in greenhouse gas emissions.

"It's an exciting time," says Gravely. "If California goes to 60, 70 or 80 percent renewables, then microgrids will play a bigger role."