What most people think they know about energy efficiency is probably wrong

What takes more energy, making a can out of recycled aluminum or making a bottle out of recycled glass?

If you think bottle recycling is the more energy efficient choice, you have a lot of company. You are among the majority of people who have misconceptions about what practices are the most energy efficient. So says Shahzeen Z. Attari, Michael L. DeKay, Cliff I. Davidson, and Wändi Bruine de Bruin, researchers who hail from the Earth Institute and Center for Research on Environmental Decisions, Columbia University, Ohio State University, and Carnegie Mellon University. The group recently completed a study wherein they asked participants for the most effective strategy they could implement to conserve energy under a variety of scenarios. In general, most participants mentioned curtailment (like turning off lights, driving less) rather than efficiency improvements like installing more efficient light bulbs and appliances. These responses were also wrong.

When guessing the energy use of specific activities, participants underestimated energy use and savings by a factor of 2.8 on average, with small overestimates for low-energy activities and large underestimates for high-energy activities. In general, participants who were better with numbers and who had stronger environmental proclivities had more accurate perceptions.

Participants had a lot of misconceptions about large appliances, say researchers, despite a 10-fold difference in actual energy use. For example, participants estimated that line-drying clothes saves more energy than changing a washer’s settings (the reverse is true) and estimated that a central air conditioner uses only 1.3 times the energy of a room air conditioner (in fact, it uses about 3.5 times as much).

Participants were better at figuring energy use of every day tasks such as using a desktop computer, changing their summer thermostat, replacing an incandescent bulb with a CFL, replacing a 100-W bulb with a 75-W model. Many of them also knew that transporting goods via airplanes consumes more energy than using other modes of transportation, and that the energy difference between trains and ships is small. However, there was a wide misconception that trucks consume about as much energy as trains and ships (trucks actually consume 10 times more energy per ton-mile).

Most of those surveyed knew that making a can or bottle from virgin aluminum or glass requires more energy than making the same container from recycled materials. However, they incorrectly thought that making a glass bottle requires less energy than making an aluminum can. In fact, the reverse is true: It takes 1.4 times as much energy to make a glass bottle as an aluminum can when virgin materials are used and 20 times as much energy when recycled materials are used. Partly because glass is so heavy, the making of a glass bottle from recycled material actually requires more energy than making a virgin aluminum can.

Surprisingly, those who engaged in energy-conserving behaviors had less accurate perceptions of energy use and savings. Researchers figure this might be due to unrealistic optimism about the effectiveness of personal energy-saving strategies. This might also be due, they say, to how people tend to focus primarily on the behaviors they have already adopted, making them poor judges of how much energy other behaviors use or save.

The study was published online by the Proceedings of the National Academy of Sciences and is available here:

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