Wind EnErgyrEsidEntial

abstract p.iMEchanical Workings p.1

turbinEtoWEr

Financial bEnEFits p.2calculating payback pEriod - a rough EstiMatEpayback pEriod analysis

poWEr output VariablEs p.3Wind spEEdrotor diaMEtEr

EnVironMEntal EFFEcts p.4Why aVoid Fossil FuEls?hoW Much doEs Wind EnErgy hElp?do turbinEs kill birds?

conclusion p.5appEndix a p.6

a MorE dEtailEd look at turbinEs

appEndix b p.7EstiMatEd payback pEriod analysis ExaMplE

appEndix c p.8dEtailEd poWEr output calculation

rEFErEncEs p.9

prEparEd by:ashlEy cartEr, brandon hunold, stEphEn noMura, Justin rilling

To: Micheal SatterwhiteFrom: Ashley Carter, Brandon Hunold, Stephen Nomura, Justin RillingSubject:Residential Wind EnergyDate: 4/25/08

Mr. Satterwhite,

As global warming gains national attention, many homeowners are realizing the importance of reducing their environ-mental impact. Most homeowners use electricity produced from fossil fuels, a non-renewable resource that pollutes the environment. An alternative to traditional non-renewable energy sources is wind energy, which has little to no impact on the environment. Households residing in areas with high wind energy potential should consider installing a residential wind energy system.

Our report educates average homeowners interested in wind energy solutions. The report focuses on the feasibility and benefits of a residential wind turbine system. We discuss general operation, profitability, power output, and en-vironmental impact of residential wind turbines. Our report is an informational guide aimed at anyone interested in learning the basics of residential wind turbine systems.

Ashley Carter, Mechanical EngineeringBrandon Hunold, Mechanical EngineeringStephen Nomura, BLS/DesignJustin Rilling, Electrical Engineering

abstractToday, with fossil fuels diminishing and increased environmental awareness, people are turning to alternative energy sources. Wind energy is renewable, environmentally friendly, and is often profitable. In areas that have high wind energy potential, homeowners should consider a residential wind turbine system as an alternative or complement to traditional energy sources.

This report will outline the basic mechanics of a wind turbine and explain which designs will suit an individual the best. The financial details will be covered, such as initial cost, operating cost, energy cost savings, and the payback period. Supporting data proves that a wind turbine is a good investment under specific conditions. Wind energy is a great alternative because it does not pollute the environment like fossil fuels. Dependency on large power plants is also decreased. This report will explain how wind energy is a feasible residential energy source that bears both personal and global benefits.

p. i

MEchanical Workings

Turbine

Wind turbines come in two types: vertical-axis and horizontal-axis. Horizontal-axis turbines resemble airplane pro-pellers. They typically bear an odd number of blades, and sit atop a tower to increase wind exposure. These are more commonly used than vertical-axis turbines.[1.1] Vertical-axis turbines are characterized by C-shaped blades. They are normally built with two or three blades. An advantage to a vertical-axis machine is the ability to place the generator, gearbox, and other hardware on the ground, instead of atop the tower. However, vertical-axis turbines are rarely ef-ficient enough to be profitable. In the remainder of the document, “turbine” will refer to horizontal-axis turbines.

Wind is the first thing needed to begin producing electrical energy. As the wind blows across the blades, the shaft turns, and a gearbox changes the blades’ slow rotation into fast rotation the generator can use, similar to a car’s transmission. The generator changes the rotational energy into elec-tricity. A built in protection system optimizes performance and keeps the machinery operating safely. All of this sits atop a tower, where wind speeds are greater, and the effect of obstructions, such as trees, houses, and hills are decreased.[1.1]

TowerThe tower supports the turbine, so it must be sturdy. Tower height is a major factor in power output. Wind speeds increase with elevation, so higher towers yield more electricity. When ground-level objects interrupt wind flow, it is called ground friction. There are three main types of tow-ers: cone, lattice, and tilt-up.ConeMost large wind turbines use cone towers, which are constructed on-site by bolting together pre-manufactured steel pieces, each of which are about 20-30 meters in length. Their shape is slightly conical, with the widest end at the base, hence the term cone tower. This type is used when high strength is needed.[1.2]

LatticeLattice towers are manufactured using welded steel profiles. The main ad-vantage of lattice towers is cost; they require only half the material of cone towers with similar strength.[1.2]

Tilt-UpSome towers are outfitted with a tilt-up mechanism, which places the structure on a hinge. When maintenance is required, the tower can be easily lowered to the ground. The main disadvantage is that a significant amount of ground space around the base must be dedicated to securing the tower with wires.[1.3]

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[1.1]

InstallationInstallation is usually simple; changing existing wires and appliances is normally unnecessary. Most people hire profession-als to do the installation. Self-installation offers significant savings, but requires a high level of technical knowledge and ability. Most dealers offer both pre-assembled and factory direct products. Pre-assembled sys-tems have the advantage of more customer service.[1.2]

For more details, see Appendix A.

[1.1]

Financial bEnEFits

Calculating Payback Period - A Rough Estimate

Payback Period AnalysisThe graph on the right shows the total cost of a residential wind turbine over time in comparison to purchasing elec-tricity from a traditional energy source provider. The point on the graph at which the two energy sources intersect is when payback is complete; the large initial investment of the wind energy system is returned to the owner through annual energy cost savings. After the payback period, the system will save the owner money in comparison to the traditional energy source.

A major benefit of residential wind turbine systems is that they produce energy at an expense lower than purchas-ing from utility companies. In most cases, the money initially invested in a residential wind turbine system can be returned during its lifetime from reduced energy costs. The payback period is an estimate of the number of years until the initial investment is returned to the owner. The system is a good investment if the payback period is less than its operational lifetime.

Total Initial CostThis is a combination of expenses associated with the wind turbine prior to being fully operational. The total initial cost includes all system components along with any deliv-ery, installation, or consultation expenses. The graph to the right shows how higher rated wind turbines generally have a lower cost per capacity. For example, the initial cost of a 10 kW system is estimated at $2400/kW versus the initial cost of a 100 kW system that is estimated at $1000/kW accord-ing to the Iowa Energy Center.[2.1]

Annual Energy Cost SavingsThis is the amount of money saved from generating energy from wind instead of purchasing it from a utility company. The annual energy cost savings are dependent on the power rating of a wind turbine and average wind speeds at its loca-tion. Average wind speeds vary by location. In the United States, the Midwest has the highest potential for wind energy production and the Southeast has the least.Annual Operating CostThis is the annual expense for a fully operational wind turbine. Annual operating costs include service, mainte-nance, and insurance. The Iowa Energy Center estimates the annual operating expenses are 1-2 cents per annual kilowatt hour.[2.1] For example, if a wind system produces 10,000 kWh in one year, the expected operating expenses would be $100 to $200.

Payback Period =

Total Initial Cost(Annual Cost Savings) — (Annual Operating Cost)

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For an example calculation, see Appendix B.

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poWEr output VariablEsMany variables affect the amount of power produced by a wind turbine. Because of this, the advertised power rating rarely coincides with the actual power output. The main variables are wind speed and rotor diameter. Power output can be roughly estimated if these two variables are understood.

Wind SpeedWind speeds directly influence power output. As speeds increase, power output increases exponen-tially. Because the relationship is exponential, wind speed is an extremely important factor. Since some locations offer higher wind speeds than others, this variable is inherently linked to location. The average annual wind speeds for the US have been mapped in detail.

The ten outlined states on the map to the right have the highest average wind speeds and thus the highest wind energy potential. The large white areas on the map represent regions with low wind energy potential.

p. 3

Rotor DiameterRotor diameter, the “wingspan” of a turbine’s blades, also effects power output exponentially. As diameter increases, so does power.Annual power output can be esti-mate by the graph on the right. As the graph indicates, an increase in either wind speed or rotor diameter increases power yields. However, there are upper limits; extremely high winds can damage equipment and oversized rotors can reduce efficiency. Consumers should not have to worry about this because reputable manufacturers take these upper limits into account.

For a more detailed calculation, see Appendix C.

ResourcePotentialMarginalFairGoodExcellentOutstandingSuperb

Wind Speedat 50 m (mph)12.5 - 14.314.3 - 15.715.7 - 16.816.8 - 17.917.9 - 19.719.7 - 24.8 [1.1]

Wind spEEds in thE us

EnVironMEntal EFFEcts

How much does wind energy help?Wind energy accounts for a measly 0.3% of energy production in the USA.[4.3] However, marketing research shows there are over 3.8 million homes with the potential to install a small wind system. If half of these homes installed a 10 kW wind turbine, an additional 20 million MW of energy could be produced each year.[4.4] Every kilowatt produced using fossil fuels releases on average 1.38 lbs of CO2., each year that just half of all capable homes produced wind energy, over 12 million metric tons less CO2 would be released into the atmosphere. Each home would reduce CO2 emissions by over 13,500 lbs per year. Although this is still a small percentage compared to the mammoth amount fos-sil fuels released, this step will do more than just reduce present day emissions. Buying a wind system now stimulates the alternative energy industry, and suppresses the fossil fuel industry, which is the first step towards independence from fossil fuels.

Installing a wind energy system has many environmental benefits; it is the first step towards preserving earth’s life-supporting environment into the future. Conventional electrical energy sources consume fossil fuels. This is a problem because consuming fossil fuels at the current rate will ultimately place many species at risk of extinction, including humans. Let’s see how wind energy can lead to a brighter future.

Why avoid fossil fuels?Fossil fuels are our main enemy; they are bad for many reasons. Obtain-ing the raw fossil fuels destroys natural habitats by excavating, digging, and drilling. To process the raw material, even more land is destroyed to erect power plants. Even worse, extracting the energy in fossil fuels releases harmful greenhouse gases (GHG) and contributes to smog pol-lution and acid rain.[4.1] Even in the most state of the art power plants, fossil fuels produce electricity with a maximum efficiency of about 50%.[4.2] Wind energy, on the other hand, does not destroy significant natural habitats; a turbine can be erected almost anywhere with sufficient wind flow. Wind energy does not release GHG while producing electricity, and does not contribute to acid rain or smog pollution. Lastly, wind energy can be captured locally, and does not require large power plants.

What are fossil fuels?Fossil fuels are composed of ancient or-ganic matter exposed to millions of years of heat and pressure, like dead dinosaurs. Since production time is several hundred million years, we consider them non-renewable. At the world’s current rate, we will run out of fossil fuels around 2300. The most commonly used fossil fuels are oil and coal, accounting for ~69% of elec-tricity production and ~85% of all energy production in the USA.[4.2]

Do turbines kill birds?Technically speaking, yes. However, the number of annual bird fatalities by wind turbines is dwarfed by the number that die from other human related fac-tors. The following are estimated bird deaths per year by various causes in the US.

Power Lines: 130 to 174 million.[4.5]

Cars: 60 - 80 million.[4.5]

Buildings: 100 million - 1 billion.[4.6]

Communications Towers: 40 - 50 million. [4.5]

Wind Turbines: 5,500.[3.4]

The wind turbine death figure value was calculated using an average of 2.19 bird deaths per turbine. The graph assumes the maximum in each range.

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conclusionIn summary, residential wind turbines come in several variations. Of the two turbine styles, horizontal-axis generally provides the best results. There are two main tower styles, cone and lattice; either may use a tilt-up system to aid in maintenance. The power output of these systems relies mainly on wind speeds and rotor diameter. A payback period analysis will help determine profitability. Wind energy is a feasible residential energy source that bears both personal and global benefits.

p. 5

appEndix a p. 6A more detailed look at turbines

appEndix b p. 7Consider a residential wind turbine rated at 5 kW that has an initial cost of $15,000. The wind turbine will be located in an area that has an average windspeed of 14 mph which corresponds to an annual output of 10000 kWh for that particular wind turbine. A local utility company provides electricity using a traditional energy source at $.085/kWh. The annual operating expense of the wind turbine is estimated at $100/year.

Total Initial Cost: $15,000

Annual Energy Cost Savings: 1,000 kWh ( $0.085 / 1 kWh ) = $850

Annual Operating Cost: $100

Payback Period = $15,000 / ( $850 - $100 ) = 20 Years

Payback Period =

Total Initial Cost(Annual Cost Savings) — (Annual Operating Cost)

Estimated Payback Period Analysis Example

appEndix c p. 8

P = rated power (watts)α = efficiency of the turbine designρ = mass density of air (kilograms/cubic meter)r = rotor blade radius (meters)v = air speed (meters per second)

Detailed Power Output CalculationPower Output P is given by:

P = ½αρπr2v3

Temperature at elevation h is given by:

T = T0 + L · hAir Density is given by:

ρ = ( p · M ) / ( R · T )Pressure at altitude h is given by:

p = p0 · [1 + (L · h )/(T0)]^(g ·M / -R ·L)

The density of the air varies with elevation, temperature, and whether the air is ideally dry or contains moisture. To locate the density of air for a particular location you will need to know the altitude above sea level. There are a couple of additional variables needed:

Atmospheric pressure @ sea level: po = 101325 PaStandard temperature @ sea level: T0 = 288.15 KEarth-surface gravitational acceleration: g = 9.80665 m/s2

Temperature lapse rate: L = -6.5°C/kmUniversal gas constant: R = 8.31447 J/(mol•K)Molar mass of dry air: M = 28.9644 g/mol

rEFErEncEs[1.1] Layton, Julia. “How Wind Power Works.” 2008. 6 April 2008.

<http://science.howstuffworks.com/wind-power1.htm>.

[1.2] “Wind Turbine Towers.” Danish Wind Industry Association. 19 Septmember 2005. 6 April 2008.

<http://www.windpower.org/en/tour/wtrb/tower.htm>.

[1.3] “Tilt up Wind Turbine Towers.” Renewable Energy UK. 22 April 2008. 23 April 2008. <www.reuk.co.uk>.

[2.1] “Wind Energy Economics.” Iowa Energy Center. 2008. 7 April 2008.

<http://www.energy.iastate.edu/renewable/wind/wem/economic_issues.htm>.

[3.1] Gipe, Paul. Wind Power for Home and Business. Post Mills, VT: Chelsea Green Company, 1993. 59-96.

[3.2] Clarke, S. “Electricity Generation Using Small Wind Turbines At Your Home or Farm.” Ontario Ministry of

Agriculture, Food, and Rural Affairs. Sept. 2003. 22 Apr. 2008

<http://www.omafra.gov.on.ca/english/engineer/facts/03-047.htm>.

[3.3] Wiser, Ryan, and Mark Bolinger. “Annual Report on U. S. Wind Power, Installation, Cost, and Performance.”

Department of Energy. May 2007. United States Government. 14 Apr. 2008

<http://www1.eere.energy.gov/windandhydro/pdfs/41435.pdf>.

[3.4] “Wind.” American Wind Energy Association. 2007. 11 Apr. 2008 <http://www.awea.org>.

[3.5] “Database of State Incentives for Renewables and Efficiency.” 24 Apr. 2008. NC State University. 14 Apr. 2008

<http://dsireusa.org/>.

[4.1] Environment Canada. 9 May 2007. 6 April 2008. <http://www.ec.gc.ca>.

[4.2] European Environmental Agency. 2008. 7 April 2008. <themes.eea.europa.eu>.

[4.3] Energy Information Administration, Annual Energy Review 2006, Sec 10.2

[4.4] American Wind Energy Association: US Small Wind Turbine Industry Roadmap

[4.5] “Avian Collisions with Wind Turbines: A Summary of Existing Studies and Comparisons to Other Sources of

Avian Collision Mortality in the United States.” National Wind Coordinating Committee. West, Inc.

August 2001.

[4.6] Eaton, Joe. “Tower Kill.” Earth Island Journal. Winter, 2003.

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