From Wikipedia, the free encyclopedia
Wind turbines are manufactured in a wide range of vertical and
horizontal axis. The smallest turbines are used for applications such as
battery charging for auxiliary power for boats or
caravans
or to power traffic warning signs. Slightly larger turbines can be used
for making contributions to a domestic power supply while selling
unused power back to the utility supplier via the
electrical grid. Arrays of
large turbines, known as
wind farms, are becoming an increasingly important source of intermittent
renewable energy and are used by many countries as part of a strategy to reduce their reliance on
fossil fuels. One assessment claimed that, as of 2009,
wind had the "lowest relative greenhouse gas emissions, the least water
consumption demands and... the most favourable social impacts" compared
to photovoltaic, hydro, geothermal, coal and gas.
History
James Blyth's electricity-generating wind turbine, photographed in 1891
The windwheel of
Hero of Alexandria (10 AD – 70 AD) marks one of the first recorded instances of wind powering a machine in history. However, the first known practical wind power plants were built in
Sistan, an Eastern province of
Persia (now Iran), from the 7th century. These "
Panemone" were vertical axle windmills, which had long vertical
drive shafts with rectangular blades. Made of six to twelve
sails covered in reed matting or cloth material, these windmills were used to grind grain or draw up water, and were used in the
gristmilling and sugarcane industries.
Wind power first appeared in Europe during the
Middle Ages. The first historical records of their use in England date to the 11th or 12th centuries and there are reports of German
crusaders taking their windmill-making skills to Syria around 1190. By the 14th century, Dutch windmills were in use to drain areas of the
Rhine delta. Advanced wind turbines were described by Croatian inventor
Fausto Veranzio. In his book Machinae Novae (1595) he described
vertical axis wind turbines with curved or V-shaped blades.
The first electricity-generating wind turbine was a battery charging machine installed in July 1887 by Scottish academic
James Blyth to light his holiday home in
Marykirk, Scotland. Some months later American inventor
Charles F. Brush was able to build the first automatically operated wind turbine after consulting local University professors and colleagues
Jacob S. Gibbs and
Brinsley Coleberd and successfully getting the blueprints peer-reviewed for electricity production in
Cleveland, Ohio. Although Blyth's turbine was considered uneconomical in the United Kingdom, electricity generation by wind turbines was more cost effective in countries with widely scattered populations.
The
first automatically operated wind turbine, built in Cleveland in 1887
by Charles F. Brush. It was 60 feet (18 m) tall, weighed 4 tons (3.6
metric tonnes) and powered a 12 kW generator.
In Denmark by 1900, there were about 2500 windmills for mechanical
loads such as pumps and mills, producing an estimated combined peak
power of about 30 (
MW).
The largest machines were on 24-meter (79 ft) towers with four-bladed
23-meter (75 ft) diameter rotors. By 1908 there were 72 wind-driven
electric generators operating in the United States from 5
kW to 25
kW.
Around the time of World War I, American windmill makers were producing
100,000 farm windmills each year, mostly for water-pumping.
By the 1930s, wind generators for electricity were common on
farms, mostly in the United States where distribution systems had not
yet been installed. In this period, high-tensile steel was cheap, and
the generators were placed atop prefabricated open steel lattice towers.
A forerunner of modern horizontal-axis wind generators was in service at
Yalta, USSR in 1931. This was a 100
kW generator on a 30-meter (98 ft) tower, connected to the local 6.3 kV distribution system. It was reported to have an annual
capacity factor of 32 percent, not much different from current wind machines.
In the autumn of 1941, the first megawatt-class wind turbine was synchronized to a utility grid in
Vermont. The
Smith-Putnam wind turbine
only ran for 1,100 hours before suffering a critical failure. The unit
was not repaired, because of a shortage of materials during the war.
Despite these diverse developments, developments in fossil fuel
systems almost entirely eliminated any wind turbine systems larger than
supermicro size. In the early 1970s, however, anti-nuclear protests in
Denmark spurred artisan mechanics to develop microturbines of 22
kW.
Organizing owners into associations and co-operatives lead to the
lobbying of the government and utilities and provided incentives for
larger turbines throughout the 1980s and later. Local activists in
Germany, nascent turbine manufacturers in Spain, and large investors in
the United States in the early 1990s then lobbied for policies that
stimulated the industry in those countries.
Resources
Wind Power Density
(WPD) is a quantitative measure of wind energy available at any
location. It is the mean annual power available per square meter of
swept area of a turbine, and is calculated for different heights above
ground. Calculation of
wind power density includes the effect of wind velocity and air density.
Wind turbines are classified by the wind speed they are designed
for, from class I to class III, with A to C referring to the turbulence
intensity of the wind.
| Class |
Avg Wind Speed (m/s) |
Turbulence
|
| IA |
10 |
16%
|
| IB |
10 |
14%
|
| IC |
10 |
12%
|
| IIA |
8.5 |
16%
|
| IIB |
8.5 |
14%
|
| IIC |
8.5 |
12%
|
| IIIA |
7.5 |
16%
|
| IIIB |
7.5 |
14%
|
| IIIC |
7.5 |
12%
|
Efficiency
Conservation of mass requires that the amount of air entering and exiting a turbine must be equal. Accordingly,
Betz's law
gives the maximal achievable extraction of wind power by a wind turbine
as 16/27 (59.3%) of the total kinetic energy of the air flowing through
the turbine.
The maximum theoretical power output of a wind machine is thus
16/27 times the kinetic energy of the air passing through the effective
disk area of the machine. If the effective area of the disk is A, and
the wind velocity v, the maximum theoretical power output P is:
,
Wind-to-rotor efficiency (including rotor blade
friction and
drag) are among the factors impacting the final
price of wind power.
Further inefficiencies, such as
gearbox
losses, generator and converter losses, reduce the power delivered by a
wind turbine. To protect components from undue wear, extracted power is
held constant above the rated operating speed as theoretical power
increases at the cube
of wind speed, further reducing theoretical efficiency. In 2001,
commercial utility-connected turbines deliver 75% to 80% of the Betz
limit of power extractable from the wind, at rated operating speed.
Efficiency can decrease slightly over time, one of the main
reasons being dust and insect carcasses on the blades which alters the
aerodynamic profile and essentially reduces the
lift to drag ratio of the
airfoil.
Analysis of 3128 wind turbines older than 10 years in Denmark showed
that half of the turbines had no decrease, while the other half saw a
production decrease of 1.2% per year.
Ice accretion on turbine blades has also been found to greatly reduce
the efficiency of wind turbines, which is a common challenge in cold
climates where
in-cloud icing and freezing rain events occur. Vertical turbine designs have much lower efficiency than standard horizontal designs.
Types
The three primary types: VAWT Savonius, HAWT towered; VAWT Darrieus as they appear in operation
Wind turbines can rotate about either a horizontal or a vertical axis, the former being both older and more common. They can also include blades, or be bladeless. Vertical designs produce less power and are less common.
Horizontal axis
Components of a horizontal axis wind turbine (gearbox, rotor shaft and brake assembly) being lifted into position
Onshore Horizontal Axis Wind Turbines in Zhangjiakou, China
Large three-bladed horizontal-axis wind turbines (HAWT), with the
blades upwind of the tower produce the overwhelming majority of
windpower in the world today. These turbines have the main
rotor shaft and
electrical generator at the top of a tower, and must be pointed into the wind. Small turbines are pointed by a simple
wind vane,
while large turbines generally use a wind sensor coupled with a yaw
system. Most have a gearbox, which turns the slow rotation of the blades
into a quicker rotation that is more suitable to drive an electrical
generator.
Some turbines use a different type of generator suited to slower
rotational speed input. These don't need a gearbox, and are called
direct-drive, meaning they couple the rotor directly to the generator
with no gearbox in between. While
permanent magnet direct-drive generators can be more costly due to the rare earth materials required, these
gearless
turbines are sometimes preferred over gearbox generators because they
"eliminate the gear-speed increaser, which is susceptible to significant
accumulated fatigue torque loading, related reliability issues, and
maintenance costs."
The rotor of a gearless wind turbine being set. This particular turbine was prefabricated in Germany, before being shipped to the U.S. for assembly.
Most horizontal axis turbines have their rotors upwind of its
supporting tower. Downwind machines have been built, because they don't
need an additional mechanism for keeping them in line with the wind. In
high winds, the blades can also be allowed to bend which reduces their
swept area and thus their wind resistance. Despite these advantages,
upwind designs are preferred, because the change in loading from the
wind as each blade passes behind the supporting tower can cause damage
to the turbine.
Turbines used in
wind farms for commercial production of electric power are usually three-bladed. These have low
torque ripple,
which contributes to good reliability. The blades are usually colored
white for daytime visibility by aircraft and range in length from 20 to
80 meters (66 to 262 ft). The size and height of turbines increase year
by year. Offshore wind turbines are built up to 8(
MW)
today and have a blade length up to 80 meters (260 ft). Usual tubular
steel towers of multi megawatt turbines have a height of 70
m to 120
m and in extremes up to 160
m.
Vertical axis
A vertical axis Twisted Savonius type turbine.
Vertical-axis wind turbines
(or VAWTs) have the main rotor shaft arranged vertically. One advantage
of this arrangement is that the turbine does not need to be pointed
into the wind to be effective, which is an advantage on a site where the
wind direction is highly variable. It is also an advantage when the
turbine is integrated into a building because it is inherently less
steerable. Also, the generator and gearbox can be placed near the
ground, using a direct drive from the rotor assembly to the ground-based
gearbox, improving accessibility for maintenance. However, these
designs produce much less energy averaged over time, which is a major
drawback.
The key disadvantages include the relatively low rotational speed with the consequential higher
torque and hence higher cost of the drive train, the inherently lower
power coefficient,
the 360-degree rotation of the aerofoil within the wind flow during
each cycle and hence the highly dynamic loading on the blade, the
pulsating torque generated by some rotor designs on the drive train, and
the difficulty of modelling the wind flow accurately and hence the
challenges of analysing and designing the rotor prior to fabricating a
prototype.
When a turbine is mounted on a rooftop the building generally
redirects wind over the roof and this can double the wind speed at the
turbine. If the height of a rooftop mounted turbine tower is
approximately 50% of the building height it is near the optimum for
maximum wind energy and minimum wind turbulence. While wind speeds
within the built environment are generally much lower than at exposed
rural sites, noise may be a concern and an existing structure may not adequately resist the additional stress.
Subtypes of the vertical axis design include:
"Eggbeater" turbines, or Darrieus turbines, were named after the French inventor, Georges Darrieus. They have good efficiency, but produce large
torque ripple
and cyclical stress on the tower, which contributes to poor
reliability. They also generally require some external power source, or
an additional Savonius rotor to start turning, because the starting
torque is very low. The torque ripple is reduced by using three or more
blades which results in greater solidity of the rotor. Solidity is
measured by blade area divided by the rotor area. Newer Darrieus type
turbines are not held up by
guy-wires but have an external superstructure connected to the top bearing.
A
subtype of Darrieus turbine with straight, as opposed to curved,
blades. The cycloturbine variety has variable pitch to reduce the torque
pulsation and is self-starting.
The advantages of variable pitch are: high starting torque; a wide,
relatively flat torque curve; a higher coefficient of performance; more
efficient operation in turbulent winds; and a lower blade speed ratio
which lowers blade bending stresses. Straight, V, or curved blades may
be used.
These are drag-type devices with two (or more) scoops that are used in anemometers, Flettner
vents (commonly seen on bus and van roofs), and in some
high-reliability low-efficiency power turbines. They are always
self-starting if there are at least three scoops.
Twisted Savonius is a modified savonius, with long helical scoops
to provide smooth torque. This is often used as a rooftop windturbine
and has even been
adapted for ships.
Parallel
The parallel turbine is similar to the crossflow fan or centrifugal fan. It uses the
ground effect. Vertical axis turbines of this type have been tried for many years: a unit producing 10
kW was built by Israeli wind pioneer Bruce Brill in the 1980s.
Unconventional types
Design and construction
Components of a horizontal-axis wind turbine
Inside view of a wind turbine tower, showing the tendon cables.
Wind turbine design is a careful balance of cost, energy output, and
fatigue life. These factors are balanced using a range of computer
modelling techniques.
Components
Wind
turbines convert wind energy to electrical energy for distribution.
Conventional horizontal axis turbines can be divided into three
components:
- The rotor, which is approximately 20% of the wind turbine cost,
includes the blades for converting wind energy to low speed rotational
energy.
- The generator, which is approximately 34% of the wind turbine cost, includes the electrical generator, the control electronics, and most likely a gear box (e.g. planetary gear box), adjustable-speed drive or continuously variable transmission component for converting the low-speed incoming rotation to high-speed rotation suitable for generating electricity.
- The surrounding structure, which is approximately 15% of the wind turbine cost, includes the tower and rotor yaw mechanism.
Nacelle of a wind turbine
A 1.5 (
MW)
wind turbine of a type frequently seen in the United States has a tower
80 meters (260 ft) high. The rotor assembly (blades and hub) weighs
22,000 kilograms (48,000 lb). The nacelle, which contains the generator,
weighs 52,000 kilograms (115,000 lb). The concrete base for the tower
is constructed using 26,000 kilograms (58,000 lb) reinforcing steel and
contains 190 cubic meters (250 cu yd) of concrete. The base is 15 meters
(50 ft) in diameter and 2.4 meters (8 ft) thick near the center.
Turbine monitoring and diagnostics
Due to data transmission problems,
structural health monitoring
of wind turbines is usually performed using several accelerometers and
strain gages attached to the nacelle to monitor the gearbox and
equipments. Currently, digital image correlation and
stereophotogrammetry are used to measure dynamics of wind turbine
blades. These methods usually measure displacement and strain to
identify location of defects. Dynamic characteristics of non-rotating
wind turbines have been measured using digital image correlation and
photogrammetry. Three dimensional point tracking has also been used to measure rotating dynamics of wind turbines.
Materials and recent developments
Materials
that are typically used for the rotor blades in wind turbines are
composites, as they tend to have a high stiffness, high strength, high
fatigue resistance, and low weight.
Typical resins used for these composites include polyester and epoxy,
while glass and carbon fibers have been used for the reinforcing
material.
Construction may use manual layup techniques or composite resin
injection molding. As the price of glass fibers is only about one tenth
the price of carbon fiber,
glass fiber is still dominant.
New designs
As
competition in the wind market increases, companies are seeking ways to
draw greater efficiency from their designs. One of the predominant ways
wind turbines have gained performance is by increasing rotor diameters,
and thus blade length. Retrofitting current turbines with larger blades
mitigates the need and risks associated with a system-level redesign.
As the size of the blade increases, its tendency to deflect also
increases. Thus, from a materials perspective, the stiffness-to-weight
is of major importance. As the blades need to function over a 100
million load cycles over a period of 20–25 years, the fatigue life of
the blade materials is also of utmost importance. By incorporating
carbon fiber into parts of existing blade systems, manufacturers may
increase the length of the blades without increasing their overall
weight. For instance, the spar cap, a structural element of a turbine
blade, commonly experiences high tensile loading, making it an ideal
candidate to utilize the enhanced tensile properties of carbon fiber in
comparison to glass fiber. Higher stiffness and lower density translates to thinner, lighter blades offering equivalent performance. In a 10 (
MW)
turbine—which will become more common in offshore systems by
2021—blades may reach over 100 m in length and weigh up to 50 metric
tons when fabricated out of glass fiber. A switch to carbon fiber in the
structural spar of the blade yields weight savings of 20 to 30 percent,
or approximately 15 metric tons.
Materials for blades
Some of the most common materials which are being used for turbine blades now and will be in the future are summarized below:
Glass and carbon fibers
The
stiffness of composites is determined by the stiffness of fibers and
their volume content. Typically, E-glass fibers are used as main
reinforcement in the composites. Typically, the glass/epoxy composites
for wind blades contain up to 75 weight % glass. This increases the
stiffness, tensile and compression strength. A promising source of the
composite materials in the future is glass fibers with modified
compositions like S-glass, R-glass etc. Some other special glasses
developed by Owens Corning are ECRGLAS, Advantex and most recently
WindStrand glass fibers.
Hybrid reinforcements
These
include E-glass/carbon, E-glass/aramid and they present an exciting
alternative to pure glass or carbon reinforcements. that the full
replacement would lead to 80% weight savings, and cost increase by 150%,
while a partial (30%) replacement would lead to only 90% cost increase
and 50% weight reduction for 8 m turbine. The world currently longest
wind turbine rotor blade, the 88.4 m long blade from LM Wind Power is
made of carbon/glass hybrid composites. However, additional
investigations are required for the optimal composition of the materials
Nano-engineered polymers and composites
Additions
of small amount (0.5 weight %) of nanoreinforcement (carbon nanotubes
or nanoclay in the polymer matrix of composites, fiber sizing or
interlaminar layers can allow to increase the fatigue resistance, shear
or compressive strength as well as fracture toughness of the composites
by 30–80%. Research has also shown that the incorporation of small
amount of carbon nanotubes/CNT can increase the lifetime up to 1500%.
Costs
While the
material cost is significantly lower for all-glass fiber blades than for
hybrid glass/carbon fiber blades, there is a potential for tremendous
savings in manufacturing costs when labor price is considered.
Utilizing carbon fiber enables for simpler designs that use less raw
material. The chief manufacturing process in blade fabrication is the
layering of plies. By reducing the number of layers of plies, as is
enabled by thinner blade design, the cost of labor may be decreased, and
in some cases, equate to the cost of labor for glass fiber blades.
Other materials
Materials
for wind turbine parts other than the rotor blades (including the rotor
hub, gearbox, frame, and tower) are largely composed of steel. Modern
turbines
use a couple of tons of copper for generators, cables, and such.
Smaller wind turbines have begun incorporating more aluminum based
alloys into these components in an effort to make the turbines lighter
and more efficient, and may continue to be used increasingly if fatigue
and strength properties can be improved. Prestressed concrete has been
increasingly used for the material of the tower, but still requires much
reinforcing steel to meet the strength requirement of the turbine.
Additionally, step-up gearboxes are being increasingly replaced with
variable speed generators, increasing the demand for magnetic materials
in wind turbines. In particular, this would require an increased supply of the rare earth metal
neodymium.
Recycling
Interest
in recycling blades varies in different markets and depends on the
waste legislation and local economics. A challenge in recycling blades
is related to the composite material, which is made of a thermosetting
matrix and glass fibers or a combination of glass and carbon fibers.
Thermosetting matrix cannot be remolded to form new composites. So the
options are either to reuse the blade and the composite material
elements as they are found in the blade or to transform the composite
material into a new source of material.
In Germany, wind turbine blades are commercially recycled as part of an
alternative fuel mix for a cement factory.
Supply
A study
of the material consumption trends and requirements for wind energy in
Europe found that bigger turbines have a higher consumption of precious
metals but lower material input per
kW
generated. The current material consumption and stock was compared to
input materials for various onshore system sizes. In all EU countries
the estimates for 2020 exceeded and doubled the values consumed in 2009.
These countries would need to expand their resources to be able to meet
the estimated demand for 2020. For example, currently the EU has 3% of
world supply of fluorspar and it requires 14% by 2020. Globally, the
main exporting countries are South Africa, Mexico and China. This is
similar with other critical and valuable materials required for energy
systems such as magnesium, silver and indium. In addition, the levels of
recycling of these materials is very low and focusing on that could
alleviate issues with supply in the future. It is important to note that
since most of these valuable materials are also used in other emerging
technologies, like
LEDs,
PVs and
LCDs, it is projected that demand for them will continue to increase.
A report by the United States Geological Survey estimated the
projected materials requirement in order to fulfill the US commitment to
supplying 20% of its electricity from wind power by 2030. They did not
address requirements for small turbines or offshore turbines since those
were not widely deployed in 2008, when the study was created. They
found that there are increases in common materials such as cast iron,
steel and concrete that represent 2–3% of the material consumption in
2008. Between 110,000 and 115,000 metric tons of fiber glass would be
required annually, equivalent to 14% of consumption in 2008. They did
not see a high increase in demand for rare metals compared to available
supply, however rare metals that are also being used for other
technologies such as batteries which are increasing its global demand
need to be taken into account. Land, whbich might not be considered a
material, is an important resource in deploying wind technologies.
Reaching the 2030 goal would require 50,000 square kilometers of onshore
land area and 11,000 square kilometers of offshore. This is not
considered a problem in the US due to its vast area and the ability to
use land for farming and grazing. A greater limitation for the
technology would be the variability and transmission infrastructure to
areas of higher demand.
Permanent magnets for wind turbine generators contain rare earth metals such as
Nd,
Pr,
Tb, and
Dy.
Systems that use magnetic direct drive turbines require higher amounts
of rare metals. Therefore, an increase in wind production would increase
the demand for these resources. It is estimated that the additional
demand for Nd in 2035 may be 4,000 to 18,000 tons and Dy could see an
increase of 200 to 1200 tons. These values represent a quarter to half
of current production levels. However, since technologies are developing
rapidly, driven by supply and price of materials these estimated levels
are extremely uncertain.
Reliance on rare earth minerals for components has risked expense
and price volatility as China has been main producer of rare earth
minerals (96% in 2009) and had been reducing its export quotas of these
materials. In recent years, however, other producers have increased production of
rare earth minerals
and China has removed its reduced export quota on rare earths leading
to an increased supply and decreased cost of rare earth minerals,
increasing the viability of the implementation of variable speed
generators in wind turbines on a large scale.
Due to increased technology and wide implementation, the global
glass fiber market might reach US$17.4 billion by 2024, compared to
US$8.5 billion in 2014. Since it is the most widely used material for
reinforcement in composites around the globe, the expansion of end use
applications such as construction, transportation and wind turbines has
fueled its popularity. Asia Pacific held the major share of the global
market in 2014 with more than 45% volume share. However China is
currently the largest producer. The industry receives subsidies from the
Chinese government allowing them to export it cheaper to the US and
Europe. However, due to the higher demand in the near future some price
wars have started to developed to implement anti dumping strategies such
as tariffs on Chinese glass fiber.
Wind turbines on public display
A few localities have exploited the attention-getting nature of wind
turbines by placing them on public display, either with visitor centers
around their bases, or with viewing areas farther away.
The wind turbines are generally of conventional horizontal-axis,
three-bladed design, and generate power to feed electrical grids, but
they also serve the unconventional roles of technology demonstration,
public relations, and education.
Small wind turbines
A small Quietrevolution QR5 Gorlov type
vertical axis wind turbine in Bristol, England. Measuring 3 m in
diameter and 5 m high, it has a nameplate rating of 6.5 kW to the grid.
Small wind turbines may be used for a variety of applications
including on- or off-grid residences, telecom towers, offshore
platforms, rural schools and clinics, remote monitoring and other
purposes that require energy where there is no electric grid, or where
the grid is unstable. Small wind turbines may be as small as a
fifty-watt generator for boat or
caravan
use. Hybrid solar and wind powered units are increasingly being used
for traffic signage, particularly in rural locations, as they avoid the
need to lay long cables from the nearest mains connection point. The
U.S. Department of Energy's National Renewable Energy Laboratory (NREL) defines small wind turbines as those smaller than or equal to 100 kilowatts. Small units often have direct drive generators,
direct current output, aeroelastic blades, lifetime bearings and use a vane to point into the wind.
Larger, more costly turbines generally have geared power trains,
alternating current output, flaps and are actively pointed into the
wind. Direct drive generators and aeroelastic blades for large wind
turbines are being researched.
Wind turbine spacing
On
most horizontal wind turbine farms, a spacing of about 6–10 times the
rotor diameter is often upheld. However, for large wind farms distances
of about 15 rotor diameters should be more economical, taking into
account typical wind turbine and land costs. This conclusion has been
reached by research conducted by
Charles Meneveau of the Johns Hopkins University, and Johan Meyers of Leuven University in Belgium, based on computer simulations
that take into account the detailed interactions among wind turbines
(wakes) as well as with the entire turbulent atmospheric boundary layer.
Recent research by John Dabiri of Caltech suggests that vertical
wind turbines may be placed much more closely together so long as an
alternating pattern of rotation is created allowing blades of
neighbouring turbines to move in the same direction as they approach one
another.
Operability
Maintenance
Wind turbines need regular
maintenance to stay
reliable and
available, in the best case turbines are available to generate energy 98% of the time.
Modern turbines usually have a small onboard
crane
for hoisting maintenance tools and minor components. However, large
heavy components like generator, gearbox, blades and so on are rarely
replaced and a
heavy lift external crane is needed in those cases. If the turbine has a difficult access road, a
containerized crane can be lifted up by the internal crane to provide heavier lifting.
Repowering
Installation of new wind turbines can be controversial. An
alternative is repowering, where existing wind turbines are replaced
with bigger, more powerful ones, sometimes in smaller numbers while
keeping or increasing capacity.
Demolition
Older
turbines were in some early cases not required to be removed when
reaching the end of their life. Some still stand, waiting to be
recycled or repowered.
A
demolition industry develops to recycle offshore turbines at a cost of DKK 2–4 million per (
MW), to be guaranteed by the owner.
Comparison with fossil-fuel turbines
Advantages
Wind
turbines are generally inexpensive. They will produce electricity at
between two and six cents per kilowatt hour, which is one of the
lowest-priced renewable energy sources.
And as technology needed for wind turbines continues to improve, the
prices will decrease as well. In addition, there is no competitive
market for wind energy, as it does not cost money to get ahold of wind.
The main cost of wind turbines are the installation process. The
average cost is between $48,000 and $65,000 to install. However, the
energy harvested from the turbine will offset the installation cost, as
well as provide virtually free energy for years after.
Wind turbines provide a clean energy source, emitting no
greenhouse gases and no waste product. Over 1,500 tons of carbon
dioxide per year can be eliminated by using a one megawatt turbine
instead of one megawatt of energy from a fossil fuel. Being environmentally friendly and green is a large advantage of wind turbines.
Disadvantages
Wind turbines can be very large, reaching over 140 metres (460 ft) tall and with blades 55 metres (60 yd) long, and people have often complained about their visual impact.
Environmental impact of wind power includes effect on wildlife, but can be mitigated if proper monitoring and mitigation strategies are implemented. Thousands of birds, including rare species, have been killed by the blades of wind turbines,
though wind turbines contribute relatively insignificantly to
anthropogenic avian mortality. For every bird killed by a wind turbine
in the US, nearly 500,000 are killed by each of feral cats and
buildings.
In comparison, conventional coal fired generators contribute
significantly more to bird mortality, by incineration when caught in
updrafts of smoke stacks and by poisoning with emissions byproducts
(including particulates and heavy metals downwind of flue gases).
Further, marine life is affected by water intakes of steam turbine
cooling towers (heat exchangers) for nuclear and fossil fuel generators,
by coal dust deposits in marine ecosystems (e.g. damaging Australia's
Great Barrier Reef) and by water acidification from combustion
monoxides.
Energy harnessed by wind turbines is intermittent, and is not a
"dispatchable" source of power; its availability is based on whether the
wind is blowing, not whether electricity is needed. Turbines can be
placed on ridges or bluffs to maximize the access of wind they have, but
this also limits the locations where they can be placed. In this way, wind energy is not a particularly reliable source of energy. However, it can form part of the
energy mix,
which also includes power from other sources. Notably, the relative
available output from wind and solar sources is often inversely
proportional (balancing)
[citation needed]. Technology is also being developed to store excess energy, which can then make up for any deficits in supplies.
Records
Fuhrländer Wind Turbine Laasow, in Brandenburg, Germany, among the world's tallest wind turbines
- Largest capacity conventional drive
- The Vestas V164 has a rated capacity of 8 MW, later upgraded to 9.5 MW.
The wind turbine has an overall height of 220 m (722 ft), a diameter of
164 m (538 ft), is for offshore use, and is the world's
largest-capacity wind turbine since its introduction in 2014. The
conventional drive train consist of a main gearbox and a medium speed PM
generator. Prototype installed in 2014 at the National Test Center Denmark nearby Østerild. Series production began end of 2015.
- Largest capacity direct drive
- The Enercon E-126 with 7.58 MW and 127 m rotor diameter is the largest direct drive turbine. However, the turbine is the world's most powerful onshore-only
wind turbine. The turbine has parted rotor blades with 2 sections for
transport. The E-126 was later overtaken by the Siemens SWT-8.0-167-DD
(DD being the acronym for "direct drive"), which is the most powerful offshore-only wind turbine.
- Largest vertical-axis
- Le Nordais wind farm in Cap-Chat, Quebec has a vertical axis wind turbine (VAWT) named Éole, which is the world's largest at 110 m. It has a nameplate capacity of 3.8 MW.
- Largest 1-bladed turbine
- The largest single-bladed wind turbine design to be put into
complete operation is the MBB Messerschmitt Monopteros M50, with a total
power output of no less than 640kW at full capacity. As far as the
number of units is concerned, only three ever have been installed at an
actual wind park, of which all went to the Jade Wind Park [de].
- Largest 2-bladed turbine
- The biggest 2-bladed turbine is built by Mingyang Wind Power in 2013. It is a SCD6.5MW offshore downwind turbine, designed by aerodyn Energiesysteme.
- Largest swept area
- The turbine with the largest swept area is the Samsung S7.0–171, with a diameter of 171 m, giving a total sweep of 22966 m2.
- Tallest
- A Nordex 3.3 MW
was installed in July 2016. It has a total height of 230m, and a hub
height of 164m on 100m concrete tower bottom with steel tubes on top
(hybrid tower).
-
- Vestas V164 was the tallest wind turbine, standing in Østerild, Denmark, 220 meters tall, constructed in 2014. It has a steel tube tower.
- Highest tower
- Fuhrländer installed a 2.5 MW turbine on a 160m lattice tower in 2003 (see Fuhrländer Wind Turbine Laasow and Nowy Tomyśl Wind Turbines).
- Most rotors
- Lagerwey has build Four-in-One, a multi rotor wind turbine with one tower and four rotors near Maasvlakte.[citation needed] In April 2016, Vestas installed a 900 kW four rotor test wind turbine at Risø, made from 4 recycled 225 kW V29 turbines.
- Most productive
- Four turbines at Rønland Offshore Wind Farm in Denmark share the record for the most productive wind turbines, with each having generated 63.2 GWh by June 2010.
- Highest-situated
- Since 2013 the world's highest-situated wind turbine was made and installed by WindAid and is located at the base of the Pastoruri Glacier in Peru at 4,877 meters (16,001 ft) above sea level. The site uses the WindAid 2.5 kW
wind generator to supply power to a small rural community of micro
entrepreneurs who cater to the tourists who come to the Pastoruri
glacier.
- Largest floating wind turbine
- The world's largest—and also the first operational deep-water large-capacity—floating wind turbine is the 2.3 MW Hywind currently operating 10 kilometers (6.2 mi) offshore in 220-meter-deep water, southwest of Karmøy, Norway. The turbine began operating in September 2009 and utilizes a Siemens 2.3 MW turbine.
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