Future of Wind Energy - Wind Energy Systems for Electric Power Generation - page 169

Table 8.1 Basic comparsion of AC and DC connections
AC

DC

Offshore installation Lower space required Larger space required

Conversion stations Conventional; less cost Converters required; higher

cost

Cable Larger loss at long

connections; cable length
limitation, higher cable cost

Lower cable cost; lower loss
at long connections

Table 8.2 HVDC design features as compared with the classical concept
Classical DC

Advanced-DC

Power semiconductors Thyristors GTOs, IGBTs, IGTCs

Switching frequency Grid frequency (50, 60 Hz),

phase control

Some kHz, PWM control

Filter devices High Low

Reactive power Reactive power supply from

grid required

Reactive power can be
supplied to grid (up to
converter rating)

Stability at no-load No, at intermittent current Yes

Maximum system
ratings

Up to 1200 MVA , ± 500 kV Up to 500 MVA , ± 150 kV

Flora, Habitat)-Guideline of 1992. A special guideline on wild-living birds was
published already in 1979.
A point of discussion is in how far wind turbines are a danger for flying bird
swarms. Available experience indicates that birds' collisions with turbines are
scarce; they even suggest that rotating rotors are better seen and avoided than
less than at standstill. It seems that HV overhead lines are more dangerous for
birds then are wind turbines.
Taking the German North Sea and the Baltic Sea as example areas, an
overview of the state of ecological research is found in [Koel06].

- Acceptance issues
Wind turbines constitute an intervention in the landscape (viewshed) and give
rise to noise emission and vibration, not principally different from systems on
land. Other source of concern are of socio-economic nature, e.g. by fisheries.
- Physical and sea traffic issues
Implications of electromagnetic fields due to undersea cable connection should
be assessed. On the other hand, risks of collision for boating and ships' traffic
require consideration. In a broader sense, hydrographic and coastal effects of
WES installation on sea are a cause for inspection.