Wednesday, September 9, 2009

Innumeracy at the Standard-Examiner

Today's Standard-Examiner has an article about a small hydroelectric unit that Ogden will be installing at its water treatment plant. According to the article:
  • The unit is being funded by a $169,000 grant;
  • It will generate 131,400 kilowatts of electricity;
  • It will save the city about $10,000 each year.
Can you see that there's something wrong here? A kilowatt of electricity is enough to power an average home, so 131,400 kilowatts would probably power the entire city of Ogden. There's no way such a plant could be built for the cost of a single home, or that the energy delivered annually would be worth less than a new car.

It isn't hard to guess what the "131,400" figure really means: It's actually the number of kilowatt-hours per year. This is a unit of power that would make my physics students groan in dismay, but it's legitimate and even useful when you're thinking about annual budgets. Divide $10,000 by 131,400 and you get an average cost of 7.6 cents per kilowatt-hour, which is about what we pay for electricity here in Ogden.

So what's the plant's output in more conventional units? Divide 131,400 by 365 (days in a year) and by 24 (hours in a day) and you get exactly 15 kilowatt-hours per hour, that is, 15 plain old kilowatts. That's comparable to what your house would use if you turned on all the big appliances at once. And it's reasonable that a water treatment plant would use that much power on a continuous basis.

This isn't rocket science--it's something every educated person can and should understand. Everyone knows what a 100-watt lightbulb is, and most people know that "kilo" means 1000. A typical toaster or hairdryer uses about a kilowatt. A kilowatt-hour is the amount of energy that such an appliance uses when it's turned on for one hour. You need to know this to understand your monthly electricity bill, but few people bother to try.

Why don't newspapers expect their reporters and editors to know what a kilowatt is? Why don't universities expect every graduate to know this? Have we really decided, as a society, that thinking about numbers is only for specialists?

1 comment:

  1. Thanks Dan. I'm one of those folks that have never even given kilo-whatever a second thought while looking over my power bill.


Not registered? Just choose "Name/URL" and enter any name you like; you can ignore the URL field.