A Microgrid Powers a Bus Fleet to Slash Emissions and Enhance Resilience

A fleet of electric buses will begin rolling quietly across Montgomery County, Maryland, their batteries charged by a new microgrid at the Brookville Smart Energy Bus Depot in Silver Spring. (AlphaStruxure)

This case, a fleet of electric buses will begin rolling quietly across Montgomery County, Maryland, their batteries charged by a new microgrid at the Brookville Smart Energy Bus Depot in Silver Spring. Designed to cut the fleet’s carbon emissions by 62 percent, the microgrid integrates several distributed generation and storage technologies working in concert: photovoltaic canopies above the depot, battery energy storage, electric bus chargers, and natural gas generators.

To create the microgrid, the county partnered with Boston-based AlphaStruxure, a joint venture of Schneider Electric and Carlyle. AlphaStruxure is responsible for designing, building, financing, owning and operating the system. “Montgomery County has aggressive climate action planning goals, and transportation emissions make up a significant portion of their current greenhouse gas inventory,” says Linda Toth, associate and senior sustainability consultant at Arup’s Washington, DC, office, which supported AlphaStruxure to upgrade the depot’s site infrastructure and connect the microgrid’s components. “They’re starting where they can really make an impact.”

Montgomery County partnered with Boston-based AlphaStruxure, a joint venture of Schneider Electric and Carlyle. AlphaStruxure is responsible for designing, building, financing, owning and operating the system. (AlphaStruxure)

Other transit agencies are adding microgrids to depots from Massachusetts to California. “Arup has been collaborating on projects with several transit agencies,” says Toth. “No two projects are similar. Sometimes agencies are leasing the depot space, so they have less control of where they can put new infrastructure. Sometimes there are different amounts of room available for equipment, as well as different regulatory requirements.”

The Brookville depot site has a significant grade change, for example, and the large battery energy storage containers and generators require a level surface. “To keep as much parking as possible, minimize costs of development, and streamline implementation, we had to think strategically about whether to regrade the site, put in retaining walls, or put in a platform structure,” Toth says. “A big partner in this was the contractor, who was on board early, so they could give us feedback on our engineering design ideas and constructability.”

Montgomery County plans to phase in at least 70 electric buses at the Brookville depot. “We helped AlphaStruxure evaluate and procure equipment options that were not proprietary, so they’re not locked in to having to buy any particular bus manufacturer in the future,” Toth says.

The battery energy storage system also participates in a demand response pilot program at Pepco, the local utility, to be a resource for local distribution during power reliability events. (AlphaStruxure)

Able to keep buses running even during extended power outages caused by extreme weather, the battery energy storage system also participates in a demand response pilot program at Pepco, the local utility, to be a resource for local distribution during power reliability events.

“Pepco is allowed to discharge the microgrid’s batteries a certain number of times per year, provided the system is not needed for service in the microgrid at that time,” Toth says. “It’s part of a pilot program to improve the resilience and reliability of the electric grid.”

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