Wind energy turns out to have a complication: reliability

Engineers have cut the cost of electricity derived from wind by about 80 percent in the last 20 years, setting up this renewable technology for a major share of the electricity market.

But for all its promise, wind also generates a big problem: Because it is unpredictable and often fails to blow when electricity is most needed, wind is not reliable enough to assure supplies for an electricity grid that must be prepared to deliver power to everybody who wants it — even when it is in greatest demand.
International Herald Trribune