How Do Fleet Operations Complicate the Charging of M/HD EVs

(Rick Sander, CEO, Tuesday October 13, 2020)

The bulk of medium and heavy duty (M/HD) vehicles in the United States, including M/HD electricvehicles (EVs), are owned by fleets, and the vast majority of these are owned by fleets with 100 or more vehicles. So how do fleet operations affect charging of M/HD EVs? There are a few factors that have to be considered when charging fleet M/HD EVs:

  • Charging power needs versus power available: As Joseph stated in last week’s blog, M/HD EVs have significantly more battery capacity than consumer electric autos, light trucks, and SUVs. Charging 100 electric school buses, each with 150kWh capacity, takes up to 15MWh of energy. Charging 100 long-range transit buses, each with 600kWh capacity, takes up to 60MWh of energy. If the vehicle yard has two 2MW utility grid feeds, it would take 3.75 hours to charge 100 school buses, or 15 hours to charge 100 long-range transit buses.
  • Prioritization of specific vehicles: In most fleets, some vehicles (or more often, routes) are more important than others. Some vehicles also have to go out before others do. This requires some level of “intelligence” in the system to decide who gets charged when, as well as the amount of charge used (on average) by each vehicle and the power remaining in each vehicles’ batteries. If this is not done in the charger, the charger must be able to interface with the vehicle scheduling software.
  • Integration of Photovoltaic (PV) Solar, Energy Storage, and Vehicle to Grid (V2G): Many fleet EV deployments also include installation of PV solar resources, and often battery-based energy storage, as a part of their deployment. Integrating these capabilities expands the need for “intelligence” described in the previous bullet. V2G, which takes energy out of vehicles and puts it onto the grid during peak hours, further complicates this calculus.

Most of these concerns are not present with consumer electric vehicles, or (such as PV solar or battery storage) do not impact or are not integrated with EV charging – they are unique to M/HD EV fleet charging. As such, M/HD EV charging infrastructure must take them into account.

Rhombus has built high-power 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 latest-generation bi-directional electric vehicle (EV) charging systems (which are designed from the start for the needs of fleet operators) and bi-directional smart inverter systems for microgrids. Rhombus expertise in energy management system (EMS) software is also embedded in our VectorStat EMS controller and software which is embedded in our EV charging systems and smart inverters. 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 and bi-directional smart inverters 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.