Windfarm Info In Yesterdays Daily Depress...

http://www.express.co.uk/posts/view/226805/Inefficient-windfarms-raise-cost-of-energy-

Efficiency --- the difficulties using this term with wind power are multiple so opponents will always be able to argue "low efficiency".

a) Even a perfect turbine in a free flow cannot extract more that a bit under 60% of the energy of the fluid passing through it (of the enegry passing through that space were the device not there). The more energy taken per parcel of air passing through the less air can pass through; if you took all the velocity then the air couldn't leave the device so none could enter). Using calculus not hard to compute how much velocity should be taken to maximize the power extracted.

b) Turbines usually have a rating, the mximum power they can produce. But the wind doesn't blow hard enough all of the time to take them there. Efficiency in these terms is horrible for most places on the planet (actual power produced compared to what the device could produce were the winds always as great or greater than the maximum the device could utilize). In truth, this is more properly a "site efficiency" than a device efficiency and measures how costly a device will be (cheaper if the "site efficiency" is high).