Wind Power Generation - Renewable Energy: Technology, Economics and Environment - page 341

With regard to offshore wind parks it is expected that additional investment
costs will considerably exceed those of onshore wind parks due to the increased
foundation and grid connection costs. Current estimates assume additional in-
vestment costs of 70 to 105 % of the actual converter investment. The costs de-
pend tremendously on the water depth and the distance from the shoreline.
Operation costs. Operation costs include land lease expenses, insurance, mainte-
nance and repair as well as technical operation. As data are based on solely a few
years of experience, for the most common commercially available converters, cost
estimates vary tremendously. However, the average annual costs are estimated at
5 to 8 % of the total investment costs (Table 7.3), whereas maintenance, service,
repair, insurance and land lease costs account for the major share. However, ad-
ministrative and managerial costs are also relevant. For offshore wind parks, by
contrast, significantly higher expenses for maintenance, repair and insurance are
expected.
Electricity generation costs. Specific power generation costs may be determined
by annuity calculation derived from the total investments, the annual costs as well
as the expectable energy yields. As usually a real discount rate of 4.5% and an
amortisation period corresponding to the technical converter service-life of 20
years are assumed. Furthermore, constant operation costs are assumed for the en-
tire service-life.
Table 7.3 shows the power generation costs pertaining to three converter types
defined in Table 7.2 located at the three reference sites. According to the figure,
power generation costs decrease tremendously with an increasing yearly full load
hour and thus an increasing mean wind velocity.
Sites with annual mean wind speeds that allow for 4,500 h/a are very rare and
can only be found very close to the coast especially on windy islands or in very
exposed locations on shore. The power generation costs corresponding to these
conditions range from 0.030 to 0.033 €/kWh for the conditions analysed here.
Compared to that, sites with 2,500 h/a are more frequently available at good loca-
tions close to the coast. Under these conditions average real specific power
generation costs between 0.054 and 0.059 €/kWh could be achieved. If the full
load hours are even lower (e.g. 1,800 h/a) the electricity provision costs increase
significantly (Table 7.3). Comparisons of different converter technologies with
different installed capacities do not reveal any significant difference in terms of
power generation costs for the same wind speeds respectively for the same full
load hours.
Independent of the above observations, especially for the capacity range from
50 to 1,000 kW, which play no significant role in Europe any more, specific
power generation costs decrease with increasing turbine capacity. This is mainly
due to the tendency towards reduced investment costs and increased tower heights
for enhanced capacities which permits to achieve higher wind speeds at hub
height at the same site as the mean airflow speed increases with increasing height