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.
Wind Turbine Selection Should Reflect:
- Wind profile at site
- Technology availability
- Electricity production and investment cost
- Experience of similar models
- Experience of similar climatic conditions
- Size of site
- Capacity availability at grid access point
- Noise level certification
- Warranty and maintenance costs
Popular modern horizontal axis wind turbines (HAWT) employ 3 distinct technology types:
Turbines that run at one rated speed regardless of wind speeds. A constant speed turbine will stall when the wind becomes too strong. Constant speed turbines are robust and relatively cheap but are liable to mechanical stress, aerodynamic efficiency and noise.
Variable Speed Double Feed Induction Generator (DFIG)
Because the DFIG turbine runs at variable speeds it offers greater aerodynamic efficiency than the constant speed turbines and lower noise levels. The stress on the gearbox is lowered using variable speed generators. The improved performance naturally comes at an increased initial investment cost.
Variable Speed Direct Drive (DD)
Direct drive generators eliminate the gearbox (and therefore, any subsequent gearbox problems) completely. They offer improved performance through her choice of components utilised but are the most expensive initial investment cost option because of this. It is vital that experienced independent professional advice is sought when choosing which wind turbine is most suitable for each specific wind farm.
Wind Farms In Ireland
Today, wind energy provides electricity to the equivalent of 40 million European citizens, and wind farms in Ireland supply enough clean green power to support over 146,000 users, equivalent to the domestic electricity needs of County Cork. Locations of wind farms in Ireland are detailed on our interactive Wind Map . You can also access this information on our List of Existing Wind Farms in Ireland.
Wind Energy Generating Plants
There are currently 35 on-shore and one offshore wind energy projects in operation in the Republic of Ireland with a total installed capacity of 230.8 Megawatts.
Wind Farm Development
Wind energy is a growth industry across Europe. Today, nearly all European countries, including Ireland, have considerable programmes for wind turbine installation.
Wind turbine technology continues to grow especially in relation to installing wind turbines at sea (offshore wind farms). 4.5 MW machines already exist and turbines of 7.5 or even 10 MW are currently being developed.
Since the first commercial wind farm in Ireland at Bellacorrick, Co. Mayo in 1992, an increasing number of projects are appearing in all regions of Ireland. As the economics of wind projects become more favourable and attractive many more areas across the country will be suitable for wind turbines.
By the end of 2003 there were 31 grid connected wind farms in the Republic of Ireland, the power output of these wind turbines totalling 190 MW (1 megawatt = 1 thousand kilowatts) generating enough green electricity to supply almost 125,000 homes, equivalent to a city the size of Limerick. A number of other projects were under construction and many more granted planning permission. The total power output should exceed 500 MW by the end of 2005.
Wind Energy Programmes
The European models for wind energy programmes are Germany, which owns half of the continent’s installed power, Spain and Denmark. In 2002 wind turbines supplied 1.5% of Europe’s electricity consumption, with Germany (over 12,000MW installed rated capacity), Spain and Denmark the top contributors.
In order to realise the potential that exists for a successful Irish wind industry, we can draw on the experience of other countries. This way the concerns and issues that can prove to be obstacles for the establishment of wind farms may be by-passed.
Visual Impacts and Landscape Integration.
To ensure that wind farms are sited appropriately and sensitively there are several rules that developers should adhere to:
- Visual harmony and balance - choice of turbines, towers, colour and implementation
- Keep secondary structures to a minimum - bury on site cabling, minimal fencing, transformers inside towers where possible
- Keep access roads to a minimum - use established roads where possible and follow natural contours if roads are necessary
- Manage the 'building site' - remove waste, avoid erosion, replant the land
- Ensure careful maintenance - a wind turbine is designed to work - if one is stopped among others working it will create disturbance and confusion.
Even though the benefits of wind energy to the global and local environment are widely acknowledged, fears and concerns still surface when discussing this new energy source for the first time.
Wind Turbines and Noise
It would be incorrect to suggest wind turbines are silent. The perception that wind farms are noisy developments is also inaccurate. Since the early days of wind farm development great strides have been taken to minimise the mechanical noise associated with the drive train of the wind turbine.
Noise levels measured at the base of modern wind turbines typically ranges between 50 and 55dB(A); similar to the day to day noise you would expect to hear in a typical office environment.
The other type of noise is aerodynamic and is related to the movement of the blades - the ‘swooshing’ as they pass through the air. This type of noise has been lowered by the employment of larger blades that turn more slowly. The noise of the wind generally camouflages this noise when it is blowing and the turbines do not turn during calm periods and thus do not emit any noise.
Manufacturing wind turbines
Wind turbines are large complex industrial equipment and their manufacture involves the use of raw materials and energy. The materials used can be recycled at the end of their useful life (the capital from this can be used to reestablish a wind farm site to it’s original state). The energy used in the manufacture of a wind turbine is typically made back within 3 months of the turbine becoming operational.
Celebration of wind farms
Sensitively designed and appropriately sited wind farms not only provide clean energy with minimal impact, they can become icons in the landscape which the public can associate with their locality.
The very low footprint of the wind turbines themselves mean that the land taken up by roads and foundations on a wind farm site is usually between 2 and 4%. This allows the land retain it’s original use - farm work can continue around the wind turbines - be it livestock or crops.
Wind farms can offer markers for hikers and ramblers cyclists and walkers. Their size will attract attention and information displayed at the site can educate regarding the benefits of wind energy. Wind farms should be seen as the providers of a clean and reliable power source. What could provide a greener image than the knowledge that energy is being respectfully and sustainably used from a source as clean as wind.