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Adding Vehicle to Grid (V2G) to Your Energy Storage + EV Charging Use Case

(Joseph Gottlieb, CTO, Thursday, May 28, 2020)

Our last blog looked into the key metrics to look at when considering whether to add energy storage to your high-ower charging infrastructure. Next, let’s consider the impact of V2G on this equation. In most cases, V2G is not an alternative to battery-based energy storage, nor is it generally a way to increase your battery storage capacity; rather, V2G provides a way to reduce energy costs by taking advantage of the difference in electricity costs between peak hours and super-off-peak hours. Here are the steps to determine what V2G can save, and how it impacts your energy storage needs:

  • Calculate the average amount of power remaining across your vehicles in each vehicle yard at the end of their shift. This is total capacity in each yard (c3) times the percentage of power left in the vehicles (1 minus (d)). In our example, this would be 50 EVs x 650kWh x 10%, or 3.25MWh. Note that should you utilize V2G, you will need to increase your battery storage by this amount, divided by the battery efficiency. This would be 3.25MWh divided by 90%, or 3.61MWh.
  • Calculate the percentage savings you can realize using V2G. This amount is peak pricing divided by super-off-peak pricing, times the amount of power remaining in your vehicles, divided by the total capacity of our vehicles. Extending our example, if there is a 2X price differential, then the amount to be saved would be: 2 x 3.25MWh ÷ (50 EVs x 650MWh) = 20%.
  • How much total energy storage is required if you utilize V2G to reduce your energy costs? In our case, it is the original 4.725MWh plus the V2G storage capacity of 3.61MWh, or 8.355MWh. This is equivalent to roughly three transport containers worth of batteries.
  • Do you now need to consider solar PV power, and how many panels would be required? In this case, the storage needs are still less than what can be provided by the electrical utility during your vehicle duty hours. However, if you decide to utilize solar PV (and assuming 10 hours of sunlight), you would need 1900 panels (assuming each panel generages 440 watts of power). With each panel taking 22 square feet, this is a total of 41,800 square feet, or slightly less than one acre of space.

As a leader in the development and manufacturing of bi-directional, high-power energy systems for both vehicle charging and photovoltaic solar applications, Rhombus is an expert in high-power charging systems for EVs, and especially in the area of vehicle-to-grid (V2G) charging. 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 Energy Storage Reference Architecture white paper

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