What is MPGe? Measuring electric vehicle carbon footprint

What does MPGe mean?

One of the most common metrics for comparing EVs to ICE vehicles is the abbreviation MPGe, which stands for miles per gallon of gasoline-equivalent. The U.S. Environmental Protection Agency developed the MPGe measurement to mathematically compare the energy efficiency of electric vehicles.

How is MPGe calculated?

We calculate MPGe by determining how far the EV can travel on 33.7 kilowatt-hours of energy, which is the electrical energy equivalent to a single gallon of gasoline. For those keeping score, burning one gallon of gasoline creates 115,000 BTUs of energy, which is the heat equivalent of 33.7 kilowatts.

Here's a real-life example of MPGe: the Tesla Model X, which is currently one of the least efficient EVs on the market, gets 96 MPGe, while the Hyundai Ioniq, one of the most efficient, gets 136 MPGe. This metric provides a great analog comparison to the efficiency of internal combustion engines, but it does not take into account actual vehicle emissions.

Carbon footprint: EV vs. Gas

EVs may not have carbon dioxide-emitting tailpipes, but an electric car still has an ecological footprint if it uses grid-based electricity for charging. In the U.S., coal produces an estimated 2.21 pounds of CO2 per 1 kWh of electricity generated in a coal-based power plant. On average, one gallon of gasoline produces roughly 18 pounds of carbon dioxide.

So, are EVs still more sustainable in terms of CO2 production than their gas (or ICE) competitors? Let's do the math:

• •  When a 2018 Hyundai Ioniq travels 136 miles, it uses 33.7 kWhs of electricity.  Assuming a coal-based power plant created this electricity, the Ioniq indirectly created 74.5 pounds of CO2 to travel those 136 miles.
• •  The similarly sized 2018 Hyundai Elantra boasts 32 MPG of gasoline, which means it will burn 4.25 gallons of gasoline to travel the same 136 miles. The 4.25 gallons of gasoline burned during that trip creates 76.5 pounds of CO2.

If EVs use coal-generated electricity to charge their batteries, they can create nearly the same amount of carbon dioxide as their ICE counterparts.

However, we must understand that among fossil fuels, coal produces the most amount of CO2 per kWh, but it was the source for only 23.5% of energy produced in the US in 2019. Regardless, any electricity production that produces carbon dioxide increases the carbon footprint of EVs that use that electricity. Unless EVs utilize 100% renewable energy (such as photovoltaics) to produce their charge-source electricity, they will continue to have a carbon footprint.

Cost of ownership: EV vs Gas

The cost per mile is one factor that makes EVs more attractive than ICE vehicles. In the U.S. in 2019, the average cost of a gallon of gasoline was $2.60, while the average cost per residential kilowatt-hour was $0.1286.

But how about the cost of ownership per mile? Using the same automobiles mentioned above―the 2018 Hyundai Ioniq and Elantra―the numbers are staggering. To make the same trip of 136 miles, it would cost the Ioniq EV $4.33, while it would cost the fuel-efficient Elantra $11.05. Therefore, the Ioniq EV in this example is 60% cheaper per mile than the comparable Elantra ICEV.

In countries like Norway, where gas can easily exceed $6.50 per gallon and 1 kWh of electricity costs $0.30, the financial advantages of EVs are amplified. It's no surprise that almost 60% of cars purchased in March 2019 in Norway were fully electric.

Conclusion: electric vehicles and renewable energy

EVs have distinct advantages over ICE vehicles from the standpoint of energy efficiency, ecological friendliness and cost of ownership. The energy used per mile of an EV is significantly less than the thermally inefficient internal combustion engine. As long as EVs do not use coal-fired electrical generators to charge them, EVs have a significantly reduced (if not non-existent) carbon footprint. Most importantly, the operation costs of EV are significantly lower than that of an ICE vehicle.