The familiar MPG, miles per gallon, is a very sensitive subject. The number of miles per gallon that you get from a car predicts how much money you will need to spend on gasoline. In an era where the electric vehicle is becoming established as an alternative, the way we come up with the numbers is extremely important.
For combustion engine vehicles the EPA has a series of drive cycles that it uses which are based on their determination of “typical” driving conditions. The car companies use the EPA standards cycles and run their test vehicles on dynamometers. The results make the published EPA City and Highway MPG for each new car. Unfortunately, the data has been challenged because consumers find the actual performance differs from the EPA estimates. This weakens the credibility of the EPA methods and makes consumers skeptical of the manufacturer’s data.
Paying more money for a high mileage vehicle is a tricky analysis. If you drive an average 12,000 miles per year at 25 mpg and switch to a 30 mpg car, you will save $260. a year in gasoline costs based on $3.25 per gallon price of gasoline. So for the individual contemplating the purchase of a new or used car, the expected MPG rating may not be a big factor in the decision making process.
Unfortunately, if the car makers in the past chose not to offer high MPG vehicles, leaving consumers unable to exercise this choice. Very little consumer activism, no boycotts or rallies. Somehow, the issue has become politicized leading to the mandate of higher MPG standards by the EPA. No legislation, no debates by politicians or discussion by you and me. Kind of weird, actually.
Then a few years ago Chevrolet started releasing data in anticipation of the Chevy Volt. 265 miles per gallon. Wow! It was a sensational claim, but totally defensible. If the car has a 32 mile range on battery power, and my daily commute to work is 16 miles, I might not use any gasoline at all! And, in fact, that was the experience of many early adopters of the Volt. As other manufacturers came up with their own ratings, the basis for performance comparisons became less and less clear.
So to harmonize the mileage performance comparisons across combustion engine, EV and hybrid vehicles, the mile-per-gallon-equivalent (MPGe) was created based on the thermodynamic energy equivalence of 1 gallon of gasoline equaling 33.4 kilowatt hours of electricity. This is an interesting metric because depending on where you live, the MPGe cost will vary with the cost of electricity. In Hawaii at $.23/kWh its $7.68 gal-e, in New York California and New Jersey at $.19/kWh its $6.35 gal-e, and in Texas its $3.51 making gasoline at the pump the best buy.
What’s up with this? (more next week)