I'm not sure why people are so concerned with wind turbine efficiency?
In the case of a nuclear, coal, oil or gas fired power station the efficiency is critical because if the efficiency is low we are using up a valuable natural resource for little benefit, i.e. wasting that resource.
In the case of a wind turbine, the efficiency is measured as the useful energy produced as electricity relative to the total available wind energy flowing through the area swept out by the turbine blades. From an economic point of view the higher this is the better but that wind energy is flowing through that area of space whether we harness any of it or not. Nothing is actually wasted. The efficiency has steadily increased since wind turbines were first used and will no doubt continue to increase as the technology matures.
A more useful measure is the cost per kWh compared to other technologies. This has to include construction costs, production costs and any decommissioning costs. Those figures may be a bit different from what people imagine? See for example http://nuclearfissionary.com/2010/04/02 ... and-solar/
This example is a pro-nuclear site so we probably suspect that the nuclear figures might be a bit optimistic but it has no advantage to be gained from presenting low wind figures. If you do some searching you will find plenty of sites that quote figures for wind generation that are comparable with other sources. It is also worth noting that the construction costs per kWh are steadily reducing as the number in service increases, as occurs with most products, i.e. economies of scale. If you follow the link for operational costs per kWh for wind from the above link you will also see that the more modern bigger turbines have a much lower operating cost than smaller turbines and much less than older turbines. I suspect that a lot of the negative publicity is based on figures for older turbines.
There is still one major problem for all renewables and that is the problem of storage. The wind does not blow all the time. The sun does not shine all the time. Wave energy is related to wind energy so is also variable and available tidal energy varies with a fortnightly cycle. Non of these are a major problem as long as renewables are providing a small proportion of the total energy consumed, e.g. less than 20 %, but become massive problems as the proportion increases. Storage is relatively easy on a small scale installation, e.g. to power a single dwelling but becomes very difficult as the generation is scaled up.