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Vehicle to Grid (V2G), UL 9741, and Where V2G is Most Likely To Be Successful

(Joseph Gottlieb, CTO, Tuesday July 21, 2020)

The second specification that is relevant to vehicle to grid (V2G) solution is UL 9741 (“Standard for Bidirectional Electric Vehicle Charging System Equipment”). UL 9741 was specifically written as a North American standard to specify how bi-directional chargers would be used in a V2G application. There are multiple “flavors” of V2G that have been proposed by V2G technology providers:

  • Consumer-based V2G for the Home: This flavor (also known as “vehicle to home” or V2H) is where an electric vehicle (EV) is connected to a bi-directional home charger. The EV can then put energy into the home during peak hours, and/or put energy back into the grid. In either case, the consumer avoids significant peak usage charges, and can recharge his/her vehicle during off-peak hours when the energy is lower cost.
  • Consumer-based V2G using Commercial Chargers: This approach is similar to V2H, except the EV’s energy is “captured” by a commercial bi-directional charging station, such as in a business park or a mixed-use commercial establishment. The value chain for this approach is a little more indirect, as is the amount of power likely to be available, which is why this approach is not as likely to be successful.
  • Fleet-based V2G: In the fleet-based approach, a fleet operator who has electric vehicles puts the energy in those vehicles back on the grid, or uses it to power their own infrastructure during peak hours. Like V2H, the value proposition for this approach is straightforward. For large fleets such as school buses, municipal transit buses, and delivery vehicles, fleet-based V2G can be a very attractive option.

Because Rhombus is focused on the needs of EV fleet operators, we are focused on the fleet-based V2G solution. Rhombus has built high-power bi-directional inverters for renewable energy such as “behind the meter” solar 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 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 V2G charging. Rhombus is also an expert 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 Energy Storage Reference Architecture white paper.

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