1. How Do Wind Turbines Operate? Environmental Benefits
Using Wind Energy to Generate Electricity
Critical Thinking
How Do Wind Turbines Operate?
Pros and Cons
Environmental Benefits
Develop Skills for ACT Science
Next Generation Science - Common Core Aligned

2. Generating Electricity with Windmills
Learning Objectives:
Learn the benefits and limitations of generating electricity with wind power
Learn how a wind turbine works
Learn to read charts and evaluate chart data on wind turbine performance.
Learn to calculate the number of turbines and land area needed to provide a certain amount of electricity to a city
Calculate the number of windmills and the land area needed to replace 1000 Mw of fossil generation

3. Generating Electricity with Windmills
The City Council of Greenville has decided to debate plans for a project to change the electricity supplier from their current supplier, Enormous Electricity Utility (EEU). They want to study the possibility of using wind turbines to generate the city’s electricity. You are the city engineer, and you will be responsible for doing the analysis and planning for the project. You will need the following information to do your analysis and report for the City Council and the Mayor

4. Why Use Wind?
People have used wind energy to do work for over a thousand years. The first applications were for pumping water and grinding grain. That remained so until recently, when we began to apply this technology to generate electricity.

5. Generating Electricity with Wind Has Many Benefits
Current technology
Most electrical generation is done by using something to boil water and create steam to drive a turbine which produces electricity.
The cost of the fuel to boil the water is a large part of the cost of electricity.
Most of our electricity is generated from burning coal or gas, and produces greenhouse gases and other pollutants.
Benefits of wind power
Wind is free
Wind can directly drive a turbine and produce electricity without burning anything, eliminating fuel costs, and providing environmental benefits.
Wind power does not generate greenhouse gasses during operation
Wind is renewable. We will not run out of wind
Wind is a domestic source of energy, created here and not imported

6. Wind Power Has Limitations and Environmental Impacts
Drawbacks for wind power
We don’t have enough wind all the time, so wind energy is not considered to be reliable.
Wind farms require much clear area to operate. This may require deforestation to set up a wind farm, and impacts the environment and wildlife habitat
Wind turbines are a potential threat to wildlife such as birds and bats.
Noise is a complaint with many wind farms that are close to communities.
Some people find wind farms to be unsightly, destroying scenic views.
Nothing is Perfect

7. How a Wind Turbine Works
A wind turbine consists of:
A tower
Rotor hub and rotor blades, and
A Nacelle, which contains all the mechanical equipment and the generator.
The wind forces the blades to rotate, which turns the low speed shaft. The gearbox connects to the high speed shaft which turns the generator to produce the electricity.
Cables run from the generator down through the interior of the tower to connect the generator output to a transformer on the ground. The transformer (D) then sends the power out to the transmission lines to ultimately reach the final customers.
Wind A C B D

8. How Much Power Can a Wind Turbine Generate?
The amount of power depends on two things. The size of the turbine used to generate the power, and the wind, both the wind speed and the number of hours the wind is actually blowing. The chart below shows how the wind speed affects the ability of a 2,500 KW wind turbine to generate electricity.
Note that the power curve shows that we need steady wind over 26 MPH to reach full power generation. Taller towers provide access to stronger and steadier winds, and larger blades will capture more wind energy.

9. How Much Power - Continued
Windmills can be seen from a great distance in flat country , and even farther if on a hilltop. Some people find these wind farms unsightly.
Towers for utility size turbines, like the ones used for major power supply, can be over 300 feet tall, with the tip of the blades reaching a height of 500 feet or more above the ground
The reason why the towers need to be so tall, and why they are often sited on hilltops is because the wind is stronger and more reliable the higher off the ground you get.
The more open and clear the terrain is, the better the wind turbines will operate.
Another option, where possible, would be to site the wind turbines off shore in the ocean

10. How much power can we expect to get from a wind turbine?
Wind turbines can be very reliable in operation but:
The wind itself is not reliable and wind turbines can’t make power with no wind.
Weak winds also lower the power output.
If winds are too strong, turbines have to be shut down to prevent damage to the turbines.
When wind power is unavailable, backup power must be obtained from other non-wind sources
Coal
Nuclear
Hydroelectric

11. Load Factor – A Measure of Efficiency
One measure of power plant efficiency is the load factor. The load factor measures the actual power produced compared to the maximum power the plant could produce if it ran at 100% power all the time. Actual experience with wind farms has shown that many wind farms have produced power ranging from 25% to 40% of full capacity.
Here’s how the calculation is done:
First, let’s figure out the maximum amount of electricity a single 2,000 kw wind turbine can generate if it operated at 100% power for a year.
2,000 Kw × 365 days × 24 hours/day = 17,520,000 kwhr in one year.
This is what the windmill, or any power plant for that matter, would produce if it operated at 100% power, 24 hours per day, every day of the year. But, that is never the case. All power plants whether wind, coal, nuclear or anything else, will have time when they are not generating electricity. We will use a load factor of 30% for wind turbines for this example, meaning that it produced 30% of its maximum possible output.
Now multiplying 17,520,000kwh by a load factor of 30% gives the amount of generation we can expect to draw in one year from a 2,000 kw windmill:
17,520,000kwhr x .30 = 5,256,000 Kwhr
So 5,256,000 Kwhrs is a reasonable amount of generation to expect from a windmill rated at 2,000kw capacity.

12. How Many Homes Can One Turbine Power?
This answer depends on two things:
The amount of generation a wind turbine produces in a year
The amount of electricity a home uses in a year
The Energy Information Agency (EIA), a government agency, has calculated that the average household in the US uses approximately 10,932 kilowatt-hours (kWh) of electricity per year. Using this number with the available generation we calculated on the last page, the number of homes one 2,000 kw turbine could reasonably power is:
5,256,000 kWh/ 10,932kWh per home = 481 homes.

13. How Much Land Does a Wind Farm Need?
Land requirements will depend on:
The amount of generation to be built
The size of the turbines
The number of turbines
The load factor of the turbines:
Additional considerations for a wind farm are:
The type of terrain available - whether it is hilly or flat
Separation distance required from residential housing
Separation distance between turbines
Deforestation - if trees need to be removed to install the turbines
One general rule of thumb states that, for estimating purposes, considering all the factors, about 50 acres of land will be needed for each 1,000 kilowatts (Kw) of generation. The actual range runs from 35 – 85 acres/1000 kw.

14. Wind Farm Land Requirements Sample Problem
Based on the criteria on the last slide, How much land area will be needed to provide the power for a city of 50,000 households?
Start with the following information:
Household Usage - Each household uses the average of 10,932 kwhr/year
Turbine Size - The wind turbines will be designed to produce a maximum generation of 2,000 kw
Single Turbine Output -Each turbine will be able to provide 5,256,000 kwhr per year (Based on a 30% load factor)
Land Needs - 50 acres of land per 1000 kw of installed generation
The calculation is shown on the following slide

15. Wind Farm Land Requirements
Solution: 4 Steps
Step 1 – Calculate the total yearly electricity usage for the 50,000 households
Each household will use 10,932 kwhr per year.
All 50,000 households will use 50,000 x 10,932 kwhr = 546,600,000 kwhr yearly
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Step 2 – Find the number of turbines needed by dividing the total usage from Step 1 by the Single Turbine Output.
Total usage = 546,600,000 kwhr
Single Turbine Output = 5,256,000 kwhr
546,600,000/5,256,000 = 104 Wind turbines. (Rounded to nearest whole turbine)
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Step 3 – Multiply the number of turbines from Step 2 by the turbine size (In this case, 2000 kw). This gives the total installed generation.
104 Turbines X 2000kw/turbine = 208,000 kw total installed generation.
Step 4 – Multiply the answer in step 3 by the land requirement of 50 acres/1000 kw to get the total number of acres needed
208,000 X 50/1000 = 10,400 acres

16. Summary
Windmills can provide a non-polluting way to generate electricity
Wind farms are being built which can provide large amounts of electricity to serve customers
Location of wind farms in areas where wind is strong and steady is important to maximize electrical output
Wind turbines are reliable, but don’t always provide maximum output because of the unreliability of the wind itself
Backup power sources must be available for those times when the wind is weak, or there is no wind
Wind turbines have environmental impacts which must be considered when siting and building wind generation

17. Questions for Discussion and/or Further Research
Is wind energy a good choice among energy alternatives?
Would wind energy be a good choice in underdeveloped countries which do not have large transmission lines or other sources of energy?
Is wind energy land use manageable? Some people only want to count the area of the foundation of a wind turbine tower as the land commitment for a turbine. Does doing that reduce the actual impact of installing a wind farm?
Is wind energy’s contribution to the environment sufficient to accept the other environmental impacts that come along with wind power?
How serious is the issue of bird and bat deaths around wind turbines? How could they be addressed?