Introducing the Nation’s Largest Transit Depot Microgrid

Where electrification meets resilience

The County has a 2035 target of a 100% carbon emissions reduction and an 80% reduction by 2027. It isn’t just putting forth these ambitious targets, it’s putting infrastructure in the ground at a rapid clip. 

The County’s 2024 fleet transition plan calls for replacing 100% of its nearly 400 fossil-fuel-powered buses with a mix of battery-electric buses (BEBs) and hydrogen fuel-cell electric buses (FCEBs), while also scaling the entire fleet to about 600 buses by 2035. The County is already thinking ahead when it comes to how it will power these zero-emissions vehicles. It’s strategically coupling procurement of both the vehicles and the infrastructure. 

The County’s planning wasn’t focused solely on emissions reductions. Service reliability and power resilience were also key. A “derecho” storm in 2012 caused extensive power outages for critical County services, which helped to change the County’s thinking about climate risk. Its transit network is critical infrastructure — experiencing hours- or days-long outages was not an option. The County needed a solution that enabled electrification and resilience for its transit fleet. The County, in short, needed microgrids. 

Microgrids, minus the risk 

What is a microgrid? Microgrids are on-site energy systems that co-locate generation and consumption. Unlike most solar systems, which are grid-connected, and contrary to back-up generators, which only provide power when the grid goes down, microgrids deliver most of the energy a facility or fleet uses day-to-day. That enables a new level of energy management; digital controls can opportunistically source, store, and send electrons at any given moment. 

The County first deployed a transit microgrid at its Brookville Smart Energy Bus Depot in Silver Spring, MD. Brookville is currently the largest transit bus depot in the country, a superlative soon to be taken by its bigger sister depot, the microgrid at the David F. Bone Equipment Maintenance & Transit Operation Center, or EMTOC. 

The EMTOC microgrid is one of the most advanced microgrids the country has seen due to how big, and how digitally intelligent it is. It’s designed to orchestrate highly variable changes in energy supply and demand. Charging several dozen electric buses at once can create a large demand spike, which the microgrid will meet with an ever-changing mix of solar, battery, and grid energy. Meanwhile, if there’s a grid outage, the system can go into “island” mode via on-site power generation.

The County also has plans to use the microgrid to power hydrogen electrolysis, another innovative use case. Nearly every other hydrogen electrolyzer in the country is powered by utility electricity, not by resilient electricity generated on-site. The microgrid is able to power the depot’s energy needs beyond electrolysis too, including five existing buildings, and battery electric bus charging. 

The EMTOC microgrid will eventually power 200 zero-emissions buses. The depot will be home to a fleet of both FCEBs and BEBs. The reason for both is to suit the County’s operational needs: FCEBs refuel faster than BEBs and can serve longer routes without refueling or recharging. Some of the County’s routes run as long as about 300 miles. 

Primary components of the EMTOC microgrid:  

• 4.8 MW_DC of rooftop and canopy solar generation  

• 2 MW / 6.9 MWh battery energy storage  

• 2.375 MW of charging capacity  

• Infrastructure ready to support a future on-site hydrogen electrolyzer

• Software tools and IoT-connected hardware  built on the Schneider Electric platform

Partners in progress 

Montgomery County needed a partner to help it deploy ambitious microgrids. Most organizations that aren’t in the energy business, such as Montgomery County, do not want to become operators of highly complex, small-scale power plants. The County knew it wanted to put this job in the hands of an expert partner. It also wanted a partner that could operate at the scale of an entire County’s fleet transition, one with financial and technical capabilities to match its needs. 

To manage the risk of deploying a large-scale microgrid, the County selected AlphaStruxure in a competitive bidding process.

AlphaStruxure enables the County to de-risk its fleet transition pursuits via Energy as a Service (EaaS). With EaaS, the County transfers away financial and operational risks of building and operating complex on-site energy infrastructure. The contract puts performance guarantees on key outcomes around construction timelines, long-term energy and maintenance costs, and system reliability. In a time when construction lead times are unpredictable, energy costs volatile, and maintenance budgets vulnerable, AlphaStruxure’s EaaS provides a key enabler to make these projects succeed on-time, on-budget, on-target, and for the long term. 

A national leader in zero-emissions transit 

With Brookville and EMTOC microgrids both achieving successful commercial operations, the County continues to set the pace among other municipalities when it comes to deploying sustainable infrastructure. 

“Projects like these are critical to achieving Maryland’s ambitious clean energy goals while making local public transit more reliable and cost-effective,” says U.S. Senator Chris Van Hollen. U.S. Representative Jamie Raskin concurs: “I’m confident this project will serve as an inspiration for other local governments exploring sustainable energy transitions … By breaking ground on America’s largest electric bus depot, Montgomery County continues to lead the country with investments in creating a clean energy future for our children and grandchildren.” 

The EMTOC microgrid’s impact extends outside the borders of the County. As the country’s largest transit depot microgrid and one that combines both hydrogen and battery electric buses, the microgrid lights the way forward for the thousands of fleets around the country yet to be transitioned. Data from the Department of Energy shows there are about 72,000 transit buses in the country. Almost all of them still emit carbon. There are also thousands of transit depots around the country. Almost none of them enable electrification and resilience at scale.  The EMTOC microgrid shows the nation that a new era of mobility remains in reach.