Notes and further reading

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60The Kentish Flats wind farm in the Thames Estuary...
See Its 30 Vestas V90 wind turbines have a total
peak output of 90 MW, and the predicted average output was 32 MW (as-
suming a load factor of 36%). The mean wind speed at the hub height is
8.7 m/s. The turbines stand in 5 m-deep water, are spaced 700 m apart, and
occupy an area of 10 km2. The power density of this offshore wind farm was
thus predicted to be 3.2 W/m2. In fact, the average output was 26 MW, so the
average load factor in 2006 was 29% [wbd8o]. This works out to a power den-
sity of 2.6 W/m2. The North Hoyle wind farm off Prestatyn, North Wales,
had a higher load factor of 36% in 2006. Its thirty 2 MW turbines occupy
8.4 km2. They thus had an average power density of 2.6 W/m2.

...shallow offshore wind, while roughly twice as costly as onshore wind, is
economically feasible, given modest subsidy
. Source: Danish wind associa-

...deep offshore wind is at present not economically feasible.
Source: BritishWind Energy Association briefing document, September 2005, Nevertheless, a deep offshore demonstration project in 2007
put two turbines adjacent to the Beatrice oil field, 22 km off the east coast
of Scotland (figure 10.8). Each turbine has a “capacity” of 5 MW and sits in
a water depth of 45 m. Hub height: 107 m; diameter 126 m. All the elec-
tricity generated will be used by the oil platforms. Isn’t that special! The
10 MW project cost £30 million – this price-tag of £3 per watt (peak) can be

Figure 10.6. Birds lost in action. Annual bird deaths in Denmark caused by wind turbines and cars, and annual bird deaths in Britain caused by cats. Numbers from Lomborg (2001). Collisions with windows kill a similar number to cats.