San Diego Gas & Electric’s (SDG&E) microgrid supplied electricity to 2,800 customers in Borrego Springs in San Diego County, Calif., on May 21, 2015, during planned grid maintenance. This marked the first time a U.S. microgrid used renewable energy to power a community, according to SDG&E.


The California Energy Commission recently awarded SDG&E a $5 million grant to use renewable energy to power Borrego Springs. The grant allowed the microgrid to connect to nearby NRG Energy’s 26-megawatt Borrego Solar facility. The funding will also increase the microgrid to cover all of Borrego Springs.


The Borrego Springs microgrid is connected to the centralized grid and can be disconnected to function independently during emergencies. Lightning damaged the transmission line that normally provided power to the community, and three transmission poles required repairs, a task that would typically involve a 10-hour sustained outage to the community. SDG&E avoided major service interruptions to customers by using the nearby Borrego Solar facility to supplement its microgrid.


On May 21, at 8:45 a.m., SDG&E switched to the microgrid for maintenance work and back to the main grid at 5:30 p.m. Customers experienced a planned outage of less than 10 minutes as SDG&E shifted from the microgrid to the repaired transmission feed.


The microgrid used automated switching, energy-storage systems, local power generation and on-site generation. The grid generated the community’s power during the maintenance work through the Borrego Solar facility. 


Solar power can be intermittent and requires backup resources. Advanced software and automated switching addressed fluctuations in real-time, while batteries and traditional distributed generation filled in gaps from the solar facility.


“Borrego Springs was entirely separated from the main grid, running on the microgrid’s local, on-site resources for nine hours as we conducted necessary maintenance,” said Dave Geier, SDG&E’s vice president of electric transmission and system engineering. “This ability to operate independently of the grid when necessary is exactly what the microgrid was designed for, and the fact that we were able to accomplish this using local renewable energy is an added benefit.”


SDG&E plans to include more advanced software and sensors in its microgrid by mid-2016 to increase its use of renewable energy to provide power to the community.