Using more than seven million monthly meter readings from Duke Energy Corp., covering nearly all the households in southern Indiana for three years, they were able to compare energy consumption before and after counties began observing daylight-saving time. Readings from counties that had already adopted daylight-saving time provided a control group that helped them to adjust for changes in weather from one year to the next.
Research on the impact of extending daylight-saving time across Indiana found:
- Residential electricity usage increased between 1 percent and 4 percent, amounting to $8.6 million a year.
- Social costs from increased emissions were estimated at between $1.6 million and $5.3 million per year.
- Possible social benefits — enhanced public health and safety and economic growth — were not studied.
Their finding: Having the entire state switch to daylight-saving time each year, rather than stay on standard time, costs Indiana households an additional $8.6 million in electricity bills. They conclude that the reduced cost of lighting in afternoons during daylight-saving time is more than offset by the higher air-conditioning costs on hot afternoons and increased heating costs on cool mornings.
"I’ve never had a paper with such a clear and unambiguous finding as this," says Kotchen, who presented the paper at a National Bureau of Economic Research conference this month.