|Region||depth 5 to 30 metres||depth 5 to 30 metres|
compared with that of Kentish Flats, £1.2 per watt (£105 million for 90 MW).
It’s possible that floating wind turbines may change the economics of deep
60The area available for offshore wind.
The Department of Trade and Industry’s (2002) document “Future Offshore”
gives a detailed breakdown of areas that are useful for offshore wind power.
Table 10.7 shows the estimated resource in 76 000 km2 of shallow and deep
water. The DTI’s estimated power contribution, if these areas were entirely
filled with windmills, is 146 kWh/d per person (consisting of 52 kWh/d/p
from the shallow and 94 kWh/d/p from the deep). But the DTI’s estimate
of the potential offshore wind generation resource is just 4.6 kWh per day
per person. It might be interesting to describe how they get down from this
potential resource of 146 kWh/d per person to 4.6 kWh/d per person. Why
a final figure so much lower than ours? First, they imposed these limits: the
water must be within 30 km of the shore and less than 40 m deep; the sea
bed must not have gradient greater than 5°; shipping lanes, military zones,
pipelines, fishing grounds, and wildlife reserves are excluded. Second, they
assumed that only 5% of potential sites will be developed (as a result of
seabed composition or planning constraints); they reduced the capacity by
50% for all sites less than 10 miles from shore, for reasons of public ac-
ceptability; they further reduced the capacity of sites with wind speed over
9 m/s by 95% to account for “development barriers presented by the hostile
environment;” and other sites with average wind speed 8–9 m/s had their
capacities reduced by 5%.
61...if we take the total coastline of Britain (length: 3000 km), and put a strip of
turbines 4 km wide all the way round... Pedants will say that “the coastline
of Britain is not a well-defined length, because the coast is a fractal.” Yes,
yes, it’s a fractal. But, dear pedant, please take a map and put a strip of
turbines 4 km wide around mainland Britain, and see if it’s not the case that
your strip is indeed about 3000 km long.
–Horns Reef (Horns Rev). The difficulties with this “160 MW” Danish wind
farm off Jutland [www.hornsrev.dk] are described by Halkema (2006).