Wind FAQs

What is wind energy?

In reality, wind energy is a converted form of solar energy. The sun's radiation heats different parts of the earth at different rates-most notably during the day and night, but also when different surfaces (for example, water and land) absorb or reflect at different rates. This in turn causes portions of the atmosphere to warm differently. Hot air rises, reducing the atmospheric pressure at the earth's surface, and cooler air is drawn in to replace it. The result is wind.

Air has mass, and when it is in motion, it contains the energy of that motion("kinetic energy"). Some portion of that energy can converted into other forms mechanical force or electricity that we can use to perform work.

More reading:
“Where Does Wind Energy Come From” and its subsections contain a very extensive description of the various geographical and geophysical factors that drive the circulation of the winds around our planet.

What is a wind turbine and how does it work?

A wind energy system transforms the kinetic energy of the wind into mechanical or electrical energy that can be harnessed for practical use. Mechanical energy is most commonly used for pumping water in rural or remote locations- the "farm windmill" still seen in many rural areas of the U.S. is a mechanical wind pumper - but it can also be used for many other purposes (grinding grain, sawing, pushing a sailboat, etc.). Wind electric turbines generate electricity for homes and businesses and for sale to utilities.

There are two basic designs of wind electric turbines: vertical-axis, or "egg-beater" style, and horizontal-axis (propeller-style) machines. Horizontal-axis wind turbines are most common today, constituting nearly all of the "utility-scale" (100 kilowatts, kW, capacity and larger) turbines in the global market.

Wind Turbine

Turbine subsystems include:

  • a rotor, or blades, which convert the wind's energy into rotational shaft energy;
  • a nacelle (enclosure) containing a drive train, usually including a gearbox* and a generator;
  • a tower, to support the rotor and drive train; and
  • electronic equipment such as controls, electrical cables, ground support equipment, and interconnection equipment.

*Some turbines do not require a gearbox

Wind turbines vary in size. This chart depicts a variety of historical turbine sizes and the amount of electricity they are each capable of generating (the turbine's capacity, or power rating).

Wind Turbine

 

1981

1985

1990

1996

1999

2000

Rotor (meters)

10

17

27

40

50

71

Rating (KW)

25

100

225

550

750

1,650

Annual MWh

45

220

550

1,480

2,200

5,600

The electricity generated by a utility-scale wind turbine is normally collected and fed into utility power lines, where it is mixed with electricity from other power plants and delivered to utility customers. Today (August 2005), turbines with capacities as large as 5,000 kW (5 MW) are being tested.

More reading:
Wind Energy—How Does It Work? is a fact sheet that gives additional basic information about wind energy in the U.S.

What are wind turbines made of?

The towers are mostly tubular and made of steel. The blades are made of fiberglass-reinforced polyester or wood-epoxy.

How big is a wind turbine?

Utility-scale wind turbines for land-based wind farms come in various sizes, with rotor diameters ranging from about 50 meters to about 90 meters, and with towers of roughly the same size. A 90-meter machine, definitely at the large end of the scale at this writing (2005), with a 90-meter tower would have a total height from the tower base to the tip of the rotor of approximately 135 meters (442 feet).

Offshore turbine designs now under development will have larger rotors—at the moment, the largest has a 110-meter rotor diameter—because it is easier to transport large rotor blades by ship than by land.

Small wind turbines intended for residential or small business use are much smaller. Most have rotor diameters of 8 meters or less and would be mounted on towers of 40 meters in height or less.

How much electricity can one wind turbine generate?

The ability to generate electricity is measured in watts. Watts are very small units, so the terms kilowatt (kW, 1,000 watts), megawatt (MW, 1 million watts), and gigawatt (pronounced "jig-a-watt," GW, 1 billion watts) are most commonly used to describe the capacity of generating units like wind turbines or other power plants.

Electricity production and consumption are most commonly measured in kilowatt-hours (kWh). A kilowatt-hour means one kilowatt (1,000 watts) of electricity produced or consumed for one hour. One 50-watt light bulb left on for 20 hours consumes one kilowatt-hour of electricity (50 watts x 20 hours = 1,000 watt-hours = 1 kilowatt-hour).

The output of a wind turbine depends on the turbine's size and the wind's speed through the rotor. Wind turbines being manufactured now have power ratings ranging from 250 watts to 5 megawatts (MW).

Example: A 10-kW wind turbine can generate about 10,000 kWh annually at a site with wind speeds averaging 12 miles per hour, or about enough to power a typical household. A 5-MW turbine can produce more than 15 million kWh in a year--enough to power more than 1, 400 households. The average U.S. household consumes about 10,000 kWh of electricity each year.

Example: A 250-kW turbine installed at the elementary school in Spirit Lake, Iowa, provides an average of 350,000 kWh of electricity per year, more than is necessary for the 53,000-square-foot school. Excess electricity fed into the local utility system earned the school $25,000 in its first five years of operation. The school uses electricity from the utility at times when the wind does not blow. This project has been so successful that the Spirit Lake school district has since installed a second turbine with a capacity of 750 kW. (For further information on this project, see at the Web site of the International Council for Local Environmental Initiatives.)

Wind speed is a crucial element in projecting turbine performance, and a site's wind speed is measured through wind resource assessment prior to a wind system's construction. Generally, an annual average wind speed greater than four meters per second (m/s) (9 mph) is required for small wind electric turbines (less wind is required for water-pumping operations). Utility-scale wind power plants require minimum average wind speeds of 6 m/s (13 mph).

The power available in the wind is proportional to the cube of its speed, which means that doubling the wind speed increases the available power by a factor of eight. Thus, a turbine operating at a site with an average wind speed of 12 mph could in theory generate about 33% more electricity than one at an 11-mph site, because the cube of 12 (1,768) is 33% larger than the cube of 11 (1,331). (In the real world, the turbine will not produce quite that much more electricity, but it will still generate much more than the 9% difference in wind speed.) The important thing to understand is that what seems like a small difference in wind speed can mean a large difference in available energy and in electricity produced, and therefore, a large difference in the cost of the electricity generated. Also, there is little energy to be harvested at very low wind speeds (6-mph winds contain less than one-eighth the energy of 12-mph winds).

How many turbines does it take to make one megawatt (MW)?

Most manufacturers of utility-scale turbines offer machines in the 700-kW to 2.5-MW range. Ten 700-kW units would make a 7-MW wind plant, while 10 2.5-MW machines would make a 25-MW facility. In the future, machines of larger size will be available, although they will probably be installed offshore, where larger transportation and construction equipment can be used. Units up to 5 MW in capacity are now under development.

How many homes can one megawatt of wind energy supply?

An average U.S. household uses about 10,655 kilowatt-hours (kWh) of electricity each year. One megawatt of wind energy can generate from 2.4 to more than 3 million kWh annually. Therefore, a megawatt of wind generates about as much electricity as 225 to 300 households use. It is important to note that since the wind does not blow all of the time, it cannot be the only power source for that many households without some form of storage system. The "number of homes served" is just a convenient way to translate a quantity of electricity into a familiar term that people can understand. (Typically, storage is not needed, because wind generators are only part of the power plants on a utility system, and other fuel sources are used when the wind is not blowing. According to the U.S. Department of Energy , "When wind is added to a utility system, no new backup is required to maintain system reliability." Wind Energy Myths, Wind Powering America Fact Sheet Series, http://www.nrel.gov/docs/fy05osti/37657.pdf .)

What is a wind power plant?

The most economical application of wind electric turbines is in groups of large machines (660 kW and up), called "wind power plants" or "wind farms." For example, a 107-MW wind farm near the community of Lake Benton, Minn., consists of turbines sited far apart on farmland along windy Buffalo Ridge. The wind farm generates electricity while agricultural use continues undisturbed.

Wind plants can range in size from a few megawatts to hundreds of megawatts in capacity. Wind power plants are "modular," which means they consist of small individual modules (the turbines) and can easily be made larger or smaller as needed. Turbines can be added as electricity demand grows. Today, a 50-MW wind farm can be completed in 18 months to two years. Most of that time is needed for measuring the wind and obtaining construction permits—the wind farm itself can be built in less than six months.

What is "capacity factor"?

Capacity factor is one element in measuring the productivity of a wind turbine or any other power production facility. It compares the plant's actual production over a given period of time with the amount of power the plant would have produced if it had run at full capacity for the same amount of time.

 

Actual amount of power produced over time

Capacity Factor =

 

Power that would have been produced if turbine
operated at maximum output 100% of the time

A conventional utility power plant uses fuel, so it will normally run much of the time unless it is idled by equipment problems or for maintenance. A capacity factor of 40% to 80% is typical for conventional plants.

A wind plant is "fueled" by the wind, which blows steadily at times and not at all at other times. Although modern utility-scale wind turbines typically operate 65% to 90% of the time, they often run at less than full capacity. Therefore, a capacity factor of 25% to 40% is common, although they may achieve higher capacity factors during windy weeks or months.

It is important to note that while capacity factor is almost entirely a matter of reliability for a fueled power plant, it is not for a wind plant—for a wind plant, it is a matter of economical turbine design. With a very large rotor and a very small generator, a wind turbine would run at full capacity whenever the wind blew and would have a 60-80% capacity factor—but it would produce very little electricity. The most electricity per dollar of investment is gained by using a larger generator and accepting the fact that the capacity factor will be lower as a result. Wind turbines are fundamentally different from fueled power plants in this respect.

If a wind turbine's capacity factor is 33%, doesn't that mean it is only running one-third of the time?

No. A wind turbine at a typical location in the Midwestern U.S. should run about 65-90% of the time. However, much of the time it will be generating at less than full capacity (see previous answer), making its capacity factor lower.

What is "availability" or "availability factor"?

Availability factor (or just "availability") is a measurement of the reliability of a wind turbine or other power plant. It refers to the percentage of time that a plant is ready to generate (that is, not out of service for maintenance or repairs). Modern wind turbines have an availability of more than 98%--higher than most other types of power plant. After more than two decades of constant engineering refinement, today's wind machines are highly reliable.

What does the U.S. wind industry contribute to the economy?

Wind power supplies affordable, inexhaustible energy to the economy. It also provides jobs and other sources of income. Best of all, wind powers the economy without causing pollution, generating hazardous wastes, or depleting natural resources—it has no "hidden costs." Finally, wind energy depends on a free fuel source—the wind—and so it is relatively immune to inflation.

More reading:
Wind Energy and Economic Development: Building Sustainable Jobs and Communities, American Wind Energy Association

Wind Energy for Rural Economic Development, U.S. Department of Energy

What are America's current sources of electricity?

Coal, the most polluting fuel and the largest source of the leading greenhouse gas, carbon dioxide (CO2), is currently used to generate more than half of all of the electricity (52%) used in the United States. Other sources of electricity are: natural gas (16%), oil (3%), nuclear (20%), and hydropower (7%).

How many people work in the U.S. wind industry?

The U.S. wind industry currently directly employs more than 2,000 people. The wind industry contributes directly to the economies of 46 states, with power plants and manufacturing facilities that produce wind turbines, blades, electronic components, gearboxes, generators, and a wide range of other equipment.

The Renewable Energy Policy Project (REPP) estimates that every megawatt of installed wind capacity creates about 4.8 job-years of employment, both direct (manufacturing, construction, operations) and indirect (advertising, office support, etc.). This means that a 50-MW wind farm creates 240 job-years of employment. According to a REPP study released in October 2004, boosting U.S. wind energy installations to approximately eight times today's levels could create 150,000 manufacturing jobs nationwide, with most jobs being added in the 20 states that have lost the most in recent years.

According to REPP, some 90 companies in 25 states currently manufacture wind turbine components, and over 16,000 companies in all 50 states have the technical potential to enter the wind turbine market. The full report is available on the REPP Web site at: http://www.repp.org/articles/static/1/binaries/WindLocator.pdf

Wind and solar energy are likely to be among the largest sources of new manufacturing jobs worldwide during the 21st Century.

What is the value of export markets for wind?

Export markets are growing rapidly. Overseas markets account for about half of the business of U.S. manufacturers of small wind turbines and wind energy developers. Small wind turbine markets are diverse and include many applications, both on-grid (connected to a utility system) and off-grid (stand-alone).

The potential economic benefits from wind are enormous. At a time when U.S. manufacturing employment is generally on the decline, the production of wind equipment is one of the few potentially large sources of new manufacturing jobs on the horizon.

AWEA estimates that wind installations worldwide will total more than 100,000 megawatts over the next decade, or more than $100 billion worth of business. If the U.S. industry could capture a 25% share of the global wind market through the year 2015, many thousands of new jobs would be created.

In what other ways does wind energy benefit the economy?

Wind farms can revitalize the economy of rural communities, providing steady income through lease or royalty payments to farmers and other landowners. Although leasing arrangements vary widely, a reasonable estimate for income to a landowner from a single utility-scale turbine is about $3,000 a year. For a 250-acre farm, with income from wind at about $55 an acre, the annual income from a wind lease could be $14,000, with no more than 2-3 acres removed from production. Such a sum can significantly increase the net income from farming. Farmers can grow crops or raise cattle next to the towers. Wind farms may extend over a large geographical area, but their actual "footprint" covers only a very small portion of the land, making wind development an ideal way for farmers to earn additional income. In west Texas, for example, farmers are welcoming wind, as lease payments from this new clean energy source replace declining payments from oil wells that have been depleted.

Farmers are not the only ones in rural communities to find that wind power can bring in income. In Spirit Lake, Iowa, the local school is earning savings and income from the electricity generated by a turbine. In the district of Forest City, Iowa, a turbine recently erected as a school project is expected to save $1.6 million in electricity costs over its lifetime.

Additional income is generated from one-time payments to construction contractors and suppliers during installation, and from payments to turbine maintenance personnel on a long-term basis. Wind farms also expand the local tax base, and keep energy dollars in the local community instead of spending them to pay for coal or gas produced elsewhere.

Finally, wind also benefits the economy by reducing "hidden costs" resulting from air pollution and health care. Several studies have estimated that 50,000 Americans die prematurely each year because of air pollution.

More reading:
From Snack Bars to Rebar: How Project Development Boosted Local Businesses Up and Down the Wind Energy ‘Supply Chain’ in Lamar, Colorado, March 2004:

Wind Energy and Economic Development: Building Sustainable Jobs and Communities, American Wind Energy Association

Wind Energy for Rural Economic Development, U.S. Department of Energy

I've heard that rising natural gas prices are hurting our economy. Is this a problem that wind energy can help to solve?

Yes. When a wind farm generates electricity in the U.S., the fuel that it is most likely to displace is natural gas. In mid-2003, when Federal Reserve Board Chairman Alan Greenspan testified before Congress that rising natural gas prices were threatening the economy's future, the American Wind Energy Association (AWEA) estimated that U.S. wind plants were already reducing the national natural gas shortage by 10-15%. AWEA has stated that enough wind plants could be built within four years to eliminate the entire gas shortage (estimated at 3-4 billion cubic feet of gas per day). For more information, see: http://www.awea.org/news/news030618gas.html

In 2001, the Colorado Public Utility Commission recognized wind's value as a hedge against volatile natural gas prices, requiring a major utility to include a wind plant in its generating mix in the state rather than relying solely on natural gas. For details on the Commission's decision, see: http://www.nrel.gov/docs/fy01osti/30551.pdf

More reading:
Electricity from the Wind: Wind Energy and the Natural Gas Crisis,
U.S. Department of Energy

Wind Energy and Natural Gas: Balancing Price and Supply Volatility, National Wind Coordinating Committee,

I own some land that is windy. How can I build a wind farm on it?

A first step is to find out more about just how windy your land is—its "wind resource." You can find out more about this and other basic things you will need to know from 10 Steps in Building a Wind Farm.

I support the concept of wind power. How can I invest in it?

The wind industry includes many companies which derive some or much of their revenue from wind-related business. To learn more about investing in one of them, see Investing in Wind Power.

What are the environmental benefits of wind power?

A basic and comprehensive reference on this issue is "The Environmental Imperative for Renewable Energy: An Update," by the Renewable Energy Policy Project (REPP), available on the Web at http://www.repp.org/repp_pubs/repp_publications.html

Wind energy system operations do not generate air or water emissions and do not produce hazardous waste. Nor do they deplete natural resources such as coal, oil, or gas, or cause environmental damage through resource extraction and transportation, or require significant amounts of water during operation. Wind's pollution-free electricity can help reduce the environmental damage caused by power generation in the U.S. and worldwide.

In 1997, U.S. power plants emitted 70% of the sulfur dioxide, 34% of carbon dioxide, 33% of nitrogen oxides, 28% of particulate matter and 23% of toxic heavy metals released into our nation's environment, mostly the air. These figures are currently increasing in spite of efforts to roll back air pollution through the federal Clean Air Act.

Sulfur dioxide and nitrogen oxides cause acid rain. Acid rain harms forests and the wildlife they support. Many lakes in the U.S. Northeast have become biologically dead because of this form of pollution. Acid rain also corrodes buildings and economic infrastructure such as bridges. Nitrogen oxides (which are released by otherwise clean-burning natural gas) are also a primary component of smog.

Carbon dioxide (CO2) is a global warming pollutant --its buildup in the atmosphere contributes to global warming by trapping the sun's rays on the earth as in a greenhouse. The U.S., with 5% of the world's population, emits 23% of the world's CO2. The build-up of global warming pollution is not only causing a gradual rise in average temperatures, but also seems to be increasing fluctuations in weather patterns and causing more frequent and severe droughts and floods. The World Meteorological Organization (WMO) warned in July, 2003, that extreme weather events appear to be increasing in number due to climate change.

Particulate matter is of growing concern because of its impacts on health. Its presence in the air along with other pollutants has contributed to make asthma one of the fastest growing childhood ailments in industrial and developing countries alike, and it has also recently been linked to lung cancer. Similarly, urban smog has been linked to low birth weight, premature births, stillbirths and infant deaths. In the United States, the research has documented ill effects on infants even in cities with modern pollution controls.

Toxic heavy metals accumulate in the environment and up the biological food chain. A number of states have banned or limited the eating of fish from fresh-water lakes because of concerns about mercury, a toxic heavy metal, accumulating in their tissue.

Development of just 10% of the wind potential in the 10 windiest U.S. states would provide more than enough energy to displace emissions from the nation's coal-fired power plants and eliminate the nation's major source of acid rain; reduce total U.S. emissions of CO2 by almost a third; and help contain the spread of asthma and other respiratory diseases aggravated or caused by air pollution in this country.

If wind energy were to provide 20% of the nation's electricity -- a very realistic and achievable goal with the current technology -- it could displace more than a third of the emissions from coal-fired power plants.

In 2006, the American Wind Energy Association estimates that wind plants in the U.S. will generate 24 billion kilowatt-hours. If instead the average utility fuel mix were used to generate that much electricity, 30 billion pounds (15 million tons) of carbon dioxide, 76,000 tons of sulfur dioxide (208 tons per day), and 36,000 tons of nitrogen oxides (100 tons per day) would be released into the atmosphere.

The comparative environmental impacts of various options for producing electricity have been extensively studied by the European Union in a 10-year effort called the "ExternE" ("external" or non-economic costs of energy). The results of that study are available at http://www.externe.info/externpr.pdf and http://externe.jrc.es . As with every other study of non-economic costs that has been conducted, the Externe study found wind energy's costs to be among the lowest, far below those of fossil fuels. The highest non-economic cost for wind in any European country, for example, was 0.25 Euro cents per kilowatt-hour, while the lowest cost for coal was 2-4 Euro cents/kWh (eight to 16 times as much).

More reading:
Comparative Air Emissions of Wind and Other Fuels

Will using more wind energy help to prevent global warming?

Yes! Carbon dioxide (CO2) is the most important of the global warming pollutants which are changing our climate. According to experts, if we are to avoid dangerous levels of warming, we must cut our CO2 emissions by 80-90 per cent by 2050. That means switching to forms of energy generation that do not produce CO2.

Wind power is a clean, renewable form of energy, which during operation produces no carbon dioxide. While some emissions of these gases will take place during the design, manufacture, transport and erection of wind turbines, enough electricity is generated from a wind farm within a few months to totally compensate for these emissions. When wind farms are dismantled (usually after 20-25 years of operation) they leave no legacy of pollution for future generation.

Given the scale of the CO2 cuts needed, wind power--as the least expensive, most developed renewable energy technology and the fastest to build--is the best placed renewable technology to deliver carbon emissions reductions on a large scale, quickly.

Will using more wind energy reduce health care costs?

Yes! In 2000, the Harvard School of Public Health looked at the human health effects from two fossil-fuel-fired power plants in Massachusetts. It estimates that the air pollution from the plants causes:

  • 159 premature deaths
  • 1,710 emergency room visits
  • 43,300 asthma attacks

each year. Replacing as much of this electricity as possible with wind energy would clearly lower associated health care costs.

More reading:
Estimated Public Health Impacts of Criteria Air Pollutant Emissions from the Salem Harbor and Brayton Point Power Plants

How does wind stack up on greenhouse gas emissions when the "total fuel cycle" (including manufacture of equipment, plant construction, etc.) is considered?

The claim is sometimes made that manufacturing wind turbines and building wind plants creates large emissions of carbon dioxide. This is false. Studies have found that even when these operations are included, wind energy's CO2 emissions are quite small — on the order of 1% of coal or 2% of natural gas per unit of electricity generated. Or in other words, using wind instead of coal reduces CO2 emissions by 99%, using wind instead of gas by 98%.

What are wind power's other environmental impacts?

Wind power plants, like all other energy technologies, have some environmental impacts. However, unlike most conventional technologies (which have regional and even global impacts due to their emissions and fuel imports), the impacts of wind energy systems are minimal and local. This makes them easier for local communities to monitor and, if necessary, mitigate.

The local environmental impacts that can result from wind power development include:

Erosion which can be prevented through proper installation and landscaping techniques. Erosion can be a concern in certain habitats such as the desert, where a hard-packed soil surface must be disturbed to install wind turbines. Erosion has also been raised as a concern in the eastern U.S., where wind farms typically must be installed on mountain ridgelines. However, standard engineering practices used by ski areas on the same kind of terrain are adequate to deal with any erosion issues that might be raised by construction of a wind farm and its service road.

Bird and bat kills and other effects

Birds occasionally collide with wind turbines, as they do with other tall structures such as buildings. Avian deaths have become a concern at Altamont Pass in California, which is an area of extensive wind development and also high year-round raptor use. Detailed studies, and monitoring following construction, at other wind development areas indicate that this is a site-specific issue that will not be a problem at most potential wind sites. Also, wind's overall impact on birds is low compared with other human-related sources of avian mortality—see "Avian Collisions With Wind Turbines," for more information. The following graph is based on data from the studies described in that report:

Source: Erickson, et.al, 2002. Summary of Anthropogenic Causes of Bird Mortality

No matter how extensively wind is developed in the future, bird deaths from wind energy are unlikely to ever reach as high as 1% of those from other human-related sources such as hunters, house cats, buildings, and autos. (House cats, for example, are believed to kill 1 billion birds annually in the U.S. alone.) Wind is, quite literally, a drop in the bucket. Still, areas that are commonly used by threatened or endangered bird species should be regarded as unsuitable for wind development. The wind industry is working with environmental groups, federal regulators, and other interested parties to develop methods of measuring and mitigating wind energy's effect on birds.

Wind energy can also negatively impact birds and other wildlife by fragmenting habitat, both through installation and operation of wind turbines themselves and through the roads and power lines that may be needed. This has been raised as an issue in areas with unbroken stretches of prairie grasslands or of forests. More research is needed to better understand these impacts.

Bat collisions at wind plants generally tend to be low in number and to involve common species which are quite numerous. Human disturbance of hibernating bats in caves is a far greater threat to species of concern. Still, a surprisingly high number of bat kills at a new wind plant in West Virginia in the fall of 2003 has raised concerns, and research at that plant and another in Pennsylvania in 2004 suggests that the problem may be a regional one. The wind industry has joined with the U.S. Fish and Wildlife Service, the U.S. Department of Energy’s National Renewable Energy Laboratory, and Bat Conservation International to form the Bats and Wind Energy Cooperative (BWEC), which funded the 2004 research program and is continuing to explore ways to avoid or reduce bat kills.

More reading:
Comparative Impacts of Wind and Other Energy Sources on Wildlife

Avian Collisions with Wind Turbines: A Summary of Existing Studies and Comparisons to Other Sources of Avian Collision Mortality in the United States

Wind Turbine Interactions With Birds and Bats: A Summary of Research Results and Remaining Questions, National Wind Coordinating Committee

Unusual Alliance Hopes to Keep Bats Out of Wind Turbines, American Wind Energy Association/Bat Conservation International/U.S. Fish and Wildlife Service

Visual impacts Which can be minimized through careful design of a wind power plant. Using turbines of the same size and type and spacing them uniformly generally results in a wind plant that satisfies most aesthetic concerns. Computer simulation is helpful in evaluating visual impacts before construction begins. Public opinion polls show that the vast majority of people favor wind energy, and support for wind plants often increases after they are actually installed and operating. For more information on public attitudes toward wind, see http://www.awea.org/faq/survpub.html

More reading:
A Summary of Opinion Surveys on Wind Power,
European Wind Energy Association .

Noisewas an issue with some early wind turbine designs, but it has been largely eliminated as a problem through improved engineering and through appropriate use of setbacks from nearby residences. Aerodynamic noise has been reduced by changing the thickness of the blades' trailing edges and by making machines "upwind" rather than "downwind" so that the wind hits the rotor blades first, then the tower (on downwind designs where the wind hits the tower first, its "shadow" can cause a thumping noise each time a blade passes behind the tower). A small amount of noise is generated by the mechanical components of the turbine. To put this into perspective, a wind turbine 300 meters away is no noisier than the reading room of a library.

More reading:
Wind Energy and Noise.
Noise from Wind Turbines: The Facts.

Shadow Flicker is occasionally raised as an issue by close neighbors of wind farm projects. A wind turbine's moving blades can cast a moving shadow on a nearby residence, depending on the time of the year (which determines how low the sun is in the sky) and time of day. It is possible to calculate very precisely whether a flickering shadow will in fact fall on a given location near a wind farm, and how many hours in a year it will do so. Therefore, it should be easy to determine whether this is a potential problem. Normally, it should not be a problem in the U.S., because at U.S. latitudes (except in Alaska) the sun's angle is not very low in the sky, and the appropriate setback for noise (see above) will be sufficient to prevent shadow flicker problems.

More reading:
Shadow Casting from Wind Turbines

Will wind energy hurt tourism in my area?

People who would rather not live near wind plants (sometimes referred to as "NIMBYs," short for "Not In My Back Yard") often raise this concern with respect to new wind project proposals.

There is no evidence that wind farms reduce tourism, and considerable evidence to the contrary. For example, in late 2002, a survey of 300 tourists in the Argyll region of Scotland, noted for its scenic beauty, found that 91% said the presence of new wind farms "would make no difference in whether they would return." Similar surveys of tourists in Vermont and Australia have produced similar results. Many rural areas in the U.S. have noted increases in tourism after wind farms have been installed, as have scenic areas in Denmark, the world's leader in percentage of national electricity supplied by wind. Other telling indicators: local governments frequently decide to install information stands and signs near wind farms for tourists; wind farms are regularly featured on post cards, magazine covers, and Web pages.

More reading:
Wind Farms and Tourism: The Facts

How popular is wind energy?

Wind energy is one of the most popular energy technologies. Opinion surveys regularly show that just over eight out of 10 people (80%) are in favor of wind energy, and less than one in ten (around 5%) are against it. The rest are undecided.

Public opinion in support of wind power tends to become even more strongly in favor once the wind turbines are installed and operating, a finding from several surveys carried out in the UK and in Spain.

Some people who live near proposed wind projects may be apprehensive about them. But when accurate information and knowledge is made available, experience shows that initial concerns are reduced and support for wind farms increases.

More reading:
A Survey of Public Attitudes on the Environment and Wind Energy

Public Attitudes to Wind Energy

Why is there sometimes opposition to wind energy projects?

Local opposition to proposed wind farms usually arises because some people perceive that the development will spoil the view that they are used to. It is true that a large wind farm can be a significant change, but while some people express concern about the effect wind turbines have on the beauty of our landscape, others see them as elegant and beautiful, or symbols of a better, less polluted future.

The visual effect of wind farms is a subjective issue, but most of the other criticisms made about wind energy today are exaggerated or untrue, and simply reflect attempts by particular groups to discredit the technology, worry local communities, and turn them against proposed projects. In the electronic age, myths and misinformation about wind power spread at lightning speed.

More reading:
An excellent resource for debunking myths about wind power is the "Yes2Wind" Web site at http://www.yes2wind.com It has been created by three major environmental groups — the World Wildlife Fund, Greenpeace, and Friends of the Earth — who believe that wind's benefits in reducing greenhouse gas emissions and air pollution far outweigh its negative impacts.

How much land is needed for a utility-scale wind plant?

In open, flat terrain, a utility-scale wind plant will require about 60 acres per megawatt of installed capacity. However, only 5% (3 acres) or less of this area is actually occupied by turbines, access roads, and other equipment--95% remains free for other compatible uses such as farming or ranching. In California, Minnesota, Texas, and elsewhere, wind energy provides rural landowners and farmers with a supplementary source of income through leasing and royalty arrangements with wind power developers.

A wind plant located on a ridgeline in hilly terrain will require much less space, as little as two acres per megawatt.

How much water do wind turbines use compared with conventional power plants?

Water use can be a significant issue in energy production, particularly in areas where water is scarce, as conventional power plants use large amounts of water for the condensing portion of the thermodynamic cycle. For coal plants, water is also used to clean and process fuel.

According to the California Energy Commission (cited in Paul Gipe's Wind Energy Comes of Age, John Wiley & Sons, 1995), conventional power plants consume the following amounts of water (through evaporative loss, not including water that is recaptured and treated for further use):

WATER CONSUMPTION--CONVENTIONAL POWER PLANTS

Technology

gallons/kWh

liters/kWh

Nuclear

0.62

2.30

Coal

0.49

1.90

Oil

0.43

1.60

Combined Cycle Gas

0.25

0.95

Small amounts of water are used to clean wind turbine rotor blades in arid climates (where rainfall does not keep the blades clean). The purpose of blade cleaning is to eliminate dust and insect buildup, which otherwise deforms the shape of the airfoil and degrades performance.

Similarly, small amounts of water are used to clean photovoltaic (solar) panels. Water use numbers for these two technologies are as follows:

WATER CONSUMPTION--WIND AND SOLAR

Technology

gallons/kWh

liters/kWh

Wind [1]

0.001

0.004

Solar [2]

0.030

0.110

Wind therefore uses less than 1/600 as much water per unit of electricity produced as does nuclear, approximately 1/500 as much as coal, and approximately 1/250 as much as natural gas, the most popular choice for new power plants.

NOTES

[1] American Wind Energy Association estimate, based on data obtained in personal communication with Brian Roach, Fluidyne Corp., December 13, 1996. Assumes 250-kW turbine operating at .25 capacity factor, with blades washed four times annually.

[2] Meridian Corp., "Energy System Emissions and Materials Requirements," U.S. Department of Energy, Washington, DC. 1989, p. 23.

I've heard that wind energy doesn't really reduce pollution, because other, fossil-fired generating units have to be kept running on a standby basis in case the wind dies down. Is this true?

No. It is true that other generating plants have to be available to the power system's operator to supply electricity when the wind is not blowing. However, the wind does not just start and stop. Typically, wind speeds increase gradually and taper off gradually, and the system operator has time to move other plants on and off line (start and stop them from generating) as needed--the fluctuations in wind plant output change more slowly than do the changes in customer demand that a utility must adjust to throughout the day. Studies indicate that for a 100-megawatt wind plant, only about 2 megawatts of conventional capacity is needed to compensate for changes in wind plant output.

Also, whenever the wind is blowing, it displaces the most expensive conventional power plant that is generating. Typically, this tends to be the oldest and dirtiest gas plants on a utility system, but in some parts of the country (notably the mid-Atlantic states such as Maryland, West Virginia, or Virginia), wind power may displace coal.

The U.S. Department of Energy puts it quite simply in its fact sheet Wind Energy Myths: "When wind is added to a utility system, no new backup is required to maintain system reliability." See http://www.nrel.gov/docs/fy05osti/37657.pdf

What about turbines throwing blades, or ice? Is wind energy dangerous to the public?

It has been estimated by a number of reliable sources that 50,000 Americans a year die from air pollution, of which about one-third is produced by power plants. By contrast, in 20 years of operation, the wind industry (which emits no pollutants) has recorded only one death of a member of the public--a German skydiver who parachuted off-course into an operating wind plant. Blade throws were common in the industry's early years, but are unheard of-today because of better turbine design and engineering. Ice throw, while it can occur, is of little danger because setbacks typically required to minimize noise (see above) are sufficient to protect against danger to the public, and because ice buildup slows a turbine's rotation and will be sensed by a turbine's control system, causing the turbine to shut down. One European group that has investigated the ice throw question recommends a setback of 1.5 times the sum of a turbine's hub height and its rotor diameter.

More reading:
Assessment of Safety Risks Arising from Wind Turbine Icing

Why not develop wind farms on mountains that are already being used for ski resorts?

Because of the potential danger from ice throw. As the above answer indicates, ice throw does not present a danger except for the area close to turbines (that is, within a few hundred meters). At ski areas, however, turbines would typically have to be sited very close to operating lifts and trailheads, making ice throw a safety concern.

I've heard that stray voltage from wind power plants can be transmitted through the ground, disturbing or harming livestock. Is this true?

No. There is nothing different or unusual about managing the electricity flow from an operating wind plant. Standard electric wiring practices are adequate to prevent stray voltage from occurring.

Will a wind project interfere with electromagnetic transmissions such as radio, television, or cell-phone signals?

First, this is not a problem for modern small (residential) wind turbines. The materials used to make such machines are non-metallic (composites, plastic, wood) and small turbines are too small to create electromagnetic interference (EMI) by "chopping up" a signal.

Large wind turbines, such as those typically installed at wind farms, can interfere with radio or TV signals if a turbine is in the "line of sight" between a receiver and the signal source, but this problem can usually be easily dealt with improving the receiver's antenna or installing relays to transmit the signal around the wind farm. Use of satellite or cable television is also an option.

Will a wind project interfere with radar?

Yes. Radar is basically designed to filter out stationary objects and display moving ones, and moving wind turbine blades create radar echoes. It is possible to modify a radar installation to eliminate this problem, according to a consulting firm that has studied it for the British government-see http://www.bwea.com/aviation/ams_report.html. According to the study: "This study concludes that radars can be modified to ensure that air safety is maintained in the presence of wind turbine farms. Individual circumstances will dictate the degree and cost of modification required, some installations may require no change at all whilst others may require significant modification."

If a wind project is proposed near an airport or military airfield, this issue will likely require further technical investigation. The interference is generally limited to objects (airplanes) that are physically shadowed by the turbines (that is, very low-flying aircraft), so the further the turbines are from an airfield and the lower their altitude, the less interference should occur.

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