Does daylight savings time actually result in substantial energy savings? Other countries have done away with it because, as I understand it, the evidence is tenuous. What do you think?
Asked by Stella Aslibekyan, ’05, Ann Arbor, Mich.
What's the Point of Daylight Saving Time?
Modern Daylight Saving Time has its roots in World War I, when Germany and its allies adopted the practice as a way to save coal during wartime in 1916. The other European nations soon followed suit, as did the United States in 1918. The argument went that by turning clocks forward and back to track the daylight hours more closely, we used less power, especially lighting. It proved unpopular in the United States and was repealed after the war—only to be reinstated during World War II. The practice was first closely examined only after the 1973 OPEC Oil Embargo, when Congress placed the country on extended Daylight Saving Time for two years in order, they said, to conserve energy. The U.S. Department of Transportation, which oversees DST in the States, reviewed the results of the extended 1974-1975 daylight saving time, and confirmed that in March and April, the equivalent of 10,000 barrels of oil a day had been conserved, presumably because more daily activities were conducted during daylight hours. Reductions in crime and traffic accidents were also reported. There is even some evidence that "rising with the sun," a practice at least in theory supported by DST, may help mitigate depression.
Still, a great many countries do not observe DST. China doesn't, and Japan abandoned DST in 1952 after U.S. occupation ended. Similarly, most countries near the equator do not observe DST. On the other hand, both Mexico and the European Union implemented forms of Daylight Saving Time in 1996. But the specifics of DST vary significantly from country to country, and that may explain the marginal results in certain parts of the globe. Are there better ways to standardize Daylight Saving Time to conserve a more appreciable amount of energy for our nation?
Alternate Implementations of Daylight Saving Time
During the California energy crisis in 2001, the California Energy Commission (CEC) compiled a report on the effect of DST on California energy use. Reducing energy demands during peak hours was a prime concern during the crisis, so the CEC looked at two modified computer models of Daylight Saving Time: Winter Daylight Saving Time and Summer-Season Double Daylight Saving Time. The Winter model extended DST year-round, through the period when we normally observe standard time. Double DST kept Daylight Saving to the typical time period, but shifted the clock forward two hours during the change, not just one. For the study, the Federal Energy Regulatory Commission and the California Independent System Operator (ISO) collected hourly electrical load data for throughout the state.
The Winter DST model was the more effective of the two. Though it would only drop daily electric consumption by about half a percent (3,400 MWh a day), the simulation found, peak electric demand would drop by 3 percent. That drop in peak demand would be enough to have major implications for using renewable energy sources (more on that in the next section). In the Double DST model, California would save about 1,500 MWh a day, or 0.2 percent. This is about the benefit that we obtained when, in 2007, we extended Daylight Saving Time by a month.
The study also looked at doing away with DST entirely. Interestingly, total electricity use was virtually unchanged under this model. However, the demand at peak hours was impacted highly: up by 600 MWh in April and October, 250 MWh in May and September, and 100 MWh in midsummer. Presumably, this meant that heating and cooling demands during peak hours were much higher when our waking hours didn't coordinate as closely with available sunlight.
The CEC's report, then, shows a marginal energy benefit in switching to a year-round ("Winter") DST model, but also evidence of your concern: that our current DST practice doesn't really reduce overall energy usage. However, we are tangibly reducing peak demand, and could reduce it further if we switched to year-round DST. We'll look next at why this might be important as California and other states increase their number of renewable energy sources.
Why Daylight Saving Time Helps Renewable Energy
Recently, the National Renewable Energy Laboratory (NREL) released its Western Wind and Solar Integration Study, and project manager Debra Lew gave a lecture on the study at Stanford. The goal was to model whether supplying 35 percent of power through renewable wind and solar sources would be viable for the power system supporting Arizona, Colorado, Nevada, New Mexico and Wyoming. The study explains that this is feasible with enough cooperation and crosstalk between these (traditionally very independent) regions. However, Lew stressed in her talk at Stanford that with an energy portfolio that was increasingly heavy in renewable energy sources, power generation would be more unreliable and subject to variations in local weather. Accurate forecasting of energy generation was necessary, and reducing peaks in energy demand would help balance the dips and spikes in renewable energy production. (Demand for electricity tends to peak when you have extremely hot summer days that prompt AC usage when the sun is high in the sky, while wind farms tend to be less productive at midday, and solar shuts down at night.) As we can see below, midsummer generation-to-load is much more stable than in April. This is wide fluctuation in load is due to more weather variability in the spring months:
From the National Renewable Energy Laboratory WWSI study. This is a model of balancing variable generation against net load (blue line at bottom). The case is much simpler in July than in April.
If we remember the CEC's modeling, our existing daylight saving time model reduces the peak load at precisely the times that are most variable as the power grid is supplied by renewable energy sources. This effect is even more pronounced in the Winter DST model.
So what does all this mean? By keeping our schedules in sync with the daylight hours, we may not be saving total energy. However, we are keeping additional stress off the power grid at key times, and distributing our energy use more evenly throughout the day and the seasons. Already, that means we don’t have to build as many power plants as we would need otherwise. And the effect will become even more as more renewable sources are added into our energy portfolios. So yes, our current DST practice is limited in its benefits. But it is potentially crucial for the future of renewable energy, especially if we shift to a year-round, "winter," DST model. That would not only significantly reduce the stress on our energy grid during peak hours, but also spare us the hassle and stress of twice-yearly clock-changes.
Nik Sawe, '07, is a PhD student in the Emmett Interdisciplinary Program in Environment and Resources.
