The Problem with Numbers
1st September 2009
Dennis Harding
Are the latest developments in energy in danger of becoming tainted due to deliberate confusion over how it calculates the numbers indicating their efficiency?
1st September 2009
Earlier this week T. Lau wrote about the importance of numbers when it comes to the climate debate. This is a follow up article.
The debate over the meaning of numbers is coming to a head when it comes to electric vehicles. Electric cars, it seems, may be on the verge of a renaissance of sorts after the debacle of GM's EV1 and other short-lived efforts. They're quiet, eco-friendly, and apparently pretty damn quick as well. Compared to a regular engine or even a hybrid, forthcoming electric cars promise some pretty amazing fuel mileage numbers. GM's $40,000 volt is promising 230 mpg, while Nissan's forthcoming Leaf is promising 367 mpg. Hang on just a second, though. MPG stands for Miles Per Gallon, right? If electric cars don't use any fuel, how can the term "gallon" make any sense in measuring the fuel efficiency of electric cars?
It turns out that it doesn't make much sense at all, and that the 230 and 367 mpg numbers are pretty much just marketing hogwash. Worse, although they are expressed in "mpg," the two numbers aren't even comparable to each other, so it would be false to say that the Leaf gets 137 mpg better than the Volt. They are computed using different methodologies and assumptions, and are really virtually useless.
Take the Volt, for example. Its drivetrain is driven exclusively by electricity generated from its onboard batteries. If you plug it into the grid to charge the batteries to full capacity, you should be able to get 40 miles of range before it needs to be recharged. If you don't plug it in after 40 miles, a small engine fires up and charges the battery. Therefore, if you keep all your trips to less than 40 miles and charge it using only the grid, theoretically you could own a Volt and not burn a drop of gasoline! On the other hand if you routinely drive more than 40 miles between charges, you'll use a lot more gasoline. GM used a 51 mile daily cycle to arrive at the 230 mpg figure.
The Leaf, on the other hand, has no engine at all. It's driven exclusively by electricity and boasts a 100 mile range per charge for its batteries. Its 367 mpg figure is calculated based on a "theoretical" calculation converting electricity into a petroleum equivalent.
The Volt and the Leaf are revolutionary vehicles and have the potential to transform the automotive and battery industries. The trickle-down effects to IT and green tech will be awesome to watch. The accompanying marketing hype, however, threatens to dilute the transformative power of these vehicles until the industry can figure out a more meaningful way to communicate efficiency to consumers.
For the whole article in context see:
http://blog.enterpriseitplanet.com/green/blog/2009/08/more-on-the-pro.html