By Andrew Farris
Humans have harnessed wind power for thousands of years, using sails to propel ships and windmills to pump water. It has, however, only been in the past 30 years that wind has been viewed as a viable means of generating utility-scale electricity.
The appeal of deriving power from the wind is obvious: the wind is free, inexhaustible, and it is always blowing somewhere. The modern wind turbine, pioneered by American and Danish companies following the oil shocks of the 1970s, employed the tried and true angled propeller used by aircraft, to catch the wind, spin, and then use the rotational motion to drive an electric generator. Although other designs exist, the propeller-based Horizontal-Axis Wind Turbine (HAWT) is the one most commonly associated with wind power. Its primacy has been cemented in recent years by its continued technological development.
Like all the
Denmark, the world's leader in wind power, already gets approximately 20% of its electricity from wind turbines, both onshore and offshore. Wind power is expected to continue growing for at least another decade alongside other renewables, such as solar. Canada is 9th in the world for installed wind power capacity, and plans for the rapid development of wind farms are on the board in all the provinces and territories, with Ontario and Quebec leading the way. B.C. was the last province to take to wind power, but its geography makes it well-suited for wind power generation; with long coastlines, large plains and mountains generating high wind speeds. Two wind farm projects have come online in the province since 2009, with another seven currently under development.
Wind does face many challenges. Even though wind turbines are massive, standing hundreds of metres tall, they only generate a comparatively small amount of energy: The typical turbine being built right now has a
Residents living near proposed wind farms often oppose them on visual grounds, or because of the irritating swishing noise they make. The swiftly rotating blades have also been known to kill birds.
Wind farm developers are working hard to improve the integration of wind-based electricity into the power grid and mitigate these and other other concerns. Serious progress is being made in terms of development, improved efficiency of turbines and getting locals on board with installation in public areas.
As a result many governments are putting their faith in wind power. The U.S. Department of Energy recently released a plan to generate an ambitious 20% of the country's electricity from wind power by 2030. The E.U. has set similar targets. China, which recently became the country with the most installed wind-capacity in the world, seeks to have 100 GW of capacity by 2020. Because of developments in the past fifteen years, wind is likely to play a prominent role in any future renewable energy economy.
The winds that travel around the earth have two different driving mechanisms. The first mechanism is uneven heating of the earth by the sun: equatorial latitudes receive more of the Sun's rays than the polar latitudes. The differential heating of the earth is manifested in variations in atmospheric pressure, and wind is merely the rush of gases from high pressure areas to low pressure areas. In this sense wind power is actually another form of solar power. The second mechanism is the rotation of the earth, which, through the
There are two main designs of wind turbines that capture the wind's energy. The basic, most commonly used wind turbine, the Horizontal Axis Wind Turbine (HAWT) is rather simple. Much like medieval windmills used to grind flour, modern turbines harness wind by using large angled propeller blades to catch the wind. When the wind passes through the blades, it causes the entire blade assembly, known as a rotor, to spin around a central
Modern wind turbines employ a number of refinements that make them safer and more efficient than their predecessors just 20 years ago. The nacelles on most HAWT turbines can be controlled to face into the wind where they will have the greatest efficiency. On small turbines this can be done with an
Many of the newest utility-grade wind turbines are very tall. That way they can access windd higher off the ground, which are stronger and more constant. They also have longer blades, increasing efficiency through a larger area interacting with the wind. The most common size of wind turbine, 1.5 MW, is usually between 40 to 60 metres tall. They are getting bigger and more powerful though: at 7MW the most powerful wind turbine in the world, the Enercon E-126 is 198 metres tall, as high as a 50-storey building.
Thus far the discussion has focused on the design of wind turbines most people would recognize, the HAWT. There is another wind turbine design that has been developed alongside the HAWT: the VAWT, or, Vertical-Axis Wind Turbine. Though comprising only about 10% of all modern wind turbines currently in operation, there are a wider variety of VAWT designs. The designs include the
The disadvantages of VAWTs are the reason they have such a small market share. Generally VAWTs are less efficient than the HAWTs since, as they are placed perpendicular to the wind, when one side is being blown by the wind, the other is moving in the opposite direction against the wind. As a result the
VAWTs do, however, have several important advantages over their propeller-blade cousins. They do not have to be faced into the wind and can therefore generate power in areas where wind comes from a variety of directions. They can continue to generate power at lower wind speeds than is possible with HAWTs, and also at the highest wind speeds when the more conventional designs have to be turned off. These advantages make VAWT turbines more suitable for the more variable-wind conditions in urban environments. Politicians in the E.U. have expressed interest in expediting the integration of VAWT turbines into buildings.
VAWTs may have a brighter future than most people reailze. Though HAWT turbines are individually more efficient, they create huge shadows of aerial turbulence, so as a result HAWTs must be placed far apart to keep them from interfering with one another, making less efficient use of land. VAWTs can be placed in much closer proximity and increase the overall electricity output from a given plot of land used as a wind farm. Scientists at the California Institute of Technology proved that a ten-fold increase in efficiency over HAWT farms could be achieved by carefully locating VAWT turbines close together.
There are also smaller scale wind turbines available. These turbines can be set up for individual household, rural or agricultural use. The cost of residential wind turbines has decreased substantially since the 1980s and the turbines have become more efficient.
Small scale wind turbines are mainly horizontal axis wind turbines but there are small scale vertical axis wind turbines as well. Most small scale wind turbines are less than 25 metres tall and have rapidly rotating blades. Some of these turbines are put on rooftops. Some turbines also have vanes that will point them into the wind to increase their efficiency. Small wind turbines can be purchased for as little as $800.
In the USA tax credits are available to people who have installed wind turbines. As of 2008 small scale turbines generated a miniscule 5.5 MW of power in Canada. Nevertheless the small scale wind energy market was worth $11 million.
Wind farms obviously require high wind speed. There are four main factors that affect wind speed. The first is pressure gradient which is generated by differences in atmospheric pressure between two adjacent areas. The second is frictional force which is increased by features on the earth's surface such as trees and mountains. The third factor is the
These factors make certain sites particularly well suited for wind farm development. Some of the best sites for wind turbines are in mountainous areas, such as the Rocky and Appalachian Mountains. Wide open plains such as Tornado Alley and the open ocean are also great for wind power. Another good area for a wind turbine could be in farmer's fields, since their bases don't take up much space and farms are usually in open plains with high wind and can provide more income to farmers.
The suitability of a site can be determined by measuring the
In practice only the most efficient wind turbines, which are just entering the market today, can reach capacity factors above 40%. Wind developers will ideally aim to develop sites with capacity factors above 35%, meaning sites with winds upwards of 5 m/s and to a maximum of 25 m/s.
This chart compares the quality of sites for wind turbines and what the expected capacity factor will be depending upon the wind speed.
Other factors must be considered when choosing a site for a wind turbine. For instance, at what times of day and what times of year is the wind most likely to blow? Finding a site where the winds coincide with times of highest electricity demand is helpful in integrating wind energy into the power grid. In most jurisdictions, power use peaks in the late afternoon and evening. In British Columbia people are far more apt to desire home heating during winter, rather than air-conditioning in the summer.
Local residents will often have objections to wind farms and proposals near human habitations, resulting in protracted permitting processes and legal battles. To expedite the process wind farmers seek to build away from densely populated areas.
There are a few other considerations. To keep down costs it is also helpful to find sites that are not difficult to access utilizing existing logging or mine roads. This requirement rules out much of British Columbia as wind turbines are expensive to erect and maintain on mountain slopes, and mountain winds contribute to wind shear which has the potential to damage the rotor blades.
Finally, it is helpful to find sites that are in close proximity to existing transmission lines, as the building of new transmission lines can add significantly to costs. This is especially the case for offshore wind farms and has contributed to the slower development of that sector.
Meeting all of these requirements considerably narrows down the number of potential sites for wind farms. British Columbia is mountainous, with many areas that are hard to access or there are populations who object to having wind turbines in plain sight. These are some of the reasons why British Columbia has lagged behind the other provinces in developing its wind capacity.
From 1900 to 1973 small wind turbines were used to generate tiny amounts of electricity in remote locations, while governments and businesses in Europe and the United States experimented with larger wind turbines for power generation, but investors showed little interest in the technology. It was not until 1973 however, when the Arab oil embargoes spurred interest in finding fossil fuel alternatives, that wind got its first serious boost. Several departments of the United States government including NASA, the NSF (National Sciences Foundation) and the DOE (Department of Energy) combined funding to experiment with a number of wind turbine designs during the 1970s and 1980s.
These first utility-scale wind turbines came in a variety of two and three bladed designs and were revolutionary in their day, though small and inefficient by modern standards. The world`s first wind-farm, the MOD-2 cluster of turbines, built by Boeing, was completed in Washington in 1981. The cluster could produce a record-breaking output of 7.5 MW.
These early developments laid the groundwork for modern wind turbine design. They allowed engineers to address many of the problems of intermittency, wind speed changes, gearbox design and aesthetics, proving wind power could one day be economically competitive with conventional fossil fuels.
Wind power's development stalled during the 1990s when fossil fuel prices sank again, undercutting its economic competitiveness. In 1996 America's largest wind turbine producer, Kenetech, went bankrupt.
In the past decade however, wind and solar power have taken off.
Wind power is well-suited geographically for Europe and the United States, both global leaders in the industry since the 1990s. In the former case, the Baltic Sea basin and Spain's rugged topography are well suited for large offshore and onshore wind farms. Denmark leads the world in reliance upon wind power, producing 20% of its electricity from wind turbines. Germany, the world's fourth largest economy, has 21,607 turbines in operation, producing 27 GW of power.
In the United States, the notoriously windy 'Tornado Alley', stretching north from the Texas Panhandle to Minnesota and Wyoming, is an ideal location for widespread wind farm construction. Oil tycoon T. Boone Pickens has proposed the
China surpassed the United States in installed wind capacity in 2011, with approximately 41.8 GW. This development has astonished experts in the wind field, a twenty-fold increase in just over five years. This growth has stemmed from Chinese government policies mandating that all renewable energy produced must be purchased by grid operators, as well as large subsidies to wind turbine manufacturers and operators. China is long coastlines and giant windswept plains helped too. Despite this massive growth in wind power, it's still only 2-3% of China's electricity mix and China's coal-fired power plant sector is growing almost as quickly.
Other countries around the world are adopting wind energy at a rapid pace, and now 86 countries have wind farms. India has a large and expanding fleet of wind turbines. Wind farms are being built in Latin America, Africa and the Middle East. Following the Fukushima nuclear accidents in March 2011 Japan`s prime minister has stated his country intends to move decisively towards renewable energies, specifically wind, and away from nuclear power in the decades ahead.
Canada currently has the 9th largest installed wind capacity in the world, at 4.6 GW, around 2% of Canada's total electricity demand. This is impressive for a country that had almost no wind farms at all ten years ago. Since then Ontario, Alberta and Quebec have emerged as the leaders of Canada's wind industry with 1,656 MW, 807 MW and 759 MW of generating capacity respectively.
Geographically, Canada is well suited for wind power. The windswept belt that stretches across America's central plains extends into Canada's Prairie Provinces, and is a large part of the reason Alberta has a number of small wind farms. Further east, Ontario's government has been undertaking aggressive economic policies aimed at reducing the province's carbon footprint, and they succeeded in passing the
Quebec has been referred to as the "Saudi Arabia of Wind" by a spokesperson of the Canadian Wind Energy Association.
Geographically, the Maritimes are blessed with an abundance of wind, and in the past decade a number of small wind farms, ranging in size from a single turbine to 44 at Prince Edward Island's West Cape 2 farm, have been built. These smaller wind turbines go a long way to satisfying the smaller electricity demands of these provinces: wind energy accounts for 18% of P.E.I.'s electricity demand. By 2013 that number is projected to rise as high as 30%, one of the highest rates in the world for any jurisdiction.
The Canadian Wind Energy Association is aiming for wind power to produce 20% of the country's energy by 2025. In order to reach this goal the total installed capacity has to increase to 55,000 MW by that time.
If one were to examine Environment Canada's Wind Atlas, British Columbia's onshore wind energy potential stands above all the other provinces except Quebec.
The first wind farm in BC was the Bear Mountain Wind Park built near Dawson Creek, featuring 34 Enercon turbines. Run by AltaGas, the farm provides 102 MW of electricity to the B.C. power grid.
The Peace River valley in the north-east is the likely scene for the development of future wind power capacity because of its favorable geography. Opening out onto the Alberta prairies, the region is subject to strong and constant winds. It is not so remote as to be difficult to access, while the many dams along the Peace River which provide the bulk of the province's power mean the transmission grid is near at hand. The region is also sparsely populated, making it easier to overcome the aesthetic and noise-based objections of local residents. Other regions meeting these criteria include northern Vancouver Island, the Okanagan and the Kootenays.
B.C. Hydro has already signed
The politics surrounding wind power are similar to some of the other second generation renewables: solar, geothermal and tidal. Interest in all of them is propelled by the desire of many governments to find an alternative to fossil fuels. A number of reasons can be listed for this shift: fossil fuels are the primary driver of global climate change, they are finite resources that will be depleted, many countries are worried about the security risks of relying upon imported fossil fuel and the volatility in the price of oil. (See: Peak Oil).
Many governments have mandatory renewable energy targets which determine how much energy must be generated by renewable sources. The British, Chinese and American governments have announced plans to generate 15% of their electricity from renewable sources by 2020.
In fulfilling these new mandatory targets, governments are increasingly turning to second-generation renewable technologies. Primarily it's the economics of wind power that is fueling its rapid growth in world power generation. Unlike solar, geothermal or tidal, wind is already broadly cost-competitive with fossil fuel-based forms of electricity generation.
In the past decade this form of energy has also benefitted from the development of an economy of scale. There are now massive Danish (Vestas), German (Enercon), American (GE Wind Energy) and Chinese (Sinovel and Goldwind) firms rapidly expanding and bidding for contracts to build wind farms all over the world.
So how well does wind stack up against the other energy sources economically? On-shore does quite well, but offshore wind has a long ways to go.
Wind power is a domestic power source; this helps to create a more stable economy. However, the price of wind energy can vary significantly depending on the location of the wind farm and the consistency of the wind. In their Annual Energy Outlook of 2011, the American Energy Information Administration (EIA) predicted what the
On-shore wind comes off highly competitive, averaging $97 per MWh over its lifetime, ahead of Gen. III+ nuclear power plants and all the other renewables (except hydroelectric: ~$75 per MWh). Crucially, onshore wind is competitive with coal, which averages $94.8, though it still remains far behind combined cycle natural gas plants. In the most favorable regions, wind comes in at $81.9 per MWh, cheaper than coal can be in even the best circumstances.
The fact that wind energy is competitive now with coal is the reason many jurisdictions that have heretofore relied upon coal for their electricity demand, are the ones investing most heavily in wind power (China, USA, Germany, India, Alberta) (See: Coal). China is reaching the upper limit of the amount of coal it can produce without rapidly exhausting its own resources, and is now the world's leader in wind energy. Denmark and Germany used to rely on poor quality lignite coal for their power, but high percentages of their electrical grid now rely upon the wind. Ontario is phasing out all of its coal power plants and building wind farms. The lesson here is that economic competitiveness is key for any renewable energy to catch on.
There are many advantages of wind power over fossil fuel based power: there are no air emissions during production, no water required and of course, it is a renewable resource. Yet wind, which has no fuel costs, is still more expensive than advanced natural gas plants. Why?
For onshore wind about 75% of the costs are up-front one-time costs just to get the turbines up and runing. Thus it is very capital intensive. Of that, three quarters is for construction of the turbines, and another 9% for the transmission lines connecting t to the power grid. The remainder goes to building foundations and access roads, and paying rent to landowners. Once the wind farm is built the other 25% of costs all go into routine maintenance, spare parts, and the eventual decommissioning of the turbines 20 years later.
Wind power wasn't always as competitive as it is today: continuous technological innovations and the development of an economy of scale have meant that the price of wind energy has dropped 80% since the first wind farms came online in 1980.
Future development of wind power is looking to move offshore where winds are stronger, more constant, and away from urban areas. Offshore wind energy is still in its infancy: As of 2009 only 20 offshore wind farms existed in the world, all in Northern Europe (two thirds in the U.K. and Denmark), comprising only 1% of global installed wind capacity.
Offshore wind energy remains an expensive way to generate electricity. This is despite the fact that offshore winds are much stronger than onshore, averaging 4,000 hours per year of full-load generation, as opposed to 2,000-2,500 for onshore.
The problem lies in an offshore wind farms different cost structure. As the Wall Street Journal reported,
"Offshore, turbines only make up one-third of the project cost, says the U.S. National Renewable Energy Laboratory. About 25% of the cost comes from the platform to hold the turbine up, 24% from increased maintenance costs, and fully 15% from building new undersea transmission lines."
The turbines used for offshore are larger, and cost about 20% more than their onshore counterparts, while the foundation and transmission lines cost 2.5 times as much as a comparable onshore development, though they can generate twice the amount of energy.
Offshore wind also presents a solution for people who dislike the sight of wind turbines. Wind turbines installed at least 11 km off shore are hidden by the curvature of the earth.
There are also different environmental factors to consider in an offshore wind farm, such as salt build up on blades and increased corrosion of the structure from salt water.
One intensely debated aspect of wind energy is NIMBYism—which stands for Not In My Back Yard. It is a term used to describe people who may support an idea like renewable energy in principle, but are opposed to developments happening near where they live. With wind energy this most commonly manifests itself in complaints about the way wind turbines impact the landscape visually, and with the noise they create. We will see the effect these concerns have had upon the advance of wind power.
Since wind turbines can stand several hundred meters tall, and they are grouped together into farms, their visual impact on a landscape can be large. In this context one essay writer describes the two differing reactions people have to the visual impact wind farms have on a landscape.
The point is not whether or not one of these views are right, but that many people who live near wind farms developments take the latter view.
The second major issue of concern to local residents is the noise created by wind turbines, both low frequency and therefore inaudible to humans, and high frequency which is audible. Some doctors, such as Nina Pierpont, say that the low-frequency noise created by wind turbines can have adverse health effects, including migraines, high-blood pressure, ringing in the ears and other stress related illnesses. They term these effects "wind-turbine syndrome".
Epsilon Associates, an acoustic consulting firm, studied low-frequency noise effects and have concluded that though early American wind turbine designs (that is, over a decade old) did create low frequency noise which could potentially lead to health problems, newer models that employed sound-dampeners have gone a long way towards minimizing this problem. The study concluded "wind turbines at maximum noise at a distance more than 1,000 feet from a residence do not pose a low frequency noise or infrasound problem." At this distance wind turbines met all low frequency noise regulations, including the most stringent ones set out for classrooms and hospitals.
Another study, "Wind Turbine Sound and Health Effects" by a panel of independent scientists commissioned by the American Wind Energy Association found that the audible noise created by wind turbines did not directly cause any severe health problems either. The sounds wind turbines create could in fact cause "annoyance" and lead to sleep deprivation among a "small" part of the population living near wind turbines. Their findings show however, that despite the widespread media attention the supposed health impacts of wind power have received, there remains no peer-reviewed evidence that "wind-turbine syndrome" exists.
Concerns about the the aesthetics of wind, and the (largely debunked) health impacts, have helped contribute to a groundswell of opposition to wind farm development. In Canada and around the world, ambitious policies to expand wind power are running into fierce opposition. Studies show that people support wind power in principle above all other forms of energy generation. That support tends to become more muted, or downright hostile, when people find out they are going to be living near a wind farm.
The most widely-reported case of NIMBYism around wind energy is the Cape Wind project, America's first proposed offshore wind farm in Nantucket Sound. In 2001 it was proposed to build 130 turbines between 6 and 17 km offshore with a maximum generating capacity of 454 MW.
Immediately some local residents objected and formed the Alliance to Protect Nantucket Sound, seeking to derail the project. The region is a vacation location for many of America's most powerful families and for once America's political class, both Democrat and Republican, stood united in their opposition to America's first offshore wind farm. The Alliance received the support and money of the Kennedys, Secretary of State John Kerry, Republican Governor Mitt Romney and oil and coal magnate Bill Koch.
Robert Kennedy Jr. wrote an oped for the New York Times in 2005 that could be said to encapsulate the NIMBY position. Opening with "As an environmentalist, I support wind power, including wind power on the high seas," he then argued that the farm's "Hundreds of flashing lights to warn airplanes away from the turbines will steal the stars and nighttime views." That the spoilt views, Kennedy continued, would cost "up to 2,533 jobs because of the loss of tourism - and over a billion dollars to the local economy."
Polls taken in 2007, after the project had been hotly debated for six years, without a decision on the matter, showed that a majority of the state's population (84%) and local residents (58%) supported the Cape Wind Farm. Despite this support continual lawsuits and legislative maneuvering has meant the project has yet to begin construction a decade later. Though the project received the federal government's go-ahead in April 2011, the chief of a local first nations tribe has launched a lawsuit against the project on the grounds that it impacts the historical, spiritual and cultural resources on the Horseshoe Shoal, leading to further delays in construction.
Though many commentators argue that the power and influence of those opposed to Cape Wind are an exceptional case of NIMBYism, Canada's own local NIMBY activists have forced the scuttling of several wind farm developments.
Some early studies show that the silent majority do in fact support wind farms near their homes. A wind development in Berkeley Vale in the United Kingdom was abandoned because of lobbying by a group calling themselves Save Berkeley Vale. A poll of those living within six miles of the proposed wind turbines however found that 66% of residents supported the turbines and only 12% opposed.
Opposition to wind farms from local residents is one of the biggest hurdles an expansion of wind power faces. Though wind power is the most popular alternative energy today, intense and directed lobbying from NIMBY groups has managed to stall and even force the cancellation of projects. They argue that the massive turbines are eyesores and cause adverse health effects. Polling however indicates that the silent majority of people, at least in some areas, support wind farms even within sight of their homes. Educating the public about the validity (or lack thereof) of the alleged health effects, and creating consensus on the use of wind power, will determine the future of wind power.
There is a third reason for loud public opposition to wind farms: They kill birds. The towers are hundreds of metres tall, and in high wind conditions the blades spin at speeds of 80 metres per second.
It was one of the first utility-scale wind farms in the U.S., California's 4,000 turbine Altamont Pass development, that first drew publicity to the issue. It was found to be killing on average 4,700 birds of prey a year, including such rare species as raptors, burrowing owls, golden eagles and red-tailed hawks. This farm raised the ire of conservationists and turned the issue of bird deaths into a major stumbling block for wind development. The farm is however, a prime example of the need to properly locate wind farms. The site in the Altamont Pass is a key route for migratory birds and, in the early stages of wind technology, not much thought was given to this. Furthermore, the now-obsolete turbines that make up the Altamont Pass wind farm attract birds with their lattice-work towers and blades. These appear to birds as attractive places to perch. The blades on these turbines also have small surface areas and therefore spin much faster just to generate the same amount of power as newer turbines models.
Today, greater experience with wind farms has allowed scientists to make huge strides in mitigating bird deaths and garnering crucial support from bird conservation groups. Regulations have been enacted banning the construction of wind farms near migratory bird routes.
Secondly, wind turbine technology has improved markedly. The turbines now sit atop solid concrete round towers which do not look to birds like appealing perches. The blades are solid and now have a much wider surface area, meaning they spin more slowly and are therefore less likely to harm birds in flight. In addition, it is thought future wind farm development will be redirected offshore, where birds do not usually fly. Studies show that offshore wind farms pose a reduced risk to birds.
While tragic, it is worth comparing the number of bird deaths related to wind turbines to deaths caused by other human factors. As this table illustrates, it may be a case of failing to see the forest for the trees:
Hundreds of millions, if not billions of birds are killed annually flying into windows, being poisoned by pesticides, getting electrocuted by power lines or eaten by cats. The number killed by wind farms is an estimated 0.1% of the total.
Since the actual running of the turbines contributes no greenhouse gases to the atmosphere, it is the construction, maintenance and eventual decommissioning of the turbines that contribute to emissions and ultimately climate change. So how much of a climate impact does building wind turbines have? And how effective are they at offsetting carbon from other sources of energy?
A 2006 study by Britain's Parliamentary Office of Science and Technology compared the carbon footprints of the various non-fossil fuel based forms of energy generation. Wind energy was found to be in a virtual dead-heat with nuclear power: offshore wind releasing 5.25 and onshore 4.64 grams of CO2 equivalent into the atmosphere per kWh while nuclear emitted approximately 5 grams. hydroelectric was close behind, ranging from 2 to 10 gCO2eq/kWh, but tidal, solar photovoltaic (PV) and biomass lagged well back: they ranged from 25 to 80 gCO2eq/kWh. Though of course all of these are still several orders of magnitude better than the fossil fuels.
For wind, 98% of the carbon emissions released are during the manufacturing and construction process. The tower and foundations are made of steel and concrete while the rotors are made of fiberglass, all of which are materials that are fairly carbon-intensive to manufacture. Once the turbine is erected the other 2% is accounted for by the regular maintenance trips to the turbines, for any spare parts, and then the eventual decommissioning of the turbine after 20 years. Offshore turbines emit slightly higher emissions since, though the construction techniques are largely the same as onshore, more concrete is required for the foundations.
One may be surprised to see wind's carbon emissions in such a close tie with nuclear power. After all, the construction of nuclear facilities, the mining and refining of nuclear fuel and then dealing with the waste undoubtedly emits substantial amounts of carbon emissions. This can be explained by the differences in scale. Just a few tons of nuclear fuel can create tremendous amounts of electricity and run a 1,000 MW reactor for months or even years.
Individual wind turbines are tiny by comparison: the standard size in the world is 1.5 MW, though 2.5 MW and 5 MW models are becoming more widespread, and a 10 MW turbine may be on the horizon. Using 2 MW turbines, would then require at least 500 wind turbines to replace a single 1,000 MW reactor (and most nuclear stations have several reactors). And keep in mind these wind turbines are very large: the Spanish 2 MW Gamesa G87 is fairly average, standing as high as 142.5 meters, and weighing up to 350 tons.
We must also take into account the capacity factor. Because of the intermittency of the wind, a wind farm has an annual capacity factor of around 30-40%, that is, the farm produces only about 30-40% of its actual rated power throughout the year.
If wind is to start actually making a sizable contribution to global electricity production and begin to unseat fossil fuels, it will require many thousands of wind farms and hundreds of thousands, or even millions, of massive wind turbines across the world.
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