Standard windmill properties

The typical windmill of today has a rotor diameter of around 54 metres
centred at a height of 80 metres; such a machine has a “capacity” of 1 MW.
The “capacity” or “peak power” is the maximum power the windmill can
generate in optimal conditions. Usually, wind turbines are designed to
start running at wind speeds somewhere around 3 to 5 m/s and to stop if
the wind speed reaches gale speeds of 25 m/s. The actual average power
delivered is the “capacity” multiplied by a factor that describes the fraction
of the time that wind conditions are near optimal. This factor, sometimes
called the “load factor” or “capacity factor,” depends on the site; a typical
load factor for a good site in the UK is 30%. In the Netherlands, the typical
load factor is 22%; in Germany, it is 19%.

Other people’s estimates of wind farm power per unit area

In the government’s study []
the UK onshore wind resource is estimated using an assumed wind farm
power per unit area of at most 9 W/m2 (capacity, not average production).
If the capacity factor is 33% then the average power production would be
3 W/m2.

The London Array is an offshore wind farm planned for the outer
Thames Estuary. With its 1 GW capacity, it is expected to become the
world’s largest offshore wind farm. The completed wind farm will consist
of 271 wind turbines in 245 km2 [6o86ec] and will deliver an average power
of 3100 GWh per year (350 MW). (Cost £1.5 bn.) That’s a power per unit
area of 350 MW/245 km2 = 1.4 W/m2. This is lower than other offshore
farms because, I guess, the site includes a big channel (Knock Deep) that’s
too deep (about 20 m) for economical planting of turbines.

I’m more worried about what these plans [for the proposed London Array wind farm] will do to this landscape and our way of life than I ever was about a Nazi invasion on the beach.

Bill Boggia of Graveney, where the undersea cables
of the wind farm will come ashore.
Figure B.8. The qr5 from Not a typical windmill.