Wind Energy and the Environment

previous Steps to Planning and Building a Wind Farm
Positive environmental benefits of Wind energy

It must be stressed that wind energy involves no combustion or nuclear reaction, so it is pollution free. It is renewable and plentiful and free, and what is more it is available everywhere, especially in remote areas and often it is windier in mountains and near costal areas. There are significant environmental benefits obtained from using a renewable energy device attributed to preventing the release of Green house gases associated with fossil fuels. The general equation for estimating the reduction in emitted gas is:

Gas-emission reduction (in tonnes) = A × 0.8 × h × kG
Where
A is the rated capacity of the development in kW
h is the number of operational hours per year, = 8000 h
kG is the specific emitted gas constant.
Hence the following equations are used to predict environmental benefits from based on 1 kWe system:
CO₂ emission reduction (in tonnes) = 1 × 0.8x8000 × 862/106 = 5.5
SO₂ emission reduction (in tonnes) = 1 × 0.8 × 8000 × 9.9/106 = 0.063
NO₂ emission reduction (in tonnes) = 1 × 0.8 × 8000 × 862/106 = 0.018
Negative Impacts of Wind energy

These issues are often raised, some are valid, some are opinion driven, and others could be due to personal preferences or biasness.

a. Noise

Wind turbines rely on the movement of the rotor affected by wind to rotate the generator and make electricity. Virtually everything with moving parts will make some sound, and wind turbines are no exception. Turbines are an established and well developed technology, and well designed wind turbines are generally quiet in operation, and compared to the noise of road traffic, trains, aircraft and construction activities, the noise from wind turbines is relatively low. Outside the nearest houses, which are at least half a mile away, and more often further, the sound of a wind turbine generating electricity is likely to be about the same level as noise of leaves rustling in a gentle breeze. This is similar to the sound level inside a typical living room with a gas fire switched on, or the reading room of a library or in an unoccupied, quiet, air-conditioned office.

Source/Activity	Indicative noise level dB (A)
Threshold of hearing	0
Rural night-time background	20-40
Quiet bedroom	35
Wind farm at 350m	35-45
Car at 40mph at 100m	55
Busy general office	60
Truck at 30mph at 100m	65
Pneumatic drill at 7m	95
Jet aircraft at 250m	105
Threshold of pain	140

Table 2.1 Comparative noise levels

There are two potential sources of noise related to wind turbines: the turbine blades passing through the air as the hub rotates, and the gearbox and generator in the nacelle. Noise from the blades is minimised by careful attention to the design and manufacture of the blades. The noise from the gearbox and generator is contained within the nacelle by sound insulation and isolation materials.

Preliminary recommendations from the Wind Turbine Noise Working Group, established by the DTI in the UK, are that turbine noise level should be kept to within 5 dB(A) of the average existing evening or night-time background noise level. A fixed low level of between 35 and 40 dB(A) may be specified when background noise is very low, ie. Less than 30 dB(A).

b. Bird-kill

This is a very emotionally charged subject. Bird conservationists tend to view wind turbines as death machines and refer to bloody bird corpses lying at the foot of turbine towers and entire species migrating from the areas surrounding wind farms.

Birds occasionally collide with wind turbines, as they do with other tall structures such as buildings. Detailed studies and monitoring following construction, at wind development areas indicate that this is a site-specific issue that will not be a problem at most potential wind sites. Also, wind's overall impact on birds is low compared with other human-related sources of avian mortality. See Figure 2.4

Figure 2.4 Causes of Bird-kill

c. Visual impacts

Wind turbines are just normal structures to look at, just like trees, better looking than boiler chimneys. In comparison to other energy developments, such as nuclear, coal and gas power stations or open cast coal mining, wind farms have relatively little visual impact. Wind farm developers recognise that visual impact can be a concern for neighbouring communities. Considerable effort is therefore committed to the planning stages in order to reduce the impact and gain their consent.

A number of national wind energy associations have established detailed best practice guidelines for the development of wind farms, including their visual impact.

Surveys of public opinion show that most people who live near wind developments find them less intrusive once they are operating than they might have feared beforehand. Other surveys, for instance in Scotland, have shown that there is no evidence that tourism is seriously affected by the presence of wind farms. The authors experience is the opposite to that, I found myself going to places never thought I would, for the simple reason to see how the wind turbines work and enjoy the view of clean energy machine.

Although a wind energy project can spread across a large total land area, it does not occupy all that space. Farming or leisure activities can still continue around the turbines. The European Wind Energy Association has estimated that the number of wind farms required to contribute 20% of Europe’s electricity supply would take up only a few hundred square kilometres.

d. Shadow Flicker

is occasionally raised as an issue by some people. A wind turbine's moving blades can cast a moving shadow on a nearby residence, depending on the time of the year (which determines how low the sun is in the sky) and time of day. It is possible to calculate very precisely whether a flickering shadow will in fact fall on a given location near a wind farm, and how many hours in a year it will do so. Therefore, it should be easy to determine whether this is a potential problem.

e. Communication interference

Wind turbines, like all structures, can interfere with communication or radar signals when these signals are interrupted by the turbine structure or the rotor plane. Wind turbines can sometimes cause electromagnetic interference affecting TV and radio reception. Electromagnetic interference can be caused by near-field effects, diffraction, or reflection and scattering. Such interference can typically be mitigated by using satellite TV or wireless cable TV. Although instances of TV or radio interference are infrequent and typically straightforward to mitigate, the interaction of wind turbines and navigational or defence radar signals is the subject of considerable recent attention.

A number of tools and practices are available to manage or mitigate the potential impact of wind turbine
interference:

Farm layout optimization, terrain masking, or reduction of the radar cross-section area may be sufficient to address identified interference problems.
Coating equipment with absorbent or reflective materials to minimize the turbine's radar signature.
Often the easiest and least costly approaches involve software optimization. Other options include installing post-processors or adding hardware (such as processors, transmitters, or receivers). When such changes alone are insufficient, more involved approaches can sometimes be implemented. These include deploying extra radars to cover the shadow spots, relocating radar installations to accommodate the new wind farms, or altering air traffic routes around new wind farms.

Even with these mitigation methods, there will be some proposed locations where wind turbines will cause disruptive radar interference. In such cases, wind projects would likely be unable to proceed at the proposed site.

Figure 2.5 “Not” a perfect place to site a wind farm.