Energy

Embodied Energy

July 28, 2017

View down Michigan Avenue, June 2010. Photo © Lloyd DeGrane

When most of us think about the energy we use to drive a car, we focus on the gas mileage. We buy fuel, use it to propel the car, and expect that the exhaust (largely carbon dioxide and water vapor) will leave the tailpipe. Few of us think of the energy used to build the car, including the energy it takes to convert the raw materials into car parts.

What is often called “embodied” or “embedded” energy is the energy that has been used to produce the materials of everyday life: steel, glass, PVC pipe and wood. When you look at a skyscraper being constructed, it is easy to overlook the embodied energy in all the construction materials involved. Carpet and aluminum have high embodied energy content, 150 kWhr and 53 kWhr, respectively.[1] It will be of little surprise that wood (2 kWhr) and stone (1.0 kWhr) have relatively little embodied energy content, and it is largely derived from how they are cut and shipped to the site of use.

Nearly all of the embodied energy in aluminum is derived from the electricity that is used to smelt aluminum ore, which is why recycling aluminum is so important. Jet airliners use a lot of fuel, but they are also made of aluminum, with a lot of embodied energy.

David MacKay of the University of Cambridge estimates that the embodied energy in the average car amounts to about 76000 kWhr. That is equivalent to about five years of electricity used in a 3200-square-foot house in Durham, NC.

Scaled across the range of available sizes, the energy used to manufacture a car is about equivalent to one year’s worth of gasoline to drive it. But there are important differences between brands. When Ford changed the bed liners in its pickup trucks from steel to aluminum, the decision was made to increase the expected gas mileage, since aluminum is a lighter material. The embodied energy in steel is only about 13% of that in the same weight of aluminum. We can hope that the improved mileage will pay back the carbon dioxide emissions associated with smelting aluminum.

Overall, embodied energy represents about a third of the energy used in modern society. This accounts for the energy used to produce the products of everyday life, dominated by chemicals (especially fertilizers), steel, paper and cement. The rest of the energy is used in more obvious ways: transportation, heating and lighting.

[1] (One kilowatt hour of electricity is equivalent to 3.6 megajoules).

This post originally appeared on William H. Schlesinger’s blog Citizen Scientist, published by Duke’s Nicholas School of the Environment.

William H. Schlesinger

William H. Schlesinger is one of the nation’s leading ecologists and earth scientists and a passionate advocate for translating science for lay audiences. A member of the National Academy of Sciences, he has served as dean of the Nicholas School of the Environment at Duke and president of the Cary Institute of Ecosystem Studies. More from William

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2 comments

  1. I’ve also heard the term life cycle cost used to describe this same concept. How do you feel embodied energy is different?

    Also, I wish cars would start describing gas mileage in how much money it costs to drive 100 miles in your car. Could use $2.00/gallon as a benchmark value. So if you had a 10mpg vehicle, it’d be advertised as $20/100 miles. Might better inform buyers about energy costs.

  2. Studies of the concept of embodied energy are also known as life-cycle analyses

    And, I like your idea of expressing the cost per 100 miles driven for cars