Renewable Energy Wind - On the Effect of Offshore Wind Farms on the Atmosphere and Ocean Dynamics - page 9

have a really weak effect on ocean dynamics; they just support weak vertical
mixing, which leads to very small changes, being smaller than natural variability
(Burchard et al. 2008 ).
However, the hub height of the tower and the rotor diameter show an increase
through time, having a common height of 135 m and a common diameter of 126 m
in 2008.
As mentioned, onshore wind turbines become bigger to catch stronger winds,
which are less influenced and weakened by surface friction (through bushes, tress,
and other surface constitutions), which again supports a higher energy production.
In case of offshore wind farming, it is not necessary to counteract wind reduction by
surface friction because ocean surface friction is less and no structures disturb the
wind filed. Therefore, wind is quite consistent in offshore areas, as well as strong
enough to allow lower towers that provide the same capacity like much higher
onshore turbines. For example, a capacity of 3,000 kW can be reached by 80 m
offshore towers, while at onshore, a hub height of 110 m is required (BWE 2014 ).
Meanwhile, in dealing with offshore cases, hub heights of used towers are set to
80 m.
2.2 Wind Farming in the North Sea: Example Germany
The advantages of offshore wind farms regarding space, productivity, and minor
harassment of humans support constructions of wind turbines in the North Sea. The
use of the German part of North Sea for wind farming is the only possibility to reach
political energy aims mentioned in the introduction of the topic. Wind farming in
the North Sea is used by the United Kingdom, the Netherlands, Belgium, Norway,
and Denmark. Based on statistics of LORC Knowledge, a Danish database
collecting all offshore information supervised by Lindoe Offshore Renewable
Center, North Sea, has the strongest offshore wind farm development besides
China. Germany cabs tap the potential of offshore wind farming in the North Sea.
The following section will shortly define the North Sea and its availability for use
of OWFs.
2.2.1 The North Sea
The North Sea is located in Europe, having coasts to Norway, Great Britain, France,
the Netherlands, Germany, and Denmark. It is defined as a shallow shelf sea with a
mean depth of 80 m and a maximum water depth that is in the Norwegian Trench of
about 800 m (S¨ndermann and Pohlmann 2011 ; Mathis 2013 ). The North Sea has
got a strong tide and is famous for its Wadden Sea, declared as UNESCO world
culture heritage.