Why extending Daylight Savings Time won't lower your energy bill.

As part of last year’s Energy Policy Act, Congress decided that DST will be extended by four weeks.

Sometimes, the little things mean a lot. I normally get out of bed at about 6:00 a.m. In the foothills of the Adirondacks in mid-June, this means that the sky has been light for an hour. I like this. For whatever reason, my brain just doesn’t want to fully engage in the morning when it’s dark out. This makes the winter months a drag but, come summer, I’m in heaven. Mind you, I don’t need it to be light at 4:00 a.m., so I am a big fan of Daylight Savings Time (DST). I love the extra hour of sun in the evening, seeing the final rays disappear well after 9:00 p.m. during the longest days.

One of the initial ideas behind starting DST was energy savings; most folks don’t get up early enough to benefit from early morning sun but could use the extra hour of summer sunlight at the day’s end. Heck, in June and July the lights in our house might only be on for an hour a day. I’m not keen about the change-over in spring and fall, but it’s one of those markers of the season that you get used to. Until somebody screws with them, that is.

As a result of the high oil prices in 2005, Congress decided to “do something” to address our energy needs; so they extended DST. Well, at least that’s what they said—and what the news media reported. As part of last year’s Energy Policy Act, Congress decided that, beginning in 2007, DST will be extended by four weeks, from the second Sunday of March until the first Sunday of November. Using data from the 1970s, one of the Congressmen who sponsored the legislation claimed that adjusting DST would save an equivalent of 100,000 barrels of oil per day for the extension period. Jeez, that sounds like a lot of oil, but is it? And for that matter, is it a reasonable estimate?

In 2001, a California Energy Commission report examined how much energy might be saved by changing when we change the clocks. Overall, it found that extension of DST into the winter months does little to save energy because it is accompanied by an increased need for electric light in the morning. The study projected that extending DST for the entire month of March would reduce energy use in that period by an average of 0.5 percent. (Note that the results may be different in the most northern states.)

Alternately, the 100,000-barrel claim can be examined with respect to current consumption patterns. The U.S. currently consumes about 20 million barrels of oil per day. If the DST extension saves 100,000 barrels of oil each day, that’s a daily oil savings of 0.5 percent. But since oil comprises somewhat less than half of the nation’s total energy consumption, extending DST results in a total daily energy savings of less than 0.25 percent—about half the savings the California study predicted. 

Whichever figure you prefer, it’s clear that the DST change will do little to alter our energy use. Remember, the savings occur only during the extension period, which in this case is four weeks. Even by generously using the 0.5 percent figure, we would only reduce our annual energy use by approximately 0.04 percent. Saving four-hundredths of one percent is like shaving about 200 feet off of 100 miles. Does any sane person think this will make a serious dent in our energy use? Well, some congressmen and news reporters do.

Here’s an interesting contrast. Suppose the fuel efficiencies of passenger cars and light trucks were increased by a mere one mile per gallon. These vehicles, which use approximately 40 percent of the oil consumed by Americans, currently average between 24 and 25 miles per gallon. A one mile per gallon increase would create a 4 percent reduction in fuel use—that translates to a 1.6 percent savings in overall oil consumption, and somewhat less than 0.8 percent savings in total energy use year-round. This represents about twenty times as much savings as the best-case DST change.

Now here’s the real kicker: In the late 1980s, light trucks made up only 28 percent of the fleet of passenger vehicles on the road. Today, they make up 50 percent. The proliferation of light trucks has decreased the average mileage of the fleet by two miles per gallon. Yep, if we simply went back to populating the roads with personal cars instead of personal trucks and SUVs, we’d save perhaps forty times the projection from the DST change. (Taking into account the design efficiency increases in engines from the past 15 years, the real savings would be even higher.)

There might be good reasons to extend DST, but let’s not fool ourselves into thinking it’s going to do anything about our energy problem. Sometimes the little things mean a lot. Sometimes they don’t mean squat.

Jim Fiore is a college professor living and working in the foothills of the Adirondack mountains of New York. He contributes to the blog Dr. Joan Bushwell’s Chimpanzee Refuge on ScienceBlogs

Originally published October 30, 2006

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