Exploring the Use Cases for Vehicle to Grid
Joseph Gottlieb, CTO, Tuesday December 7, 2021
One use case (or set of use cases) that we didn’t explore in our EV charging blog series is that of Vehicle to Grid (V2G). The concept ofV2G is straightforward – it allows energy to be taken from vehicles and put back onto the grid. There are two main scenarios of interest for V2G:
- Using vehicle power to mitigate the impact of peak usage on both the grid (reduced generation needs) and on energy prices (lower bills because of peak usage); and
- Using vehicle power to establish a grid (typically for a critical building) during power outages; this is known as vehicle to building (V2B).
In this blog, we will primarily explore V2G for fleets, since V2B is generally an “emergency” condition. While any EV could theoretically be utilized for V2G (or V2B), the vehicles that are of most interest are medium- and heavy-duty (M/HD) EVs. As we have seen in our previous blogs, these M/HD EVs have significant battery capacity (150kWh to well over 600kWh), the fleets have robust DC fast charging infrastructure (with charging capacities of 60kW up to 500kW), and fleet operating hours that are generally complimentary to peak hours. A recent study by the US Public Interest Group (US PIRG) has predicted that V2G can reduce the lifecycle costs of an electric school bus by up to $130,000; with a 12-year lifespan, that is about $11,000/year.
The two primary impacts that V2G has on M/HD EV use cases are: i) it potentially shortens the window for charging; and ii) during this shorter window, the vehicles of interest may need to be fully charged. We say “potentially shorter window” because in most cases, fleets avoid charging during peak usage hours because of the increased energy costs. The impact of having to fully recharge a vehicle is easier to quantify. With a charging window of 9pm-5am (8 hours), a 675kW public transit bus would need a charger that can put nearly 85 kW of power into the bus per hour. Since these vehicles are generally run to 80%-90% of their battery capacity (68kWh-100kWh of remaining charge), V2G requires an increase in charging capacity of roughly 10 kW (i.e., a non-V2G bus could utilize a 75kW charger vs the 85kW charger needed for V2G). For an electric school bus, V2G would increase the charging required from 125kWh in non-V2G mode to 150kWh in V2G mode – an increase of 25kWh, or 3kW per hour over an 8-hour charging window. In both the public transit bus and school bus use cases, the impact of V2G is relatively small – an increase in charger capacity of only 10%- 17%. Of course, the main requirement is that the charger can operate in bidirectional mode.
And if you are looking for high-reliability, made in the USA high-power DC fast charging systems for your M/HD EV fleet that support V2G, look to Rhombus Energy Solutions. Our market-leading bi-directional EV charging systems (which are designed from the start for the needs of fleet operators) are designed and built in the USA. Rhombus also excel in the design of high-power smart inverters for next-generation renewable energy and energy storage deployments. Our 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. We have built over a thousand V2G-capable high-power, high-reliability chargers and bi-directional smart inverters for a variety of different sizes and classes of EVs.