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| Fig. 1: An example of how Daylight Saving Time shifts sunlight hours later in the day (Source: Wikimedia Commons) |
Twice a year, millions of people adjust their clocks an hour forward or an hour backward as they transition between Standard Time and Daylight Saving Time. The idea can be traced back to Benjamin Franklin, who suggested it as a means to save candle wax. The idea was not implemented, however, until the First World War, when Germany enacted Daylight Saving Time as a means to save coal for the war effort. Today, 60 countries and 1.8 billion people practice Daylight Saving Time in some capacity, ostensibly with the goal of saving power. Recently, many have advocated for the abandonment of Daylight Saving Time for myriad reasons while conversely, several other countries have proposed adopting it. [1] An important consideration in the decision is whether Daylight Saving Time actually saves energy, and if so, how much?
Studies of the effects of Daylight Saving Time have been famously inconclusive. [2] While many studies disagree about the effects of DST on energy consumption, most agree that the results are fairly limited usually claiming energy consumption is either increased or decreased by around 1%. One meta-analysis of 44 studies concluded that, on average, reports indicate a 0.34% reduction in electricity consumption on Daylight Saving days. [3] However, varied results can also be explained by a variety of factors such as methodology and location of the study.
The first major study in the United States was conducted by the Department of Transportation in 1975. The results concluded that in terms of electricity consumption, Daylight Savings saved the United States 49,200 megawatts per day or about 4.25 × 109 MJ. On the other hand, more recent studies within the United States have shown the opposite to be true. A study which examined the energy consumption levels in Indiana, has shown an increase in residential electricity consumption of 1%. Lastly, some studies suggest that while daylight saving time may increase overall consumption, it limits peak demand for electricity. In the next section, I will discuss the mechanisms by which DST is thought to save energy in some cases and waste it in others. [1]
Most of the electricity savings due to daylight savings are a result of what has been termed the Benjamin Franklin effect. Essentially, because in the summer people wake up after the sun has risen, but go to sleep after it has set, some daylight is wasted in the morning. By shifting wake-up times earlier, daylight can be used instead of electric lighting later in the afternoon and evening. Fig. 1 shows how DST adjusts at which hours there is sunlight to produce this effect. However, electricity usage for heating and cooling of houses has been found to increase during daylight savings time. This is hypothesized to occur because people spend more time at home at warmer hours during daylight saving time, and are more likely to crank up the AC. Conversely, an increase in warming may occur in the morning as people are awake during colder temperatures than they otherwise would be. Regardless of the exact cause, these effects often overpower the decrease in electric lighting needed. [4]
Further, evidence suggests that because of DST, people are more willing to stay out later into the day. This causes an increase in car usage, which corresponds to an increase in gasoline consumption by as much as 0.5 - 1% during DST. [2] This could mean an additional 8,000 barrels of gasoline used per day based on US consumption, which further offsets electricity savings. [5]
While many studies show conflicting or inconclusive results regarding the ultimate effect on energy consumption from DST, it seems that future trends will make energy savings from DST less likely. In short, when the early analysis was done in the 1970s, energy consumption was much different. Remember that energy savings from DST come from a reduction in use of electric lighting. However, today's 10 Watt LED Light Bulbs can provide the same lumen output as a traditional 100 Watt Incandescent bulb, showing a 90% increase in efficiency. [6] While climate-control systems have also improved, not nearly to the same degree, only showing an increase of 30% to 50%. [7] Even more important, climate control has become much more prevalent than it was in the 1970s and is moving towards ubiquity.
Therefore, as the energy required to provide power decreases due to advancements in technology and continued adoption of LEDs and fluorescents over incandescents, and energy used by climate control systems increases both due to widespread adoption, and perhaps even climate change, we can expect further increases in energy used during Daylight Savings.
In conclusion, it seems that while there is still disagreement about whether or not Daylight Saving Time saves or wastes energy, trends in technology seem to show that the energy returns are and will continue to diminish. However, it should be noted that while energy saving was indeed the exigence and origin of DST, there are other harms and benefits it may confer. For example, some studies have shown that the later daylight prevents car accidents and deters crime. [5] Meanwhile, many simply prefer the "extra" daylight given by DST. Therefore, even if a consensus is reached that DST wastes energy, we may see it continue for other reasons.
© Sam Segal. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] P. Hancevic and D. Margulis, "Horario de Verano y Consumo de Electricidad: El Caso de Argentina (Daylight Saving Time and Energy Consumption: The Case of Argentina)," El Trimestre Económico 85, 515 (2018).
[2] M. B.C. Aries and G. R. Newsham, "Effect of Daylight Saving Time on Lighting Energy Use: A Literature Review," Energy Policy 36, 1858 (2008).
[3] T. Havranek, D. Herman, and Z. Irsova, "Does Daylight Saving Save Electricity? A Meta-Analysis," Energy J. 39, 35 (2018).
[4] M. J. Kotchen and L. E. Grant, "Does Daylight Saving Time Save Energy? Evidence from a Natural Experiment in Indiana," Rev. Econ. Stat. 93, 1172 (2011).
[5] "Impact of Extended Daylight Saving Time on National Energy Consumption," U.S. Department of Energy, October 2008.
[6] M. S. Islam et al., "Power Quality Effect of Using Incandescent, Fluorescent, CFL and LED Lamps on Utility Grid," 2015 First Workshop on Smart Grid and Renewable Energy (SGRE), IEEE 7208731, 22 Mar 15.
[7] "Energy-Efficient Air Conditioning," U.S. Department of Energy, DOE/GO-10099-379, June 1999.
