Technologies and Applications

Wind Energy

Technologie: Windenergie
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Windenergie

The use of wind energy to generate electricity is among the most widely developed and most used renewable energy technologies, and is on the increase in more and more countries. Because of the economies of scale resulting from falling system costs in production and project development and the high natural potential, wind energy is becoming economically viable in more and more countries. A distinction is made in the wind energy sector between onshore, small wind and offshore turbines.


Onshore wind energy
Nowadays, onshore wind farms are often set up alongside or close to the coast. To achieve high yields, turbines were developed with high towers and long blades that allow for a large sweep area. Mountain tops or elevated positions are particularly suitable for generating wind energy. There is a wide range of wind power plants for all kinds of applications. Two technologies have been developed for the efficient conversion of wind energy into electricity: The gearless system and the classic drive type with variable rotation speed, gears and fast-running generator.


Grid-connected onshore wind power plants
Wind power plants are either grouped together in so-called wind farms or set up as single units, which normally feed their electricity directly into the available grid. When setting up wind farms, the main expense is the connection to the power grid, which includes cables to the overland grid, control units and transformer substations.


Advantages of onshore wind energy
Investment costs are lower than for offshore plants, which need to be positioned, cabled, installed, operated and maintained at sea, in some cases a long way from land. In addition, decentralised onshore electricity generation is carried out closer to centres of consumption, which requires less investment for grid expansion and operation.


Small wind turbines
So far, there is no consistent definition of a small wind turbine. The most common definitions are: The tower is not normally higher than 20 m, and the average capacity lies between 5 and 10 kW. According to IEC standard 61400-2:2006, small wind turbines are those with a maximum rotor area of 200 m², corresponding to a nominal power of about 50 kW at a voltage of below 1,000 volts AC or 1,500 volts DC. Germany’s Wind Energy Association (BWE) distinguishes between three types of small wind turbines: Micro wind turbines (up to 5 kW nominal output), Mini wind turbines (from 5 kW to 30 kW), Medium wind turbines (from 30 to 100 kW).
Small wind turbines are increasingly becoming an alternative for independent and self-sufficient electricity gen-eration. Great potential for this is seen particularly in developing and newly industrialising countries with low electrification rates. Small wind turbines can supply electricity as stand-alone systems or can easily be integrated into existing island networks or hybrid systems. According to a forecast by the World Wind Energy Association (WWEA), the accumulated installed capacity of small wind turbines could reach over 2 GW by 2020.
Advantages of small wind turbines in off-grid regions
In addition to supplying electricity for households, small wind turbines can also replace diesel generators and thus conserve fuel. Combined with other renewable energy technologies such as photovoltaic, these turbines are especially suited for basic electricity supply in off-grid regions.


Offshore wind energy
Offshore wind farms may partly replace conventional power stations in the long term because of the greater capacity utilisation as a result of the higher wind speeds at sea. The expected energy yields here exceed any of those on land by up to 100 per cent. Offshore plants have to be sited, cabled, installed, operated and maintained in deep water. The installation of an offshore wind farm is far more technically demanding than that of an onshore wind farm because of the foundations and a complicated grid connection. The construction stages are much more dependent upon the weather and are largely restricted to the period from April to November. In regular operation exposure to strong wind and waves, together with the effects of salty air pose particular challenges for the materials used. As a result, the system costs are significantly higher than those for onshore plants.

The hub height of a 5 MW offshore wind turbine is currently about 90 metres above sea level. The rotor diameter is approximately 125 m, while the rotor blades cover an area about the size of one and a half football fields. The nacelle is as large as a detached house and weighs up to 400 tons; an offshore wind turbine with a total weight of up to 1,000 tons weighs as much as 250 elephants.

Advantages of offshore wind energy
Offshore wind farms create new opportunities for more jobs, especially for specialised services such as those that focus on the existing requirements at sea. This can benefit economically disadvantaged coastal regions. Wind farms with several hundred megawatts of installed capacity deliver constant electricity and can replace large-scale power plants and provide system services such as frequency stabilisation. Offshore wind energy has low competition for the use of the area of water, since there is little potential for alternative applications.