What is the energy efficiency of wind?
Approximately 20 percent
There are many factors that affect production of electricity using wind turbines. Topography, wind availability, maintenance/care of the systems, failures, etc. are some of them.
According to one article (Telegraph, 2011) wind energy efficiency was found to be 22% in the UK.
You can read the full story: http://www.telegraph.co.uk/news/earth/energy/renewableenergy/8236254/Wind-turbines-less-efficient-than-claimed.html