The London Array offshore wind farm will make a crucial contribution to the UK’s renewable energy targets.James Smith, chairman of Shell UK
Electric power is too vital a commodity to be used as a job-creation programme for the wind turbine industry.David J. White
At sea, winds are stronger and steadier than on land, so offshore wind
farms deliver a higher power per unit area than onshore wind farms. The
Kentish Flats wind farm in the Thames Estuary, about 8.5 km offshore from
Whitstable and Herne Bay, which started operation at the end of 2005, was
predicted to have an average power per unit area of 3.2 W/m2. In 2006, its
average power per unit area was 2.6 W/m2.
I’ll assume that a power per unit area of 3 W/m2 (50% larger than our
onshore estimate of 2 W/m2) is an appropriate figure for offshore wind
farms around the UK.
We now need an estimate of the area of sea that could plausibly be cov-
ered with wind turbines. It is conventional to distinguish between shallow
offshore wind and deep offshore wind, as illustrated in figure 10.2. Conven-
tional wisdom seems to be that shallow offshore wind (depth less than 25–
30 m), while roughly twice as costly as land-based wind, is economically
feasible, given modest subsidy; and deep offshore wind is at present not
economically feasible. As of 2008, there’s just one deep offshore windfarm
in UK waters, an experimental prototype sending all its electricity to a
nearby oilrig called Beatrice.
Within British territorial waters, the shallow area is about 40 000 km2, most
of it off the coast of England and Wales. This area is about two Waleses.
The average power available from shallow offshore wind farms occu-
pying the whole of this area would be 120 GW, or 48 kWh/d per person.
But it’s hard to imagine this arrangement being satisfactory for shipping.
Substantial chunks of this shallow water would, I’m sure, remain off-limits
for wind farms. The requirement for shipping corridors and fishing areas
must reduce the plausibly-available area; I propose that we assume the
available fraction is one third (but please see this chapter’s end-notes for
a more pessimistic view!). So we estimate the maximum plausible power
from shallow offshore wind to be 16 kWh/d per person.
Before moving on, I want to emphasize the large area – two thirds of
a Wales – that would be required to deliver this 16 kWh/d per person. If