Twenty years ago last week the Hubble Space Telescope was launched. It’s been an awesome scientific tool, and a well-known symbol of astronomic achievement. It’s told us a lot about the universe.
The success of the Toyota Prius means that North America is getting more hybrid cars (as well as more smaller, European cars). One of those hybrids is the Chevy Volt, one you can plug into your house’s electricity supply.
GM is claiming that the Volt can get up to 230 miles per gallon.
That claim is misleading. You can’t do a simple mileage calculation for a hybrid, especially one that works like the Volt where the gas engine only kicks in when your electric juice has run out.
Mark at Scienceblogs’ Good Math, Bad Math – which is where I found out about this story – explains why:
The “mileage” figure, as it’s presented, is really meaningless – because it’s being presented for a situation in which the gasoline engine almost never runs at all.
They compute it by basically saying: “If I fully charge the car battery every night, how far will I drive the car in typical city commuting conditions before it’s consumed a gallon of gas”.
What if you drive your volt around the city all day? Your mileage will drop to around 50 miles per gallon once you’ve driven more than 40 miles. If you drive your car 100 miles in a day, you’ll consume a bit over a gallon of gas. That’s very impressive. But it’s absolutely notwhat you’d expect after being told that it gets 230 miles per gallon.