small wind energy systems 110702042021 small wind guide

8/9/2019 Small Wind Energy Systems 110702042021 Small Wind Guide

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A

MinnesotaConsumers Guide

Small Wind Electric Systems


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Small Wind Electric Systems 1

ContentsI n t r o d u c t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

First, How Can I Make My Home More Energy Efficient? . . . . 2

Is Wind Energy Practical for Me? . . . . . . . . . . . . . . . . . . . . . . 3

What Size Wind Turbine Do I Need? . . . . . . . . . . . . . . . . . . . . 4

What are the Basic Parts of a Small Wind Electric System? . . 5

What Do Wind Systems Cost? . . . . . . . . . . . . . . . . . . . . . . . . 7

Where Can I Find Installation and Maintenance Support?. . . . 8How Much Energy Will My System Generate? . . . . . . . . . . . . 9

Is There Enough Wind on My Site?. . . . . . . . . . . . . . . . . . . . 11

How Do I Choose the Best Site for My Wind Turbine? . . . . . 14

Can I Connect My System to the Utility Grid? . . . . . . . . . . . . 15

Can I Go Off-Grid? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Glossary of Terms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

For More Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Small Wind Electric SystemsA U.S. Consumers Guide

Homeowners, ranchers, and small businesses can use wind-generated electricity to reduce their utility bills. This grid-connected system installed for a home in Norman, Oklahoma,reduces the homeowners utility bill by $100 per month.

BergeyWindpower/PIX

01476

Introduction

Can I use wind energy to power myhome? This question is being askedacross the country as more peoplelook for affordable and reliable sourc-es of electricity.

Small wind electric systems can makea significant contribution to ournations energy needs. Although windturbines large enough to provide asignificant portion of the electricityneeded by the average U.S. home gen-erally require one acre of property ormore, approximately 21 million U.S.homes are built on one-acre and largersites, and 24% of the U.S. populationlives in rural areas.

A small wind electric system willwork for you if:

There is enough wind where youlive

Tall towers are allowed in yourneighborhood or rural area

You have enough space

You can determine how muchelectricity you need or want toproduce

It works for you economically.

The purpose of this guide is to pro-vide 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 oneof the most cost-effective home-based renewable energy systems.Depending on your wind resource, a


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Small Wind Electric Systems2

small wind energy system can loweryour electricity bill by 50% to 90%,help you avoid the high costs ofextending utility power lines toremote locations, prevent powerinterruptions, and it is nonpolluting.

How Do Wind Turbines Work?

Wind is created by the unequal heat-ing of the Earths surface by the sun.Wind turbines convert the kineticenergy in wind into mechanicalpower that runs a generator toproduce clean electricity. Todays

turbines are versatile modular sourcesof electricity. Their blades are aero-dynamically designed to capture themaximum energy from the wind. Thewind turns the blades, which spin ashaft connected to a generator thatmakes electricity.

First, How Can I Make

My Home More EnergyEfficient?

Before choosing a wind system foryour home, you should considerreducing your energy consumption bymaking your home or business moreenergy efficient. Reducing yourenergy consumption will signifi-cantly lower your utility bills and willreduce the size of the home-basedrenewable energy system you need.To achieve maximum energy effi-ciency, you should take a whole-building approach. View your homeas an energy system with interrelatedparts, all of which work synergisti-cally to contribute to the efficiencyof the system. From the insulation inyour homes walls to the light bulbsin its fixtures, there are many ways tomake your home more efficient.

Reduce your heating andcooling needs by up to 30% byinvesting just a few hundreddollars in proper insulation andweatherization products.

Save money and increasecomfort by properly maintainingand upgrading your heating,ventilation, and air-conditioning

systems. Install double-paned, gas-filled

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

Replace your lights in high-useareas with fluorescents. Replacing

25% of your lights can save about50% of your lighting energy bill.

When shopping for appliances,look for the ENERGYSTAR label.ENERGYSTAR appliances havebeen 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 tomake your home energy efficient,see Energy Savers in the For MoreInformation section.

Lighting,cooking,and otherappliances

33%

Refrigerator 9%

Heating andcooling44%

Water

heating14%

02979309m

Home Energy UseBased on national averages

The largest portion of a utility bill for a typicalhouse is for heating and cooling.


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What Size Wind TurbineDo I Need?

The size of the wind turbine you needdepends on your application. Small

turbines range in size from 20 wattsto 100 kilowatts (kW). The smaller ormicro (20- to 500-watt) turbines areused in a variety of applications suchas charging batteries for recreationalvehicles and sailboats.

One- to 10-kW turbines can be used inapplications such as pumping water.Wind energy has been used for centu-

ries to pump water and grind grain.Although mechanical windmills stillprovide a sensible, low-cost optionfor pumping water in low-wind areas,farmers and ranchers are finding thatwind-electric pumping is a little moreversatile and they can pump twicethe volume for the same initialinvestment. In addition, mechanical

windmills must be placed directlyabove the well, which may not takethe best advantage of available windresources. Wind-electric pumpingsystems can be placed where the windresource is the best and connected tothe pump motor with an electric cable.

Turbines used in residential applica-tions can range in size from 400 wattsto 100 kW (100 kW for very largeloads), depending on the amount ofelectricity you want to generate. Forresidential applications, you shouldestablish an energy budget to helpdefine the turbine size you will need.Because energy efficiency is usuallyless expensive than energy produc-tion, making your house more energyefficient first will probably be morecost effective and will reduce the size

of the wind turbine you need (seeHow Can I Make My Home MoreEnergy Efficient?). Wind turbinemanufacturers can help you sizeyour system based on your electricityneeds and the specifics of local windpatterns.

A typical home uses approximately10,000 kilowatt-hours (kWh) of elec-

tricity per year (about 830 kWh permonth). Depending on the averagewind speed in the area, a wind tur-bine rated in the range of 5 to 15 kWwould be required to make a signifi-cant contribution to this demand. A1.5- kW wind turbine will meet theneeds of a home requiring 300 kWhper month in a location with a 14-

mile-per-hour (6.26-meters-per-sec-ond) annual average wind speed. Themanufacturer can provide you withthe expected annual energy outputof the turbine as a function of annualaverage wind speed. The manufac-turer will also provide information onthe maximum wind speed at whichthe turbine is designed to operate

safely. Most turbines have automaticoverspeed-governing systems to keepthe rotor from spinning out of controlin very high winds. This information,along with your local wind speed andyour energy budget, will help youdecide which size turbine will bestmeet your electricity needs.

This 1-kW Whisperturbine providesdirect AC power forthe water pump forstock tanks on aranch in Wheeler,Texas.

ElliottBayly/PIX09681


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What are the Basic Partsof a Small Wind ElectricSystem?

Home wind energy systems gener-

ally comprise a rotor, a generator oralternator mounted on a frame, a tail(usually), a tower, wiring, and thebalance of system components:controllers, inverters, and/or batter-ies. Through the spinning blades, therotor captures the kinetic energy ofthe wind and converts it into rotarymotion to drive the generator.

Wind Turbine

Most turbines manufactured todayare horizontal axis upwind machineswith two or three blades, which areusually made of a composite materialsuch as fiberglass.

The amount of power a turbine willproduce is determined primarily by

the diameter of its rotor. The diameterof the rotor defines its swept area,or the quantity of wind intercepted bythe turbine. The turbines frame is thestructure onto which the rotor, genera-tor, and tail are attached. The tailkeeps the turbine facing into the wind.

Tower

Because wind speeds increase withheight, the turbine is mounted ona tower. In general, the higher thetower, the more power the windsystem can produce. The tower alsoraises the turbine above the airturbulence that can exist close tothe ground because of obstructionssuch as hills, buildings, and trees. A

general rule of thumb is to install awind turbine on a tower with the bot-tom of the rotor blades at least 30 feet(9 meters) above any obstacle thatis within 300 feet (90 meters) of thetower. Relatively small investments inincreased tower height can yield veryhigh rates of return in power produc-tion. For instance, to raise a 10-kW

generator from a 60-foot tower heightto a 100-foot tower involves a 10%increase in overall system cost, but itcan produce 29% more power.

There are two basic types of tow-ers: self-supporting (free standing)

and guyed. Most home wind powersystems use a guyed tower. Guyedtowers, which are the least expensive,can consist of lattice sections, pipe, ortubing (depending on the design), andsupporting guy wires. They are easierto install than self-supporting tow-ers. However, because the guy radiusmust be one-half to three-quarters

of the tower height, guyed towersrequire enough space to accommodatethem. Although tilt-down towers aremore expensive, they offer the con-sumer an easy way to performmaintenance on smaller light-weightturbines, usually 5 kW or less.

02979312m

Rotor

Tail

Tower

Generator/alternator

02979311m

Tilt-Down Tower

Tilt-up towerin the normaloperatingpositionTilt-up tower in the

lowered position formaintenance orhurricanes

Tilt-down towersprovide easymaintenance forturbines.


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Tilt-down towers can also be low-ered to the ground during hazard-ous weather such as hurricanes.Aluminum towers are prone tocracking and should be avoided.Most turbine manufacturers providewind energy system packages thatinclude towers.

Mounting turbines on rooftops is notrecommended. All wind turbinesvibrate and transmit the vibrationto the structure on which they aremounted. This can lead to noise and

structural problems with the building,and the rooftop can cause excessiveturbulence that can shorten the life ofthe turbine.

Balance of System

The parts that you need in additionto the turbine and the tower, or thebalance of system parts, will depend

on your application. Most manufac-turers can provide you with a systempackage that includes all the parts youneed for your application. For exam-ple, the parts required for a waterpumping system will be much differ-ent than what you need for a residen-tial application. The balance of systemrequired will also depend on whether

the system is grid-connected, stand-alone, or part of a hybrid system.For a residential grid-connected

application, the balance of systemparts may include a controller, storagebatteries, a power conditioning unit(inverter), and wiring. Some windturbine controllers, inverters, or otherelectrical devices may be stampedby a recognized testing agency, likeUnderwriters Laboratories.

Stand-Alone Systems

Stand-alone systems (systems notconnected to the utility grid) requirebatteries to store excess power gener-ated for use when the wind is calm.

They also need a charge controller tokeep the batteries from overcharging.Deep-cycle batteries, such as thoseused for golf carts, can dischargeand recharge 80% of their capacityhundreds of times, which makes thema good option for remote renewableenergy systems. Automotive batteriesare shallow-cycle batteries and should

not be used in renewable energysystems because of their short lifein deep-cycling operations.

A Bergey XL.10,10-kW windturbine is part ofa grid-connectedwind/photovoltaichybrid system thatreduces the utility

power used by thishome in Vermont.The balance ofsystem (upper right)includes from leftto right, a Traceinverter for thePV system, abreaker box, and aPowersync inverterfor the wind system.

TrudyForsyth,NREL/PIX09122andPIX09123


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Small wind turbines generate directcurrent (DC) electricity. In very smallsystems, DC appliances operatedirectly off the batteries. If you want touse standard appliances that use con-ventional household alternating cur-rent (AC), you must install an inverterto convert DC electricity from thebatteries to AC. Although the inverterslightly lowers the overall efficiencyof the system, it allows the home tobe wired for AC, a definite plus withlenders, electrical code officials, and

future homebuyers.For safety, batteries should be iso-lated from living areas and electron-ics because they contain corrosiveand explosive substances. Lead-acidbatteries also require protection fromtemperature extremes.

Grid-Connected Systems

In grid-connected systems, the onlyadditional equipment required is apower conditioning unit (inverter)that makes the turbine output electri-cally compatible with the utility grid.Usually, batteries are not needed.

What Do Wind SystemsCost?

Installation costs vary greatly depend-ing on local zoning, permitting,and utility interconnection costs.According to the American WindEnergy Association, small windenergy systems cost from $3,000 to$5,000 for every kilowatt of generatingcapacity. This is much cheaper thansolar electric systems, but the payback

period can still be lengthy.Wind energy becomes more cost effec-tive as the size of the turbines rotorincreases. Although small turbinescost less in initial outlay, they areproportionally more expensive. Thecost of an installed residential windenergy system with an 80-foot tower,batteries, and inverter typically

ranges from $15,000 to $50,000 fora 3- to 10-kW wind turbine.

Although wind energy systemsinvolve a significant initial invest-ment, they can be competitive withconventional energy sources whenyou account for a lifetime of reducedor avoided utility costs. The lengthof the payback periodthe timebefore the savings resulting from yoursystem equal the cost of the systemitselfdepends 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.

A SouthwestWindpower Air303, 300-wattturbine is the solesource of electricityfor this remote

home in northernArizona.

SouthwestWindpower/PIX09156


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Things to Consider WhenPurchasing a Wind Turbine

Once you determine you can installa wind energy system in compliancewith local land use requirements, youcan begin pricing systems and compo-nents. Comparatively shop for a wind

system as you would any major pur-chase. Obtain and review the productliterature from several manufacturers.As mentioned earlier, lists of manu-facturers are available from AWEA,(see For More Information), but notall small turbine manufacturers aremembers of AWEA. Check the yellowpages for wind energy system dealers

in your area.Once you have narrowed the field,research a few companies to be surethey are recognized wind energybusinesses and that parts and servicewill be available when you need them.You may wish to contact the BetterBusiness Bureau to check onthe companys integrity and ask for

references of past customers withinstallations similar to the one you areconsidering. Ask the system ownersabout performance, reliability, andmaintenance and repair requirements,and whether the system is meetingtheir expectations. Also, find out howlong the warranty lasts and what itincludes.

Where Can I FindInstallation andMaintenance Support?

The manufacturer/dealer should beable to help you install your machine.Many people elect to install themachines themselves. Before attempt-ing to install your wind turbine, askyourself the following questions:

Can I pour a proper cementfoundation?

Do I have access to a lift or a way oferecting the tower safely?

Do I know the difference betweenAC and DC wiring?

Do I know enough about electricityto safely wire my turbine?

Do I know how to safely handleand 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 helpor call your state energy office andlocal utility for a list of local systeminstallers. You can also check the yel-low pages for wind energy system

service providers. A credible installerwill provide many services such aspermitting. Find out if the installer is alicensed electrician. Ask for referencesand check them out. You may alsowant to check with the Better BusinessBureau.

Although small wind turbines arevery sturdy machines, they do require

Small windturbines like this10-kW BergeyXL.10 provideelectricity forhome, farm, andranch applications.

W

arrenGretz,NREL/PIX09615


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some annual maintenance. Boltsand electrical connections should bechecked and tightened if necessary.The machines should be checked forcorrosion and the guy wires forproper tension. In addition, youshould check for and replace anyworn leading edge tape on the blades,if appropriate. After 10 years, theblades or bearings may need to bereplaced, but with proper installationand maintenance, the machine shouldlast up to 20 years or longer.

If you do not have the expertise tomaintain the machine, your installermay provide a service and mainte-nance program.

How Much Energy Will MySystem Generate?

Most U.S. manufacturers rate theirturbines by the amount of power they

can safely produce at a particularwind speed, usually chosen between24 mph (10.5 m/s) and 36 mph (16 m/s). The following formulaillustrates factors that are importantto the performance of a wind turbine.Notice that the wind speed, V, has anexponent of 3 applied to it. Thismeans that even a small increase in

wind speed results in a large increasein power. That is why a taller towerwill increase the productivity of anywind turbine by giving it access tohigher wind speeds as shown in theWind Speeds Increase with Heightgraph. The formula for calculatingthe power from a wind turbine is:

Power = k Cp1/2 A V3

Where:

P = Power output, kilowatts

Cp= Maximum power coefficient,

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

= Air density, lb/ft3

A = Rotor swept area, ft2 or D2/4 (D is the rotordiameter in ft, = 3.1416)

V = Wind speed, mph

k = 0.000133 A constant to yieldpower in kilowatts. (Multiplyingthe above kilowatt answer by1.340 converts it to horse-power [i.e., 1 kW = 1.340horsepower]).

The rotor swept area, A, is importantbecause the rotor is the part of theturbine that captures the wind energy.

8

7

6

5

4

3

2

1

0

1 2 3 4 5 6 7

Rotor Diameter, m

RotorDiameter,m

Relative Size of Small Wind Turbines

40

30

20

10

0

Sweptarea,m2

7 m

6 m

5 m

4 m

3 m

2 m

1 m

02979303m

Source: Paul Gipe, Wind Energy Basics


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So, the larger the rotor, the moreenergy it can capture. The air density,, changes slightly with air tempera-ture and with elevation. The ratingsfor wind turbines are based onstandard conditions of 59 F (15 C)at sea level. A density correctionshould be made for higher elevationsas shown in the Air Density Changewith Elevation graph. A correction fortemperature is typically not neededfor predicting the long-term perfor-mance of a wind turbine.

Although the calculation of windpower illustrates important featuresabout wind turbines, the best mea-

sure of wind turbine performance isannual energy output. The differencebetween power and energy is thatpower (kilowatts [kW]) is the rate atwhich electricity is consumed, whileenergy (kilowatt-hours [kWh]) is thequantity consumed. An estimate ofthe annual energy output from yourwind turbine, kWh/year, is the best

way to determine whether a particularwind turbine and tower will produceenough electricity to meet your needs.

A wind turbine manufacturer can helpyou estimate the energy productionyou can expect. They will use a cal-culation based on the particular windturbine power curve, the averageannual wind speed at your site, the

height of the tower that you plan touse, and the frequency distribution ofthe windan estimate of the numberof hours that the wind will blow ateach speed during an average year.They should also adjust this calcula-tion for the elevation of your site.Contact a wind turbine manufactureror dealer for assistance with thiscalculation.

To get a preliminary estimate of theperformance of a particular wind tur-bine, use the formula below.

AEO = 0.01328 D2V3

Where:

AEO = Annual energy output,kWh/year

D = Rotor diameter, feet

V = Annual average wind speed,mph

The Wind Energy Payback PeriodWorkbook found at www.nrel.gov/wind/docs/spread_sheet_Final.xls isa spreadsheet tool that can help youanalyze the economics of a small windelectric system and decide whetherwind energy will work for you. Thespreadsheet can be opened usingMicrosoft Excel 95 software. It asksyou to provide information about how

youre going to finance the system,the characteristics of your site, andthe properties of the system youreconsidering. It then provides you witha simple payback estimation in years.If it takes too long to regain your capi-tal investmentthe number of yearscomes too close or is greater than thelife of the systemwind energy willnot be practical for you.

10,000

9,000

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

070 75 80 85 90 95 100

Density change compared to sea level, %

Elevation,ft

Air Density Change with Elevation

02979302m


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Is There Enough Windon My Site?

Does the wind blow hard and con-sistently enough at my site to make a

small wind turbine system economi-cally worthwhile? That is a key ques-tion and not always easily answered.The wind resource can vary signifi-cantly over an area of just a few milesbecause of local terrain influenceson the wind flow. Yet, there are stepsyou can take that will go a long waytowards answering the above

question.As a first step, wind resource mapslike the one on pages 12 and 13 canbe used to estimate the wind resourcein your region. The highest averagewind speeds in the United States aregenerally found along seacoasts, onridgelines, and on the Great Plains;however, many areas have wind

resources 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 con-siderably from these estimates. More

detailed wind resource information,including the Wind Energy ResourceAtlas of United States, published by theU.S. Department of Energy (DOE),can be found at the National WindTechnology Center Web site at www.nrel.gov/wind/ and the DOE WindPowering America Web site at www.windpoweringamerica.gov.

Another way to indirectly quantifythe wind resource is to obtain averagewind speed information from anearby airport. However, cautionshould be used because local terraininfluences and other factors maycause the wind speed recorded atan airport to be different from your

particular location. Airport wind dataare generally measured at heightsabout 2033 ft (610 m) above ground.Average wind speeds increase withheight and may be 15%25% greaterat a typical wind turbine hub-heightof 80 ft (24 m) than those measuredat airport anemometer heights. TheNational Climatic Data Center collectsdata from airports in the United Statesand makes wind data summariesavailable for purchase. Summariesof wind data from almost 1000 U.S.

airports are also included in theWind

Energy Resource Atlas of the UnitedStates (see For More Information).

Another useful indirect measurementof the wind resource is the observa-tion of an areas 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 offlagging, you may want to obtain

Wind Speeds Increase with Height

02979308m

150

120

90

60

30

00

Increase in wind power, %

Towerheight,ft

41 75 100 124


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Small Wind Electric Systems12 Small Wind Electric Systems 13


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A Siting Handbook for Small WindEnergy Conversion Systems(see ForMore Information).

Direct monitoring by a wind resourcemeasurement system at a site pro-vides the clearest picture of the avail-able resource. A good overall guideon this subject is the Wind ResourceAssessment Handbook(see For More

Information). Wind measurementsystems are available for costs as lowas $600 to $1200. This expense may ormay not be hard to justify dependingon the exact nature of the proposedsmall wind turbine system. The mea-surement equipment must be set highenough to avoid turbulence createdby trees, buildings, and other obstruc-

tions. The most useful readings arethose taken at hub-height, the eleva-tion at the top of the tower where thewind turbine is going to be installed.If there is a small wind turbine sys-tem in your area, you may be able toobtain information on the annualoutput of the system and also windspeed data if available.

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 aboutthe annual wind speeds, you need toknow about the prevailing directionsof the wind at your site. If you live incomplex terrain, take care in selecting

the 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 lee-ward (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 build-ings and trees, and it needs to be 30feet above anything within 300 feet.You also need enough room to raiseand lower the tower for maintenance,

0Nodeformity

Flagging

Prevailing wind

IBrushingand slightflagging

IISlightflagging

IIIModerateflagging

IVCompleteflagging

VPartialthrowing

VICompletethrowing

VIICarpeting

02979310m

Griggs-Putnam Index of Deformity

Index I II III IV V VI VII

Wind mph 7-9 9-11 11-13 13-16 15-18 16-21 22+

Speed m/s 3-4 4-5 5-6 6-7 7-8 8-9 10

Flagging, the effectof strong winds onarea vegetation,can help determinearea wind speeds.


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and if your tower is guyed, you mustallow room for the guy wires.

Whether the system is stand-aloneor 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 resistancethe lon-ger the wire run, the more electric-ity 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 distribu-tion system and are called grid-

connected systems. A grid-connectedwind turbine can reduce your con-sumption of utility-supplied electric-ity for lighting, appliances, andelectric heat. If the turbine cannotdeliver the amount of energy youneed, the utility makes up the differ-ence. When the wind system producesmore electricity than the household

requires, the excess is sent or sold tothe utility.

Grid-connected systems can be practi-cal if the following conditions exist:

You live in an area with averageannual wind speed of at least10 mph (4.5 m/s)

Utility-supplied electricity isexpensive in your area (about 10 to15 cents per kilowatt-hour)

The utilitys requirements forconnecting your system to its gridare not prohibitively expensive

There are good incentives for thesale of excess electricity or for thepurchase of wind turbines.

Federal regulations (specifically, thePublic Utility Regulatory Policies Actof 1978, or PURPA) require utilitiesto connect with and purchase powerfrom small wind energy systems.However, you should contact your

utility before connecting to their dis-tribution lines to address any powerquality and safety concerns. Yourutility can provide you with a list ofrequirements for connecting your sys-tem to the grid. The American WindEnergy Association is another goodsource for information on utilityinterconnection requirements. The

20 H2 H

Obstruction of the Wind by a Building

or Tree of Height (H)

02979307m

H

2 H

Region

of highly

turbulent

flow

The farther youplace your windturbine fromobstacles suchas buildings ortrees, the lessturbulence youwill encounter.


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following information about utilitygrid connection requirements wastaken from AWEAs Web site. Formore detailed information, visit www.awea.org/ or contact AWEA (see ForMore Information).

Net Metering

The concept of net metering programsis to allow the electric meters of cus-

tomers with generating facilities toturn backwards when their generatorsare producing more energy than thecustomers demand. Net meteringallows customers to use their genera-tion to offset their consumption overthe entire billing period, not justinstantaneously. This offset wouldenable customers with generating

facilities to receive retail prices formore of the electricity they generate.

Net metering varies by state andby utility company, depending onwhether net metering was legis-lated or directed by the Public UtilityCommission. Net metering programsall specify a way to handle the net

excess generation (NEG) in terms ofpayment for electricity and/or lengthof time allowed for NEG credit. Ifthe net metering requirements defineNEG on a monthly basis, the consum-er can only get credit for their excessthat month. But if the net meteringrules allow for annual NEG, the NEGcredit can be carried for up to a year.

Most of North America gets morewind in the winter than in the sum-mer. 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 turbineis connected to the utility grid, theinstallation and operation of the windturbine is probably subject to theelectrical codes that your local gov-ernment (city or county), or in someinstances your state government, hasin place. The governments principal

concern is with the safety of thefacility, so these code requirementsemphasize proper wiring and installa-tion and the use of componentsthat have been certified for fire andelectrical safety by approved testinglaboratories, such as UnderwritersLaboratories. Most local electricalcodes requirements are based on

the National 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 facilitiesconsequently wind energy installa-tions are governed by the genericprovisions of the NEC.

Inverter

Load

AC

Wind

turbine

Grid-connected Systems

02979301m

Meter

A grid-connectedwind turbinecan reduce yourconsumption ofutility-suppliedelectricity.


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If your wind turbine is connected tothe local utility grid so that any of thepower produced by your wind tur-bine is delivered to the grid, then yourutility also has legitimate concernsabout safety and power quality thatneed to be addressed. The utilitysprincipal concern is that your windturbine automatically stops deliver-ing any electricity to its power linesduring a power outage. Otherwiseline workers and the public, thinkingthat the line is dead, might not take

normal precautions and might behurt or even killed by the power fromyour turbine. Another concern amongutilities is whether the power fromyour facility synchronizes properlywith the utility grid and it matches theutilitys own power in terms of volt-age, frequency, and power quality.

A few years ago, some state govern-

ments started developing newstandardized interconnection require-ments for small renewable energygenerating facilities (including windturbines). In most cases, the newrequirements are based on consen-sus-based standards and testing pro-cedures developed by independentthird-party authorities, such as the

Institute of Electrical and ElectronicEngineers and UnderwritersLaboratories.

Interconnection Requirements

Most utilities and other electricityproviders require you to enter into aformal agreement with them beforeyou interconnect your wind turbine

with the utility grid. In states thathave retail competition for electricityservice (e.g., your utility operatesthe local wires, but you have achoice of electricity provider)you may have to sign a separateagreement with each company.Usually these agreements are writ-ten by the utility or the electricity

provider. In the case of private (inves-tor-owned) utilities, the terms andconditions in these agreements mustbe reviewed and approved by stateregulatory authorities.

Insurance

Some utilities require small windturbine owners to maintain liabilityinsurance in amounts of $1 million ormore. Utilities consider these require-ments necessary to protect them fromliability for facilities they do not ownand have no control over. Others

consider 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, therehas never been a liability claim, letalone a monetary award, relating toelectrical safety.

In seven states (California, Georgia,Maryland, Nevada, Oklahoma,Oregon, and Washington), lawsor regulatory authorities prohibit

This grid-connected,10-kW Bergeywind turbine

offsetselectrical powerconsumption fora small businessin Norman,Oklahoma.

BergeyWindpower/PIX07166


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utilities from imposing any insurancerequirements on small wind sys-tems that qualify for net metering.In at least two other states (Idaho,Virginia), regulatory authorities haveallowed utilities to impose insurancerequirements but have reduced therequired coverage amounts to levelsconsistent with conventional residen-tial or commercial insurance policies(e.g., $100,000 to $300,000). If yourinsurance amounts seem excessive,you can ask for a reconsideration from

regulatory authorities (in the case ofprivate investor-owned utilities) orthe utilitys governing board (in thecase of publicly owned utilities).

Indemnification

An indemnity is an agreementbetween two parties in which oneagrees to secure the other against lossor damage arising from some act or

some assumed responsibility. In thecontext of customer-owned generat-ing facilities, utilities often wantcustomers to indemnify them for anypotential liability arising from theoperation of the customers generating

facility. Although the basic principleis soundutilities should not beheld responsible for property dam-age or personal injury attributableto someone elseindemnity provi-sions should not favor the utility butshould be fair to both parties. Look forlanguage that says, each party shallindemnify the other . . . rather thanthe customer shall indemnify theutility . . .

Customer Charges

Customer charges can take a variety

of forms, including interconnectioncharges, metering charges, andstandby charges. You should nothesitate to question any charges thatseem inappropriate to you. Federallaw (Public Utility Regulatory PoliciesAct of 1978, or PURPA, Section 210)prohibits utilities from assessing dis-criminatory charges to customers who

have their own generation facilities.

Connecting to the Utility Grid:

A Success Story

This 10-kW Bergey wind turbine, installed ona farm in Southwestern Kansas in 1983, pro-duces an average 17001800 kilowatt-hours permonth, reducing the users monthly utility billsby approximately 50%. The turbine cost about$20,000 when it was installed. Since then, thecost for operation and maintenance has beenabout $50 per year. The only unscheduled main-

tenance activity over the years was repair to theturbine required as a result of a lightning strike.Insurance covered all but $500 of the $9000 cost ofdamages. The basic system parts include:

Bergey XL.10 wind turbine100-foot free-standing lattice towerInverter

WarrenGretz,NREL/PIX09634


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Can I Go Off-Grid?

Hybrid Systems

Hybrid wind energy systems canprovide reliable off-grid power forhomes, farms, or even entire com-munities (a co-housing project, forexample) that are far from the near-est utility lines. According to manyrenewable energy experts, a hybridsystem that combines wind andphotovoltaic (PV) technologies offers

several 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 less sunlight is available.Because the peak operating timesfor wind and PV occur at differenttimes of the day and year, hybrid

systems are more likely to producepower when you need it. (For moreinformation on solar electric or PVsystems, contact the Energy Efficiencyand Renewable Energy InformationPortalsee For More Information.)

For the times when neither the windturbine nor the PV modules are pro-ducing, most hybrid systems providepower through batteries and/or anengine-generator powered by conven-tional fuels such as diesel. If the bat-teries run low, the engine-generatorcan provide power and rechargethe batteries. Adding an engine-generator makes the system morecomplex, but modern electroniccontrollers can operate these systemsautomatically. An engine-generatorcan also reduce the size of the othercomponents needed for the system.Keep in mind that the storage capac-ity must be large enough to supplyelectrical needs during non-chargingperiods. Battery banks are typicallysized to supply the electric load forone to three days.

An off-grid hybrid system may bepractical for you if:

You live in an area with averageannual wind speed of at least9 mph (4.0 m/s)

A grid connection is not availableor can only be made through an

Regulation and

conversion

Load

Battery bank

AC or

DC

Windturbine

PV modules

Generator

Hybrid Power SystemsCombine multiple sources to deliver non-intermittent electric power

02979301m

A hybrid systemthat combines awind system with asolar and/or dieselgenerator canprovide reliable off-

grid power aroundthe clock.


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expensive extension. The cost ofrunning a power line to a remotesite to connect with the utility gridcan be prohibitive, ranging from$15,000 to more than $50,000 permile, depending on terrain.

You would like to gain energyindependence from the utility

You would like to generate cleanpower.

Living Off-Grid: A Success Story

This home, built near Ward, Colorado (at an elevation of 9000 feet), has beenoff-grid since it was built in 1972. When the house was built, the nearest util-ity was over a mile away, and it would have cost between $60K$70K (basedon 1985 rates) to connect to the utility lines. The owners decided to install a

hybrid electric system powered by wind,solar, and a generator for a cost of about$19,700. The parts of the system include:

Bergey 1.5-kW wind turbine, 10-ft (3-m)diameter rotor, 70-ft. (21-m) tower

Solarex PV panels, 480 watts

24 DC battery bank, 375 ampere-hours

Trace 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 bya well pump and washing machine. The

generator runs about 20% of the time, par-ticularly when the washing machineis 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.

JimGreen,NREL/PIX02796


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Glossary of Terms

AirfoilThe shape of the blade cross-section, which for most modern hori-zontal axis wind turbines is designed

to enhance the lift and improve tur-bine performance.

Ampere-hourA unit for the quantityof electricity obtained by integratingcurrent flow in amperes over the timein hours for its flow; used as a mea-sure of battery capacity.

AnemometerA device to measurethe wind speed.

Average wind speedThe mean windspeed over a specified period of time.

BladesThe aerodynamic surface thatcatches the wind.

BrakeVarious systems used to stopthe rotor from turning.

ConverterSee Inverter.

Cut-in wind speedThe wind speedat which a wind turbine begins togenerate electricity.

Cut-out wind speedThe wind speedat which a wind turbine ceases togenerate electricity.

DensityMass per unit of volume.

DownwindOn the opposite sidefrom the direction from which thewind blows.

FurlingA passive protection for theturbine in which the rotor folds eitherup or around the tail vane.

GridThe utility distribution system.The network that connects electricitygenerators to electricity users.

HAWTHorizontal axis wind turbine.

InverterA device that converts directcurrent (DC) to alternating current(AC).

kWKilowatt, a measure of power forelectrical current (1000 watts).

kWhKilowatt-hour, a measureof energy equal to the use of onekilowatt in one hour.

MWMegawatt, a measure of power

(1,000,000 watts).NacelleThe body of a propeller-typewind turbine, containing the gearbox,generator, blade hub, and other parts.

O&M costsOperation and mainte-nance costs.

Power coefficientThe ratio of thepower extracted by a wind turbine

to the power available in the windstream.

Power curveA chart showing awind turbines power output acrossa range of wind speeds.

PUCPublic Utility Commission, astate agency which regulates utilities.In some areas known as Public Service

Commission (PSC).PURPAPublic Utility RegulatoryPolicies Act (1978), 16 U.S.C. 2601.18CFR 292 that refers to smallgenerator utility connection rules.

Rated output capacityThe outputpower of a wind machine operatingat the rated wind speed.

Rated wind speedThe lowest windspeed at which the rated outputpower of a wind turbine is produced.

RotorThe rotating part of a windturbine, including either the bladesand blade assembly or the rotatingportion of a generator.

Rotor diameterThe diameter of the

circle swept by the rotor.Rotor speedThe revolutions perminute of the wind turbine rotor.

Start-up wind speedThe wind speedat which a wind turbine rotor willbegin to spin. See also Cut-in windspeed.


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Swept areaThe area swept by theturbine rotor, A = R2, where R is theradius of the rotor.

Tip speed ratioThe speed at the tip

of the rotor blade as it moves throughthe air divided by the wind velocity.This is typically a design requirementfor the turbine.

TurbulenceThe changes in windspeed and direction, frequentlycaused by obstacles.

UpwindOn the same side as the

direction from which the wind isblowingwindward.

VAWTVertical axis wind turbine.

Wind farmA group of wind tur-bines, often owned and maintained byone company. Also known as a windpower plant.

YawThe movement of the tower top

turbine that allows the turbine to stayinto the wind.

mailto:[email protected]


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Government Agencies

U.S. Department of Energys EnergyEfficiency and Renewable EnergyInformation Portal

www.eere.energy.govNational Climatic Data CenterFederal Building, 151 Patton AvenueAsheville, North Carolina, 28801-5001Phone: (828) 271-4800www.ncdc.noaa.gov

U.S. Department of CommerceNational Technical InformationService5285 Port Royal RoadSpringfield, Virginia 22161(800) 553-6847www.ntis.gov

Non-Government Organizations

American Wind Energy Association1101 14th St., NW12th Floor

Washington, D.C. 20005Phone: (202) 383-2500www.awea.org

Solar Energy InternationalShort courses on renewable energyand sustainable developmentPhone: (970) 963-8855www.solarenergy.org

Periodicals

Apples and OrangesMick SagrilloA comprehensive comparison ofavailable small wind turbines avail-able on the Home Power MagazineWeb site: www.homepower.comwww.homepower.com

Home Power Magazine

The definitive bimonthly magazinefor the homemade power enthusiast.Phone: (800)707-6586www.homepower.com

Videos

An Introduction to Residential WindSystems with Mick SagrilloA 63-minute video answering ques-

tions most often asked by homeown-ers as they consider purchasing andinstalling wind power systemsAmerican Wind Energy AssociationPhone: (202) 383-2500www.awea.org

Web Sites

Database of State Incentives forRenewable Energywww.dsireusa.org

Green Power Network Net MeteringNet metering programs are now avail-

able in more than 35 states.www.eere.energy.gov/greenpower/markets

Small Wind Talk on the WebAWEAs Home Energy Systems elec-tronic mailing list is a forum for thediscussion of small-scale energy sys-tems that include wind. To subscribe,send a subscription request to [email protected].



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A Strong Energy Portfolio for a Strong AmericaEnergy 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

Energys Office of Energy Efficiency and Renewable Energy invests in a diverse portfolio of energy technologies.

Produced for the U.S. Department of Energy by theNational Renewable Energy Laboratory,a DOE national laboratory

DOE/GO 102007 2411 A il 2007

For more information contact:EERE Information Center1-877-EERE-INF (1-877-337-3463)www.eere.energy.gov

Wind Powering America

www.windpoweringamerica.gov

U.S. Department of EnergyWind Energy Programwww.eere.energy.gov/windandhydro/

Contact:

Brian Antonich, M.S.

Small Wind Program AnalystWindustry2105 First Avenue SouthMinneapolis, MN 55404Phone: 612-870-3465Fax: 612-813-5612E-mail: [email protected]

Lisa Daniels2105 First Avenue SouthMinneapolis, MN 55404Phone: 612-870-3462Fax: 612-813-5612E-mail: [email protected]

Ron StimmelSmall Wind AdvocateAmerican Wind Energy Association1101 14th Street NW, 12th FloorWashington, DC 20005Phone: 202-383-2500Fax: 202-383-2505

E-mail: [email protected]/smallwind

small wind energy systems 110702042021 small wind guide

Documents