Wind turbines harness power from the wind to generate electricity.

The UK is the windiest country in Europe and offers a great resource to generate renewable electricity. At a sufficient wind speed the blades of the wind turbine rotate, driving a generator and producing electricity. The most common turbines operate with two or three blades on a horizontal axis, however, there are differing designs including a vertical axis turbine. 

Wind Turbine

Wind turbines vary in size according to their rated capacity (kW) at a specified wind speed. The manufacturer of the turbine should provide a power curve which is a graph of the power output against differing wind speeds. Electricity generated from a turbine is measured in kilowatt-hours (kWh). The turbine’s output will vary according to the wind speed, to maximise electricity generation, turbines should be sited where there are both high and steady wind speeds, away from obstructions such as buildings and trees. 

Typical sizes of different capacity turbines and approximate cost of installation

Rated Power

Height of tower

Cost of installation

1.5kW

10-18m

£1.5-£5k

1.5-15kW

12-25m

£2-£50k

15-100kW

15-50m

£50-£250k

100kW-1MW

65-80m

£1m/MW

Feasibility and Development

There are a number of stages involved in assessing the feasibility of wind  developments including:

Siting and design considerations

Wind Speed – Windspeed is very site specific.An annual average wind speed above 5m/s is desirable for useful generation. Average wind speed databases give estimates of speeds at locations around the UK.  Wind speed database (NOABL) - www.rensmart.com/Weather/BERR

However, these may not take into account local topography. Local knowledge is useful to further understand good wind sites.

  • The power generated is proportional to the cube of the wind speed, which means that doubling the wind speed gives eight times as much power.
  • Height - Raising a turbine can impact on energy output, for example, raising the height by just five metres can improve output by around 30%.
  • Exposed sites - Identify an exposed site, clear of nearby obstructions to maximise wind speed.
  • Grid Connection - This is essential for any wind installation if electricity is to be exported to the grid. Wind installations in rural areas with limited grid capacity will be restricted by the gird connection capability, without grid strengthening.

Planning

There are a number of issues that will be considered by a Local Authority assessing a planning application for wind development. Things that will be considered include:

  • Proximity to dwellings – To ensure noise, visual and shadow flicker impacts on nearby dwellings are minimised. Shadow flicker is the shadow created from the tower and the moving blades.
  • Noise – A noise assessment may be required to ensure there will be no disturbance from the installation.
  • Visual Impacts – To include an assessment of whether or not the turbine will be classed as an eyesore in its surroundings.
  • Cumulative impact - this depends on what other wind turbines are visible within the proximity of the planned turbine
  • Bird/bat strike – Birds and bats flying between nesting sites have potential to be struck by moving blades. The impact upon these animals needs to be considered.
  • Proximity to local assets – potential impact on roads, railway lines, public rights of way and airports must be considered.
  • Radar - Any interference with local airbases and airports

 The planning process depends on the nature of the development and the local planning authority, but can range from  6 weeks to 24 months.

 

 Management and maintenance

Wind turbine systems are robust and designed to withstand specified maximum wind speeds.  They have a design life of up to 20–25 years, but will require maintenance and servicing. A warranty and maintenance agreement could be put into place with the supplier.

Next steps:

Read Sharenergy's : Community led wind power

Community wind projects:

http://www.baywind.co.uk/baywind_home.asp

Norton community wind has a report on structure of community schemes : www.nortonenergycommunity.org

South Brent Community Energy

Roseland Community Energy Trust

Energy4all

Case Study

A farm in North Yorkshire commissioned a 5 kW turbine with a rotor diameter of 5.5m and a 12m tower with an installed cost of £22,500. The site has no obstructions and average wind speeds, at the height of the tower, of 5.0m/s. The turbine generates 8490kWh of electricity annually producing a generation and export tariff from the FiT of £2,481/year. There would also be a saving of £750 from displacing the 5000kWhs of electricity consumed by the farm previously bought from the utility company. The revenue and savings would give a payback of 7years with a return on investment over 20 years of 9.3%

Useful Resources

Wind speed database (NOABL) - www.rensmart.com/Weather/BERR