Daylight Saving Time Is Supposed to Save Energy--Does It? The Answer Is Mixed.

Does it save energy? There are conflicting answers.

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By Robert Schlesinger, Thomas Jefferson Street blog

Daylight saving time kicks back in this weekend: We "spring ahead" on Sunday, losing an hour of sleep that we'll retrieve when we "fall back" in November.

But is it all worth it?

One of the reasons for daylight saving time is to conserve energy. And there are arguments each way as to whether it works. We ran an op-ed in October which, citing a handful of studies, argued that daylight saving time actually wastes more energy than it saves.

According to the authors of the study, Daylight Saving Time raises energy usage overall because the potential savings from replacing artificial light with sunlight at the end of a summer's day are more than offset by the increased residential use of air conditioning (and of heating, as temperatures cool later in the season).

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Whether time is leaping forward or falling back, body clocks are thrown off. Productivity inevitably falls in the days following a switch, as people report groggily to work.

That op-ed was published, however, before a Depart of Energy study was released in early November showing that daylight savings time does save energy, though perhaps not very much.

  • The total electricity savings of Extended Daylight Saving Time were about 1.3 Tera Watt-hour (TWh). This corresponds to 0.5 percent per each day of Extended Daylight Saving Time, or 0.03 percent of electricity consumption over the year. In reference, the total 2007 electricity consumption in the United States was 3,900 TWh.
  • In terms of national primary energy consumption, the electricity savings translate to a reduction of 17 Trillion Btu (TBtu) over the spring and fall Extended Daylight Saving Time periods, or roughly 0.02 percent of total U.S. energy consumption during 2007 of 101,000 TBtu.

Is two one-hundredths of a percent annual energy consumption reduced worth it? Quite possibly, but the study doesn't put a dollar figure on the savings and it's hard to get a sense of whether these seemingly small numbers make a difference.

One other interesting item from the Energy Department study: That there's no statistically significant correlation between daylight saving time and motor traffic volume or automobile gasoline consumption.

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