60The Kentish Flats wind farm in the Thames Estuary...
See www.kentishflats.co.uk. 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% [ ]. 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,
www.bwea.com. 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