How EV Charger Reliability Impacts Fleet TCO

Rick Sander, CEO, Tuesday November 23, 2021

Total cost of ownership (TCO) is one of the critical metrics that fleets look at when they look at making investments, as well as measuring how well those investments are performing. Without getting into too much accounting, TCO is generally comprised of both acquisition cost and operation cost, which itself is composed of operator salaries, energy costs, maintenance costs, and other fees such as licensing, permits, etc. And all of the per-vehicle TCO metrics are then multiplied by the number of vehicles, which is where it gets more complicated. Generally speaking, if a fleet wants (for instance) 100 vehicles in service on a given day, it “overbuys” vehicles with the assumption that not all of them will be functional at any given time.

Like any complex system, vehicle availability is the product of the availability of its components. For internal combustion engine (ICE) buses, the availability/reliability of the vehicle itself is the driving factor; the rest of the “components” (fuel pumps, drivers, etc.) are essentially 100% available. For electric vehicles, the availability/reliability of the charger also becomes relevant. Back to our 100-vehicle example, if the vehicle availability is 95%, 105 vehicles would need to be purchased to have 100 vehicles on the road. If the availability of the charger is also 95%, then the total system availability is 95% x 95%, which is 90.25%. That increases the number of vehicles required for a 100 operational  vehicles to 111 vehicles – an increase of six vehicles, which increases the fleet TCO by 6% (at a minimum), irrespective of the cost of the charger itself. And unfortunately, many chargers being used for medium- and heavy-duty (M/HD) electric vehicle fleets have availability that is well below 95%. When your vehicles costs $1M or more apiece, an increase in reliability by 1% for a 100-vehicle fleet reduces the acquisition cost portion of TCO by $1M, or about $10K per charger (assuming a 1:1 ratio of chargers to vehicles). This is why increasing the reliability of EV chargers for M/HD fleets is so important!

And if you are looking for high-reliability, made in the USA high-power DC fast charging systems for your M/HD EV fleet, 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.