21
Frequently Asked Questions About Wind Energy
This page is also available in German, French, Spanish and Danish.
- Are wind turbines noisy?
- Do wind turbines really save energy?
- Are there enough wind resources around?
- Can wind contribute significantly to electricity production?
- Is there any progress in wind turbine technology?
- Is wind energy expensive?
- Is wind energy safe?
- Are wind turbines reliable?
- How much land is required to site wind Turbines?
- Can wind turbines blend into the landscape?
- How is the landscape affected after a wind turbine has been dismantled?
- Do wind turbines bother wildlife?
- Can wind turbines be placed anywhere?
- Can wind turbines be used economically in inland areas?
- How can the varying output from wind turbines be used in the electrical grid?
- Will wind energy work on a small scale?
- Can wind energy be used in developing countries?
- Does wind energy create jobs?
- Is wind energy popular in countries which already have many wind turbines?
- What is the wind energy market like?
- Why are Danish wind turbines well known around the world?
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
(2000), wind energy is covering 13 per cent of Danish electricity
consumption, a figure which will increase to at least 16 per
cent by 2003. 50 per cent of that country's electricity consumption
will come from wind by the year 2030 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 1980 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 1000 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 2001, 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 1970.
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 1980 and 1995). 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 2005.
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 0.0036 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.
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 (2001) 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 1993, 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 2000 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 2000.
Development
of modern wind energy for electricity generation has a long tradition
in Denmark. It began in more than a hundred years ago, in 1891.
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.
If you are interested in more comprehensive answers, take
a Guided Tour of Wind Energy.
If we have missed an answer to one of your questions, please
e-mail us.
© Copyright 2001 Danish Wind Turbine Manufacturers Association
Updated 16 April 2001
http://www.windpower.org/faqs.htm