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, annual average wind speeds greater than four meters per second (m/s) (9 mph) are 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 will generate about 29% more electricity than one at an 11-mph site.
How many turbines does it take to make one megawatt
What is a wind power plant?
What is "capacity factor"?
A wind plant is "fueled" by the wind, which blows steadily at times and not at all at other times. Most modern utility-scale wind turbines operate with a capacity factor of 25% to 40%, although they may achieve higher capacity factors during windy weeks or months. It is possible to achieve much higher capacity factors by combining wind with a storage technology such as pumped hydro or compressed-air energy storage (CAES).
What is "availability factor"?
Wind energy costs
How much does wind energy cost?
How do utility-scale wind power plants compare in
cost to other renewable energy sources?
What is the "production tax credit" for
The wind PTC expired June 30, 1999, and an effort is currently underway to extend it for five years. For information on the status of that effort, contact the American Wind Energy Association (AWEA), phone (202) 383-2500, e-mail <email@example.com>.
Wind energy's potential
The wind doesn't blow all the time. How much can it
really contribute to a utility's generating capacity?
The studies, by the Tellus Institute of Boston, Mass., and the Prince Edward Island (Canada) Energy Corp., concluded that when wind turbines are added to a utility system, they increase the overall statistical probability that the system will be able to meet demand requirements. They noted that while wind is an intermittent resource, conventional generating systems also experience periodic outages for maintenance and repair.
The exact amount of capacity value that a given wind project provides depends on a number of factors, including average wind speeds at the site and the match between wind patterns and utility load requirements.
How much energy can wind realistically supply to the
U.S. wind resources are even greater, however. North Dakota alone is theoretically capable (if there were enough transmission capacity, storage capability, etc.) of producing enough wind-generated power to meet more than one-third of U.S. electricity demand. The theoretical potentials of the windiest states are shown in the following table.
Experience also shows that wind power can provide at least up to a fifth of a system's electricity, and the figure could probably be higher. Wind power currently provides more than 20% of the electricity distributed by Energia Hidroelectrica de Navarra, the regional electric utility of the industrial state of Navarra in northern Spain. In western Denmark, wind supplies more than 25% of the electricity that is used during windy winter nights.
How much energy can wind supply worldwide?
A recent study performed by Denmark's BTM Consult for the European Wind Energy Association and Greenpeace found that by the year 2017, wind could provide 10% of world electricity supplies, meeting the needs of 500 million average European households.
The potential of wind to improve the quality of life in the world's developing countries, where more than two billion people live with no electricity or prospect of utility service in the foreseeable future, is vast.
What is the "energy payback time" for a
Wind energy and the economy
What does the U.S. wind industry contribute to the
What are America's current sources of electricity?
How many people work in the U.S. wind industry?
The European Wind Energy Association (EWEA) estimates that every megawatt of installed wind capacity creates about 60 person-years of employment and 15-19 jobs, directly and indirectly. A typical 50-MW wind farm, therefore, creates some 3,000 person-years of employment. The rate of job creation will decline as the industry grows and becomes able to make more use of efficiencies of volume, but wind and solar energy are still likely to furnish one of the largest sources of new manufacturing jobs worldwide during the 21st Century.
What is the value of export markets for wind?
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 has estimated that wind installations worldwide will total more than 48,000 megawatts over the next decade, or more than $45 billion worth of business. If the U.S. industry could capture a 25% share of the global wind market through the year 2010, more than 150,000 new jobs would be created.
In what other ways does wind energy benefit the
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 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. Alameda (Calif.) County, for example, collected $725,000 in property taxes during 1998 from wind turbine installations valued at $66 million.
Wind energy and the environment
What are the environmental benefits of wind power?
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.
Carbon dioxide (CO2) is a greenhouse gas--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 greenhouse gases is not only causing a gradual rise in average temperatures, but also seems to be increasing fluctuations in weather patterns and causing more severe droughts.
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. Toxic heavy metals accumulate in the environment and up the biological food chain.
Development of 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 world emissions of CO2 by 4 %; 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, or all of radioactive waste and water pollution from nuclear power plants.
The 6 billion kilowatt-hours currently generated by wind plants in the U.S. each year displaced some 9 billion pounds (4.5 million tons) of carbon dioxide, 23,500 tons of sulfur dioxide (64 tons per day), and 15,500 tons of nitrogen oxides (42 tons per day).
What are wind power's other environmental impacts?
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.
* Bird 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 at other wind development areas indicate that this is a site-specific issue that will not be a problem at most potential wind sites. However, areas that are commonly used by threatened or endangered 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.
* 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.
* Noise was 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 adjusting the thickness of the blades' trailing edges and by orienting blades upwind of the turbine tower. A small amount of noise is generated by the mechanical components of the turbine. To put this into perspective, a wind turbine 250 meters from a residence is no noisier than a kitchen refrigerator.
How much land is needed for a utility-scale wind
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?
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
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 photovoltaics (solar) panels. Water use numbers for these two technologies are as follows:
WATER CONSUMPTION--WIND AND SOLAR
Technology gallons/kWh liters/kWh
Wind therefore uses less than 1/600 as much water per unit of electricity produced as does nuclear, and approximately 1/500 as much as coal.
 Meridian Corp., "Energy System Emissions and Materials Requirements," U.S. Department of Energy, Washington, DC. 1989, p. 23.
Wind industry statistics
How much wind generating capacity currently exists in
the U.S.? How much will be added over the next several years?
In what states is there significant wind power
How much wind generating capacity currently exists
worldwide? How fast is it growing and where?
Wind power plants are heavily concentrated in Europe and the United States, with the exception of India and China. The "top 10" nations listed below accounted for over 95% of the total wind energy produced in 1998.
World Leaders in Wind Capacity, December 1998
Elsewhere, wind is catching on slowly but steadily, with new plants having been built recently in Costa Rica, Australia, New Zealand, and many other countries.
How much is currently invested in the U.S. wind
How much electricity does wind generate in the U.S.
What U.S. utilities are participating in wind power development?
In what states is there significant wind power
Small wind energy systems
How many turbines are needed to power a household or
For village electrification applications, both single and multiple turbine installations are common, and turbines up to 100 kW in capacity may be used.
How much land is needed for a small wind system?
What size tower is used for a small-scale wind
How do small turbine costs compare to the costs of
The Congressional Office of Technology Assessment has found wind to be cheaper for meeting remote loads than diesel generators, photovoltaics, or utility transmission line extensions. (Micro-hydro also was found to be less expensive in many locations.)
Hybrid systems--wind/photovoltaic, wind/diesel, and other combinations--can often provide the most efficient and cost-effective option for rural electrification. Photovoltaics (PV)--the direct conversion of sunlight into electricity--is often used to supplement wind power since PV tends to operate best in low wind months. Diesel generators or batteries can be used for backup power and to maintain power production during low wind seasons.
A recent study of an Arctic community with annual average wind speeds of 15 mph compared the cost of a 500-kW diesel system to that of a 200-kW diesel generator and four mid-sized wind turbines. If found that the wind/diesel combination cost considerably more to install ($378,000 versus $125,000), but would deliver fuel savings of $90,000 per year, paying for itself in less than three years.*
*For more information, see Proceedings of the Seventh Wind-Diesel Workshop, 1993.
Why are small wind turbines better than diesel
generators or extension of utility lines in developing countries?
How do small wind turbines compare with other
renewable energy technologies suitable for decentralized rural
Aren't wind turbines too "high-tech" for
What companies make small wind electric systems?
What companies make water pumping wind turbines?
Wind energy policy issues
I've heard that the U.S. utility industry is being
"restructured." How will that affect wind energy?
On the positive side, as with long-distance telephone service, restructuring will offer consumers a chance to choose to buy their electricity from among a number of different service providers. Since electricity generation, unlike phone service, has major environmental impacts, it seems likely that some of these service providers will choose to offer "green" (environmentally-friendly) products from clean power sources like wind. Indeed, many electric utilities are already offering wind-generated electricity as an option today.
On the negative side, the primary purpose of restructuring is to allow large industrial companies to shop among power suppliers for the cheapest price. It will do this regardless of the environmental impacts of the sources that are used. Already, this appears to be leading to increasing generation from older, dirtier coal-fired plants that were "grandfathered" (exempted from having to install new pollution controls) under the Clean Air Act. To the degree that restructuring encourages cheap generation regardless of environmental costs, it will be harmful to wind energy.
One solution that has been suggested to some of the problems posed by restructuring is the Renewables Portfolio Standard (RPS).
What is the Renewables Portfolio Standard and how
does it work?
Aside from the "minimum renewable content" requirement, the RPS imposes very few other requirements on companies--they are free to buy, trade, or generate electricity from renewables in whatever fashion is most efficient and economical for them. The RPS is therefore often described by its supporters as being "market-friendly."
Several federal restructuring bills have included an RPS, and at least eight states have also adopted RPS laws. Typically, the RPS gradually increases over time, by 1% per year or some such number, in order to encourage the sustained, orderly development of renewable energy industries.
What exactly is "green power"? Can you tell
me more about it?
Utility green power programs vary, but one common approach is for a utility to offer its customers the option of buying electricity generated from wind at a premium price. For example, a customer might be able to sign up to receive a certain number of 100-kilowatt-hour "blocks" of electricity from wind each month for an extra $2 each (that is, for 2 cents to 4 cents per kilowatt-hour). A customer signing up for 2 blocks at $2 would pay $4 more for electricity each month and receive 200 kilowatt-hours of wind-generated electricity. The utility would then add enough wind capacity to its generating mix to provide the additional electricity required. (The utility cannot deliver specific electrons from any of its plants to a specific customer. Instead, its generating mix should be thought of as a pool. Power plants add electricity to the pool and customers take it out. With green power, the utility adds more wind energy to the pool based on the amount customers have said they will purchase.)
No one knows yet how successful green programs and products will be in the electricity marketplace. If consumers learn more about the air pollution, strip mining, and other harmful environmental impacts of electricity generation and decide to "vote with their dollars" for clean energy, green power could be come a large and growing business over the next decade and beyond.
Customers in parts or all of the states of California, Colorado, Idaho, Kansas, Michigan, Minnesota, Nebraska, New Mexico, Ohio, Oregon, Pennsylvania, Texas, Washington, and Wisconsin have the option today to sign up for green power.
What about government purchases? Do federal and state
governments use their purchasing power to encourage clean energy?
In 1998, the federal government alone consumed 1,077 trillion British thermal units (Btu) of energy, or 1.14% of total energy use. Within that total, it consumed approximately 54 billion kilowatt-hours of electricity, or about 1.6% of total national electricity use. The federal government's total energy bill was $8 billion, or 2% of the federal consumption of goods and services. Its electricity bill was approximately $3.5 billion. Perhaps more important, in 1998 the federal government used more than twice as much electricity as was generated by all the solar, wind, and geothermal facilities owned by utilities and the industrial sector nationwide. Federal energy dollars could have a great impact on renewable energy markets.
By and large, the potential of government purchases to encourage clean energy industries has not been realized. In early 1999, President Clinton issued an Executive Order that urges government agencies to consider the federal government's policy of supporting renewable energy in making energy purchases. More recently, the federal Environmental Protection Agency (EPA) has announced that one of its facilities in California will be entirely supplied by green power, and the U.S. Army has announced plans to develop wind energy at Fort Bliss, New Mexico. More commonly, though, government agencies, like industrial companies, look for the cheapest electricity source, regardless of environmental consequences.
Is wind energy heavily subsidized? More than other
forms of energy?
All energy technologies are subsidized by the U.S. taxpayer. Subsidies come in various forms, including payment for production, tax deductions, guarantees, and leasing of public lands at below-market prices. Subsidies can also be provided indirectly, for example through federal research and development programs, and provisions in federal legislation and regulations. For example, loopholes in the Clean Air Act currently exempt older power plants from compliance with federal pollution standards and become, in effect, a kind of subsidy that lowers the price of electricity from coal-fired power plants.
Here are some conclusions from a detailed 1993 study of energy subsidies by the Alliance to Save Energy (Federal Energy Subsidies: Energy, Environmental, and Fiscal Impacts):
"Energy subsidies in 1989 favored mature, conventional energy supply resources by $32.3 billion to $3.8 billion over non-conventional energy resources." $21 billion went to fossil fuels, $11 billion to nuclear, and $900 million to all renewable energy sources including wind. "There is currently no free market in energy. Given the size of federal energy subsidies, now and in the past, it is erroneous to speak of a 'free market' in energy. . . It may be appropriate to subsidize emerging energy resources, but mature resources should stand the test of the market. When this test is applied to subsidies in 1989, the pattern appears to be almost completely backward. In other words, the mature, conventional technologies received almost 90% of the subsidies."
The pattern of subsidies that the Alliance found is also flatly opposed to the views of the American public. In numerous public opinion surveys over the past several years, those surveyed have favored providing government assistance to clean energy sources and not to nuclear or fossil fuels. For example, in one national poll conducted in mid-1999, 80% of respondents said they favor the use of tax incentives to increase the use of renewable energy for the production of electricity.
What is "net metering" ("net
billing") and how does it work?
Example: During a one-month period, John Doe's wind turbine generates 300 kilowatt-hours (kWh) of electricity. Most of the electricity is generated at a time when equipment in John's household (refrigerator, lights, etc.) is drawing electricity and is used on site. However, some is generated at night when most equipment is turned off. At the end of the month, the turbine has generated 100 kWh in excess of John's instantaneous needs and has been transmitted to the utility system. The utility has also supplied John with a total of 500 kWh for his use at times when the wind turbine has not been generating or has been insufficient for his needs. Since the meter ran backward while 100 kWh was being transmitted to the utility, the utility will only bill John for 400 kWh, rather than 500 kWh.
Net metering can dramatically improve the economics of a residential wind turbine by allowing the turbine's owner to use her excess electricity to offset utility-supplied power at the full retail rate, rather than having to sell the power to the utility at the price the utility pays for the wholesale electricity it buys or generates itself. Many utilities have argued against net metering laws, saying that they are being required, in effect, to buy power from wind turbine owners at full retail rates, and are therefore being deprived of a profit on part of their electricity sales. However, wind energy advocates have successfully argued that what is going on is a power swap, and that it is standard practice in the utility industry for utilities to trade power among themselves without accounting for differences in the cost of generating the various kilowatt-hours involved.
Today, net metering's popularity is growing. Twenty-nine states have enacted it in some form, and others are considering it.
Wind energy resource guide
Where can I go for more information?
Kern Wind Energy Association
National Renewable Energy Laboratory
National Wind Technology Center (303) 384-6900
*Wind Power for Home & Business
*Wind Energy Resource Atlas
* Provides a listing of wind turbine manufacturers, project developers and others, including contact information. (The directory is available only on the World Wide Web, at http://www.awea.org.)
Wind Energy Publications
Mother Nature Takes a Part: Wind Energy
The Wind Energy Production Tax Credit: A User's Guide published by AWEA
International Wind Power Markets
Renewable Energy for New York State--Policy Options for
a Clean Energy Future
Workshop Report: Seventh International Wind-Diesel
Workshop, August 22-25, 1993
Electricity Transmission Pricing Report
The Tellus Institute, Boston, Mass.
More information on wind power
Alternative energy index