Period for Wind Turbines
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
This is one of the main results of a life cycle analysis of wind turbines
done by the Danish Wind Turbine Manufacturers 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
You may download the 16 page report from the Publications
page on this web site.
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
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).
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.
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.