Frequently asked questions on wind energy

By more than a third of the world&#;s energy will come from wind. Wind technology doesn&#;t only make a vital contribution to the fight against climate change, but it also supports local economies by creating jobs and helping the communities that host wind farms. Here are the answers to any questions you might have about this renewable source of energy.

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21 Frequently Asked Questions About Wind Energy

This page is also available in German, French, Spanish and Danish.

1. Wind Turbines Whisper Quietly, Now
Large, modern wind turbines have become very quiet. At distances above 200 metres, the swishing sound of rotor blades is usually masked completely by wind noise in the leaves of trees or shrubs.
There are two potential sources of noise from a wind turbine: Mechanical noise from the gearbox or generator, and aerodynamic noise from the rotor blades.

Mechanical noise has virtually disappeared from modern wind turbines. This is due to better engineering with more concern about avoiding vibrations. Other technical improvements include elastically dampened fastenings and couplings of the major components in the nacelle, and to a certain extent sound insulation. Finally, the basic components themselves, including gearboxes, have developed considerably over the years. Modern wind turbine gearboxes use "soft" gearwheels, i.e. toothed wheels with hardened surfaces and relatively elastic interiors. Read more in the guided tour page on designing for low mechanical noise.

Aerodynamic noise i.e. the "swish" sound of the rotor blades passing the tower of a wind turbine primarily arises at the tip and the back edge of the rotor blade. The higher the rotational speed, the louder the sound. Aerodynamic noise has been cut dramatically during the past ten years due to better design of rotor blades (particularly blade tips and back edges). Read more in the guided tour page on designing for low aerodynamic noise.
Pure tones can be very annoying to a listener, while "white noise" is hardly noticed at all. Rotor blade manufacturers take extreme care to ensure a smooth surface which is important to avoid pure tones. Likewise, manufacturers who install wind turbines take great care to ensure that the rotor blades are not damaged when a wind turbine is being installed.
Read more in the guided tour section on sound from wind turbines.

2. Wind Energy is Clean, and Saves Energy
Can a wind turbine ever recover the energy spent in producing maintaining, and servicing it?
Wind turbines use only the energy from the moving air to generate electricity. A modern 1,000 kW wind turbine in an average location will annually displace 2,000 tonnes of carbon dioxide from other electricity sources, i.e. usually coal fired power stations.
The energy produced by a wind turbine throughout its 20 year lifetime (in an average location) is eighty times larger than the amount of energy used to build, maintain, operate, dismantle, and scrapping it again.
In other words, on average it takes only two to three months for a wind turbine to recover all the energy required to build and operate it.
Read more in the guided tour section on the energy payback period for wind turbines

3. Wind Energy is Abundant
Wind resources are plentiful. Wind will not run out.
Denmark is one of the countries which is planning for substantial amounts of electricity consumption to be provided by wind energy. Already (), wind energy is covering 13 per cent of Danish electricity consumption, a figure which will increase to at least 16 per cent by . 50 per cent of that country's electricity consumption will come from wind by the year according to Government plans ("Energy 21").
The wind resources above the shallow waters in the seas around Europe could theoretically provide all of Europe's electricity supplies several times over.
In Denmark alone, 40 per cent of the country's present electricity consumption could be covered from offshore wind parks located in an area of some 1,000 square kilometres of shallow sea territory.

4. Wind Energy Makes a Difference
Wind Turbines have grown dramatically in size and power output.
A typical Danish wind turbine of vintage had a 26 kW generator and a rotor diameter of 10.5 metres. A modern wind turbine has a rotor diameter of 54 metres and a kW generator. It will produce between 2 and 3 million kilowatt hours in a year. This is equivalent to the annual electricity consumption of 500 to 800 European households.
The latest generation of wind turbines has a 1,000-2,500 kW generator and a 50-80 metre rotor diameter.
In Europe more than 13,000 megawatts of wind power were on-line as of January , covering the average domestic electricity consumption of seven million people. Worldwide 18,000 MW have been installed. This is equivalent to the amount of nuclear power installed worldwide by .

5. Wind Energy is an Advancing Technology
Technological advances in aerodynamics, structural dynamics and micro-meteorology have contributed to a 5 per cent annual increase in the energy yield per square metre wind turbine rotor area (as recorded in Denmark between and ). New technology is continuously being introduced in new wind turbines.
The weight of Danish wind turbines has halved in 5 years, the sound level has halved in 3 years, and the annual energy output per turbine has increased 100-fold in 15 years.
Check the guided tour section on research and development.

6. Wind Energy is Inexpensive
Wind energy has become the least expensive renewable energy technology in existence.
Since the energy contents of the wind varies with the cube (i.e. the third power of the wind speed, the economics of wind energy depends heavily on how windy the site is. In addition, there are generally economies of scale when building wind parks of many turbines.
Today, according to the Danish electrical power companies, the energy cost to society (the social cost) per kilowatt-hour of electricity from wind is the same as for new coal-fired power stations fitted with smoke scrubbing equipment, i.e. around 0.04 USD per kWh for an average European site.
R&D studies in Europe and the US point to a further fall in energy costs from wind of some 10 to 20 per cent between now and the year .
Read more about the economics of wind energy in the guided tour.

7. Wind Energy is Safe
Wind energy leaves no harmful emissions or residue in the environment.
Wind Energy has a proven safety record.
Fatal accidents in the wind industry have been related to construction and maintenance work only. Read more about wind turbine safety in the Guided Tour section.

8. Wind Turbines are Reliable
Wind turbines only produce energy when the wind is blowing, and energy production varies with each gust of wind.
The variable forces acting on a wind turbine throughout its expected lifetime of 120,000 operating hours could be expected to exert significant tear and wear on the machine. Turbines therefore have to be built to very exacting industrial standards.
High quality modern wind turbines have an availability factor above 98 per cent, i.e. the turbines are on average operational and ready to run during more than 98 per cent of the hours of the year. This availability factor is beyond any other electricity generating technology.
Modern wind turbines only require a maintenance check every six months.

9. Wind Energy Uses Land Resources Sparingly
Wind turbines and access roads occupy less than one per cent of the area in a typical wind park. The remaining 99 per cent of the land can be used for farming or grazing, as usual.
Since wind turbines extract energy from the wind, there is less energy in the wind shade of a turbine (and more turbulence) than in front of it.
In a wind park, turbines generally have to be spaced between three and nine rotor diameters apart in order not to shade one another too much. (Five to seven rotor diameters is the most commonly used spacing).
If there is one particular prevailing wind direction, e.g. West, turbines may be spaced very closely in the direction at a right angle to that direction, (i.e. North-South).
Whereas a wind turbine uses 36 square metres, or 0. hectares to produce between 1.2 and 1.8 million kilowatt hours per year, a typical biofuel plant would require 154 hectares of willow forest to produce 1.3 million kilowatt hours per year. Solar cells would require an area of 1.4 hectares to produce the same amount of electricity per year.

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10. Wind Energy Can and Must Respect Landscape Values
Wind turbines obviously have to be highly visible, since they must be located in windy, open terrain to be economic.
Better design, careful choice of paint colours - and careful visualisation studies before siting is decided - can improve the visual impact of wind farms dramatically.
Some people prefer lattice towers instead of tubular steel towers, because they make the tower itself less visible.
There are no objective guidelines, however. Much depends on the landscape and the match with architectural traditions in the area.
Since wind turbines are visible in any case, it is usually a good idea to use them to emphasise natural or man-made features in the landscape. See some examples in the guided tour section on wind turbines in the landscape.
Like other man-made structures, well designed wind turbines and wind parks can give interesting perspectives and furnish the landscape with new architectural values.
Wind turbines have been a feature of the cultural landscape of Europe for more than 800 years.

11. Wind Projects Minimise Ecological Impact
Wind turbine manufacturers and wind farm developers have by now substantial experience in minimising the ecological impact of construction work in sensitive areas such as moors, or mountains, or when building wind farms in offshore locations.
Restoring the surrounding landscape to its original state after construction has become a routine task for developers.
After the useful life of a wind farm has elapsed, foundations can be reused or removed completely.
The scrap value of a wind turbine can normally cover the costs of restoring its site to its initial state.

12. Wind Turbines Coexist Peacefully with Wildlife
Deer and cattle habitually graze under wind turbines, and sheep seek shelter around them.
While birds tend to collide with man-made structures such as electrical power lines, masts, or buildings, they are very rarely affected directly by wind turbines.
A recent Danish study suggests that the impact of overhead power lines leading electricity away from wind farms have far greater impact on bird mortality than the wind farms themselves.
Falcons are in fact nesting and breeding in cages attached to two Danish wind turbines!
Studies from the Netherlands, Denmark, and the US show that the total impact on birds from wind farms is negligible compared to the impact from road traffic.
Read more about birds and wind turbines in the Guided Tour.

13. Wind Turbines Require Careful Siting
The energy content of the wind varies with the cube, (i.e. the third power) of the wind speed. Twice as much wind yields eight times as much energy. Manufacturers and wind farm developers therefore take extreme care in siting wind turbines in as windy areas as possible.
The roughness of the terrain, i.e. the terrain surface, its contours, and even the presence of buildings, trees, plants, and bushes affect the local wind speed. Very rough terrain or nearby large obstacles may create turbulence which may decrease energy production and increase tear and wear on the turbines.
Calculating the annual energy production from a wind turbine is quite a complex task: It requires detailed maps of the area (up to three kilometres in the prevailing wind directions), and accurate meteorological wind measurements for a at least a one year period. You may read more in the Guided Tour section on wind energy resources.
Qualified advice from experienced manufacturers or consulting firms is therefore essential for the economic success of a wind project.

14. Wind Turbines can be Quite Economic in Inland Areas
Although wind conditions near seashores tend to be ideal for wind projects, it is indeed possible to find highly economic inland areas for wind turbines.
As the wind passes over a hill, or through a mountain pass, it becomes compressed and speeds up significantly. Rounded hilltops with a wide view in the prevailing wind directions are therefore ideal as wind turbine sites. See the Guided Tour on speed up effects.
Tall wind turbine towers is a way of increasing the energy yield of a wind turbine, since wind speed usually increases significantly with height above ground level.
In low wind areas, manufacturers may be able to supply special wind turbine versions with large rotors compared to the size of the electrical generator.
Such machines will reach peak production at relatively low wind speeds, although they will waste some of the energy potential of high winds. Manufacturers are increasingly optimising their machines to local wind conditions worldwide.

15. Wind Energy Integrates Well into the Electrical Grid
The major drawback of wind power is variability.
In large electrical grids, however, consumers' demand also varies, and electricity generating companies have to keep spare capacity running idle in case a major generating unit breaks down.
If a power company can handle varying consumer demand, it can technically also handle the "negative electricity consumption" from wind turbines.
The more wind turbines on the grid, the more short term fluctuations from one turbine will cancel out the fluctuations from another.
In the Western part of Denmark, more than 25 per cent of the electricity supply today comes from wind during windy winter nights.
Read more in the Guided Tour section on wind energy in the electrical grid

16. Wind Energy is a Scalable Technology
Wind energy can be used in all sorts of applications - from small battery chargers in lighthouses or remote dwellings to industrial scale turbines of 1.5 megawatts capable of supplying the equivalent of the electricity consumption of one thousand families.
Other interesting and highly economic applications include wind energy used in combination with diesel powered backup generators in several small, isolated electrical grids throughout the world.
Desalination plants in island communities in the Atlantic and the Mediterranean Sea is another recent application.

17. Wind Energy is an Ideal Developing Country Technology
Although wind turbine design has become a high tech industry, wind turbines can easily be installed in developing countries, and serviced and maintained locally. Turbine manufacturers provide training courses for personnel.
Installation of wind turbines provides jobs in the local community, and manufacturers will often manufacture heavy parts of the turbine, e.g. towers, locally once the installation rate reaches a certain level.
Wind turbines require no subsequent expensive provision of fuel, a major stumbling block for several other electricity generating technologies in developing areas.
India has become one of the large wind energy nations of the world with substantial local manufacturing. P. R. of China is presently taking the lead in East Asia.

18. Wind Energy Provides Jobs
The wind industry today () provides more than 50,000 jobs worldwide. The wind industry is becoming more multinational, as the industry matures and more manufacturing is established in new markets.
In Denmark alone, more than 15,000 people make a living from wind energy, designing and manufacturing wind turbines, components, or rendering consultancy and engineering services.
Today employment in the Danish wind industry is larger than e.g. the fishing industry.
The Danish production of wind turbines demands another 5,000 jobs in other countries which erect wind turbines or manufacture turbine components such as generators and gearboxes.
Read more on the page on employment in the guided tour.

19. Wind Energy is Popular
Opinion polls in several European countries, Denmark, Germany, Holland, and the UK, show that more than 70 per cent of the population is in favour of using more wind energy in the electricity supply.
People who live near wind turbines are on average even more favourable towards wind energy, with a score of more than 80 per cent in favour of wind energy.
In Denmark, more than 100,000 families own shares in one of the 6,000 modern wind turbines scattered throughout the country.
More than 80 per cent of the wind power capacity in Denmark is owned by private individuals or wind co-operatives.

20. Wind Energy is a Rapidly Growing Market
Since , growth rates in the wind turbine market have been around 40 per cent per annum, and growth rates of 20 per cent per annum are expected for the next ten years.
Currently there are some 40 wind turbine manufacturers worldwide. Around half of the turbines in the world come from Danish manufacturers.
Wind energy is gaining ground in developed and developing countries alike.
In developed countries wind energy is mostly in demand because of its pollution-free qualities.
In developing countries its popularity is linked to the fact that turbines can be installed quickly, and require no subsequent fuel supplies.
The wind turbine industry is now a 3.5 billion USD industry with an extremely bright future, particularly if environmentally friendly energy policies gain ground internationally.
Read more in the publications section of this web site.

21. The Danish Wind Turbine Industry is the World's Largest
In Danish wind turbine companies supplied 2,500 megawatts of new generating capacity, equivalent to a medium-sized nuclear power station.
Danish manufacturers had a 50 per cent share of the world market for wind turbines in .
Development of modern wind energy for electricity generation has a long tradition in Denmark. It began in more than a hundred years ago, in . Read more about this exciting technology history in the Pictures section of this web site.

Read more about the basic design of modern wind turbines, and the so called Danish concept in the guided tour.