The message
from David Hansen contains these words:

You can download the report on the weather data work from
http://www.eci.ox.ac.uk/publications/downloads/sinden05-dtiwindreport.pdf
In essence they looked at weather records going back to the 1970s
and then compared them the cut in and cut out speeds of wind
turbines. There has been no convincing attack which undermines the
work, though the usual suspects have tried.

Doesn't much help if you are looking for actual figures. Scaling off the
graph appears to show that as much as 60% of the UK would have had
insufficient wind to turn a turbine for 5% of the time and nothing at
all is said about the feeble nature of the wind in the rest of the UK
when that is the case. 5% is some 18 days and if the 1 year/5 year
summe/ winter ratio holds there is still approaching 100 hours of winter
generating time when over half the country wouldn't have a single
turbine turning.

--
Roger Chapman