Montgomery County Completes EMTOC, Nation’s Largest Transit Depot Microgrid
- EVs Fleet & Depot Charging News
Marin Holt
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- 7 minutes read
- Completed April 30, 2026: 6.8 MW microgrid, the largest U.S. transit depot microgrid
- 4.8 MW solar (9,800 panels / 16 canopies), 2 MW / 6.9 MWh BESS, 2.375 MW EV bus charging
- AlphaStruxure EaaS model, zero upfront county capital; $1.6M Maryland Energy Administration grant
- Powers 5 buildings and up to 200 Ride On buses; ~4,000 metric tons CO2 cut per year
- Green hydrogen fueling station is the next phase, backed by nearly $15M in 2022 federal grants
Montgomery County, Maryland’s Equipment Maintenance and Transit Operations Center (EMTOC) was completed on April 30, 2026 as the largest renewable energy-powered transit depot microgrid in the United States. The project combines 4.8 MWDC of rooftop and canopy solar, a 2 MW / 6.9 MWh battery storage system, and 2.375 MW of electric bus charging into an integrated 6.8 MW microgrid capable of indefinite island-mode operation. The solar array spans 9,800 panels across 16 canopies and powers five campus buildings plus a fleet of up to 200 Ride On buses. AlphaStruxure developed, owns, and operates the system under an Energy-as-a-Service model with no upfront county capital; Mortenson served as design-build partner, and the Maryland Energy Administration contributed $1.6 million through its Resilient Maryland Grant Program.
Why It Matters
Transit agencies electrifying bus fleets face a hard constraint: depot charging loads often double a facility’s peak demand and strain local feeders. EMTOC shows that pairing on-site solar and storage with an Energy-as-a-Service contract lets a county add 2.375 MW of charging without upfront capital or a utility upgrade, a template other agencies chasing 2035 zero-emission targets are likely to copy. The open question is cost: the county has not disclosed the rate it pays AlphaStruxure over the contract term.
System Architecture and Construction
The Derwood, Maryland facility serves Montgomery County’s mixed fleet of battery-electric and fuel cell buses while powering five existing campus buildings. The microgrid interconnects with Pepco’s distribution grid and maintains full island-mode capability, with the battery storage system providing bridging power during transition between grid-connected and islanded states. Construction ran from Q2 2024 across a 28-phase sequence that kept the depot fully operational throughout the build, a significant constraint given the facility’s role in daily transit operations serving the Washington DC metro area.
A green hydrogen fueling station and 13 hydrogen fuel cell buses are planned as the next phase, backed by nearly $15 million in 2022 federal grants. When fully operational, the system is projected to offset approximately 4,000 metric tons of carbon annually. Montgomery County structured the project with zero upfront capital expenditure under AlphaStruxure’s EaaS contract, transferring project financing and long-term operational risk to the developer.
EV Bus Charging and Demand Management
The 2.375 MW EV bus charging subsystem supports CCS and fuel cell bus refueling at the depot, with energy management software coordinating charge dispatch against real-time solar generation and battery state of charge. On-route charging at select terminal stops supplements depot charging, reducing the peak demand at the facility during overnight charging windows. Industry data shows smart charging management at fleet depots reduces electricity costs up to 40% and improves charger utilization by 38% compared to unmanaged simultaneous charging.
The EMTOC project scale exceeds comparable transit microgrid deployments: Camber delivered a 2.9 MW depot charging system for 48 CapMetro electric buses in Austin, Texas in February 2025, while Charlotte Area Transit deployed 150 kW Siemens chargers across two depots as the first phase of a 300-bus electrification program. EMTOC’s integration of solar generation and battery storage into the charging architecture establishes a benchmark for transit agencies seeking to combine energy cost reduction, resilience, and zero-emission operations in a single EaaS structure.
Critical Analysis
The EMTOC microgrid manages 2.375 MW of simultaneous bus charging load against 4.8 MWDC of variable solar generation on Pepco’s distribution grid in PJM. The 4.8 MWDC solar array creates bidirectional power flow on Pepco feeders in Derwood, exporting up to 3 MW during midday when bus charging demand falls.
5-Year Projection
By 2031, operational data from facilities like this will become the standard requirement for securing interconnection agreements, as ISOs prioritize proven Rooftop & Canopy Solar profiles.
Critical Perspective
The project aims for 4.8 MWDC of solar. The Los Angeles DWP’s Harbor Solar Project achieved 100 MW of solar. The Alameda County Central Shops microgrid, completed in 2018, also faced operational constraints. What is the projected return on investment for this specific 4.8 MWDC solar installation?
