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Published: October 25, 2009
Q. Since 2007, daylight-saving time has started earlier in the year, and ended later. The change was supposed to save energy. How much energy does extending daylight-saving time actually save? -- J.W.
A. From the beginning, the idea of daylight-saving time was to save energy. Benjamin Franklin suggested it in a 1784 essay titled "An Economical Project for Diminishing the Cost of Light."
In 2007, the start of daylight-saving time was changed to the first Sunday in November.
The U.S. Department of Energy released a study in October 2008 on the "Impact of Extended Daylight Saving Time on National Energy Consumption." It found that "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."
Though the savings don't sound particularly impressive when expressed as a percentage of total electricity use, the amount saved is enough to "power 100,000 households for a year," according to an article on daylight-saving time in the March 2009 issue of Scientific American.
Results can vary by region. The Department of Energy found that "areas of the southern United States exhibited smaller impacts of EDST compared to areas of the North."
Other studies indicate that in some areas, daylight-saving time can cause more energy to be used. For example, the Scientific American article mentioned what happened when Indiana started using daylight-saving time statewide in 2006. A study found that "daylight time led to a 1 percent overall rise in residential electricity use" as less use of lighting was offset by higher demand for cooling and heating.
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