Hi Don, thank you for your great question.
The comparison of energy used in manufacture of a wind turbine with the energy produced by that turbine is known as the ‘Energy Balance’ i.e. the time needed to generate the equivalent amount of energy that was required for its manufacture and construction.
Typically a wind turbine will produce enough clean electricity in a matter of 6 – 18 months (depending on variables including turbine type, project size, average wind speed, etc.) to offset all of the greenhouse gas emissions emitted in its manufacture – in addition it will produce clean electricity for another 20-25 years.
Several studies have looked at this question over the years and have concluded that wind energy has one of the shortest energy payback times of any energy technology.
The National Renewable Energy Laboratory published a large volume of studies on the Life Cycle Analysis of GHG emissions for a number of different sources of electricity, including wind energy. All of the studies can be obtained at the following link: http://onlinelibrary.wiley.com/doi/10.1111/jiec.2012.16.issue-s1/issuetoc.
(Question answered Feb. 2013)