Apparently the Times has a story on the continuing failure of windmills to deliver sufficient energy. It's not online, but this looks like the key excerpt (H/T Philip Bratby)
Concern over huge fluctuations in the supply of electricity from Britain’s 3,000 wind turbines has prompted National Grid to begin detailed forecasts of wind strength.
The turbines have delivered well below their usual output this winter and in the 24 hours to 5pm yesterday contributed only 0.5 per cent of the country’s power. Parts of the day were so still that wind power’s contribution fell below 0.2 per cent. On the windiest days, the turbines deliver about 8 per cent. A record of 10 per cent over a 24-hour period was set on September 6 last year.
But since the beginning of December, turbines have been operating at only 20 per cent of their maximum capacity compared with an annual average of about 30 per cent.