Clean energy journalism for a cooler tomorrow

The country’s biggest electric bus microgrid is open for business

Low-cost solar and batteries plus backup power come together in one Maryland county’s all-electric transportation hub.
By Jeff St. John

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An employee plugs in an electric transit bus in a large industrial facility
Charging an electric bus under a solar canopy at Montgomery County, Maryland’s Brookville bus depot and microgrid (Schneider Electric)

What do you get when you combine a fleet of electric buses with solar panels, backup batteries and microgrid control systems? 

For the transit agency in Montgomery County, Maryland, the answer is a self-sustaining island of power when the grid goes down and low-cost, self-generated energy when the grid is up to help the agency meet its clean power and transportation goals.

In fact, the Brookville Smart Energy Bus Depot microgrid, which officially opened on Monday, is being built at no upfront cost to the county. Instead, developer AlphaStruxure — a joint venture of global electric equipment maker Schneider Electric and private equity firm Carlyle Group — has financed the project in exchange for monthly energy-as-a-service payments from the county.

That allows AlphaStruxure to anticipate the future value of the 6.5-megawatt microgrid — including solar energy at a locked-in price and revenue earned from helping utility Pepco balance its peak grid demands — and build it into a low-cost present-day offer for Montgomery County.

Meanwhile, the always-available power from the site’s mix of 1.6 megawatts of solar canopies, 3 MW of stationary batteries and 1.8 MW of fossil-gas-fired backup generators will enable the county transit agency to scale up its electric fleet to 70 buses by 2026, without the risk of grid constraints limiting the megawatts of necessary charging capacity or blackouts leaving the buses without the fuel they need.

In that sense, the Brookville microgrid is a national model for municipalities and private fleet owners…to efficiently deploy the charging infrastructure and distributed energy resources that the energy transition requires,” AlphaStruxure CEO Juan Macias said at Monday’s ribbon-cutting event.

Canary Media has detailed how microgrids can solve multiple problems for heavy-duty electric vehicle fleets. The same mix of benefits that made the Brookville depot possible is driving similar projects across the country.

Montgomery County Executive Marc Elrich noted that the Brookville microgrid is the third solar-powered transit bus charging depot in the country to date. The first was built by the Antelope Valley Transit Authority in California and the second by Vineyard Transit Authority, which serves the Massachusetts island of Martha’s Vineyard.

But a growing number of transit agencies are building solar panels and backup batteries into their bus depots to help provide clean and self-generated power for their growing electric bus fleets. Many are being built in sunny and solar-rich California, but others are being developed in markets with fewer incentives for solar power.

Maryland has taken an early lead in terms of the sheer number of electric buses being charged in one place. Beyond the Brookville project, Montgomery County is also the home of the single-largest deployment of electric school buses in the country. Along with setting aggressive targets for reducing carbon emissions from electricity generation and building, Maryland’s recently passed Climate Solutions Now Act sets specific targets for the state’s bus fleet to be made up of at least 50 percent zero-emissions vehicles by 2030.

Finding ways for the existing power grid to handle enormous new loads is a key challenge for scaling up electric bus fleets. Installing solar panels to provide power when the sun is shining is one step to reducing those grid pressures, and storing that power in batteries for when the sun isn’t shining is another.

Structuring these systems as stand-alone microgrids adds the benefit of resiliency to this on-site energy equation. At the same time, electric buses themselves can serve as backup batteries during grid emergencies when they’re not driving their routes.

All of this does require careful coordination of charging schedules with the interplay of on-site and grid-supplied power, of course. It is a complex and very quickly evolving landscape,” said Greg Hintler, U.S. managing director for Mobility House, the German company that’s managing the charging systems at the Brookville depot. There’s a lot of work we as an industry still have to do around standardization and interoperability, and making sure our solutions can work together for the customers and for the fleets.”

Just how to translate these future gains into reduced upfront costs for electric buses — which are still quite a bit more expensive than their diesel-fueled counterparts — is a major challenge for accelerating the shift to electric transit. But as more projects like the Brookville depot are built, the blueprint for making it happen could become more standardized, lowering costs for transit agencies looking at their own electrification options. 

Jeff St. John is director of news and special projects at Canary Media. He covers innovative grid technologies, rooftop solar and batteries, clean hydrogen, EV charging and more.