Wind Energy

The sun heats the earth unevenly, creating thermal air currents. In order to achieve equal temperatures around the earth these air pockets move about the earth as global wind. The energy that travels in the wind can be captured and converted to provide electricity.

Wind energy provides a clean, sustainable solution to our energy problems. It can be used as an alternative to fossil fuels in generating electricity, without the direct emission of greenhouse gases. And there will always be wind; it is inexhaustible and renewable.

It is envisaged that wind power will make the most significant contribution to the achievement of national and international targets for green electricity, due to its environmental benefits, technological maturity and increasing competitiveness.

Wind Energy Converters

Since the beginning of the 20th century numerous types of wind turbine have been tested to identify the most effective designs to capture the energy in the wind. Present day wind turbines may vary in their appearance particularly in relation to size.

Development trends are towards larger turbines that use higher towers to avail of the higher wind speeds further from the ground. They also use longer blades to maximise the energy capture from the wind.

These turbines use proportionately less raw materials than smaller turbines and require a smaller ground area per power output than their smaller predecessors. Larger turbines have the advantage of a slower blade rotation than smaller turbines. For reasons of visual harmony, projects should incorporate the same turbine types and ensure that the blades of each turbine rotate in the same direction.

How a wind turbine works

Most wind turbines operating commercially today in Ireland consist of 3 rotor blades that rotate around a horizontal hub. The blades face into the wind and rotate as the wind passes through them. The rotor is connected to a nacelle (a housing for the transmission equipment) that is located at the top of a tower to ensure a higher and less interrupted wind flow.

Wind turbines start operating at approximately 4 – 5 metres per second (approximately 16-18 km.p.h.) reach a maximum output at 12 – 14 m/s and automatically shut down for safety at wind speeds greater than 25 m/s (approximately 80 km.p.h.).

The rotating motion is accelerated through the turbine transmission (which usually includes a gearbox) into the generator that converts the motion to electricity. When more air passes through the blades, more electricity can be produced.

The low voltage electricity from the generator is stepped up through a transformer to match the national grid voltage. The electricity is transported from the wind turbine to the grid along electric cables which may be buried underground within the wind farm site.

Choosing a Wind Turbine

Wind turbines are available in various sizes from a number of wind turbine manufacturers, agents and developers. Size however is not the only aspect of the wind turbine that should be thoroughly investigated by developers when deciding which turbine to use with their project.

The wind profile and wind speeds at each specific site need to be evaluated to identify which turbine is suitable for the particular site conditions. As the wind turbine itself may be as much as 70% of the total project cost it is vital that it produces optimal electricity for the given site. To assist the decision, manufacturers are requires to classify their turbines in accordance with International standards (IEC 61 400-1 second edition 1999-02).

The most common wind turbine installed these days is between 750 kW and 2.5 MW. A 750 kW machine may have a rotor 48 metres in diameter with the nacelle perched on the tower at a height of typically 45 metres above the ground, which with the blades, gives a total height of about 70 metres.

For a 2.5 MW wind turbine the rotor diameter may be up to 70 or 80 metres with the nacelle typically located 80 metres above the ground and a maximum blade tip height of almost 120 metres. Improvements in turbine design and efficiency means that we can expect wind turbines to continue to increase in size for some time yet. Where larger turbines are used, less are required to produce the equivalent power output achieved by a greater number of the their smaller predecessors.

Content courtesy of Sustainable Energy Authority of Ireland