Introduction - Wind Power Integration: Connection and System Operational Aspects - page 11

1.5.1 Offshore wind
Offshore wind energy has several attractions, including huge resources and mini-
mal environmental impacts. In Europe the resources are reasonably well located
relative to the centres of electricity demand.
Wind speeds are generally higher offshore than on land, although the upland
regions of the British Isles, Italy and Greece do yield higher speeds than offshore.
Ten kilometres from the shore, speeds are typically around 1 m/s higher than at the
coast. There are large areas of the North Sea and Baltic with wind speeds above
8 m/s at 50 m (Hartnell and Milborrow, 2000). Turbulence is lower offshore, which
reduces the fatigue loads. However, wind/wave interactions must be taken into
account during design. Wind speeds are inevitably less well characterised than
onshore, but accurate estimates are needed to establish generation costs. Potential
offshore operators are currently making measurements and further studies are also
underway.
Denmark, Sweden, Belgium, the Netherlands, Germany, the United Kingdom
and Ireland were early entrants into the offshore market. They have already built
wind turbines in marine environments, either in the sea or on harbour breakwaters.
Further activity is planned, more recently including Italy, Norway and China.
Several manufacturers are now offering machines specifically for the offshore
market. Most are in the range 3-6 MW in size and with design modifications such
as sealed nacelles and special access platforms for maintenance. Larger machines
tend to be more cost effective, because the more expensive foundations are at least
partially justified by a higher energy yield.
The construction, delivery to site and assembly of the MW-size machines
demands specialist equipment, suitable ports and careful timetabling to maximise
the possibilities of calm weather windows. Although it was anticipated that access
for maintenance might be a problem, early experience from Danish installations is
encouraging, although, again, experience from some of the more hostile seas is
still lacking.

1.6 Economics

1.6.1 Wind turbine prices
Large machines have been developed as they offer lower costs, as well as better
energy productivity, as discussed earlier. Machine costs (per unit area of rotor) fall
with increasing size, and the use of larger machines means that fewer machines are
needed for a given amount of energy, and so the costs of transport, erection and
cabling are all reduced.

1.6.2 Electricity-generating costs
There is no single answer to the question, what is the generation cost of wind, and
is it economic? The capital costs depend on the nature of the site and the
ease (or difficulty) of access. Remote onshore or offshore sites will inevitably incur