Dr. Stat

Dr. Stat is a Statistics Professor. This blog is his opportunity to share ideas and opinions about education (especially math education), politics, and whatever else comes up.

Friday, April 08, 2005

Daylight Saving Time is a Peeve of Mine

And many of our esteemed legislators have fallen prey to the absurdity:
"The more daylight we have, the less electricity we use," said Markey, who cited Transportation Department estimates that showed the two-month extension would save the equivalent of 10,000 barrels of oil a day. (In an April 7 AP article quoted rom CNN.com.)


The California Energy Commission has a nice article called Saving Time, Saving Energy which explains the history and advantages of DST.

It seems convincing, but I'm not yet convinced. First of all, it is not true that changing our clocks changes the amount of daylight available. Therefore, it is not automatic that extending DST would save oil. Second, the statement, "The more daylight we have, the less electricity we use," appears to be false. I obtained monthly electricity usage data for the US for the years 2001 to 2004. The amount of daylight available varies across the country, but as an operational "average," I used the number of minutes from sunup to sundown in Omaha, Nebraska on the 15th of each month. A simple linear regression of electricity usage to minutes of sun shows a significant (p=.03) positive relationship of 66 million kwhrs per additional minute of daylight! (That's about .02% of the monthly average). The explanatory power of the model is poor (R-square=.0981).

Indeed, my calculations are rough and the Transportation Department probably had better data and did more extensive analysis. However, if the real issue in saving energy is the number of hours of lighting needed, it is still not necessary to change the clocks! People who can benefit from a change in rising and retiring times should adjust their schedules accordingly. If businesses can influence this factor, they can change their hours of operation. None of this requires a change in clocks. In fact, we could change business hours at any time throughout the year! NOTHING prevents that. Why not start work one hour after sunrise no matter what time of year it is? Or perhaps time the start of work in such a way that people have to get up eight hours after sunset. It seems to me this would result in the maximum electrical savings. Indeed, it is often managing the peak of electrical usage that is most important to saving energy. This is best accomplished by having different people in the same region on different schedules!

Truck and Barter has some supporting thoughts here.