Energy Payback Period for Wind Turbines
Two to Three Months Required
Modern wind turbines rapidly recover all the energy spent in manufacturing, installing, maintaining, and finally scrapping them. Under normal wind conditions it takes between two and three months for a turbine to recover all of the energy involved.
This is one of the main results of a life cycle analysis of wind turbines done by the Danish Wind Industry Association.
The study includes the energy content in all components of a wind turbine, and it includes the global energy content in all links of the production chain.
Input Output Analysis Method
To find the results, the study employs a so called input output model of the Danish economy published by the Danish Central Bureau of Statistics. The input output model divides the economy into 117 sub sectors, and accounts for the flows of 27 different energy goods (fuels etc.) between the 117 sectors.
The basic advantage of using this method instead of engineering calculations, is that we are able to account properly for the amount of energy used by producers of components and manufacturing equipment, buildings etc. in all links of the production chain. The result is a large 117 by 117 table of energy flows. (Doing a mathematical operation on the table called matrix inversion we obtain the amount of energy per dollar of output).
The Energy Balance for Offshore Wind Turbines
Offshore wind turbines may have a slightly more favourable energy balance than onshore turbines, depending on local wind conditions. In Denmark and the Netherlands, where wind turbines onshore are typically placed in flat terrain, offshore wind turbines will generally yield some 50 per cent more energy than a turbine placed on a nearby onshore site. The reason is the low roughness of the sea surface.
On the other hand, the construction and installation of foundations require 50 per cent more energy than onshore turbines.
It should be remembered, however, that offshore wind turbines have a longer expected lifetime than onshore turbines, in the region of 25 to 30 years. The reason is that the low turbulence at sea gives lower fatigue loads on the wind turbines.
Analysis of 1980 Vintage Turbines
1980 wind turbines do surprisingly well in the studies of the energy balance. The analysis shows that while small Danish 1980 turbines of 10-30 kW took almost a year to recover the energy spent in manufacturing, installing and decommissioning them, turbines of 55 kW took some 6 months to recover all of the energy.
© Copyright 1997-2003 Danish Wind Industry Association
Updated 10 May 2003
http://www.windpower.org/en/tour/env/enpaybk.htm
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