Energy Payback of Wind Turbines

Energy payback for a wind turbine is the length of time the wind turbine must produce in order to supply all of the energy used in its manufacture, construction, maintenance and decomissioning.
Of course, the energy payback of a turbine will depend on a number of things. The wind resource in particular is crucial, as a windier site will produce energy more quickly than a less windy site.

This issue of energy is a crucial issue both to cost, and to supplying energy for people in the future. Fortunately, the energy payback for wind turbines is very good. All of the energy used to produce, install, maintain, and decomission a wind turbine is earned by the turbine in 2-3 months of production. Because wind turbines will last at least 20 years, the net energy output from wind far exceeds the energy used.

This compares favourably with photovoltaic, which is estimated at 2-3 years. And it compares favourably with nuclear and coal fired plants which have more embodied energy in them per kWh produced than wind. http://www.awea.org/wew/851-1.html

Energy payback is closely related to the concept of Energy Return On Energy Invested (EROEI). Obtaining oil from shallow pools, like conventional fields in Saudi Arabia, uses very little energy compared to the energy produced. As conventional fields are depleted, we have to drill very deep holes, such as offshore in the Gulf of Mexico, or go long distances, like the McKenzie Valley natural gas pipeline. The tar sands are quite bad, consuming large amounts of natural gas generated steam to loosen the bitumen from the sand. Some have called the tar sands an expensive way to convert natural gas into oil.

Ethanol from corn has a poor EROEI. Some studies have demonstrated a negative EROEI, although these studies have largely been refuted. The most common number accepted now is that there is a 30-40% energy gain in energy when making ethanol. Growing corn on mechanically irrigated fields, such as they have in Nebraska, would have a lower EROEI, because of the large amount of energy consumed in pumping water. The low EROEI is largely because of the intensive use of fossil fuels in fertilizer to grow corn. Sugar cane is better. Biodiesel from virgin feedstock is better as well, but making biodiesel from waste oil streams is very good.

It seems to me that the EROEI for consuming fossil fuels is going down. We have tapped the easy to access oil and natural gas, with a good EROEI, and are now moving on to the harder to access sources like tar sands, arctic, and deep offshore. But with wind and solar, the EROEI is going up. The energy payback for wind turbines has dropped from 5 months to 2-3 months over the past 15 years. And solar technology is advancing rapidly. Even basic things like slicing the silicon thinner is reducing the energy required to make solar cells. And new solar technologies will be even better.

Perhaps the renewable revolution will be driven more by technology advance in renewables, and higher costs for fossil fuels, than by carbon constraints.

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