Roger wrote:
The message
from David Hansen contains these
words:

For one turbine.

They do come in groups, and wind doesn't vary significantly across
one installation however large.

The average velocity over a relatively long time period doesn't vary
significantly, though gusts can do and can be watched progressing
past farms on occasion.

However, that's beside the point. While the wind at one farm may be
less than forecast it is likely at the same time to be higher at
another farm.

Your point is beside the point, another red herring in fact. Get the
translation velocity wrong and wind speeds changes will indeed lag or
lead but forecast the wrong wind speed for one place and the
likelihood is that the errors for hundreds of miles around will all
be the same sign since they all depend on the predicted pressure
gradients in the local disturbance.

And errors in forecasting are a minor blot on the landscape compared
with the unavoidable consequence of lack of wind. The 1 hour/90%/5
years nonsense may well be completely accurate but unfortunately it is
completely irrelevant. What matters is the situation at the wind farm
sites but trying to find out any information about the extent of
low/non existent output with the current set-up is possibly
impossible.

I drove almost the whole length of Wales at the end of October last
year. Not a breath of wind the whole way (not even on the top of a few
minor hills) and I doubt very much whether there was a single wind
turbine turning either in Wales or in a sizeable chunk of adjacent
England and winds would have been light even further afield.

I'm all for wind turbines as a part of the mix, but they can only be that.
We do experience periods when anticyclonic weather affects large parts of
the UK at one time.