What is wind energy?

A wind turbine is a system that converts the kinetic energy of the wind into electricity. Electricity produced this way is often referred to as wind energy.

The turbines can be individual or grouped in wind farms and can be placed onshore as well as offshore. They differ in size and power, from small, residential wind systems to larger, commercial turbines. Based on power they can be from 2 kilowatt (kW) to 8 megawatt (MW). For wind energy to be viable, the wind speed should be at least 5m/s average.

Types of ownership

Wind turbines can be owned by either development companies, citizens or a partnership between them.  The issue of ownership has been one of the major problems in the development of wind energy in Ireland. Big companies have proposed wind farms having at least 8 turbines of 2.5 or 3MW capacity. But wind energy can be developed by citizens as well, either as a farm through Co-operative or community ownership or just small capacity wind turbines owned by a family – residential wind turbines.

Based on the capacity and purpose, wind turbines can be:

  • Residential
  • Commercial
What is a residential wind turbine?

A residential wind system is comprised of a turbine that has the capacity to produce enough electricity to power a house. The electricity for an average household can be supplied by a 5kW turbine, with a height of around 25m (80ft.) and a diameter of 5.5m (18ft.). Residential wind turbines can vary from 2kW to 10kw, with a height between 9 and 42m (30 – 140 ft.) and a diameter between 3.5 and 7.7m (12 – 25 ft.).


Residential wind turbines

Residential wind turbines

What is a commercial wind turbine?

Wind turbines used to supply energy for a community or that are part of wind farms tend to be of higher power, usually over 100kW capacity. The turbines that comprise most of the wind farms are between 2MW and 5MW, but there are some of higher capacities. The biggest one is 8MW and is developed by a Danish company, having the rotor diameter of 164m – a swept area of more than 21,000 m2, equivalent to almost three football pitches.

Evolution of wind turbines

Evolution of wind turbines

Examples of commercial projects and the turbines used:

  • Two 2.3MW turbines for Templederry Wind Farm, Co. Tipperary, Ireland – the only community owned wind farm in Ireland.
  • Three 0.7MW turbines for Isle of Gigha Wind Farm, Scotland
  • Twenty 0.3MW turbines for Bellacorrick, Co Mayo, Ireland


What is the capacity factor of a wind turbine?

The capacity factor of any electricity generating system  is the electricity that the system actually produces in a given time compared with the electricity that could be produced if it operated to its full capacity.  No system operates at full capacity all the time.  Wind turbines actually produce electricity 90 – 95% of the time, but the output depends on wind speed.  So, over the course of a year, a wind turbine will generate 30% of its theoretical maximum output, which is its capacity factor.

  • Capacity factor of wind turbines is 30%
  • Capacity factor of solar panels is between 11% and 15%
  • Capacity factor of fossil fuel power stations is around 50%
What can be done when the wind is not blowing?

Wind and solar are renewable resources that this planet has to offer and, exploited in certain areas, they could provide the global requirement for energy in just a few hours.   A problem with these resources is that they are intermittent.  However, there are solutions to this problem.

  1. Wind turbines, just like solar systems, can use batteries to store the excess of energy from peak productions, energy that will be used later when the wind is not blowing or the sun is not shining.  This technology is not advanced enough to solve the problem on its own.
  2. Wind-powered electricity generating systems can be backed up with biogas power plants or by natural gas used as a transition fuel.  Using natural gas is not seen as the ideal solution in the context of carbon emissions.
  3. Another solution is ‘net-metering’. In general terms this means using the electricity grid as a storage option. So, owners of a wind turbine can feed extra electricity generated during windy days into the electricity grid and then, on days with no wind, they use electricity from the grid.  The downside of this is that the grid supply is generally from power plants using fossil fuels.
  4. Wind or solar powered pumped hydro storage systems solve this issue. How does this work? During low demand periods, the excess of wind or solar electricity is fed into the grid from where a pumped hydro system uses it to pump water from a lower reservoir to an upper one. During high demand periods or when wind does not blow the water from the upper reservoir is used to produce electricity.
Wind powered pumped hydro storage

Wind powered pumped hydro storage

What are the health impacts of a wind farm?

Two very debated health issues related to wind turbines are noise and shadow flicker. Although some may argue that noise from the turbines is significant and interferes with day to day life, many researchers combat this idea. It has been proven that the perceived noise from the turbines depends on the individual and how sensitive their hearing is. Furthermore, noise perception is directly linked with the person’s acceptance of the turbines. Those who are against wind development tend to be more annoyed by their presence than those who favour wind energy.

Shadow flicker can be observed in some areas, only in certain months, usually depending on the angle of the sun. Most of the wind farms that operate now deal with this problem by turning off the turbines at those times. A special system is installed on the turbine and based on the analyses done regarding the shadow flicker, the system automatically turns off the turbines.


What are the environmental impacts of wind farms?

Many studies have discovered that, although wind farms are harmful to the wildlife, the impacts they have are less significant than those of fossil fuels.

Erickson et al. in the “A Summary and Comparison of Bird Mortality from Anthropogenic Causes with an Emphasis on Collisions” paper (2005) presents wind turbines as having the lowest impact on bird mortality with a percentage of just 0.003% compared with buildings, power lines and cats (82%); vehicles (8%); pesticides (7%); communication towers (0.5%) and so on.

With proper studies of several areas, done before the approval of the project, the location of the wind farm can be chosen in the least harmful place, having little to no impact on wildlife or birds and their migratory patterns.


Did you know?
  • The first wind farm in Ireland was built in 1992 at Bellacorrick, Co Mayo and comprised of21 wind turbines with a total installed capacity of 6.54 megawatts (MW);
  • In 2013 wind power supplied 16.4% of the total energy consumption in Ireland;
  • In Ireland, for the 2010 – 2014 period, wind generation meant €1 billion less spend on energy imports, a 12 million tones reduction in CO2 emissions (GEAI position paper on wind or SEAI);
  • Even if the capacity factor is 30%, wind turbines produce electricity 90 – 95% of the time. The capacity factor of conventional power stations is 50%;
  • The pay back of an average wind farm for the electricity used in its manufacture is 3 to 5 months and a modern wind turbine is designed to operate for more than 20 years;
  • A survey done in 2013 in the Republic of Ireland by the Irish Wind Energy Association shows that 80% of the people are in favour of wind development while only 7% oppose it;
  • The largest wind turbine has 8MW capacity, with an overall height of 220m (722 ft.) and a diameter of 164m (538 ft.). It is owned by Vestas, a Danish company, and is situated in Østerild, Denmark;
  • In Europe, London Array, UK is the biggest offshore wind farm (630MW of installed capacity) and Fântânele-Cogealac Wind Farm, Romania is the biggest onshore wind farm (600MW of installed capacity).


  1. Agnes Doolan. says:

    An industrial engineer friend tells me that the Capacity Factor of the Mount Lucas wind turbines is 15%.Impressive, isn’t it?

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