Miles Per Gallon Equivalent and the Determinants of EV Charging Costs

Making accurate and easily consumable comparisons between battery electric vehicles, hybrids and an efficient gas powered model in the same class can still feel abstract. Explaining the value proposition to those not as keen on Evs can be even more daunting. It helps to begin with the key metrics of the mile per gallon equivalent (MPGe) and kWh per mile for electric vehicles.

Known as an “equivalent”, the MPGe of an electric vehicle is calculated by determining how far an electric vehicle can travel with the energy contained in 1 gallon of gasoline. Sound confusing? Each gallon of gasoline contains a finite amount of energy; 115,000 BTUs to be exact when that gallon is burned. To generate that same amount of heat by way of electricity that would take 33.7 kWH kilowatt hours. If a EV can travel 80 miles on 33.7 KWH of electricity then the vehicle would have an 80 MPGe rating. If it travels 100 miles on 33.7 kWh electricity, then it would have a 100 MPGe rating.

For matters of cost and determining a vehicle’s fuel costs, the metric of kWh/100 miles is used, or the number of kWh necessary to travel 100 miles. Here, the lower the number of kWH used to travel 100 miles, the more efficient and less costly the EV is to run. This stands in contrast to the MPG rating or even a “miles per kWh” rating where the higher the number the more efficient the vehicle.  The lower the number of kWH to go 100 miles the better. Real world number for some common EVs include highly efficient EVs like the Hyundai Ioniq electric vehicle at 25 kWH/100 miles with an annual fuel cost of $500 to the less efficient Tesla Model X 75D with a rating of “only” 36 kWh per 100 miles (remember a lower kWh per 100 miles rating the better).  In either the Hyundai or the Tesla’s case, both vehicles will have lower running costs (charging) if using the average U.S. electricity price of 12.89 cents per kWh.

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Utilities will factor into this equation in so far as their average charging costs can be kept at reasonable levels. They range from Hawaii’s astronomical peak of 31.21 cents per kWh to Washington State’s cost of 9.74 kWh. The true determinants of that cost can be broken down into:

  • The cost of fuel (coal, natural gas)
  • Power plant costs (maintenance, etc)
  • Transmission and distribution systems in use
  • Weather conditions (wind for wind power, rain and snow for hydropower)
  • Regulations (some states have public service commissions that fully regulate prices, and in others, generation is unregulated while transmission and distribution is regulated)

It still feels like a sizeable set of factors that determine electric costs and corresponding costs for running electric vehicles. But understanding key metrics like the MPGe and kWH per 100 mile rating can make things more straightforward. Eventually, Electric vehicles will be compared with other EVs and ICEs will be a thing of the past; but for now, a little gasoline to electric conversion help goes a long way.

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