Small Wind Electric Systems

Cover photo: Wisconsin residents take advantage of their wind resource to generate power for homes 

and businesses. Top row, left to right: PIX12968 — 3.5-kW Jacobs wind turbine; PIX12967 — 14-foot

Jacobs (remanufactured) on 100-foot freestanding tower; PIX12970 — African Wind Power 3.5-meter

wind turbine. Bottom row, left to right: PIX12966 — Bergey Excel wind turbine on a 122' guyed tower;

PIX12969 — Southwest Windpower Whisper H40 wind turbine; PIX13054 — Proven WT6000 wind 

turbine (first U.S. installation) on a 12-ft. tower.

Miles per Hour (MPH)

7 - 10

10 - 12

12 - 13

13 - 14

14 - 15

15 - 16

16 - 17

17 - 18

Average Annual 

Wind Speeds

47.2%

5.8%

41.1%

5.8%

0.1%

60 meters

Average annual wind speeds depicted in these maps were calculated in February 2003 using

WindMap software. The State of Wisconsin Division of Energy developed this map.

Many factors help determine the wind resource in Wisconsin. Major factors include elevation, land

cover, wind speed, and wind direction. Wind data can come from a number of sources. Currently, 

the main source for wind data is tall tower data in Wisconsin collected through the Wisconsin Wind

Resource Assessment Program. Other sources include tall tower data from Minnesota and data from

navigation structures on Lake Superior and Lake Michigan.

Use this map as a guide or reference. Site assessment is always necessary for identifying sites with

good wind resources.

For more information regarding wind power, please visit www.focusonenergy.com or

www.doa.state.wi.us. Copies of this map can be obtained through the Focus on Energy or

Department of Administration Web site. 
our nation's energy needs. Althoughwind turbines large enough to provide a significant portion of the electricity needed by the average U.S.home generally require one acre ofproperty or more, approximately21 million

U.S. homes are built on

one-acre and larger sites, and 24%of the U.S. population lives in ruralareas.A small wind electric system

will

work for you if:• T

here is enough

wind w

here you

live

• Tall towers are allowed in your

neighborhood or rural area

• You

have enough space

• You can determine how

m

uch

electricity you

need or want to

produce

• It works for you economically.

T

he purpose of this guide is to provide you

with the basic information

about small wind electric systems tohelp you decide if wind energy willwork for you.Why Should I Cho

ose Wind?

Wind energy systems are one of themost cost-effective home-basedrenewable energy systems.

ContentsIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1First, How Can I Make My Home More Energy Efficient? . . . .2Is Wind Energy Practical for Me? . . . . . . . . . . . . . . . . . . . . . .3What Size Wind Turbine Do I Need? . . . . . . . . . . . . . . . . . . . .4What are the Basic Parts of a Small Wind Electric System? . .5What Do Wind Systems Cost? . . . . . . . . . . . . . . . . . . . . . . . .7Where Can I Find Installation and Maintenance Support? . . . .8How Much Energy Will My System Generate? . . . . . . . . . . . .9Is There Enough Wind on My Site? . . . . . . . . . . . . . . . . . . . .11How Do I Choose the Best Site for My Wind Turbine? . . . . .14Can I Connect My System to the Utility Grid? . . . . . . . . . . . .15Can I Go "Off-Grid"? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21For More Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Homeowners, ranchers, and small businesses can use windgenerated electricity to reduce their utility bills. This gridconnected system installed for a home in Norman, Oklahoma,reduces the homeowner's utility bill by $100 per month.

Bergey Windpower/PIX01476
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proper insulation andweatherization products. 

• Save money and increase comfort

by properly maintaining andupgrading your heating,ventilation, and air-conditioningsystems. 

• Install double-paned, gas-filled

windows with low-emissivity (low-e) coatings to reduce heat loss in cold climates and spectrallyselective coatings to reduce heatgain in warm climates. 

• Replace your lights in high-use

areas with fluorescents. Replacing25% of your lights can save about50% of your lighting energy bill. 

• When shopping for appliances,

look for the ENERGY STAR® label.

ENERGY STAR® appliances have

been identified by the U.S.Environmental Protection Agencyand U.S. Department of Energy as being the most energy-efficientproducts in their classes.

• For more information on how to

make your home energy efficient,see Energy Savers, in the For MoreInformation section.

g

p

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yp

house is for heating and cooling.
p

• your property is in a remote

location that does not have easyaccess to utility lines

• you are comfortable with long-term

investments.

Zoning IssuesBefore you invest in a wind energysystem, you should research potentialobstacles. Some jurisdictions, forexample, restrict the height of the

Most zoning and aesthetic concernscan be addressed by supplying objective data. For example, the ambientnoise level of most modern residentialwind turbines is around 52 to 55 decibels. This means that while the soundof the wind turbine can be picked outof surrounding noise if a consciouseffort is made to hear it, a residentialsized wind turbine is no noisier thanyour average refrigerator.

In Clover Valley,Minnesota, this 3-kW WhisperH175 turbine on a 50-foot tower isconnected to theutility grid to offsetthe farm's utilitysupplied electricity.

World Power Technology/PIX07168
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More Energy Efficient?). Wind turbinemanufacturers can help you size yoursystem based on your electricity needs and the specifics of local windpatterns.A typical home uses approximately9400 kilowatt-hours (kWh) of electricity per year (about 780 kWh permonth). Depending on the averagewind speed in the area, a wind turbine rated in the range of 5 to 15 kilowatts (kW) would be required tomake a significant contribution to thisdemand. A 1.5- kW wind turbine willmeet the needs of a home requiring300 kWh per month in a location witha 14-mile-per-hour (6.26-meters-persecond) annual average wind speed.The manufacturer can provide youwith the expected annual energy output of the turbine as a function ofannual average wind speed. The manufacturer will also provide information on the maximum wind speedat which the turbine is designed tooperate safely. Most turbines haveautomatic overspeed-governing systems to keep the rotor from spinningout of control in very high winds. Thisinformation, along with your localwind speed and your energy budget,will help you decide which size turbine will best meet your electricityneeds. 

speed over a specified period of time.

Blades—The aerodynamic surface

that catches the wind.

Brake—Various systems used to stop

the rotor from turning.

Converter—See Inverter.Cut-in wind speed—The wind speed

at which a wind turbine begins togenerate electricity.

Cut-out wind speed—The wind speed

at which a wind turbine ceases to generate electricity.

Density—Mass per unit of volume.Downwind—On the opposite side

from the direction from which thewind is blowing.

Furling—A passive protection for the

turbine where typically the rotor foldseither up or around the tail vane.

Grid—The utility distribution system. 

The network that connects electricitygenerators to electricity users.

HAWT—Horizontal axis wind turbine.Inverter—A device that converts direct

current (DC) to alternating current(AC).

kW—Kilowatt, a measure of power

for electrical current (1000 watts).

Power curve—A chart showing a

wind turbine's power output across a range of wind speeds.

PUC—Public Utility Commission, a

state agency which regulates utilities.In some areas known as Public Service

Commission (PSC).

PURPA—Public Utility Regulatory

Policies Act (1978), 16 U.S.C. § 2601.18CFR §292 that refers to small generator utility connection rules.

Rated output capacity—The output

power of a wind machine operating at the rated wind speed.

Rated wind speed—The lowest wind

speed at which the rated outputpower of a wind turbine is produced.

Rotor—The rotating part of a wind

turbine, including either the bladesand blade assembly or the rotatingportion of a generator.

Rotor diameter—The diameter of the

circle swept by the rotor.

Rotor speed—The revolutions per

minute of the wind turbine rotor.

Start-up wind speed—The wind speed

at which a wind turbine rotor willbegin to spin. See also cut-in windspeed.

Elliott Bayly/PIX09681
Most turbines manufactured todayare horizontal axis upwind machinesthat have two or three blades, whichare usually made of a composite material such as fiberglass. The amount of power a turbine willproduce is determined primarily bythe diameter of its rotor. The diameterof the rotor defines its "swept area," orthe quantity of wind intercepted bythe turbine. The turbine's frame is thestructure onto which the rotor, generator, and tail are attached. The tailkeeps the turbine facing into thewind.TowerBecause wind speeds increase withheight, the turbine is mounted on a tower. In general, the higher thetower, the more power the wind system can produce. The tower alsoraises the turbine above the air turbulence that can exist close to the ground because of obstructionssuch as hills, buildings, and trees. Ageneral rule of thumb is to install awind turbine on a tower with thebottom of the rotor blades at least30 feet (9 meters) above any obstaclethat is within 300 feet (90 meters) ofthe tower. Relatively small investments in increased tower height canyield very high rates of return in

power production. For instance, toraise a 10-kW generator from a 60-foottower height to a 100-foot towerinvolves a 10% increase in overall system cost, but it can produce 25%more power. There are two basic types of towers:self-supporting (free standing) andguyed. Most home wind power systems use a guyed tower. Guyed towers, which are the least expensive, canconsist of lattice sections, pipe, or tubing depending on the design, andsupporting guy wires. They are easierto install than self-supporting towers.However, because the guy radiusmust be one-half to three-quarters of the tower height, guyed towersrequire enough space to accommodatethem. While tilt-down towers aremore expensive they offer the consumer an easy way to perform 

02979311m

Tilt-Down Tower

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the batteries from overcharging.Deep-cycle batteries, such as thoseused for golf carts, can discharge andrecharge 80% of their capacity hundreds of times, which makes them agood option for remote renewableenergy systems. Automotive batteriesare shallow-cycle batteries and shouldnot be used in renewable energy systems because of their short life indeep-cycling operations. 

Can I Go "Off-Grid"?Hybrid SystemsHybrid wind energy systems can provide reliable off-grid power forhomes, farms or even entire communities (a co-housing project, for example) that are far from the nearestutility lines. According to manyrenewable energy experts, a "hybrid"system that combines wind and photovoltaic (PV) technologies offersseveral advantages over either singlesystem. In much of the United States,wind speeds are low in the summerwhen the sun shines brightest andlongest. The wind is strong in thewinter when there is less sunlightavailable. Because the peak operatingtimes for wind and PV occur at different times of the day and year, hybridsystems are more likely to producepower when you need it. (For moreinformation on solar electric or PV systems, contact the EnergyEfficiency and Renewable EnergyClearinghouse—see For MoreInformation.)

For the times when neither the windnor the PV modules are producing,most hybrid systems provide powerthrough batteries and/or an enginegenerator powered by conventionalfuels such as diesel. If the batteriesrun low, the engine-generator can provide power and recharge the batteries. Adding an engine-generatormakes the system more complex, butmodern electronic controllers canoperate these systems automatically.An engine-generator can also reducethe size of the other componentsneeded for the system. Keep in mindthat the storage capacity must be large enough to supply electricalneeds during non-charging periods.Battery banks are typically sized tosupply the electric load for one tothree days. An off-grid hybrid system may bepractical for you if:• You live in an area with average

annual wind speed of at least9 mph (4.0 m/s).

• A grid connection is not available

or can only be made through an

Trudy Forsyth, NREL/PIX09122 and PIX09123
For safety, batteries should be isolated from living areas and electronics because they contain corrosiveand explosive substances. Lead-acidbatteries also require protection fromtemperature extremes. Grid-Connected SystemsIn grid-connected systems, the onlyadditional equipment required is apower conditioning unit (inverter)that makes the turbine output electrically compatible with the utility grid.Usually, batteries are not needed. What Do Wind SystemsCost?A small turbine can cost anywherefrom $3,000 to $35,000 installed,depending on size, application, andservice agreements with the manufacturer. (The American Wind EnergyAssociation [AWEA] says a typicalhome wind system costs approximately $32,000 (10 kW); a comparablephotovoltaic [PV] solar system wouldcost over $80,000.)A general rule of thumb for estimatingthe cost of a residential turbine is$1,000 to $3,000 per kilowatt. Windenergy becomes more cost effective as the size of the turbine’s rotorincreases. Although small turbinescost less in initial outlay, they are 

proportionally more expensive. Thecost of an installed residential windenergy system that comes with an 80-foot tower, batteries, and inverter,typically ranges from $13,000 to$40,000 for a 3 to 10 kW wind turbine.Although wind energy systemsinvolve a significant initial investment, they can be competitive withconventional energy sources whenyou account for a lifetime of reducedor avoided utility costs. The length ofthe payback period—the time beforethe savings resulting from your system equal the cost of the systemitself—depends on the system youchoose, the wind resource on yoursite, electricity costs in your area, andhow you use your wind system. Forexample, if you live in California andhave received the 50% buydown ofyour small wind system, have netmetering, and an average annualwind speed of 15 miles per hour(mph) (6.7 meters per second [m/s]),your simple payback would beapproximately 6 years.

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able to help you install your machine.Many people elect to install themachines themselves. Before attempting to install your wind turbine, askyourself the following questions:• Can I pour a proper cement

foundation?

• Do I have access to a lift or a way of

erecting the tower safely?

• Do I know the difference between

AC and DC wiring?

• Do I know enough about electricity

to safely wire my turbine?

• Do I know how to safely handle

and install batteries?

If you answered no to any of theabove questions, you should probablychoose to have your system installedby a system integrator or installer.Contact the manufacturer for help or call your state energy office andlocal utility for a list of local systeminstallers. You can also check the yellow pages for wind energy systemservice providers. A credible installerwill provide many services such aspermitting. Find out if the installer isa licensed electrician. Ask for references and check them out. You mayalso want to check with the BetterBusiness Bureau.

the line is "dead," might not take normal precautions and might be hurt oreven killed by the power from yourturbine. Another concern among utilities is that the power from your facility synchronize properly with theutility grid, and that it match the utility’s own power in terms of voltage,frequency, and power quality.A few years ago, some state governments started developing new standardized interconnection requirements for small renewable energygenerating facilities (including windturbines). In most cases the newrequirements have been based on consensus-based standards and testingprocedures developed by independent third-party authorities, such as theInstitute of Electrical and ElectronicEngineers and UnderwritersLaboratories.Interconnection RequirementsMost utilities and other electricityproviders require you to enter into aformal agreement with them beforeyou interconnect your wind turbinewith the utility grid. In states thathave retail competition for electricityservice (e.g., your utility operates the local wires, but you have a choice of electricity provider) you may have to sign a separate

y 

y 

own and have no control over. Othersconsider the insurance requirementsexcessive and unduly burdensome,making wind energy uneconomic. Inthe 21 years since utilities have beenrequired to allow small wind systemsto interconnect with the grid there has never been a liability claim, letalone a monetary award, relating toelectrical safety.

Warren Gretz, NREL/PIX09
If you do not have the expertise tomaintain the machine, your installermay provide a service and maintenance program.How Much Energy Will MySystem Generate?Most U.S. manufacturers rate theirturbines by the amount of power theycan safely produce at a particularwind speed, usually chosen between24 mph (10.5 m/s) and 36 mph(16 m/s). The following formula illustrates factors that are important to the performance of a wind turbine.Notice that the wind speed, V, has an 

ranging from 0.25 to 0.45, dimension less (theoretical maximum = 0.59)

ρ = Air density, lb/ft3

A = Rotor swept area, ft2 or 

π

D2/4 (D is the rotor 

diameter in ft, 

π = 3.1416)

V =

Wind speed, mph

k = 0.000133 A constant to yield 

power in kilowatts. (Multiplyingthe above kilowatt answer by 1.340 converts it to horsepower. [i.e., 1 kW = 1.340 horsepower]).

876543210

1 2 3 4 5 6 7

Rotor Diameter, m

Rotor Diameter, m

Relative Size of Small Wind Turbines

40302010

0

Swept area, m2 7 m6 m

5 m

4 m

3 m

2 m

1 m

02979303m

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Where:AEO = Annual energy output, 

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D = Rotor diameter, feetV = Annual average wind speed, 

mph

The Wind Energy Payback PeriodWorkbook found at http://www.nrel.gov/wind/ under consumer information is a spreadsheet tool that can helpyou analyze the economics of a smallwind electric system and decidewhether wind energy will work foryou. The spreadsheet can be openedusing Microsoft Excel 95 software. It asks you to provide informationabout how you're going to finance thesystem, the characteristics of your site, and the properties of the systemyou're considering. It then providesyou with a simple payback estimationin years. If it takes too long to regainyour capital investment—the numberof years comes too close or is greaterthan the life of the system—windenergy will not be practical for you.

above anything within 300 feet. Youalso need enough room to raise andlower the tower for maintenance, andif your tower is guyed, you mustallow room for the guy wires. Whether the system is stand-alone or grid-connected, you will also needto take the length of the wire runbetween the turbine and the load(house, batteries, water pumps, etc.)into consideration. A substantialamount of electricity can be lost as aresult of the wire resistance—thelonger the wire run, the more electricity is lost. Using more or larger wirewill also increase your installationcost. Your wire run losses are greaterwhen you have direct current (DC)instead of alternating current (AC).So, if you have a long wire run, it isadvisable to invert DC to AC.Can I Connect My Systemto the Utility Grid?Small wind energy systems can beconnected to the electricity distribution system and are called gridconnected systems. A grid-connectedwind turbine can reduce your consumption of utility-supplied electricity for lighting, appliances, and electric heat. If the turbine cannotdeliver the amount of energy you

ence. When the wind system producesmore electricity than the householdrequires, the excess is sent or sold tothe utility. Grid-connected systems can be practical if the following conditions exist:• You live in an area with average

annual wind speed of at least10 mph (4.5 m/s).

• Utility-supplied electricity is

expensive in your area (about 10 to15 cents per kilowatt-hour). 

• The utility's requirements for

connecting your system to its gridare not prohibitively expensive.

• There are good incentives for the

sale of excess electricity or for thepurchase of wind turbines.

Federal regulations (specifically, thePublic Utility Regulatory Policies Actof 1978, or PURPA) require utilities to connect with and purchase powerfrom small wind energy systems.However, you should contact yourutility before connecting to their distribution lines to address any powerquality and safety concerns. Your utility can provide you with a list ofrequirements for connecting your system to the grid. The American WindEnergy Association is another goodsource for information on utility 
p

p

like the one on pages 12 and 13 can

be used to estimate the wind resource

in your region. The highest averagewind speeds in the United States aregenerally found along seacoasts, onridgelines, and on the Great Plains;however, many areas have windresources strong enough to power asmall wind turbine economically. Thewind resource estimates on this mapgenerally apply to terrain features thatare well exposed to the wind, such asplains, hilltops, and ridge crests. Localterrain features may cause the windresource at a specific site to differ considerably from these estimates. Moredetailed wind resource information,including the 

Wind Energy Resource

Atlas of United States, published by theU.S. Department of Energy (DOE),can be found at the National WindTechnology Center web site athttp://www.nrel.gov/wind/ and theDOE Windpowering America web site at http://www.eren.doe.gov/windpoweringamerica/.Another way to indirectly quantifythe wind resource is to obtain averagewind speed information from a nearby airport. However, cautionshould be used because local terraininfluences and other factors maycause the wind speed recorded at an

Energy Resource Atlas of the UnitedStates (see For More Information).Another useful indirect measurementof the wind resource is the observation of an area’s vegetation. Trees,especially conifers or evergreens, canbe permanently deformed by strongwinds. This deformity, known as"flagging," has been used to estimatethe average wind speed for an area.For more information on the use of

Wind Speeds Increase with Height

02979308m 150

120

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0 0

Increase in wind power, %

Tower height, ft

41 75 100 124
Small Wind Electric Systems 13
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How Do I Choose the BestSite for My Wind Turbine?You can have varied wind resourceswithin the same property. In additionto measuring or finding out about theannual wind speeds, you need toknow about the prevailing directionsof the wind at your site. If you live incomplex terrain, take care in selectingthe installation site. If you site yourwind turbine on the top of or on thewindy side of a hill, for example, youwill have more access to prevailingwinds than in a gully or on the leeward (sheltered) side of a hill on thesame property. In addition to geologicformations, you need to considerexisting obstacles such as trees, houses, and sheds, and you need toplan for future obstructions such asnew buildings or trees that have notreached their full height. Your turbineneeds to be sited upwind of buildings

p

p

like the one on pages 12 and 13 can

be used to estimate the wind resource

in your region. The highest averagewind speeds in the United States aregenerally found along seacoasts, onridgelines, and on the Great Plains;however, many areas have windresources strong enough to power asmall wind turbine economically. Thewind resource estimates on this mapgenerally apply to terrain features thatare well exposed to the wind, such asplains, hilltops, and ridge crests. Localterrain features may cause the windresource at a specific site to differ considerably from these estimates. Moredetailed wind resource information,including the 

Wind Energy Resource

Atlas of United States, published by theU.S. Department of Energy (DOE),can be found at the National WindTechnology Center web site athttp://www.nrel.gov/wind/ and theDOE Windpowering America web site at http://www.eren.doe.gov/windpoweringamerica/.Another way to indirectly quantifythe wind resource is to obtain averagewind speed information from a nearby airport. However, cautionshould be used because local terraininfluences and other factors maycause the wind speed recorded at an

Energy Resource Atlas of the UnitedStates (see For More Information).Another useful indirect measurementof the wind resource is the observation of an area’s vegetation. Trees,especially conifers or evergreens, canbe permanently deformed by strongwinds. This deformity, known as"flagging," has been used to estimatethe average wind speed for an area.For more information on the use of

02979310m

ggs-Putnam Index of Deformity

II III IV V VI VII

9-11 11-13 13-16 15-18 16-21 22+

4-5 5-6 6-7 7-8 8-9 10
above anything within 300 feet. Youalso need enough room to raise andlower the tower for maintenance, andif your tower is guyed, you mustallow room for the guy wires. Whether the system is stand-alone or grid-connected, you will also needto take the length of the wire runbetween the turbine and the load(house, batteries, water pumps, etc.)into consideration. A substantialamount of electricity can be lost as aresult of the wire resistance—thelonger the wire run, the more electricity is lost. Using more or larger wirewill also increase your installationcost. Your wire run losses are greaterwhen you have direct current (DC)instead of alternating current (AC).So, if you have a long wire run, it isadvisable to invert DC to AC.Can I Connect My Systemto the Utility Grid?Small wind energy systems can beconnected to the electricity distribution system and are called gridconnected systems. A grid-connectedwind turbine can reduce your consumption of utility-supplied electricity for lighting, appliances, and electric heat. If the turbine cannotdeliver the amount of energy you

ence. When the wind system producesmore electricity than the householdrequires, the excess is sent or sold tothe utility. Grid-connected systems can be practical if the following conditions exist:• You live in an area with average

annual wind speed of at least10 mph (4.5 m/s).

• Utility-supplied electricity is

expensive in your area (about 10 to15 cents per kilowatt-hour). 

• The utility's requirements for

connecting your system to its gridare not prohibitively expensive.

• There are good incentives for the

sale of excess electricity or for thepurchase of wind turbines.

Federal regulations (specifically, thePublic Utility Regulatory Policies Actof 1978, or PURPA) require utilities to connect with and purchase powerfrom small wind energy systems.However, you should contact yourutility before connecting to their distribution lines to address any powerquality and safety concerns. Your utility can provide you with a list ofrequirements for connecting your system to the grid. The American WindEnergy Association is another goodsource for information on utility 

place your windturbine fromobstacles suchas buildings ortrees, the lessturbulence youwill encounter.
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Most of North America gets morewind in the winter than in the summer. For people using wind energy todisplace a large load in the summerlike air-conditioning or irrigationwater pumping, having an annualNEG credit allows them to produceNEG in the winter and be credited inthe summer.

Safety RequirementsWhether or not your wind turbine isconnected to the utility grid, theinstallation and operation of the windturbine is probably subject to the electrical codes that your local government (city or county) or in someinstances your state government hasin place. The government’s principalconcern is with the safety of the facility, so these code requirementsemphasize proper wiring and installation, and the use of components that have been certified for fire andelectrical safety by approved testinglaboratories, such as UnderwritersLaboratories. Most local electricalcodes requirements are based on theNational Electrical Code (NEC),which is published by the NationalFire Protection Association. As of1999, the latest version of the NEC didnot have any sections specific to theinstallation of wind energy facilities,

If you do not have the expertise tomaintain the machine, your installermay provide a service and maintenance program.How Much Energy Will MySystem Generate?Most U.S. manufacturers rate theirturbines by the amount of power theycan safely produce at a particularwind speed, usually chosen between24 mph (10.5 m/s) and 36 mph(16 m/s). The following formula illustrates factors that are important to the performance of a wind turbine.Notice that the wind speed, V, has an 

ranging from 0.25 to 0.45, dimension less (theoretical maximum = 0.59)

ρ = Air density, lb/ft3

A = Rotor swept area, ft2 or 

π

D2/4 (D is the rotor 

diameter in ft, 

π = 3.1416)

V =

Wind speed, mph

k = 0.000133 A constant to yield 

power in kilowatts. (Multiplyingthe above kilowatt answer by 1.340 converts it to horsepower. [i.e., 1 kW = 1.340 horsepower]).
the line is "dead," might not take normal precautions and might be hurt oreven killed by the power from yourturbine. Another concern among utilities is that the power from your facility synchronize properly with theutility grid, and that it match the utility’s own power in terms of voltage,frequency, and power quality.A few years ago, some state governments started developing new standardized interconnection requirements for small renewable energygenerating facilities (including windturbines). In most cases the newrequirements have been based on consensus-based standards and testingprocedures developed by independent third-party authorities, such as theInstitute of Electrical and ElectronicEngineers and UnderwritersLaboratories.Interconnection RequirementsMost utilities and other electricityproviders require you to enter into aformal agreement with them beforeyou interconnect your wind turbinewith the utility grid. In states thathave retail competition for electricityservice (e.g., your utility operates the local wires, but you have a choice of electricity provider) you may have to sign a separate

y 

y 

own and have no control over. Othersconsider the insurance requirementsexcessive and unduly burdensome,making wind energy uneconomic. Inthe 21 years since utilities have beenrequired to allow small wind systemsto interconnect with the grid there has never been a liability claim, letalone a monetary award, relating toelectrical safety.

This gridconnected,10 kW Bergeywind turbineoffsets electricalpowerconsumption fora small businessin Norman,Oklahoma.

Bergey Windpower/PIX07166
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Customer ChargesCustomer charges can take a varietyof forms, including interconnectioncharges, metering charges, and standby charges, among others. Youshould not hesitate to question anycharges that seem inappropriate toyou. Federal law (Public UtilityRegulatory Policies Act of 1978, orPURPA, Section 210) prohibits utilitiesfrom assessing discriminatory chargesto customers who have their own generation facilities.

For safety, batteries should be isolated from living areas and electronics because they contain corrosiveand explosive substances. Lead-acidbatteries also require protection fromtemperature extremes. Grid-Connected SystemsIn grid-connected systems, the onlyadditional equipment required is apower conditioning unit (inverter)that makes the turbine output electrically compatible with the utility grid.Usually, batteries are not needed. What Do Wind SystemsCost?A small turbine can cost anywherefrom $3,000 to $35,000 installed,depending on size, application, andservice agreements with the manufacturer. (The American Wind EnergyAssociation [AWEA] says a typicalhome wind system costs approximately $32,000 (10 kW); a comparablephotovoltaic [PV] solar system wouldcost over $80,000.)A general rule of thumb for estimatingthe cost of a residential turbine is$1,000 to $3,000 per kilowatt. Windenergy becomes more cost effective as the size of the turbine’s rotorincreases. Although small turbinescost less in initial outlay, they are 

proportionally more expensive. Thecost of an installed residential windenergy system that comes with an 80-foot tower, batteries, and inverter,typically ranges from $13,000 to$40,000 for a 3 to 10 kW wind turbine.Although wind energy systemsinvolve a significant initial investment, they can be competitive withconventional energy sources whenyou account for a lifetime of reducedor avoided utility costs. The length ofthe payback period—the time beforethe savings resulting from your system equal the cost of the systemitself—depends on the system youchoose, the wind resource on yoursite, electricity costs in your area, andhow you use your wind system. Forexample, if you live in California andhave received the 50% buydown ofyour small wind system, have netmetering, and an average annualwind speed of 15 miles per hour(mph) (6.7 meters per second [m/s]),your simple payback would beapproximately 6 years.

Connecting to the Utility Grid—A Success StoryThis 10-kW Bergey wind turbine, installed on afarm located in Southwestern Kansas in 1983,produces an average 1700–1800 kilowatt-hoursper month, reducing the user's monthly utilitybills by approximately 50%. The turbine costabout $20,000 when it was installed. Since then,the cost for operation and maintenance has beenabout $50 per year. The only unscheduled maintenance activity over the years was repair to theturbine required as a result of damage caused bya lightning strike. Insurance covered all but $500of the $9000 cost of damages. The basic systemparts include:Bergey XL.10 wind turbine100-foot free-standing lattice towerInverter 

, 
Can I Go "Off-Grid"?Hybrid SystemsHybrid wind energy systems can provide reliable off-grid power forhomes, farms or even entire communities (a co-housing project, for example) that are far from the nearestutility lines. According to manyrenewable energy experts, a "hybrid"system that combines wind and photovoltaic (PV) technologies offersseveral advantages over either singlesystem. In much of the United States,wind speeds are low in the summerwhen the sun shines brightest andlongest. The wind is strong in thewinter when there is less sunlightavailable. Because the peak operatingtimes for wind and PV occur at different times of the day and year, hybridsystems are more likely to producepower when you need it. (For moreinformation on solar electric or PV systems, contact the EnergyEfficiency and Renewable EnergyClearinghouse—see For MoreInformation.)

For the times when neither the windnor the PV modules are producing,most hybrid systems provide powerthrough batteries and/or an enginegenerator powered by conventionalfuels such as diesel. If the batteriesrun low, the engine-generator can provide power and recharge the batteries. Adding an engine-generatormakes the system more complex, butmodern electronic controllers canoperate these systems automatically.An engine-generator can also reducethe size of the other componentsneeded for the system. Keep in mindthat the storage capacity must be large enough to supply electricalneeds during non-charging periods.Battery banks are typically sized tosupply the electric load for one tothree days. An off-grid hybrid system may bepractical for you if:• You live in an area with average

annual wind speed of at least9 mph (4.0 m/s).

• A grid connection is not available

or can only be made through an

Battery bank

turbine

029
Most turbines manufactured todayare horizontal axis upwind machinesthat have two or three blades, whichare usually made of a composite material such as fiberglass. The amount of power a turbine willproduce is determined primarily bythe diameter of its rotor. The diameterof the rotor defines its "swept area," orthe quantity of wind intercepted bythe turbine. The turbine's frame is thestructure onto which the rotor, generator, and tail are attached. The tailkeeps the turbine facing into thewind.TowerBecause wind speeds increase withheight, the turbine is mounted on a tower. In general, the higher thetower, the more power the wind system can produce. The tower alsoraises the turbine above the air turbulence that can exist close to the ground because of obstructionssuch as hills, buildings, and trees. Ageneral rule of thumb is to install awind turbine on a tower with thebottom of the rotor blades at least30 feet (9 meters) above any obstaclethat is within 300 feet (90 meters) ofthe tower. Relatively small investments in increased tower height canyield very high rates of return in

power production. For instance, toraise a 10-kW generator from a 60-foottower height to a 100-foot towerinvolves a 10% increase in overall system cost, but it can produce 25%more power. There are two basic types of towers:self-supporting (free standing) andguyed. Most home wind power systems use a guyed tower. Guyed towers, which are the least expensive, canconsist of lattice sections, pipe, or tubing depending on the design, andsupporting guy wires. They are easierto install than self-supporting towers.However, because the guy radiusmust be one-half to three-quarters of the tower height, guyed towersrequire enough space to accommodatethem. While tilt-down towers aremore expensive they offer the consumer an easy way to perform 

y 

install a hybrid electric system poweredby wind, solar, and a generator for a costof about $19,700. The parts of the systeminclude:Bergey 1.5 kW wind turbine, 10-ft (3-m)diameter rotor, 70-ft. (21-m) tower Solarex PV panels, 480 watts24 DC battery bank, 375 ampere-hoursTrace sine wave inverter, 120 AC, 1 phase,4 kWOnan propane-fueled generator, 6.5 kWrated (3 kW derated for altitude) Electric appliances in the home includetelevision, stereo, two computers, toaster,blender, vacuum cleaner, and hair dryer.The largest electric loads are created by a well pump and washing machine. Thegenerator runs about 20% of the time,particularly when the washing machine is in use. Propane serves the other majorloads in the home: range, refrigerator, hotwater, and space heat. Solar collectors onthe roof provide pre-heating for the hotwater.

Jim Green, NREL/PIX02796
speed over a specified period of time.

Blades—The aerodynamic surface

that catches the wind.

Brake—Various systems used to stop

the rotor from turning.

Converter—See Inverter.Cut-in wind speed—The wind speed

at which a wind turbine begins togenerate electricity.

Cut-out wind speed—The wind speed

at which a wind turbine ceases to generate electricity.

Density—Mass per unit of volume.Downwind—On the opposite side

from the direction from which thewind is blowing.

Furling—A passive protection for the

turbine where typically the rotor foldseither up or around the tail vane.

Grid—The utility distribution system. 

The network that connects electricitygenerators to electricity users.

HAWT—Horizontal axis wind turbine.Inverter—A device that converts direct

current (DC) to alternating current(AC).

kW—Kilowatt, a measure of power

for electrical current (1000 watts).

Power curve—A chart showing a

wind turbine's power output across a range of wind speeds.

PUC—Public Utility Commission, a

state agency which regulates utilities.In some areas known as Public Service

Commission (PSC).

PURPA—Public Utility Regulatory

Policies Act (1978), 16 U.S.C. § 2601.18CFR §292 that refers to small generator utility connection rules.

Rated output capacity—The output

power of a wind machine operating at the rated wind speed.

Rated wind speed—The lowest wind

speed at which the rated outputpower of a wind turbine is produced.

Rotor—The rotating part of a wind

turbine, including either the bladesand blade assembly or the rotatingportion of a generator.

Rotor diameter—The diameter of the

circle swept by the rotor.

Rotor speed—The revolutions per

minute of the wind turbine rotor.

Start-up wind speed—The wind speed

at which a wind turbine rotor willbegin to spin. See also cut-in windspeed.
 turbine.

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Energy

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modern small

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y

Paul Gipe—A comprehensive guide to modern small wind technology.Available through AWEA. (202) 383-2500. http://www.awea.org andChelsea Green Publishing Company,White River Junction, Vermont. 1999.ISBN - 0-930031-64-4. http://www.chelseagreen.comWind Power Workshop by Hugh

Piggott—Provides an overview onhow to design a home-built wind turbine. Available from The Center forAlternative Technology, Machynlleth,Powys, SY20 9AZ, UK Phone: 06154-702400, FAX: 01654 702782. E-mail:help@catinfo.demon.co.uk,http://www.foe.co.uk/CATWind Resource Assessment Handbook:Fundamentals for Conducting aSuccessful Monitoring Program—Thishandbook presents industry-acceptedguidelines for planning and conducting a wind resource measurementprogram. These guidelines, which aredetailed and highly technical, emphasize the tasks of selecting, installing,and operating wind measurementequipment, as well as collecting andanalyzing the associated data.Prepared by AWS Scientific, Inc.Available electronically in NREL'spublication database at http://www.nrel.gov/publications.

p

• your property is in a remote

location that does not have easyaccess to utility lines 

• you are comfortable with long-term

investments.

Zoning IssuesBefore you invest in a wind energysystem, you should research potentialobstacles. Some jurisdictions, forexample, restrict the height of the

Most zoning and aesthetic concernscan be addressed by supplying objective data. For example, the ambientnoise level of most modern residentialwind turbines is around 52 to 55 decibels. This means that while the soundof the wind turbine can be picked outof surrounding noise if a consciouseffort is made to hear it, a residentialsized wind turbine is no noisier thanyour average refrigerator.
p

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553-6847. http://www.ntis.gov/ordering.htmNon-Government OrganizationsAmerican Wind Energy Association,122 C Street, N.W. 4th Floor,

Washington, D.C. 20001. (202) 383-2500. http://www.awea.orgSolar Energy International—Shortcourses on renewable energy and sustainable development, inCarbondale, Colorado. (970) 963-8855.http://www.solarenergy.org

Periodicals"Apples and Oranges" by MickSagrillo—A comprehensive comparison of available small wind turbines.On Home Power Magazine Web site:http://www.homepower.comHome Power Magazine—The definitive bimonthly magazine for thehomemade power enthusiast.(800)707-6586 or on the Web at:http://www.homepower.comVideosAn Introduction to Residential WindSystems with Mick Sagrillo—A 63-minute video answering questionsmost often asked by homeowners as they consider purchasing andinstalling their own wind power 

now available in 30 states. Visit thisDOE Web site for information:http://www.eren.doe.gov/greenpower/netmeteringSmall Wind "Talk" on the Web—AWEA's Home Energy Systems electronic mailing list is designed as aforum for the discussion of small-scaleenergy systems that include wind. Tosubscribe, send a subscription requestawea-wind-home-subscribe@egroups.com.Wind Energy for Homeowners—This

Web site discusses things you shouldconsider before investing in a smallwind energy system and providesbasic information about the systems.http://www.eren.doe.gov/wind/homeowner.html
our nation's energy needs. Althoughwind turbines large enough to provide a significant portion of the electricity needed by the average U.S.home generally require one acre ofproperty or more, approximately21 million U.S. homes are built onone-acre and larger sites, and 24% of the U.S. population lives in ruralareas.A small wind electric system willwork for you if:• There is enough wind where you

live 

• Tall towers are allowed in your

neighborhood or rural area 

• You have enough space• You can determine how much

electricity you need or want toproduce 

• It works for you economically. 

The purpose of this guide is to provide you with the basic information

about small wind electric systems tohelp you decide if wind energy willwork for you. Why Should I Choose Wind?Wind energy systems are one of themost cost-effective home-basedrenewable energy systems.

Homeowners, ranchers, and small businesses can use windgenerated electricity to reduce their utility bills. This gridconnected system installed for a home in Norman, Oklahoma,reduces the homeowner's utility bill by $100 per month.

Bergey Windpower/PIX01476

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Wind Energy Equipment Exemption 

The value added by a qualified wind energy system,

as well as transmission equipment, is exempt for

property tax purposes. Commercial, industrial, and

residential applications are eligible. The value of

equipment or components for conventional energy

systems that operate without mechanical means 

is not eligible for tax exemption.

Authority: Wis. Stat. § 70.111

www.dsireusa.org/library/docs/incentives/WI01F.htm

Contact

Alex De Pillis 

Wisconsin Department of Administration 

Division of Energy 

P.O. Box 7868 

Madison, WI 53707-7868 

Phone: (608) 266-1067 

Fax: (608) 267-6931 

E-mail: alex.depillis@doa.state.wi.us 

Web site: www.doa.state.wi.us/energy/index.asp 

Wisconsin Focus on Energy 

Focus on Energy is a public/private partnership that

offers energy information and services to residential,

business, and industrial customers throughout

Wisconsin. These services are delivered by a group

of firms contracted by the Wisconsin Department of

Administration's Division of Energy. The goals of this

program are to encourage energy efficiency and use

of renewable energy, enhance the environment, and

ensure the future supply of energy for Wisconsin.

Three programs support these goals, including 

cash-back rewards, grant, and loan programs.

Cash-Back Rewards

Businesses and homes installing or expanding

renewable energy systems are eligible for a partial

reimbursement of expenses through the Cash-Back

Rewards Program. Payments are based on the estimated amount of electricity generated annually.

Nonresidential and residential wind energy systems

(20 kW or less) are eligible for up to 25% of project

cost or $35,000. Customer property must be located

in the service territory of a participating electric or

natural gas provider. Applications are available at

www.focusonenergy.com/page.jsp?pageId=904.

Contacts

Niels Wolter 

WisconSUN 

c/o MSB Energy Associates Inc. 

7507 Hubbard Ave., Suite 200 

Middleton, WI 53562 

Phone: (608) 831-1127 Ext.308 

Fax: (608) 836-1290 

E-mail: Wolter@msbnrg.com 

Web site: www.wisconsun.org 

Beth Shippert 

Wisconsin Energy Conservation Corporation 

211 S Paterson St. 3rd Floor 

Madison, WI 53703 

Phone: (608) 249-9322 Ext.320 

Fax: (608) 249-0339 

E-mail: beths@weccusa.org 

Web site: www.weccusa.org 

Implementation Grant

Focus on Energy offers an Implementation Grant to

provide financial support for large renewable energy

projects (greater than 20 kW or 5,000 therms per

year). Eligible wind systems may receive grants 

of up to 25% of project costs with a maximum of

$35,000. The amount is based on the estimated

annual kWh generated or thermal energy saved or

utilized. Businesses, individuals, organizations, institutions, and municipal or tribal governments located

in the service territory of a participating electric or

natural gas utility are eligible. Renewable energy

systems can be off-grid. For more information, visit

www.focusonenergy.com/page.jsp?pageId=725.

Loan Program 

Low-interest loans, ranging from $2,500 to $20,000,

for financing wind projects on existing owner-occupied

single-family and duplex homes are available. A participating contractor must install eligible systems.

Loan terms vary from 3 to 10 years with an interest

rate of 1.99% APR. Applicants may be asked to 

verify income when loans exceed $4,000.

Customers must be located in the service territory of

a participating electric or natural gas provider.

Applications for low-interest loans are available at

www.

focusonenergy.com/page.jsp?pageId=904.

Contact

Niels Wolter (see Cash-Back Rewards above)

Interconnection Standards 

Wisconsin is developing distributed generation (DG)

interconnection rules and revising outdated interconnection rules for small renewable generators, including wind. Both residential and nonresidential sectors

will be eligible. The interconnection guidelines

(www.dsireusa.org/library/docs/additionaldocs/WIDG

IntrGuidelinesv6.pdf) categorize DG systems by

capacity as follows:

Category 1: 20 kW or less 

Category 2: Greater than 20 kW to 200 kW 

Category 3: Greater than 200 kW to 1 MW 

Category 4: Greater than 1 MW to 15 MW 

The interconnection rules (PSC 119) will establish

both a Standard Application Form and a Standard

Small Wind Electric Systems 

Wisconsin Incentives
Interconnection Agreement. In both cases, separate,

simplified documents will be used for small systems

up to 20 kW. These smaller systems will also be eligible for net metering. Insurance requirements and

interconnection application fees are also based 

on these categories. For more information, visit

psc.wi.gov/electric/cases/electgen/electgen.htm.

Authority: Wis. Stat. § 196.025 (www.dsireusa.

org/library/docs/incentives/WI11R.htm)

Net Metering 

The Public Service Commission of Wisconsin

(PSCW) authorized net metering for commercial,

industrial, and residential customer-owned systems

(up to 20 kW). The order applies to all utilities under

the jurisdiction of PSCW. All technologies, including

renewables such as wind and cogeneration, are 

eligible. There is no limit on the amount of energy 

a utility can receive through net metering. 

Utilities pay customer generators the retail rate for

net excess generation from renewable energy facilities. Customer generators producing energy from

non-renewable resources receive the avoided-cost

rate for net excess generation. 

Authority 1: Rate Schedules; PSC of Wisconsin

Order 6690-UR-107 (www.dsireusa.org/library/

docs/incentives/WI11R.htm)

Contact 

Paul Helgeson 

Public Service Commission of Wisconsin 

610 North Whitney Way 

P.O. Box 7854 

Madison, WI 53707-7854 

Phone: (608) 266-3905 

Fax: (608) 266-3957 

E-mail: paul.helgeson@psc.state.wi.us 

Web site: psc.wi.gov/ 

Other Contacts

William Hui 

U.S. Department of Energy

Chicago Regional Office

One South Wacker Drive, Suite 2380

Chicago, IL 60606-4616

Phone: (312) 885-8586

Fax: (312) 886-8561

E-mail: william.hui@ee.doe.gov

Web site: www.eere.energy.gov/cro

Wind Powering America

www.windpoweringamerica.gov

A Strong Energy Portfolio for a Strong America

Energy efficiency and clean, renewable energy will mean a stronger economy, a cleaner environment, and greater energy

independence for America. Working with a wide array of state, community, industry, and university partners, the U.S.

Department of Energy’s Office of Energy Efficiency and Renewable Energy invests in a diverse portfolio of energy technologies. 

Produced for the U.S. Department of Energy by the 

National Renewable Energy Laboratory, 

a DOE national laboratory

DOE/GO-102004-1807 • May 2004

Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste.

For more information contact:

EERE Information Center

1-877-EERE-INF (1-877-337-3463)

www.eere.energy.gov