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Report Reveals Daylight Saving “Saves” Energy

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Published 10-Nov-2008. Changed 10-Nov-2008

The United States’ extended daylight saving schedule, which resulted from the Energy Policy Act of 2005, has saved energy for the nation according to a newly released government report. The report also found that changes in national traffic volume and gas usage for passenger vehicles were not attributed to the extended schedule.

Illustration image

Daylight saving time in the United States may prove to be a beneficial way of saving electricity, thanks to findings from a recent report.

©iStockphoto.com/Jacom Stephens

What is the Report About?

Published in October 2008 for Congress to review, the report, titled Impact of Extended Daylight Saving Time on National Energy Consumption, evaluates the impact of extended daylight saving time on energy consumption in the United States. It presents the key findings of a study on changes in electricity use, motor gasoline use and total energy. The study uses two methods to calculate changes in national energy consumption associated with electricity consumption.

The “heuristic” method compared the average changes in the pattern of electricity consumption between 2006 and 2007 during the periods of extended daylight saving time in March and November. The statistical method examined daily and hourly electricity consumption for a sample of electric utilities across the country.

The Report’s Findings

The report showed that extended daylight saving time’s total electricity savings were about 1.3 terawatt hours, which corresponds to 0.5 percent per each day of extended daylight saving time, or 0.03 percent of electricity consumption over the year. The total electricity consumption in the United States was 3,900 terawatt hours in 2007.

The study also showed that in terms of national primary energy consumption, the electricity savings translate to a reduction of 17 trillion British thermal units (TBtu) over the spring and fall extended daylight saving schedule, or roughly 0.02 percent of total US energy consumption of 101,000 TBtu in 2007. A British thermal unit (Btu) is a unit of heat equal to the amount of heat needed to raise 1 lb of water at maximum density through one degree Fahrenheit.

The electricity savings are small compared to the national total for the year, representing about 0.03 percent of the total national electricity consumption of 3,900 terawatt hours in 2007. On a daily basis, the total electricity savings due to extended daylight saving time was 0.46 to 0.48 percent per each day of extended daylight saving time.

During the extended daylight saving period, electricity savings occurred over three to five hours in the evening with small increases in usage during the early morning hours. On a daily percentage basis, electricity savings were slightly greater in the March (spring) extension of extended daylight saving time than the November (fall) extension. Moreover, northern parts of the United States saved slightly more energy than some southern parts of the country, possibly due to a small, offsetting increase in household air conditioning usage.

Interestingly, the study found that changes in national traffic volume and motor gas usage for passenger vehicles in 2007 were statistically insignificant and could not be attributed to the extended daylight saving schedule.

What the Study Did Not Cover

The study did not include an economic analysis of the extended daylight saving schedule, which compares the relative costs and outcomes, such as cost-benefit or cost-effectiveness. This is because section 110 of the Act directed the Department of Energy to focus only on the extended schedule’s impact on “energy consumption in the United States”.

The study did not analyze non-energy impacts that could result from the extended daylight saving time, as section 110 of the Act focused only on energy consumption. So the study did not examine issues such as health issues, traffic accidents, crime rates, airline scheduling changes, agricultural work scheduling or people travelling to their places of work or study in darkness.

The Need for a Report

Daylight saving time in many parts of the United States begins on the second Sunday of March until the first Sunday in November. The new schedule came into effect in the United States for the first time in 2007 as a result of the 2005 Act, which extended the daylight saving period from the original schedule of the first Sunday of April to the last Sunday of October.

When the US government implemented the extended schedule to save energy, it was anticipated that the extra evening daylight hours during daylight saving time would lower electricity consumption because of the delayed need for lighting. The extended schedule would also give people the chance to participate in more outdoor activities during the afternoon/evening hours.

The government acknowledged that there would be advantages and disadvantages with the extended schedule but hoped that the pros would outweigh the cons. It acknowledged that extra daylight could lead to more driving, and therefore higher gas consumption and energy use. Moreover, morning electricity consumption could increase and daylight saving time could change the amount of electricity used for heating and air-conditioning. The extended schedule also faced criticism, doubt, and protests from those were against this initiative.

Therefore, the Department of Energy planned a report to Congress under section 110(c) of the Energy Policy Act of 2005. The report, which examined the impact of the extended schedule on the country’s energy consumption, was published in October 2008.

Note: References to spring, summer, fall and winter in this article relate to the seasons in the northern hemisphere. It is also important to note that not all parts of the United States observe daylight saving time.

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