New research from the journal Energy Policy sheds some light on the UK’s experience with wind power and its most damning drawback: variability. As my good friend and fellow Planet Gore contributor Sterling Burnett writes:

Because wind is an intermittent resource, wind farms must rely on conventional power plants to back up their supply. Wind farms generate power only when the wind is blowing within a certain range of speed. When there is too little wind, the towers don’t generate power; but when the wind is too strong, they must be shut down for fear of being blown down. And even when they function properly, wind farms’ average output is less than 30 percent of their theoretical capacity.

Even according to the American Wind Energy Association, “A reasonable capacity factor would be 0.25 to 0.30. A very good capacity factor would be 0.40.”

Europe’s experience with offshore wind turbines also highlights wind’s volatility and intermittent nature:

They start generating electricity when the wind speed reaches nine miles per hour, and have to shut down if it exceeds 55 mph. They generate electricity somewhere between 70 percent and 90 percent of the time, but in lower wind speeds much less than their capacity. According to an analysis by Denmark’s Incoteco energy consulting firm, in 2002 there were 54 days in western Denmark on which the wind power systems ‘supplied less than 1% of demand.’

As opposed to peak demand occurring in the winter in the UK, here in Texas, peak demand is during the summer, when wind blows the least. The Electric Reliability Council of Texas, which manages about 85 percent of Texas’ electric grid, relies on just 8.7 percent of wind power’s capacity when determining available power during peak summer hours. Not exactly there when we need it.

Regardless of when peak demand occurs, the wind doesn’t always blow. Meanwhile, the traditional power sources we count on to deliver reliable, affordable energy are there to back up the turbines. As are the subsidies and tax credits.