The Impact of Charger Reliability on the V2G Use Case for M/HD EVs

Joseph Gottlieb, CTO, Tuesday December 14, 2021

Our last blog explored the impact that V2G can have on reducing the total cost of ownership (TCO) for medium- and heavy-duty (M/HD) electric vehicle (EV) fleets. Wrapping up our blog series on EV use cases, let’s now look at the impact that charger reliability can have on M/HD EV fleets that employ V2G to reduce their TCO. Let’s start with “what does it mean to have a 1% drop in charger reliability for M/HD EV fleets?” An 8-hour per day charging window and 260 charging days annually results in a total of 2,080 charging hours per year. The straightforward math would say that a 1% charger outage reduces charger availability by 21 hours. However, V2G chargers must also operate during the 4-hour peak usage time, where they put power back onto the grid, essentially increasing their usage by 50% to 3,120 operating hours per year; 1% of this now becomes 31 hours. This is nearly 3 days of downtime. To this must be added the time to service the charger, which could itself be at least a day per outage (and in some cases as much as 2 days per outage). Assuming that the three days of downtime above are not concurrent but are isolated from each other, AND assuming an average of 1.5 days to service each outage results in 7.5 days, or an effective non-availability percentage of 2.8%.

Now imagine a reduction in reliability from 99% to 95% (a 4% reduction!). Given the assumptions above about servicing, this would represent a non-availability of 30 days, or a percentage of 11.2%. For a school bus, this would impact V2G’s TCO reduction ($130,000 according to the US PIRG) by $14,560 (and this is on top of the impact of reliability of unidirectional chargers on fleet EV costs). Unfortunately, a reliability rate of 95% is more the norm than not for “commercial” chargers today (those that charge private autos in multi-family or mixed-use settings), and their reliability when charging M/HD EVs (which have a significantly higher charging cycle than private autos) would be even less. This represent real and significant costs over the lifetime of a M/HD EV fleet, especially for a fleet utilizing V2G.

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.

Find out how we can help you by contacting us at, or by reading our Vehicle to Grid Solution Brief.