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Electric Vehicle Charging Basics

There are many things about EVs that are similar to an internal combustion engine (ICE) powered vehicle, but there are also some important differences and some less understood equivalencies. In this article, I will discuss some of these comparisons related to charging EVs versus filling up at the gas station.

Relating EV Charging and Energy Use to Internal Combustion Engine Powered Vehicles

Most people are very familiar with the basic operation of their car, so let's draw some general comparisons between EVs and ICE-powered cars.

Miles that Can be Driven per Gallon of Gasoline or per kWh

There are two ways to quantify mileage in EVs: Miles per Gallon Equivalent (MPGe) and Miles per Kilowatt-Hour (MPkWh). MPGe is best for comparing fuel efficiency of EVs and ICE vehicles. MPkWh is more relevant for an EV owner day-to-day as they look to drive and re-charge their battery.

MPGe

We are used to Miles Per Gallon (MPG) which is the miles driven on one gallon of gasoline. The Environmental Protection Agency (EPA) introduced MPGe in 2010 to aid in comparing the mileage of ICE vehicles and EVs. MPGe is based on one gallon of gasoline being equal to 33.7 kWh of electrical energy. We can then find out how far an EV can go on 33.7 kWh of energy and compare that to the MPG of an ICE powered vehicle. If an EV gets 37 MPGe, then it uses the same energy to travel one mile as an ICE powered vehicle that gets 37 MPG. However, many EVs get 100 MPGe or more.

MPkWh

Another way to quantify mileage of EVs is by looking at how far an EV will travel in Miles per kWh (MPkWh). If an EV gets 100 MPGe, we divide that by 33.7 to determine the EV gets about 3 MPkWh.

How to Quantify EV Charging

When we are pumping gasoline into a vehicle, it usually does not take long so we don't think in terms of how far we can drive for each minute we pump gasoline. We just fill up the tank in a few minutes and know that we can drive maybe 300 miles or that we won't have to stop at a gasoline station for another week. But charging an EV usually takes much longer than filling a gasoline tank, so we can think of it in terms of how many miles we are adding to the range of the EV for each minute, or hour, of charging. Let's look at some examples. We will ignore inefficiencies and charge curves in these examples for simplicity.

If an EV gets 3 MPkWh and we use a small residential 7kW charger, for every hour we charge we add 7kWh to the EV battery. This gets the EV 21 miles of range for each hour of charging. If we charge for 10 hours, we would add 70kWh or 210 miles of range. What if we wanted to add 200 miles in an hour? We would need a charger that could provide around 66.7kW, which most Tesla superchargers can provide. If we wanted to add 200 miles in 15 minutes, we would need to charge at 267kW. Tesla's newest 3rd generation supercharges can do up to 250kW. As you can see, shortening the charging time requires larger and larger EV chargers.

Pure Power Engineering is an expert at designing commercial and fleet EV charging systems. High power chargers create high electrical demand, which could overload the service if not designed properly. Fortunately, we are experienced with both AC and DC charging architectures and can design a system that will balance the high charge rates vs impact on your existing service. Contact us today for help adding EV charging to your next project.