This NebFact contains basic information on wind power

Hubbard, Kenneth G.

Stooksbury, David E.

English

UNL | Libraries

University of Nebraska - Lincoln 
DigitalCommons@University of Nebraska - Lincoln 
Historical Materials from University of 
Nebraska-Lincoln Extension Extension 
1996 
NF96-304 An Introduction to Wind Power for Nebraskans 
David E. Stooksbury 
University of Nebraska--Lincoln, dstooksbury2@unl.edu 
Kenneth G. Hubbard 
University of Nebraska--Lincoln, khubbard1@unl.edu 
Follow this and additional works at: https://digitalcommons.unl.edu/extensionhist 
 Part of the Agriculture Commons, and the Curriculum and Instruction Commons 
Stooksbury, David E. and Hubbard, Kenneth G., "NF96-304 An Introduction to Wind Power for Nebraskans" 
(1996). Historical Materials from University of Nebraska-Lincoln Extension. 576. 
https://digitalcommons.unl.edu/extensionhist/576 
This Article is brought to you for free and open access by the Extension at DigitalCommons@University of Nebraska - 
Lincoln. It has been accepted for inclusion in Historical Materials from University of Nebraska-Lincoln Extension by an 
authorized administrator of DigitalCommons@University of Nebraska - Lincoln. 
Nebraska Cooperative Extension NF96-304
An Introduction to Wind Power for Nebraskans 
David E. Stooksbury, Renewable Energy Specialist; 
Kenneth G. Hubbard, Extension Climate Resource Specialist  
Windmills are a common sight in Nebraska. The historian Walter Prescott Webb argued that the 
windmill, barbed wire and the six-shooter made homesteading on the Great Plains possible.  
Windmills ensured early homesteaders had a constant supply of water, and early in this century, they 
were used to produce electricity for homesteads. Many Nebraskans remember the 32-volt Wincharger. 
With the coming of inexpensive public power to rural Nebraska, most small electric windmills were 
abandoned.  
During the 1970s, the sudden increase in energy costs coupled with spot shortages of oil caused a 
renewed interest in wind energy. Federal tax breaks encouraged the development of utility-scale 
windmills. However, these early developments were plagued with technological and economic 
problems. With the end of tax breaks in 1985, wind farm development came to a virtual halt. Many 
thought the wind energy industry was dead.  
However, in the last few years, several technological advances have made wind power economically 
competitive with more traditional energy forms such as coal and oil. Nebraska has many promising 
locations for large utility-scale wind farm development. However, before wind farm development can 
take place, an assessment of the wind power potential must be made. Identifying the most promising 
sites will take several years. Thus major wind farm development in Nebraska will not occur until after 
the turn of the century.  
Wind Energy Fundamentals 
In this section we will show that wind power depends on the wind speed raised to the third power 
(wind speed cubed). This means that an increase in wind speed from 13 mph (5.8 m/s) to 15 mph (6.7 
m/s) will increase wind power production by 54 percent. The cubic relationship between wind power 
and wind speed makes it important that the true wind speed at a location be known before developing a 
wind farm.  
In general, most people overestimate the wind speed at a location. Therefore, a multiyear monitoring 
program is the only reliable method to determine the true wind speed at a location. The mathematical 
form of the wind power-wind speed relationship is  
Equation 1  
Power = k × (wind speed) × (wind speed) × (wind speed)  
 
or  
Equation 2  
Power = k × (wind speed)³  
where k is a constant of proportionality.  
In physics, energy is defined as the ability to do work. While this definition is technically correct, it is 
not very meaningful in this form. We can ask, how much energy is required to lift a bucket of water 
from the bottom of a well? But we can also ask, how much work is required to lift a bucket of water 
from the bottom of a well? These are really the same question.  
It is useful to differentiate between kinetic energy and potential energy. Kinetic energy is the energy 
associated with motion. All moving objects have kinetic energy. A windmill transfers kinetic energy 
from the wind to an electrical generator (the wind makes the windmill blades turn on a shaft that 
connects to the generator). The turning generator creates a field that forces electrons to move through 
the power line. Moving electrons form an electric current. Thus, a windmill transforms the kinetic 
energy of air into electric current. Potential energy is stored energy. Batteries, food, and water behind a 
dam are examples of potential energy.  
How much power is produced by a windmill? To answer this question, we must first calculate kinetic 
energy of the wind. Kinetic energy has the mathematical form  
Equation 3  
KE = 1/2 × (mass of the object) × (speed of object) × (speed of the object)  
The kinetic energy equation is usually written  
Equation 4  
KE = 1/2mv²  
where m is the mass of the object (mass of air in this case) and v is the speed of the object (the wind 
speed in this case).  
In order to calculate the kinetic energy of the air moving a windmill blade, we first must calculate the 
mass of the air. It is easier to calculate mass per unit of time (mass/time) of air instead of the mass of air. 
The mass/time of air depends on the air density, the area swept by the windmill blades, and the speed of 
the wind. This brings us to the following equation  
Equation 5  
mass/time = (air density) × (area) × (wind speed) 
where area is the area swept by the wind mill blades.  
We can now calculate the kinetic energy (KE). However, our mass term (Equation 5) is mass per time. 
This is not the problem that it appears. If we divide the kinetic energy by time (KE/time), we have the 
definition of power. Thus it will be easier to calculate power than to calculate kinetic energy. Since 
calculating the power is our ultimate goal, we will calculate power instead of KE.  
Equation 6  
Power = KE/time = 1/2 × (mass/time) × (wind speed) × (wind speed)  
Now substitute [(air density) × (area) × (wind speed)] for mass/time, we get  
Equation 7  
Power = 1/2 × [(air density) × (area) × (wind speed)] × (wind speed) × (wind speed)  
This can be simplified to  
Equation 8  
Power = 1/2 × (air density) × (area) × (wind speed)³  
In wind energy, it is common to use Power per area swept by the windmill blade (Power/area). 
Power/area is called Power Density. Power density allows us to compare windmills of different sizes.  
Equation 9  
Power Density = Power/area = 1/2 × (air density) × (wind speed)³  
If we use the MKS (meter, kilogram, second) units system, the Power/area equation will give us our 
answer in watts/m2. The average density of air is almost 1 kg/m³. This allows us to simplify the power 
density equation to  
Equation 10  
Power Density = 1/2 kg/m³ × (wind speed)³  
Equation 10 requires that the wind speed be expressed in m/s, not mph. From equation 10, we see that 
the power density is a function of the wind speed raised to the third power (or wind speed cubed). As a 
specific example, increasing the wind from 13 mph (5.8 m/s) to 15 mph (6.7 m/s) will increase the wind 
power by 54 percent.  
Wind Farm Siting 
As shown in the Wind Energy Fundamental section above, it is imperative to know what the actual wind 
speed is at a site before developing a wind farm. Three years of wind data are usually considered the 
minimum data requirement. In addition to wind speed there are economic and environmental 
considerations in choosing a wind farm site.  
A major economic concern for utilities is the distance from the proposed wind farm to existing high-
voltage power lines. Construction of high-voltage lines is very expensive. As a general rule, wind farm 
sites cannot be more than 10 miles from an existing high-voltage power line.  
Another economic concern is the cost of constructing a wind farm. Is the site already accessible by road 
or will a road need to be built? What is the slope of the site. Steep sites will require extra construction 
expense.  
Other economic concerns include: What are the property taxes? How long will it take for the wind farm 
to make a profit?  
The environmental impact of a wind farm is also a concern. Some people are concerned because of the 
large land area required by wind farms. Large wind farms may require hundreds of acres. However, only 
five percent (5 percent) of the land on a wind farm is needed for towers, roads, and support structures. 
The remaining 95 percent of the land may be used for other purposes such as row crops or ranching.  
Another environmental concern is the "avian problem." In California, birds of prey (raptors) were killed 
by windmills. Current research indicates that this may be a local problem and seems to be associated 
with fog. A third environmental concern is noise from windmills. Early generation windmills were very 
noisy. The new windmills are much quieter; at a distance of 100 yards, they are barely audible. A final 
environmental concern is aesthetics — the looks of windmills. Some people consider them a blight on 
the landscape. Others find their turning in the wind graceful.  
Current Developments in Nebraska 
As of 1996, there are several wind energy monitoring sites in Nebraska. Most of the sites are being 
monitored by public power. A few sites are being monitored by private individuals or companies. The 
most promising sites for wind energy development are in the western quarter of the state and along the 
South Dakota border. The Sand Hills also have some promising sites. As shown above, it will be 
necessary to monitor these sites for several years in order to obtain the necessary data. It will be several 
years before we see large utility-scale wind farms being developed in Nebraska.  
File NF304 under: GENERAL AGRICULTURE 
D-2, C-5, Miscellaneous 
Issued December 1996 
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation 
with the U.S. Department of Agriculture. Elbert C. Dickey, Director of Cooperative Extension, 
University of Nebraska, Institute of Agriculture and Natural Resources.  
University of Nebraska Cooperative Extension educational programs abide with the non-discrimination 
policies of the University of Nebraska-Lincoln and the United States Department of Agriculture.


NF96-304 An Introduction to Wind Power for Nebraskans

DigitalCommons@University of Nebraska

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Historical Materials from University of Nebraska-Lincoln Extension Extension 1996 NF96-304 An Introduction to Wind Power for Nebraskans David E. Stooksbury University of Nebraska--Lincoln, dstooksbury2@unl.edu Kenneth G. Hubbard University of Nebraska--Lincoln, khubbard1@unl.edu Follow this and additional works at: https://digitalcommons.unl.edu/extensionhist  Part of the Agriculture Commons, and the Curriculum and Instruction Commons Stooksbury, David E. and Hubbard, Kenneth G., "NF96-304 An Introduction to Wind Power for Nebraskans" (1996). Historical Materials from University of Nebraska-Lincoln Extension. 576. https://digitalcommons.unl.edu/extensionhist/576 This Article is brought to you for free and open access by the Extension at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Historical Materials from University of Nebraska-Lincoln Extension by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Nebraska Cooperative Extension NF96-304An Introduction to Wind Power for Nebraskans David E. Stooksbury, Renewable Energy Specialist; Kenneth G. Hubbard, Extension Climate Resource Specialist  Windmills are a common sight in Nebraska. The historian Walter Prescott Webb argued that the windmill, barbed wire and the six-shooter made homesteading on the Great Plains possible.  Windmills ensured early homesteaders had a constant supply of water, and early in this century, they were used to produce electricity for homesteads. Many Nebraskans remember the 32-volt Wincharger. With the coming of inexpensive public power to rural Nebraska, most small electric windmills were abandoned.  During the 1970s, the sudden increase in energy costs coupled with spot shortages of oil caused a renewed interest in wind energy. Federal tax breaks encouraged the development of utility-scale windmills. However, these early developments were plagued with technological and economic problems. With the end of tax breaks in 1985, wind farm development came to a virtual halt. Many thought the wind energy industry was dead.  However, in the last few years, several technological advances have made wind power economically competitive with more traditional energy forms such as coal and oil. Nebraska has many promising locations for large utility-scale wind farm development. However, before wind farm development can take place, an assessment of the wind power potential must be made. Identifying the most promising sites will take several years. Thus major wind farm development in Nebraska will not occur until after the turn of the century.  Wind Energy Fundamentals In this section we will show that wind power depends on the wind speed raised to the third power (wind speed cubed). This means that an increase in wind speed from 13 mph (5.8 m/s) to 15 mph (6.7 m/s) will increase wind power production by 54 percent. The cubic relationship between wind power and wind speed makes it important that the true wind speed at a location be known before developing a wind farm.  In general, most people overestimate the wind speed at a location. Therefore, a multiyear monitoring program is the only reliable method to determine the true wind speed at a location. The mathematical form of the wind power-wind speed relationship is  Equation 1  Power = k × (wind speed) × (wind speed) × (wind speed)   or  Equation 2  Power = k × (wind speed)³  where k is a constant of proportionality.  In physics, energy is defined as the ability to do work. While this definition is technically correct, it is not very meaningful in this form. We can ask, how much energy is required to lift a bucket of water from the bottom of a well? But we can also ask, how much work is required to lift a bucket of water from the bottom of a well? These are really the same question.  It is useful to differentiate between kinetic energy and potential energy. Kinetic energy is the energy associated with motion. All moving objects have kinetic energy. A windmill transfers kinetic energy from the wind to an electrical generator (the wind makes the windmill blades turn on a shaft that connects to the generator). The turning generator creates a field that forces electrons to move through the power line. Moving electrons form an electric current. Thus, a windmill transforms the kinetic energy of air into electric current. Potential energy is stored energy. Batteries, food, and water behind a dam are examples of potential energy.  How much power is produced by a windmill? To answer this question, we must first calculate kinetic energy of the wind. Kinetic energy has the mathematical form  Equation 3  KE = 1/2 × (mass of the object) × (speed of object) × (speed of the object)  The kinetic energy equation is usually written  Equation 4  KE = 1/2mv²  where m is the mass of the object (mass of air in this case) and v is the speed of the object (the wind speed in this case).  In order to calculate the kinetic energy of the air moving a windmill blade, we first must calculate the mass of the air. It is easier to calculate mass per unit of time (mass/time) of air instead of the mass of air. The mass/time of air depends on the air density, the area swept by the windmill blades, and the speed of the wind. This brings us to the following equation  Equation 5  mass/time = (air density) × (area) × (wind speed) where area is the area swept by the wind mill blades.  We can now calculate the kinetic energy (KE). However, our mass term (Equation 5) is mass per time. This is not the problem that it appears. If we divide the kinetic energy by time (KE/time), we have the definition of power. Thus it will be easier to calculate power than to calculate kinetic energy. Since calculating the power is our ultimate goal, we will calculate power instead of KE.  Equation 6  Power = KE/time = 1/2 × (mass/time) × (wind speed) × (wind speed)  Now substitute [(air density) × (area) × (wind speed)] for mass/time, we get  Equation 7  Power = 1/2 × [(air density) × (area) × (wind speed)] × (wind speed) × (wind speed)  This can be simplified to  Equation 8  Power = 1/2 × (air density) × (area) × (wind speed)³  In wind energy, it is common to use Power per area swept by the windmill blade (Power/area). Power/area is called Power Density. Power density allows us to compare windmills of different sizes.  Equation 9  Power Density = Power/area = 1/2 × (air density) × (wind speed)³  If we use the MKS (meter, kilogram, second) units system, the Power/area equation will give us our answer in watts/m2. The average density of air is almost 1 kg/m³. This allows us to simplify the power density equation to  Equation 10  Power Density = 1/2 kg/m³ × (wind speed)³  Equation 10 requires that the wind speed be expressed in m/s, not mph. From equation 10, we see that the power density is a function of the wind speed raised to the third power (or wind speed cubed). As a specific example, increasing the wind from 13 mph (5.8 m/s) to 15 mph (6.7 m/s) will increase the wind power by 54 percent.  Wind Farm Siting As shown in the Wind Energy Fundamental section above, it is imperative to know what the actual wind speed is at a site before developing a wind farm. Three years of wind data are usually considered the minimum data requirement. In addition to wind speed there are economic and environmental considerations in choosing a wind farm site.  A major economic concern for utilities is the distance from the proposed wind farm to existing high-voltage power lines. Construction of high-voltage lines is very expensive. As a general rule, wind farm sites cannot be more than 10 miles from an existing high-voltage power line.  Another economic concern is the cost of constructing a wind farm. Is the site already accessible by road or will a road need to be built? What is the slope of the site. Steep sites will require extra construction expense.  Other economic concerns include: What are the property taxes? How long will it take for the wind farm to make a profit?  The environmental impact of a wind farm is also a concern. Some people are concerned because of the large land area required by wind farms. Large wind farms may require hundreds of acres. However, only five percent (5 percent) of the land on a wind farm is needed for towers, roads, and support structures. The remaining 95 percent of the land may be used for other purposes such as row crops or ranching.  Another environmental concern is the "avian problem." In California, birds of prey (raptors) were killed by windmills. Current research indicates that this may be a local problem and seems to be associated with fog. A third environmental concern is noise from windmills. Early generation windmills were very noisy. The new windmills are much quieter; at a distance of 100 yards, they are barely audible. A final environmental concern is aesthetics — the looks of windmills. Some people consider them a blight on the landscape. Others find their turning in the wind graceful.  Current Developments in Nebraska As of 1996, there are several wind energy monitoring sites in Nebraska. Most of the sites are being monitored by public power. A few sites are being monitored by private individuals or companies. The most promising sites for wind energy development are in the western quarter of the state and along the South Dakota border. The Sand Hills also have some promising sites. As shown above, it will be necessary to monitor these sites for several years in order to obtain the necessary data. It will be several years before we see large utility-scale wind farms being developed in Nebraska.  File NF304 under: GENERAL AGRICULTURE D-2, C-5, Miscellaneous Issued December 1996 Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Elbert C. Dickey, Director of Cooperative Extension, University of Nebraska, Institute of Agriculture and Natural Resources.  University of Nebraska Cooperative Extension educational programs abide with the non-discrimination policies of the University of Nebraska-Lincoln and the United States Department of Agriculture.

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NF96-304 An Introduction to Wind Power for Nebraskans

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