Environmental impact of wind energy

6 Environmental impact of wind energy

Wind energy development has both positive and negative environmental impacts. On the positive side, the generation of electricity by wind turbines does not involve:

• the release of carbon dioxide or other greenhouse gases
• pollutants leading to acid rain or smog, causing various diseases
• radioactivity
• contamination of land, sea or water courses
• the consumption of water – unlike many conventional (and some renewable) energy sources. This could be important if water shortages occur with increasing frequency in the future.

Large-scale implementation of wind energy within the UK is turning out to be one of the most economic and rapid means of reducing carbon dioxide emissions. Over its working lifetime, a wind turbine can generate approximately 40 to 80 times the energy required to produce it (Everett et al., 2012).

But wind power is not without negative (or perceived negative) impacts. These include

• noise
• electromagnetic interference
• aviation-related issues
• wildlife
• public attitudes and planning.

• 6.1 Wind turbine noise

  Wind turbines are often described as noisy by opponents of wind energy, but they are not especially noisy compared with other machines of similar power rating – see Figure 15.

  

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  Figure 15 Wind turbine noise pattern from a typical wind turbine (source: EWEA. 1991)

  There are two main sources of wind turbine noise:

  1. Mechanical noise, produced by equipment such as the gearbox or generator, which can be reduced significantly by the using quieter gears, mounting equipment on resilient mounts, and using acoustic enclosures.

  2. Aerodynamic noise, due to the interaction of the airflow with the rotor, which can best be described as a ‘swishing’ sound. It is affected by the trailing edge of the blades and the interaction of the airflow with the blades and the tower. It tends to increase with the speed of rotation, so some turbines are designed to operate at lower rotation speeds during periods of low wind.

  Most commercial wind turbines undergo noise measurement tests and the measured noise levels provide information that enables the turbines to be sited at a sufficient distance from habitations to minimise (or avoid) noise nuisance. In the UK current limits are set at 35 – 40 dB (A) for daytime and 43 dB (A) for night-time.

  If noise is not given careful consideration at both turbine design and project planning stages, accounting for the concerns of people who may be affected, opposition to wind energy development is likely.

  You’ll now look at electromagnetic interference.

  6.2 Electromagnetic interference


  When a wind turbine is positioned between a radio, television or microwave transmitter and receiver as shown in figure 16 it can sometimes reflect some of the electromagnetic radiation in such a way that the reflected wave interferes with the original signal as it arrives at the receiver. This can cause the received signal to be distorted significantly.

  

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  Figure 16 Scattering of radio signals by a wind turbine

  The extent of electromagnetic interference caused by a wind turbine depends mainly on the materials used to make the blades and on the surface shape of the tower. In the UK, Ofcom maintains a website that provides guidance on wind farms and electromagnetic interference (Ofcom, 2011).

• 6.3 Wind turbines and aviation

  The UK Ministry of Defence (MOD) has voiced concern about the interference with military radar that could be caused by wind turbines. In addition, it is concerned that wind turbines (particularly those with large diameters and tall towers), when located in certain areas, will penetrate the lower portion of the low flying zones used by military aircraft. MOD intervention has impeded the development of several wind farms in the UK.
  Renewable UK maintains a website (Renewable UK, 2011a) giving information about wind turbines and aviation, including a series of maps from NATS (National Air Traffic Services), MOD and RESTATS (RESTATS, 2011) showing the consultation zone areas in the UK for which NATS requires notification of wind turbine planning applications.
  One potential solution involves adapting the design of wind turbine blades to include RAMs (radar absorbing materials). In a joint project between QinetiQ and Vestas (Appleton, 2010) a ‘stealth’ turbine equipped with a set of RAM blades has demonstrated a substantially reduced impact on radar.
  Another approach is the development of systems that can filter out interference to radar from wind turbines, such as BAE’s ADT (Advanced Digital Tracking) system (Butler, 2007).

• 6.4 Impact on wildlife

  In the UK, English Nature has produced a guidance document (English Nature et al., 2001) for nature conservation organisations and developers when consulting over wind farm proposals in England. Similar documents have been produced for Wales and Scotland.
  In the case of offshore wind, there are concerns about the possible impact on fish, crustaceans, marine mammals, marine birds and migratory birds. These are the subject of ongoing research by organizations including Natural England, Scottish Natural Heritage, COWRIE (Collaborative Offshore Wind Research Into the Environment) and CEFAS (Centre for Environment, Fisheries and Aquaculture Science).
  The main potential hazard to birds is that they could be killed by flying into turbine blades (Drewitt and Langston, 2006). However the American Bird Conservancy (ABC) reports that 100 000–440 000 bird collisions occur per year with wind turbines, compared with 4–50 million with towers, 10–154 million with power lines, 10.7–380 million with roads/vehicles, over 31 million with urban lights and 100 million–1 billion with glass on buildings (ABC, 2011).
  Natural England (2010) suggests that there is little evidence that wind farms in England have a significant impact on birds, but it provides guidance about wind turbines and birds, and post-construction monitoring of bird impacts.
  It is possible to install radar systems that automatically detect approaching birds and, if there is a likelihood of collisions, bird deterrent devices can be activated or the turbines shut down until after the birds have passed.
  Wind turbines may have an impact on bats – particularly along migration routes. Natural England has produced interim guidance (Natural England, 2009a and 2009b) to help planners and wind turbine operators take account of potential impacts on bats when developing or assessing wind turbine developments.

• 6.5 Public attitudes and planning considerations

  The visual perception of a wind turbine or a wind farm is determined by a variety of factors including:
  • turbine size
  • turbine design
  • number of blades
  • colour
  • number of turbines in a wind farm
  • layout of the wind farm
  • extent to which moving rotor blades attract attention.
  Figure 17 compares a wind turbine with other large constructions in the UK.
  

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  Figure 17 Comparison of wind turbines and other structures in the landscape
  An individual’s perception of a wind energy project will also depend on a variety of less easily defined psychological and sociological parameters, with much of the controversy due to opposition to changes to the visual appearance of the landscape. Whether this is due to a visual dislike of wind turbines specifically, or simply to a general dislike of changes in the appearance of the landscape is often unclear.
  Since the 1990s surveys of public attitudes have consistently shown that on average 70% to 80% support the development of wind farms in the UK (see for example NOP, 2005 and YouGov, 2010). However, there is still opposition to change and it is important for projects to be well designed and planned. Developers should engage with local communities to provide trusted and reliable information, together with meaningful community benefits.
  Planning considerations and controls have a major influence on the deployment of wind turbines.
  The UK Government includes planning guidance for wind energy in its National Planning Policy Framework, (DCLG, 2011). Guidelines for developers and planners have also been prepared by Natural England, Scottish Natural Heritage and the Countryside Council for Wales. Some UK local authorities have also developed policy guidelines on planning aspects of wind energy.