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Tailoring V2G Solutions for Medium and Heavy Duty Electric Vehicle Fleets

(Joseph Gottlieb, CTO, Tuesday August 18, 2020)

One of the electric vehicle (EV) segments where Vehicle to Grid (V2G) is making significant inroads is for fleets of medium/heavy-duty (M/HD) EVs – those that are greater than 20,000 pounds gross vehicle weight, also known as Department of Transportation (DoT) Class 6 through Class 8. These vehicles are particularly suited for V2G for several reasons:

  • M/HD EVs generally have significant battery capacity: Battery capacity for these vehicles generally runs from 100kWh to well over 500kWh, with some transit buses having over 600kWh of capacity. Given that the average home in the US utilized roughly 10kWH in 2017, this is a LOT of power.
  • Most M/HD EVs operate during the day: Most classes of M/HD EVs operate between 6AM and 6PM, meaning that they are in the “vehicle yard” during peak demand hours of 5PM to 9AM.
  • The daily energy consumption of M/HD EVs is fairly predictable: Whether buses, refuse trucks, or delivery vehicles, most M/HD EVs drive fairly fixed routes. This means that they power that these vehicles have left at the end of the day is generally well-known.

On the other side of things, M/HD EVs are fairly demanding when it comes to their charging infrastructure. For instance, a 125kW charger would take over 5 hours at full power to charge a bus with a 600kWh battery capacity; if the same bus had 200kWh of power left at the end of the shift, it would take nearly 2 hours to discharge that capacity for V2G uses. A 60kW charger would take over 10 hours to charge the same bus, and over 3 hours to discharge 200kWh for V2G. That means that M/HD chargers have to be able to operate at full power rating essentially continuously, whether in charging or V2G mode. Designing a charger to support this performance requires both exceptional thermal and reliability design capabilities. Charger maintainability is also critical, as a down charger can sideline an extremely expensive vehicle. This is above and beyond the complexity of designing a bi-directional EV charger.563

Rhombus has built high-power bi-directional inverters for renewable energy such as “behind the meter” grid energy storage systems for several years. We have applied that expertise to the design of our bi-directional charger systems, which are designed from the start for the needs of fleet operators. As a leader in the development and manufacturing of bi-directional, high-power control systems for both vehicle charging and grid energy storage applications, Rhombus is unusually experienced in high-power charging systems for EVs, and  the area of V2G charging. Rhombus  also excels in the design and testing of high-power electrical equipment to meet the requirements of UL and other certification organizations. We have built hundreds of V2G-capable high-power, high-reliability chargers for a variety of different sizes and classes of EVs. Find out how we can help you by contacting us at, or by reading our Vehicle to Grid Solution Brief.

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