Renewable Energy Wind - On the Effect of Offshore Wind Farms on the Atmosphere and Ocean Dynamics - page 7

century in the mid-western United States. They were mainly used for water
pumping. Proposed by the Danish government, which is looking for possibilities
to supply rural areas with electricity, Danish professor Poul La Cour built in 1891
an experimental wind turbine driving a dynamo in Askov, Denmark. While in the
past windmills were mainly used for transforming wind energy into mechanical
energy, generating electricity is prioritized today.
Enhancing Poul La Cour s construction, nowadays wind turbines comprise a

huge development in engineering. A sophisticated technique transforms wind
energy into electricity by controlling the blades and the turbine ' s conditions,
focusing on high efficiency. Over the years, wind turbines of a high technical
standard were developed to transform wind energy into electrical power.

'

2.1.1 Today ' s Wind Turbines

The main concept of windmill nowadays is a tower, mostly three rotor blades and a
turbine in a nacelle (Morris 2006 ). Such a wind turbine is illustrated in Fig. 2.1 .
Today, various turbines are available for different conditions and power sup-
plies. The first turbines dealt with energy of 2 megawatts (MW). Now 5-MW
turbines are common, but the turbines will be developed by ten, 15 (promoted by
Spanish companies Gamesa, Iberdrola, and Acciona in 2010), and maybe more in
future times. The diameter of the rotor started with a couple of meters; 80 to a 100 m
are currently used, and bigger rotor blades up to 200 m are in the testing phase
(Vestas Wind Systems 2013 ).
With regard to energy production, there exist two different styles of nacelles—
construction with gear mechanism and one without gear mechanism. As regards
construction with gear mechanism, the power is lead from a rotating motion of the
rotor through a driveshaft and gear in the dynamo. A dynamo can only work with a
high driving speed, which cannot be supported by wind turbines. This issue is
solved with the help of the gear, which transforms power with low driving speed
and high turning moment into power with high driving speed and low turning
moment. In contrast, constructions without gear have an advantage of less machine
components. This means less rotating materials, hence less maintenance works.
Therefore, they are proposed for offshore turbines where maintenance is compli-
cated, time and cost intensive, and weather dependent.
Such constructions offer a synchronous generator activated by a permanent
magnet. They transform the rotor motion directly into electricity. In sum, nearly
45 % of wind energy can be transformed into electrical power (BWE 2014 ). The
rest is lost during the transformation process. Around 41 % of wind energy cannot
be extracted; the rest of 59 % is reduced by aerodynamic rotor losses, mechanical
losses, and electrical losses through the driveshaft and generator (BWE 2014 ).
Wind turbines need a strong basement structure to fix them. On one hand, a
rotating turbine leads to imbalance and vibration during rotation; on the other hand,
wind and waves exert force on construction. While onshore turbines mostly fixed by