Wind power
From Wikipedia, the free encyclopedia
Burbo Bank Offshore Wind Farm, at the entrance to the
River Mersey in northwest England.
Wind power is the conversion of wind energy into a useful form of energy, such as using wind turbines to produce electrical power, windmills for mechanical power, windpumps for water pumping or drainage, or sails to propel ships.
Large
wind farms consist of hundreds of individual wind turbines which are connected to the
electric power transmission
network. For new constructions, onshore wind is an inexpensive source
of electricity, competitive with or in many places cheaper than fossil
fuel plants.
[1][2]
Offshore wind is steadier and stronger than on land, and offshore farms
have less visual impact, but construction and maintenance costs are
considerably higher. Small onshore wind farms can feed some energy into
the grid or provide electricity to isolated off-grid locations.
[3]
Wind power, as an alternative to
fossil fuels, is plentiful,
renewable, widely distributed,
clean, produces no
greenhouse gas emissions during operation and uses little land.
[4] The
effects on the environment are generally less problematic than those from other power sources. As of 2011,
Denmark is generating
more than a quarter of its electricity from wind and 83 countries
around the world are using wind power to supply the electricity grid.
[5]
In 2010 wind energy production was over 2.5% of total worldwide
electricity usage, and growing rapidly at more than 25% per annum.
Wind power is very consistent from year to year but has significant
variation over shorter time scales. As the proportion of windpower in a
region increases, a need to upgrade the grid, and a lowered ability to
supplant conventional production can occur.
[6][7]
Power management techniques such as having excess capacity storage,
geographically distributed turbines, dispatchable backing sources,
storage such as
pumped-storage hydroelectricity,
exporting and importing power to neighboring areas or reducing demand
when wind production is low, can greatly mitigate these problems.
[8] In addition,
weather forecasting permits the electricity network to be readied for the predictable variations in production that occur.
[9][10] Wind power can be considered a topic in
applied eolics.
[11]
History
Wind power has been used as long as humans have put
sails into the wind. For more than two millennia
wind-powered machines
have ground grain and pumped water. Wind power was widely available and
not confined to the banks of fast-flowing streams, or later, requiring
sources of fuel. Wind-powered pumps drained the
polders of the Netherlands, and in arid regions such as the
American mid-west or the
Australian outback,
wind pumps provided water for live stock and steam engines.
The first windmill used for the production of electricity was built in
Scotland in July 1887 by
Prof James Blyth of
Anderson's College, Glasgow (the precursor of
Strathclyde University).
[12] Blyth's 10 m high, cloth-sailed wind turbine was installed in the garden of his holiday cottage at
Marykirk in
Kincardineshire and was used to charge
accumulators developed by the Frenchman
Camille Alphonse Faure, to power the lighting in the cottage,
[12] thus making it the first house in the world to have its electricity supplied by wind power.
[13]
Blyth offered the surplus electricity to the people of Marykirk for
lighting the main street, however, they turned down the offer as they
thought electricity was "the work of the devil."
[12] Although he later built a wind turbine to supply emergency power to the local Lunatic Asylum, Infirmary and Dispensary of
Montrose the invention never really caught on as the technology was not considered to be economically viable.
[12]
Across the Atlantic, in
Cleveland, Ohio a larger and heavily engineered machine was designed and constructed in the winter of 1887-1888 by
Charles F. Brush,
[14] this was built by his engineering company at his home and operated from 1886 until 1900.
[15]
The Brush wind turbine had a rotor 17 m (56 foot) in diameter and was
mounted on an 18 m (60 foot) tower. Although large by today's standards,
the machine was only rated at 12 kW. The connected dynamo was used
either to charge a bank of batteries or to operate up to 100
incandescent light bulbs, three arc lamps, and various motors in Brush's laboratory.
[16]
With the development of electric power, wind power found new
applications in lighting buildings remote from centrally-generated
power. Throughout the 20th century parallel paths developed small wind
plants suitable for farms or residences, and larger utility-scale wind
generators that could be connected to electricity grids for remote use
of power. Today wind powered generators operate in every size range
between tiny plants for battery charging at isolated residences, up to
near-gigawatt sized
offshore wind farms that provide electricity to national electrical networks.
Wind farms
A wind farm is a group of
wind turbines
in the same location used for production of electricity. A large wind
farm may consist of several hundred individual wind turbines distributed
over an extended area, but the land between the turbines may be used
for agricultural or other purposes. A wind farm may also be located
offshore.
Almost all large wind turbines have the same design — a horizontal
axis wind turbine having an upwind rotor with three blades, attached to a
nacelle on top of a tall tubular tower.
In a
wind farm,
individual turbines are interconnected with a medium voltage (often
34.5 kV), power collection system and communications network. At a
substation, this medium-voltage electric current is increased in voltage
with a
transformer for connection to the high voltage
electric power transmission system.
[citation needed]
Feeding into grid
Induction generators, often used for wind power, require
reactive power for
excitation so
substations used in wind-power collection systems include substantial
capacitor banks for
power factor correction.
[28] Different types of wind turbine generators behave differently during transmission grid disturbances, so
extensive modelling
of the dynamic electromechanical characteristics of a new wind farm is
required by transmission system operators to ensure predictable stable
behaviour during system faults (see:
Low voltage ride through).
In particular, induction generators cannot support the system voltage
during faults, unlike steam or hydro turbine-driven synchronous
generators.
Doubly fed machines generally have more desirable properties for grid interconnection.
[29][30] Transmission systems operators will supply a wind farm developer with a
grid code to specify the requirements for interconnection to the transmission grid. This will include
power factor, constancy of
frequency and dynamic behavior of the wind farm turbines during a system fault.
[31][32]
Offshore wind power
Offshore wind power refers to the construction of wind farms in large
bodies of water to generate electricity. These installations can
utilise the more frequent and powerful winds that are available in these
locations and have less aesthetic impact on the landscape than land
based projects. However, the construction and the maintenance costs are
considerably higher.
[33][34]
Siemens and
Vestas are the leading turbine suppliers for offshore wind power.
DONG Energy,
Vattenfall and
E.ON are the leading offshore operators.
[35] As of October 2010, 3.16 GW of offshore wind power capacity was operational, mainly in Northern Europe. According to
BTM Consult,
more than 16 GW of additional capacity will be installed before the end
of 2014 and the UK and Germany will become the two leading markets.
Offshore wind power capacity is expected to reach a total of 75 GW
worldwide by 2020, with significant contributions from China and the US.
[35]
At the end of 2012, 1,662 turbines at 55 offshore wind farms in 10
European countries are generating 18 TWh, which can power almost five
million households.
[36] As of August 2013 the
London Array in the
United Kingdom is the largest offshore wind farm in the world at 630
MW. This is followed by the
Greater Gabbard Wind Farm (504 MW), also in the UK. The
Gwynt y Môr wind farm (576 MW) is the largest project currently under construction.
[citation needed]
Wind power capacity and production
Worldwide wind generation up to 2010
Worldwide there are now over two hundred thousand wind turbines operating, with a total
nameplate capacity of 282,482 MW as of end 2012.
[37] The
European Union alone passed some 100,000 MW nameplate capacity in September 2012,
[38] while the United States surpassed 50,000 MW in August 2012 and
China's grid connected capacity passed 50,000 MW the same month.
[39][40]
World wind generation capacity more than quadrupled between 2000 and 2006, doubling about every three years.
The United States pioneered wind farms
and led the world in installed capacity in the 1980s and into the
1990s. In 1997 German installed capacity surpassed the U.S. and led
until once again overtaken by the U.S. in 2008. China has been rapidly
expanding its wind installations in the late 2000s and passed the U.S.
in 2010 to become the world leader.
At the end of 2013, worldwide
nameplate capacity of wind-powered generators was 318
gigawatts (GW), growing by 35 GW over the preceding year.
[37] According to the
World Wind Energy Association, an industry organization, in 2010 wind power generated 430 TWh or about 2.5% of worldwide electricity usage,
[41] up from 1.5% in 2008 and 0.1% in 1997.
[42] Between 2005 and 2010 the average annual growth in new installations was 27.6%.
[43] Wind power market penetration is expected to reach 3.35% by 2013 and 8% by 2018.
[43][44]
The actual amount of electricity that wind is able to generate is calculated by multiplying the nameplate capacity by the
capacity factor,
which varies according to equipment and location. Estimates of the
capacity factors for wind installations are in the range of 35% to 44%.
[45]
Several countries have already achieved relatively high levels of
penetration, such as 28% of stationary (grid) electricity production in
Denmark (2011),
[46] 19% in
Portugal (2011),
[47] 16% in
Spain (2011),
[48] 16% in
Ireland (2012)
[49] and 8% in
Germany (2011).
[50] As of 2011, 83 countries around the world were using wind power on a commercial basis.
[5]
Europe
accounted for 48% of the world total wind power generation capacity in
2009. In 2010, Spain became Europe's leading producer of wind energy,
achieving 42,976 GWh. Germany held the top spot in Europe in terms of
installed capacity, with a total of 27,215 MW as of 31 December 2010.
[51]
Top 10 countries
by nameplate windpower capacity
(2013 year-end)[37]
China |
16,088 |
91,412 |
28.7 |
United States |
1,084 |
61,091 |
19.2 |
Germany |
3,238 |
34,250 |
10.8 |
Spain |
175 |
22,959 |
7.2 |
India |
1,729 |
20,150 |
6.3 |
UK |
1,883 |
10,531 |
3.3 |
Italy |
444 |
8,552 |
2.7 |
France |
631 |
8,254 |
2.6 |
Canada |
1,599 |
7,803 |
2.5 |
Denmark |
657 |
4,772 |
1.5 |
(rest of world) |
7,761 |
48,332 |
15.2 |
World total |
35,289 MW |
318,105 MW |
100% |
|
Top 10 countries
by windpower electricity production
(2012 totals)[52]
Country |
Windpower production
(TWh) |
% world total |
United States |
140.9 |
26.4 |
China |
118.1 |
22.1 |
Spain |
49.1 |
9.2 |
Germany |
46.0 |
8.6 |
India |
30.0 |
5.6 |
UK |
19.6 |
3.7 |
France |
14.9 |
2.8 |
Italy |
13.4 |
2.5 |
Canada |
11.8 |
2.2 |
Denmark |
10.3 |
1.9 |
(rest of world) |
80.2 |
15.0 |
World total |
534.3 TWh |
100% |
|
Growth trends
Worldwide installed capacity 1997–2020 [MW], developments and prognosis. Data source: WWEA
[53]
In 2010, more than half of all new wind power was added outside of
the traditional markets in Europe and North America. This was largely
from new construction in China, which accounted for nearly half the new
wind installations (16.5 GW).
[56]
Global Wind Energy Council (GWEC) figures show that 2007 recorded an
increase of installed capacity of 20 GW, taking the total installed wind
energy capacity to 94 GW, up from 74 GW in 2006. Despite constraints
facing supply chains for wind turbines, the annual market for wind
continued to increase at an estimated rate of 37%, following 32% growth
in 2006. In terms of economic value, the wind energy sector has become
one of the important players in the energy markets, with the total value
of new generating equipment installed in 2007 reaching €25 billion, or
US$36 billion.
[57]
Although the
wind power industry was affected by the
global financial crisis in 2009 and 2010, a
BTM Consult
five-year forecast up to 2013 projects substantial growth. Over the
past five years the average growth in new installations has been 27.6%
each year. In the forecast to 2013 the expected average annual growth
rate is 15.7%.
[43][44]
More than 200 GW of new wind power capacity could come on line before
the end of 2014. Wind power market penetration is expected to reach
3.35% by 2013 and 8% by 2018.
[43][44]
Capacity factor
Since wind speed is not constant, a wind farm's annual
energy
production is never as much as the sum of the generator nameplate
ratings multiplied by the total hours in a year. The ratio of actual
productivity in a year to this theoretical maximum is called the
capacity factor.
Typical capacity factors are 15–50%; values at the upper end of the
range are achieved in favourable sites and are due to wind turbine
design improvements.
[58][59][nb 1]
Online data is available for some locations, and the capacity factor can be calculated from the yearly output.
[60][61]
For example, the German nation-wide average wind power capacity factor
over all of 2012 was just under 17.5%
(45867 GW·h/yr / (29.9 GW × 24 × 366) = 0.1746),
[62] and the capacity factor for Scottish wind farms averaged 24% between 2008 and 2010.
[63]
Unlike fueled generating plants, the capacity factor is affected by
several parameters, including the variability of the wind at the site
and the size of the
generator
relative to the turbine's swept area. A small generator would be
cheaper and achieve a higher capacity factor but would produce less
electricity
(and thus less profit) in high winds. Conversely, a large generator
would cost more but generate little extra power and, depending on the
type, may
stall out at low wind speed. Thus an optimum capacity factor of around 40–50% would be aimed for.
[59][64]
In a 2008 study released by the U.S. Department of Energy's Office of
Energy Efficiency and Renewable Energy, the capacity factor achieved by
the U.S. wind turbine fleet is shown to be increasing as the technology
improves. The capacity factor achieved by new wind turbines in 2010
reached almost 40%.
[65][66]
Penetration
A panoramic view of the United Kingdom's
Whitelee Wind Farm with Lochgoin Reservoir in the foreground.
Wind energy penetration refers to the fraction of energy produced by
wind compared with the total available generation capacity. There is no
generally accepted maximum level of wind penetration. The limit for a
particular
grid will depend on the existing generating plants, pricing mechanisms, capacity for
energy storage, demand management and other factors. An interconnected electricity grid will already include
reserve generating and
transmission capacity
to allow for equipment failures. This reserve capacity can also serve
to compensate for the varying power generation produced by wind plants.
Studies have indicated that 20% of the total annual electrical energy
consumption may be incorporated with minimal difficulty.
[67] These studies have been for locations with geographically dispersed wind farms, some degree of
dispatchable energy or
hydropower
with storage capacity, demand management, and interconnected to a large
grid area enabling the export of electricity when needed. Beyond the
20% level, there are few technical limits, but the economic implications
become more significant. Electrical utilities continue to study the
effects of large scale penetration of wind generation on system
stability and economics.
[68][69][70][71]
A wind energy penetration figure can be specified for different
durations of time. On an annual basis, as of 2011, few grid systems have
penetration levels above 5%: Denmark – 29%, Portugal – 19%, Spain –
19%, Ireland – 18%, and Germany – 11%. For the U.S. in 2011, the
penetration level was estimated at 3.3%.
[72]
To obtain 100% from wind annually requires substantial long term
storage. On a monthly, weekly, daily, or hourly basis—or less—wind can
supply as much as or more than 100% of current use, with the rest stored
or exported. Seasonal industry can take advantage of high wind and low
usage times such as at night when wind output can exceed normal demand.
Such industry can include production of silicon, aluminum, steel, or of
natural gas, and hydrogen, which allow long term storage, facilitating
100% energy from
variable renewable energy.
[73][74]
Homes can also be programmed to accept extra electricity on demand, for
example by remotely turning up water heater thermostats.
[75]
Variability
Electricity generated from wind power can be highly variable at
several different timescales: hourly, daily, or seasonally. Annual
variation also exists, but is not as significant. Because instantaneous
electrical generation and consumption must remain in balance to maintain
grid stability, this variability can present substantial challenges to
incorporating large amounts of wind power into a grid system.
Intermittency and the non-
dispatchable nature of wind energy production can raise costs for regulation, incremental
operating reserve, and (at high penetration levels) could require an increase in the already existing
energy demand management,
load shedding, storage solutions or system interconnection with
HVDC cables.
Fluctuations in load and allowance for failure of large fossil-fuel
generating units require reserve capacity that can also compensate for
variability of wind generation.
Wind power is however, variable, but during low wind periods it can
be replaced by other power sources. Transmission networks presently cope
with outages of other generation plants and daily changes in electrical
demand, but the variability of
intermittent power sources
such as wind power, are unlike those of conventional power generation
plants which, when scheduled to be operating, may be able to deliver
their nameplate capacity around 95% of the time.
Presently, grid systems with large wind penetration require a small increase in the frequency of usage of
natural gas
spinning reserve power plants to prevent a loss of electricity in the
event that conditions are not favorable for power production from the
wind. At lower wind power grid penetration, this is less of an issue.
[76][77][78]
GE has installed a prototype wind turbine with onboard battery
similar to that of an electric car, equivalent of 1 minute of
production. Despite the small capacity, it is enough to guarantee that
power output complies with forecast for 15 minutes, as the battery is
used to eliminate the difference rather than provide full output. The
increased predictability can be used to take wind power penetration from
20 to 30 or 40 per cent. The battery cost can be retrieved by selling
burst power on demand and reducing backup needs from gas plants.
[79]
A report on Denmark's wind power noted that their wind power network
provided less than 1% of average demand on 54 days during the year 2002.
[80]
Wind power advocates argue that these periods of low wind can be dealt
with by simply restarting existing power stations that have been held in
readiness, or interlinking with HVDC.
[81]
Electrical grids with slow-responding thermal power plants and without
ties to networks with hydroelectric generation may have to limit the use
of wind power.
[80]
According to a 2007 Stanford University study published in the Journal
of Applied Meteorology and Climatology, interconnecting ten or more wind
farms can allow an average of 33% of the total energy produced (i.e.
about 8% of total nameplate capacity) to be used as reliable,
baseload electric power which can be relied on to handle peak loads, as long as minimum criteria are met for wind speed and turbine height.
[82][83]
Conversely, on particularly windy days, even with penetration levels
of 16%, wind power generation can surpass all other electricity sources
in a country. In Spain, on 16 April 2012 wind power production reached
the highest percentage of electricity production till then, with wind
farms covering 60.46% of the total demand.
[84]
In Denmark, which had power market penetration of 30% in 2013, over
90 hours, wind power generated 100% of the countries power, peaking at
122% of the countries demand at 2am on the 28th October.
[85]
A 2006
International Energy Agency
forum presented costs for managing intermittency as a function of
wind-energy's share of total capacity for several countries, as shown in
the table on the right. Three reports on the wind variability in the UK
issued in 2009, generally agree that variability of wind needs to be
taken into account, but it does not make the grid unmanageable. The
additional costs, which are modest, can be quantified.
[7]
The combination of diversifying variable renewables by type and
location, forecasting their variation, and integrating them with
dispatchable renewables, flexible fueled generators, and demand response
can create a power system that has the potential to meet power supply
needs reliably. Integrating ever-higher levels of renewables is being
successfully demonstrated in the real world:
[86]
In 2009, eight American and three European authorities, writing in
the leading electrical engineers' professional journal, didn't find "a
credible and firm technical limit to the amount of wind energy that can
be accommodated by electricity grids". In fact, not one of more than 200
international studies, nor official studies for the eastern and western
U.S. regions, nor the International Energy Agency,
has found major costs or technical barriers to reliably integrating up
to 30% variable renewable supplies into the grid, and in some studies
much more. – Reinventing Fire[86]
Solar power tends to be complementary to wind.
[87][88] On daily to weekly timescales,
high pressure areas tend to bring clear skies and low surface winds, whereas
low pressure areas
tend to be windier and cloudier. On seasonal timescales, solar energy
peaks in summer, whereas in many areas wind energy is lower in summer
and higher in winter.
[nb 2][89]
Thus the intermittencies of wind and solar power tend to cancel each
other somewhat. In 2007 the Institute for Solar Energy Supply Technology
of the
University of Kassel pilot-tested a
combined power plant linking solar, wind,
biogas and
hydrostorage to provide load-following power around the clock and throughout the year, entirely from renewable sources.
[90]
Predictability
Wind power forecasting methods are used, but predictability of any
particular wind farm is low for short-term operation. For any particular
generator there is an 80% chance that wind output will change less than
10% in an hour and a 40% chance that it will change 10% or more in
5 hours.
[91]
However, studies by Graham Sinden (2009) suggest that, in practice,
the variations in thousands of wind turbines, spread out over several
different sites and wind regimes, are smoothed. As the distance between
sites increases, the correlation between wind speeds measured at those
sites, decreases.
[92]
Thus, while the output from a single turbine can vary greatly and
rapidly as local wind speeds vary, as more turbines are connected over
larger and larger areas the average power output becomes less variable
and more predictable.
[93]
Energy storage
Typically, conventional
hydroelectricity
complements wind power very well. When the wind is blowing strongly,
nearby hydroelectric plants can temporarily hold back their water. When
the wind drops they can, provided they have the generation capacity,
rapidly increase production to compensate. This gives a very even
overall power supply and virtually no loss of energy and uses no more
water.
Alternatively, where a suitable head of water is not available,
pumped-storage hydroelectricity or other forms of
grid energy storage such as
compressed air energy storage and
thermal energy storage can store energy developed by high-wind periods and release it when needed.
[94]
The type of storage needed depends on the wind penetration level – low
penetration requires daily storage, and high penetration requires both
short and long term storage – as long as a month or more. Stored energy
increases the economic value of wind energy since it can be shifted to
displace higher cost generation during peak demand periods. The
potential revenue from this
arbitrage
can offset the cost and losses of storage; the cost of storage may add
25% to the cost of any wind energy stored but it is not envisaged that
this would apply to a large proportion of wind energy generated. For
example, in the UK, the 1.7 GW
Dinorwig pumped-storage plant
evens out electrical demand peaks, and allows base-load suppliers to
run their plants more efficiently. Although pumped-storage power systems
are only about 75% efficient, and have high installation costs, their
low running costs and ability to reduce the required electrical
base-load can save both fuel and total electrical generation costs.
[95][96]
In particular geographic regions, peak wind speeds may not coincide
with peak demand for electrical power. In the U.S. states of
California and
Texas, for example, hot days in summer may have low wind speed and high electrical demand due to the use of
air conditioning. Some utilities subsidize the purchase of
geothermal heat pumps by their customers, to reduce electricity demand during the summer months by making air conditioning up to 70% more efficient;
[97]
widespread adoption of this technology would better match electricity
demand to wind availability in areas with hot summers and low summer
winds. A possible future option may be to interconnect widely dispersed
geographic areas with an HVDC "
super grid".
In the U.S. it is estimated that to upgrade the transmission system to
take in planned or potential renewables would cost at least $60 billion.
[98]
Germany has an installed capacity of wind and solar that can exceed
daily demand, and has been exporting peak power to neighboring
countries, with exports which amounted to some 14.7 billion kilowatt
hours in 2012.
[99]
A more practical solution is the installation of thirty days storage
capacity able to supply 80% of demand, which will become necessary when
most of Europe's energy is obtained from wind power and solar power.
Just as the EU requires member countries to maintain 90 days
strategic reserves
of oil it can be expected that countries will provide electricity
storage, instead of expecting to use their neighbors for net metering.
[100]
Wind power hardly ever suffers major technical failures, since
failures of individual wind turbines have hardly any effect on overall
power, so that the distributed wind power is highly reliable and
predictable,
[101] whereas conventional generators, while far less variable, can suffer major unpredictable outages.
Capacity credit and fuel savings
The capacity credit of wind is estimated by determining the capacity
of conventional plants displaced by wind power, whilst maintaining the
same degree of system security,.
[102] However, the precise value is irrelevant since the main value of wind is its fuel and
CO
2 savings,
[citation needed] and wind is not expected to be constantly available.
[103]
Economics
Wind turbines reached
grid parity
(the point at which the cost of wind power matches traditional sources)
in some areas of Europe in the mid-2000s, and in the US around the same
time. Falling prices continue to drive the levelized cost down and it
has been suggested that it has reached general grid parity in Europe in
2010, and will reach the same point in the US around 2016 due to an
expected reduction in capital costs of about 12%.
[1]
Cost trends
Estimated cost per MWh for wind power in Denmark
A turbine blade convoy passing through
Edenfield in the U.K. (2008). Even longer
two-piece blades are now manufactured, and then assembled on-site to reduce difficulties in transportation.
Wind power is
capital intensive, but has no fuel costs.
[105] The price of wind power is therefore much more stable than the volatile prices of fossil fuel sources.
[106] The
marginal cost of wind energy once a plant is constructed is usually less than 1-cent per kW·h.
[107]
This cost has additionally reduced as wind turbine technology has
improved. There are now longer and lighter wind turbine blades,
improvements in turbine performance and increased power generation
efficiency. Also, wind project capital and maintenance costs have
continued to decline.
[108]
The estimated
average cost
per unit incorporates the cost of construction of the turbine and
transmission facilities, borrowed funds, return to investors (including
cost of risk), estimated annual production, and other components,
averaged over the projected useful life of the equipment, which may be
in excess of twenty years. Energy cost estimates are highly dependent on
these assumptions so published cost figures can differ substantially.
In 2004, wind energy cost a fifth of what it did in the 1980s, and some
expected that downward trend to continue as larger multi-megawatt
turbines were mass-produced.
[109] As of 2012 capital costs for wind turbines are substantially lower than 2008–2010 but are still above 2002 levels.
[110]
A 2011 report from the American Wind Energy Association stated, "Wind's
costs have dropped over the past two years, in the range of 5 to 6
cents per kilowatt-hour recently.... about 2 cents cheaper than
coal-fired electricity, and more projects were financed through debt
arrangements than tax equity structures last year.... winning more
mainstream acceptance from Wall Street's banks.... Equipment makers can
also deliver products in the same year that they are ordered instead of
waiting up to three years as was the case in previous cycles.... 5,600
MW of new installed capacity is under construction in the United States,
more than double the number at this point in 2010. Thirty-five percent
of all new power generation built in the United States since 2005 has
come from wind, more than new gas and coal plants combined, as power
providers are increasingly enticed to wind as a convenient hedge against
unpredictable commodity price moves."
[111]
A British Wind Energy Association report gives an average generation
cost of onshore wind power of around 3.2 pence (between US 5 and 6
cents) per kW·h (2005).
[112]
Cost per unit of energy produced was estimated in 2006 to be comparable
to the cost of new generating capacity in the US for coal and natural
gas: wind cost was estimated at $55.80 per MW·h, coal at $53.10/MW·h and
natural gas at $52.50.
[113] Similar comparative results with natural gas were obtained in a governmental study in the UK in 2011.
[114]
The presence of wind energy, even when subsidised, can reduce costs for
consumers (€5 billion/yr in Germany) by reducing the marginal price, by
minimising the use of expensive
peaking power plants.
[115]
In February 2013
Bloomberg
New Energy Finance reported that the cost of generating electricity
from new wind farms is cheaper than new coal or new baseload gas plants.
When including the current
Australian federal government carbon pricing
scheme their modeling gives costs (in Australian dollars) of $80/MWh
for new wind farms, $143/MWh for new coal plants and $116/MWh for new
baseload gas plants. The modeling also shows that "even without a carbon
price (the most efficient way to reduce economy-wide emissions) wind
energy is 14% cheaper than new coal and 18% cheaper than new gas."
[116]
Part of the higher costs for new coal plants is due to high financial
lending costs because of "the reputational damage of emissions-intensive
investments". The expense of gas fired plants is partly due to "export
market" effects on local prices. Costs of production from coal fired
plants built in "the 1970s and 1980s" are cheaper than renewable energy
sources because of depreciation.
[116]
The wind industry in the USA is now able to produce more power at
lower cost by using taller wind turbines with longer blades, capturing
the faster winds at higher elevations. This has opened up new
opportunities and in Indiana, Michigan, and Ohio, the price of power
from wind turbines built 300 feet to 400 feet above the ground can now
compete with conventional fossil fuels like coal. Prices have fallen to
about 4 cents per kilowatt-hour in some cases and utilities have been
increasing the amount of wind energy in their portfolio, saying it is
their cheapest option.
[117]
Incentives and community benefits
U.S. landowners typically receive $3,000–$5,000 annual rental income per
wind turbine, while farmers continue to grow crops or graze cattle up
to the foot of the turbines.
[118] Shown: the
Brazos Wind Farm in Texas.
The U.S. wind industry generates tens of thousands of jobs and billions of dollars of economic activity.
[120]
Wind projects provide local taxes, or payments in lieu of taxes and
strengthen the economy of rural communities by providing income to
farmers with wind turbines on their land.
[118][121] Wind energy in many jurisdictions receives financial or other support to encourage its development. Wind energy benefits from
subsidies
in many jurisdictions, either to increase its attractiveness, or to
compensate for subsidies received by other forms of production which
have significant negative externalities.
In the US, wind power receives a production tax credit (PTC) of
1.5¢/kWh in 1993 dollars for each kW·h produced, for the first ten
years; at 2.2 cents per kW·h in 2012, the credit was renewed on 2
January 2012, to include construction begun in 2013.
[122] A 30% tax credit can be applied instead of receiving the PTC.
[123][124] Another tax benefit is
accelerated depreciation.
Many American states also provide incentives, such as exemption from
property tax, mandated purchases, and additional markets for "
green credits".
[125] The
Energy Improvement and Extension Act of 2008 contains extensions of credits for wind, including microturbines. Countries such as
Canada
and Germany also provide incentives for wind turbine construction, such
as tax credits or minimum purchase prices for wind generation, with
assured grid access (sometimes referred to as
feed-in tariffs). These feed-in tariffs are typically set well above average electricity prices.
[126][127] In December 2013 U.S. Senator
Lamar Alexander
and other Republican senators argued that the "wind energy production
tax credit should be allowed to expire at the end of 2013."
[128]
Secondary market forces also provide incentives for businesses to use wind-generated power, even if there is a
premium price for the electricity. For example,
socially responsible manufacturers
pay utility companies a premium that goes to subsidize and build new
wind power infrastructure. Companies use wind-generated power, and in
return they can claim that they are undertaking strong "green" efforts.
In the US the organization Green-e monitors business compliance with
these renewable energy credits.
[129]
Small-scale wind power
Small-scale wind power is the name given to wind generation systems
with the capacity to produce up to 50 kW of electrical power.
[130] Isolated communities, that may otherwise rely on
diesel
generators, may use wind turbines as an alternative. Individuals may
purchase these systems to reduce or eliminate their dependence on grid
electricity for economic reasons, or to reduce their
carbon footprint. Wind turbines have been used for household electricity generation in conjunction with
battery storage over many decades in remote areas.
[131]
Recent examples of small-scale wind power projects in an urban setting can be found in
New York City, where, since 2009, a number of building projects have capped their roofs with
Gorlov-type helical wind turbines.
Although the energy they generate is small compared to the buildings'
overall consumption, they help to reinforce the building's 'green'
credentials in ways that "showing people your high-tech boiler" can not,
with some of the projects also receiving the direct support of the
New York State Energy Research and Development Authority.
[132]
Grid-connected domestic wind turbines may use
grid energy storage,
thus replacing purchased electricity with locally produced power when
available. The surplus power produced by domestic microgenerators can,
in some jurisdictions, be fed into the network and sold to the utility
company, producing a retail credit for the microgenerators' owners to
offset their energy costs.
[133][134]
Off-grid system users can either adapt to intermittent power or use batteries,
photovoltaic
or diesel systems to supplement the wind turbine. Equipment such as
parking meters, traffic warning signs, street lighting, or wireless
Internet gateways may be powered by a small wind turbine, possibly
combined with a photovoltaic system, that charges a small battery
replacing the need for a connection to the power grid.
[135]
A
Carbon Trust
study into the potential of small-scale wind energy in the UK,
published in 2010, found that small wind turbines could provide up to
1.5 terawatt hours (TW·h) per year of electricity (0.4% of total UK
electricity consumption), saving 0.6 million tonnes of carbon dioxide
(Mt CO
2) emission savings. This is based on the assumption
that 10% of households would install turbines at costs competitive with
grid electricity, around 12 pence (US 19 cents) a kW·h.
[136] A report prepared for the UK's government-sponsored
Energy Saving Trust in 2006, found that home power generators of various kinds could provide 30 to 40% of the country's electricity needs by 2050.
[137]
Distributed generation from
renewable resources is increasing as a consequence of the increased awareness of
climate change. The electronic interfaces required to connect renewable generation units with the
utility system can include additional functions, such as the active filtering to enhance the power quality.
[138]
Environmental effects
According to the manager of this wind farm, livestock ignore wind turbines,
[139] and continue to graze as they did before wind turbines were installed.
Compared to the environmental impact of traditional energy sources,
the environmental impact of wind power is relatively minor in terms of
pollution. Wind power consumes no fuel, and emits no
air pollution,
unlike fossil fuel power sources. The energy consumed to manufacture
and transport the materials used to build a wind power plant is equal to
the new energy produced by the plant within a few months. While a wind
farm may cover a large area of land, many land uses such as agriculture
are compatible, with only small areas of turbine foundations and
infrastructure made unavailable for use.
[140][141]
There are reports of bird and bat mortality at wind turbines as there
are around other artificial structures. The scale of the ecological
impact may
[142] or may not
[143]
be significant, depending on specific circumstances. Although many
artificial structures can kill birds, wind power has a disproportionate
effect on certain endangered bird species.
[144] An especially vulnerable group are
raptors,
which are slow to reproduce and favor the high wind speed corridors
that wind turbine companies build turbines in, to maximize energy
production.
[144]
Although they have a negligible effect on most birds, in some locations
there is a disproportionate effects on some birds of conservation
concern, such as the
golden eagle and
raptor species.
[144]
However, a large
meta-analysis
of 616 individual studies on electricity production and its effects on
avian mortality concluded that the most visible impacts of wind
technology are not necessarily the most flagrant ones, as:
[145]
“ |
Wind turbines seem to present a significant threat as all their
negative externalities are concentrated in one place, while those from
conventional and nuclear fuel cycles are spread out across space and
time. Avian mortality and wind energy has consequently received far more
attention and research than the avian deaths associated with coal, oil,
natural gas and nuclear power generators [although] study suggests that
wind energy may be the least harmful to birds. |
” |
Prevention and mitigation of wildlife fatalities, and protection of
peat bogs,
[146] affect the siting and operation of wind turbines.
There are anecdotal reports of negative effects from noise on people
who live very close to wind turbines. Peer-reviewed research has
generally not supported these statements.
[147]
Politics
Central government
Nuclear power and
fossil fuels are
subsidized by many governments,
and wind power and other forms of renewable energy are also often
subsidized. For example a 2009 study by the Environmental Law Institute
[148]
assessed the size and structure of U.S. energy subsidies over the
2002–2008 period. The study estimated that subsidies to fossil-fuel
based sources amounted to approximately $72 billion over this period and
subsidies to renewable fuel sources totalled $29 billion. In the United
States, the federal government has paid US$74 billion for energy
subsidies to support
R&D for
nuclear power ($50 billion) and
fossil fuels ($24 billion) from 1973 to 2003. During this same time frame,
renewable energy technologies and
energy efficiency
received a total of US$26 billion. It has been suggested that a subsidy
shift would help to level the playing field and support growing energy
sectors, namely
solar power, wind power, and
biofuels.
[149] History shows that no energy sector was developed without subsidies.
[149]
According to the
International Energy Agency
(IEA) (2011), energy subsidies artificially lower the price of energy
paid by consumers, raise the price received by producers or lower the
cost of production. "Fossil fuels subsidies costs generally outweigh the
benefits. Subsidies to renewables and low-carbon energy technologies
can bring long-term economic and environmental benefits".
[150] In November 2011, an IEA report entitled
Deploying Renewables 2011
said "subsidies in green energy technologies that were not yet
competitive are justified in order to give an incentive to investing
into technologies with clear environmental and energy security
benefits". The IEA's report disagreed with claims that renewable energy
technologies are only viable through costly subsidies and not able to
produce energy reliably to meet demand.
In the U.S., the wind power industry has recently increased its
lobbying efforts considerably, spending about $5 million in 2009 after
years of relative obscurity in Washington.
[151]
By comparison, the U.S. nuclear industry alone spent over $650 million
on its lobbying efforts and campaign contributions during a single
ten-year period ending in 2008.
[152][153][154]
Following the
2011 Japanese nuclear accidents, Germany's federal government is working on a new plan for increasing
energy efficiency and
renewable energy commercialization,
with a particular focus on offshore wind farms. Under the plan, large
wind turbines will be erected far away from the coastlines, where the
wind blows more consistently than it does on land, and where the
enormous turbines won't bother the inhabitants. The plan aims to
decrease Germany's dependence on energy derived from coal and nuclear
power plants.
[155]
Public opinion
Environmental group members are both more in favor of wind power (74%) as well as more opposed (24%). Few are undecided.
Surveys of public attitudes across
Europe and in many other countries show strong public support for wind power.
[156][157][158] About 80% of EU citizens support wind power.
[159] In
Germany,
where wind power has gained very high social acceptance, hundreds of
thousands of people have invested in citizens' wind farms across the
country and thousands of small and medium sized enterprises are running
successful businesses in a new sector that in 2008 employed 90,000
people and generated 8% of Germany's electricity.
[160][161]
Although wind power is a popular form of energy generation, the
construction of wind farms is not universally welcomed, often for
aesthetic reasons.
[140][156][157][158][159][162][163]
In
Spain,
with some exceptions, there has been little opposition to the
installation of inland wind parks. However, the projects to build
offshore parks have been more controversial.
[164]
In particular, the proposal of building the biggest offshore wind power
production facility in the world in southwestern Spain in the coast of
Cádiz, on the spot of the 1805
Battle of Trafalgar.
[165] has been met with strong opposition who fear for tourism and fisheries in the area,
[166] and because the area is a war grave.
[165]
Which should be increased in Scotland?[167]
|
In a survey conducted by
Angus Reid Strategies in October 2007, 89 per cent of respondents said that using renewable energy sources like wind or solar power was positive for
Canada,
because these sources were better for the environment. Only 4 per cent
considered using renewable sources as negative since they can be
unreliable and expensive.
[168]
According to a Saint Consulting survey in April 2007, wind power was
the alternative energy source most likely to gain public support for
future development in Canada, with only 16% opposed to this type of
energy. By contrast, 3 out of 4 Canadians opposed nuclear power
developments.
[169]
A 2003 survey of residents living around
Scotland's
10 existing wind farms found high levels of community acceptance and
strong support for wind power, with much support from those who lived
closest to the wind farms. The results of this survey support those of
an earlier Scottish Executive survey 'Public attitudes to the
Environment in Scotland 2002', which found that the Scottish public
would prefer the majority of their electricity to come from renewables,
and which rated wind power as the cleanest source of renewable energy.
[170]
A survey conducted in 2005 showed that 74% of people in Scotland agree
that wind farms are necessary to meet current and future energy needs.
When people were asked the same question in a Scottish renewables study
conducted in 2010, 78% agreed. The increase is significant as there were
twice as many wind farms in 2010 as there were in 2005. The 2010 survey
also showed that 52% disagreed with the statement that wind farms are
"ugly and a blot on the landscape". 59% agreed that wind farms were
necessary and that how they looked was unimportant.
[171] Scotland is planning to obtain 100% of electricity from renewable sources by 2020.
[172]
In other cases there is
direct community ownership of wind farm projects.
In Germany, hundreds of thousands of people have invested in citizens'
wind farms across the country and thousands of small and medium sized
enterprises are running successful businesses in a new sector that in
2008 employed 90,000 people and generated 8 percent of Germany's
electricity.
[173] Wind power has gained very high social acceptance in Germany.
[174] Surveys of public attitudes across Europe and in many other countries show strong public support for wind power.
[156][157][175]
Opinion on increase in number of wind farms, 2010 Harris Poll[176]
|
% |
% |
% |
% |
% |
% |
Strongly oppose |
3 |
6 |
6 |
2 |
2 |
4 |
Oppose more than favour |
9 |
12 |
16 |
11 |
9 |
14 |
Favour more than oppose |
37 |
44 |
44 |
38 |
37 |
42 |
Strongly favour |
50 |
38 |
33 |
49 |
53 |
40 |
Wind turbines such as these, in
Cumbria, England, have been opposed for a number of reasons, including aesthetics, by some sectors of the population.
[177][178]
Many wind power companies work with local communities to reduce
environmental and other concerns associated with particular wind farms.
[179][180][181] In other cases there is
direct community ownership of wind farm projects. Appropriate government consultation, planning and approval procedures also help to minimize environmental risks.
[156][182][183] Some may still object to wind farms
[184] but, according to
The Australia Institute, their concerns should be weighed against the need to address the threats posed by
climate change and the opinions of the broader community.
[185]
In America, wind projects are reported to boost local tax bases,
helping to pay for schools, roads and hospitals. Wind projects also
revitalize the economy of rural communities by providing steady income
to farmers and other landowners.
[118]
In the UK, both the
National Trust and the
Campaign to Protect Rural England have expressed concerns about the effects on the rural landscape caused by inappropriately sited wind turbines and wind farms.
[186][187]
Some wind farms have become tourist attractions. The
Whitelee Wind Farm Visitor Centre has an exhibition room, a learning hub, a café with a viewing deck and also a shop. It is run by the
Glasgow Science Centre.
[188]
In Denmark, a loss-of-value scheme gives people the right to claim
compensation for loss of value of their property if it is caused by
proximity to a wind turbine. The loss must be at least 1% of the
property's value.
[189]
Despite this general support for the concept of wind power in the public at large,
local opposition often exists and has delayed or aborted a number of projects.
[190][191][192]
While aesthetic issues are subjective and some find wind farms pleasant and optimistic, or symbols of
energy independence and local prosperity, protest groups are often formed to attempt to block new wind power sites for various reasons.
[184][193][194]
This type of opposition is often described as
NIMBYism,
[195]
but research carried out in 2009 found that there is little evidence to
support the belief that residents only object to renewable power
facilities such as wind turbines as a result of a "Not in my Back Yard"
attitude.
[196]
Turbine design
Typical wind turbine components : 1-
Foundation, 2-
Connection to the electric grid, 3-
Tower, 4-Access ladder, 5-
Wind orientation control (Yaw control), 6-
Nacelle, 7-
Generator, 8-
Anemometer, 9-
Electric or
Mechanical Brake, 10-
Gearbox, 11-
Rotor blade, 12-
Blade pitch control, 13-
Rotor hub.
Wind turbines are devices that convert the wind's
kinetic energy into electrical power. The result of over a millennium of
windmill development and modern engineering, today's wind turbines are manufactured in a wide range of horizontal axis and
vertical axis types. The smallest turbines are used for applications such as
battery charging
for auxiliary power. Slightly larger turbines can be used for making
small 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, have become an increasingly important source of
renewable energy and are used in many countries as part of a strategy to reduce their reliance on
fossil fuels.
Wind turbine design is the process of defining the form and specifications of a
wind turbine to extract energy from the
wind.
[197]
A wind turbine installation consists of the necessary systems needed to
capture the wind's energy, point the turbine into the wind, convert
mechanical rotation into
electrical power, and other systems to start, stop, and control the turbine.
In 1919 the physicist
Albert Betz
showed that for a hypothetical ideal wind-energy extraction machine,
the fundamental laws of conservation of mass and energy allowed no more
than 16/27 (59.3%) of the kinetic energy of the wind to be captured.
This
Betz limit can be approached in modern turbine designs, which may reach 70 to 80% of the theoretical Betz limit.
[198][199]
The
aerodynamics of a wind turbine
are not straightforward. The air flow at the blades is not the same as
the airflow far away from the turbine. The very nature of the way in
which energy is extracted from the air also causes air to be deflected
by the turbine. In addition the
aerodynamics
of a wind turbine at the rotor surface exhibit phenomena that are
rarely seen in other aerodynamic fields. The shape and dimensions of the
blades of the wind turbine are determined by the aerodynamic
performance required to efficiently extract energy from the wind, and by
the strength required to resist the forces on the blade.
[200]
In addition to the aerodynamic
design of the blades, the design of a complete wind power system must also address the design of the installation's
rotor hub,
nacelle,
tower structure,
generator, controls, and foundation.
[201] Further design factors must also be considered when integrating wind turbines into
electrical power grids.
Wind energy
Wind energy is the
kinetic energy of air in motion, also called
wind. Total wind energy flowing through an imaginary area
A during the time
t is:
- [202]
where
ρ is the
density of air;
v is the wind
speed;
Avt is the volume of air passing through
A (which is considered perpendicular to the direction of the wind);
Avtρ is therefore the mass
m passing through "A". Note that ½
ρv2 is the kinetic energy of the moving air per unit volume.
Power is energy per unit time, so the wind power incident on
A (e.g. equal to the rotor area of a wind turbine) is:
- [202]
Map of available wind power for the
United States. Color codes indicate wind power density class. (click to see larger)
Distribution of wind speed (red) and energy (blue) for all of 2002 at
the Lee Ranch facility in Colorado. The histogram shows measured data,
while the curve is the Rayleigh model distribution for the same average
wind speed.
Wind power in an open air stream is thus
proportional to the
third power
of the wind speed; the available power increases eightfold when the
wind speed doubles. Wind turbines for grid electricity therefore need to
be especially efficient at greater wind speeds.
Wind is the movement of air across the surface of the Earth, affected by areas of high pressure and of low pressure.
[203]
The surface of the Earth is heated unevenly by the Sun, depending on
factors such as the angle of incidence of the sun's rays at the surface
(which differs with latitude and time of day) and whether the land is
open or covered with vegetation. Also, large bodies of water, such as
the oceans, heat up and cool down slower than the land. The heat energy
absorbed at the Earth's surface is transferred to the air directly above
it and, as warmer air is less dense than cooler air, it rises above the
cool air to form areas of high pressure and thus pressure
differentials. The rotation of the Earth drags the atmosphere around
with it causing turbulence. These effects combine to cause a constantly
varying pattern of winds across the surface of the Earth.
[203]
The total amount of economically extractable power available from the
wind is considerably more than present human power use from all
sources.
[204] Axel Kleidon of the
Max Planck Institute
in Germany, carried out a "top down" calculation on how much wind
energy there is, starting with the incoming solar radiation that drives
the winds by creating temperature differences in the atmosphere.
He
concluded that somewhere between 18 TW and 68 TW could be extracted.
[205]
Cristina Archer and
Mark Z. Jacobson
presented a "bottom-up" estimate, which unlike Kleidon's are based on
actual measurements of wind speeds, and found that there is 1700 TW of
wind power at an altitude of 100 metres over land and sea. Of this,
"between 72 and 170 TW could be extracted in a practical and
cost-competitive manner".
[205] They later estimated 80 TW.
[206] However research at
Harvard University estimates 1 Watt/m
2 on average and 2–10 MW/km
2
capacity for large scale wind farms, suggesting that these estimates of
total global wind resources are too high by a factor of about 4.
[207]
The strength of wind varies, and an average value for a given
location does not alone indicate the amount of energy a wind turbine
could produce there. To assess the frequency of wind speeds at a
particular location, a probability distribution function is often fit to
the observed data. Different locations will have different wind speed
distributions. The
Weibull
model closely mirrors the actual distribution of hourly/ten-minute wind
speeds at many locations. The Weibull factor is often close to 2 and
therefore a
Rayleigh distribution can be used as a less accurate, but simpler model.
[208]