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November 17, 2006
Paul Gipe

Energy Balance of Wind Turbines



 


Adapted from Wind Energy Comes of Age, by Paul Gipe, John Wiley & Sons, 1995. All rights reserved. Much of this was written in 1993 and relied on reports published in the early 1990s. Studies since then have confirmed the general trend noted here.


The energy generated by wind turbines pays for the materials used in their construction within a matter of months. Yet the question as to whether they do, thought by industry analysts to have been effectively answered during the 1970s, is continually raised by critics of wind energy. It was the first avenue that desert activist Howard Wilshire sought in his quest to find a magic bullet that would kill the wind energy monster for all time.

The question possibly arises from reports about the poor energy balance of photovoltaics in the 1960s. Early solar cells consumed more energy than they produced, according to Jos Beurskens, manager of Renewable Energy for the Netherlands' Energy Research Foundation, ECN. He says contemporary products perform far better and pay back the energy contained in their manufacture within ten years. As the performance of photovoltaics continues to improve, so too will their energy balance. In contrast to photovoltaics, notes Beurskens, wind turbines pay for themselves quickly, despite the use of such seemingly energy-intensive materials as steel and fiberglass.

In the early 1990s, researchers again examined the question. Two Danish studies considered a typical Danish wind turbine of the period, operating under typical Danish conditions.(1) And a German study at Munich's Technical University, by far the most extensive at the time, examined the energy payback of wind turbines from 10 kilowatt to 3 megawatt in size.(2) The results of the three studies are comparable: medium-sized wind turbines installed in areas with commercially usable wind resources will pay for themselves easily within one year. At 7 m/s (16 mph) sites, like those on the North Sea coast or in California's mountain passes, turbines will return their energy content in 3-5 months, and at sites typical of North America's Great Plains in 4-6 months. Even at low wind sites, the turbines will pay for themselves in less than one year. As expected, much of the energy used to manufacture the turbine is represented by the rotor and nacelle. But more than one-third of the total energy consumed by the wind turbine is represented by the concrete foundation and tower.

According to the German study by Gerd Hagedorn, wind turbines produce 4 to 33 times more energy during their expected 20-year lifetimes than that used in their construction. Coal plants produce 64 times more energy and nuclear 108 times more than that used in their construction, notably because they consume a fuel. Current photovoltaic technology produces 1-3 times the energy represented by their materials. When fuel is included, coal and nuclear plants deliver only one-third of the total energy used in their construction and in their fuel supply because fuel consumption dwarfs the amount of energy in the plant's materials.(3)

A 2006 summary of all the reports and studies to date was compiled by Cutler Cleveland at Boston University. Cleveland's analysis was posted on the Oil Drum October 19, 2006.

Cleveland found that the average Energy Return on Investment (EROI)for wind turbines of the studies he evaluated varied depending upon whether the study assumed how the wind turbine would perform or whether it used actual field experience. For studies that estimated performance, the average EROI was 24.6, for those that used field experience the average EROI was 18.1. If wind turbines can be expected to operate for 20 years, then the average energy payback for those studies estimating performance is 9.8 months, for those studies using field experience the average energy payback is 13 months. While substantially longer than the paybacks determined by the early studies cited here, Cleveland's work confirms that wind turbines typically pay for their energy content within the first year of operation.


1. See Erik Grum-Schwensen, "The Real cost of Wind Turbine Construction," Wind Stats, Spring, 1990, 3:2, 1-2, and A. Gydesen, D. Maimann, and P. B. Pedersen, "Renere Teknologi pa Energiomradet," Energigruppen, Fysisk Laboratorium III, Danmarks Tekniske Hoejskole, Miljoeministeriet, Miljoeprojekt Nr. 138, Denmark, 1990, 123-127.

2. G. Hagedorn, and F. Ilmberger, "Kumulierter Energieverbrauch fur die Herstellung von Windkraftanlagen," Forschungsstelle fur Energiewirtschaft, Im Auftrage des Bundesministeriums fur Forschung und Technologie, Munich, August, 1991, 79, 98, 100, 111. In this study, the primary energy used to construct the wind turbine was given in units of kWh. However, only 35% of the energy burned in a power plant is converted to useful work.

3. Gerd Hagedorn, "Kumulierter Energieaufwand von Photovoltaik und Windkraftanlagen," Lehrstuhl fur Energiewirtschaft und Kraftwerkstechnik, Technische Universitat, Munich, 1992, 95.


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