Opinion surveys in areas of the European Union with wind farms or many wind turbines (such as Denmark and UK) indicate that 70 to 80 % of the population is "generally supportive" or "unconcerned" with respect to the wind turbines in their neighbourhood. In a referendum in a Danish municipality with a very large number of wind turbines, 77 % of the votes favoured even more machines.

The political debate is often quite polarised. On the one hand, in many countries the public in general favours renewable energy sources such as wind power. On the other hand, deploying a wind farm in a local community sometimes raises local resistance due to the neighbours' uncertainty and negative expectations about the wind turbines. The public concern is often about environmental effects of wind power such as visual intrusion, impact on birds and birds' habitat, acoustic noise emission, safety, moving shadows, etc. This has been called the NIMBY (Not-In-My-Back-Yard) dilemma.

In industrialised countries public acceptance of wind power is often the most important planning restriction and consequently also a political issue (Elliot, 1994). Experience in developing countries is still limited, but recent large-scale applications in India and China show both reliable production and a high degree of public acceptance along with private sector participation (Andersen, Jensen, Beurskens, 1995).

The public concern is rooted in the fact that the environmental advantages of wind power is on a global or national level, whereas, the environmental disadvantages of wind power is on a local or neighbourhood level, associated with the presence and operation of wind turbines.

Environmental advantages on a global or national level include:

No direct atmospheric emissions
No liabilities after decommissioning
Good energy balance
Limited use of land
Environmental disadvantages on a local or neighbourhood level, include:

Noise emission
Visual impact on landscape
Moving shadows
Erosion
Impact on birds
Interference with electromagnetic communication
Personelle safety
Some of these disadvantages are of very limited significance. Quantifying such advantages and disadvantages usually not included in economical analyses of wind energy is often made by means of external cost analyses as we shall see at the end of this paper.

Atmospheric emissions

No direct atmospheric emissions are caused by the operation of wind turbines. The indirect emission from the energy used to produce, transport and decommission a wind turbine depends on the type of primary energy used.

Liabilities after decommissioning

Electricity from wind turbines has no liabilities related to decommissioning of obsolete plants. Today, most metal parts of wind turbines can be re-cycled. In a very near future other parts, such as electronics and blades, will be recycled almost 100p.c.

Energy balance

The direct environmental effects related with manufacturing of wind turbines is similar to those of other equipment production processes, and the indirect environmental effects of the energy used to produce a wind turbine depend on the type of primary energy used. Several early investigations have shown, that the energy invested in production, installation, operation & maintenance and decommissioning of a typical wind turbine has a "pay-back" time (energy balance) of less than a year of operation (World Energy Council, 1994).

New up-dated surveys have confirmed this (Krohn, 1996). Manufacturing a state-of-the-art 600 kW wind turbine takes 3.2 TJ taking into account everything from producing raw material to installing a ready machine, including 20 years of operation and maintenance and decommissioning. In suitable locations, the wind turbine will generate 1.1 to 1.3 million kWh per year in its projected 20-year useful life. The energy invested in a state-of-the-art 600 kW wind turbine is therefore repaid over 3-4 month.

Land use

Wind energy is diffuse and collecting energy from the wind requires turbines to be spread over a wide area. As a rule of thumb wind farms require 0.08 to 0.13 km2/MW (8 - 13 MW/km2). The area needed for 100,000 MW is less than 0.3% of the territory covered by the European Union. Onshore wind farms have the advantage of dual land use. 99% of the area occupied by a wind farm can be used for agriculture or remain as natural habitat. Furthermore, part of the installations can be made offshore. Consequently, limited area of land is not a physical constrain for wind power utilisation, as it could be for large scale utilisation of biomass in energy production.

Noise emissions

Acoustic emissions from wind turbines are composed of a mechanical and an aerodynamical component, both of which are a function of wind speed. Analysis shows that for most turbines with rotor diameters up to 20 m the mechanical component dominates, whereas for larger rotors the aerodynamical component is decisive.

The nuisance caused by turbine noise is one of the important limitations of siting wind turbines close to inhabited areas. The acceptable emission level strongly depends on local regulations. An example of strict regulation is the Dutch regulation for 'silent' areas, where a maximum emission level of 40 dB(A) near residences is allowed, at a wind speed of about 5-7 ms-1. At this wind speed level the turbine noise is most distinctly audible. In Europe a typical distance between wind turbines and the nearest house is more than 150 or 200 meter.

Visual impact

Depending on the characteristics of the landscape modern wind turbines with a hub height of 40 - 60 meters and a blade length of 20 - 30 meters form a visual impact on the landscape. This visual impact, although very difficult to quantify, can be a planning restriction in most European countries.

Moving shadows

A more objective case of visual impact is the effect of moving "shadows" from the rotor blades. This is only a problem in situations where turbines are sited very close to workplaces or dwellings. The effect can easily be predicted and avoided through proper planning. A house 300 meter from a modern 600 kW machine with a rotordiameter of 40 meter will be exposed to moving shadows approx. 17-18 hours out of 8760 hours annually.

Erosion

On the typical flat on-shore sites installation of wind turbines has no erosional effects and the installation does not to any significant level affect vegetation or fauna. In most countries wind power developers are obliged to minimise any disturbance of vegetation under construction of wind farms (in combination with road works etc.) on sensitive sites such as mountainous sites and offshore.

Impact on birds

The impact of wind turbines on birds can be divided into:

direct impact including risk of collision and effect on the breeding success
indirect impact including effects caused by disturbance from the wind turbine (noise and visual disturbance). The disturbance effects of wind turbines fall into three categories:
disturbance to breeding birds
disturbance to staging and foraging birds
disturbing impact on migration/flying birds
Studies in Germany, the Netherlands, Denmark and the UK conclude, that wind turbines do not pose any substantial threat to birds (or bats or insects). Bird mortality due to wind turbines is only a small fraction of the background mortality (Still et al. 1994). A study has estimated an maximum level of birds collision with wind turbines of 6 - 7 birds/turbine/year (Clausager & Nøhr, 1995). In Denmark with approximately 4000 wind turbines this means that 25,000 to 30,000 birds annually die from collision with wind turbines. As comparison it can be mentioned that over one million birds are killed in the traffic in Denmark, and that the total number of staging and migrating birds in Denmark is 400 - 500 millions. Isolated examples have been reported of significant damages on specific species, such as the Spanish wind farm of Tarifa near the Strait of Gibraltar, which is a major bird migration route (Llamas, 1995). The problem was caused by very special circumstances, and it seems to have been solved without removing the turbines.

If not properly dealt with, wind farms sited on coastal sites can disturb breeding and resting birds. Typically, an effect has been recorded within 250-800 meter, with a highest sensitivity recorded for geese and waders. Including professional knowledge of birds and wind turbines in the planning process or wind farms can solve this problem. A European Best Practice for siting wind farms with respect to birds would be of great help for European wind farm developers in avoiding disturbance of birds.

Interference with electromagnetic communication systems

Wind turbines in some areas can reflect electromagnetic waves, which will be scattered and diffracted. This means that wind turbines may interfere with telecommunication links. An investigation made by the British company BBC concluded, that wind turbines' interference with electromagnetic communication systems is no significant problem.

The IEA has provided preparatory information on this subject, identifying the relevant wind turbine parameters (diameter, number and cross-section of blades, speed, etc.) and the relevant parameters of the potential vulnerable radio services (spatial positions of transmitter and receiver, carrier frequency, polarisation, etc.). Planning of wind farms, areas where wind turbines could interfere with telecommunication are normally avoided.

Personelle safety

Accidents with wind turbines involving human beings are extremely rare, and there is no recorded cases of persons hurt by parts of blades, parts of blades or ice loosened from a wind turbines. Insurance companies in USA, where most of the experience with large wind farms has been occurring, agree that the wind industry has a good safety profile compared to other energy producing industries. The International Electrical Committee (IEC) has issued an international official standard on wind turbine safety.

Social or external costs

External or social costs of wind power (or other energy producing technologies) are costs imposed on the society or the environment that are not accounted for by the producers and consumers of energy (Eyre, 1994). Several international surveys conclude that electricity from wind turbines has very low external costs. Several methods can be applied to determine the external cost of energy producing technologies and several ongoing research projects investigateexternal costs of different technologies. In the European study "ExternE" wind farms in the UK were analysed and the same method has been used in Spanish wind farms. The results can be seen from table 4. As can be seen, the total external costs of wind energy are of the order of 0.1 to 6.7 mECU/kWh.

In a Danish study the external costs of wind power are compared with those of N-gas, biomass and coal-burning plants (Meyer et al. 1994). As can be seen from the table external costs of coal based electricity are orders of magnitudes higher than for wind power.

The surveys conclude, that the most important impacts of wind farms are noise and visual intrusion. These issues must be dealt with when planing wind farms.