Renewable Energy Research Lab: wind technology_1


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From windy locations by installing 'wind farms' the turbines rotating due to gusty winds will produce Electric power that can be stored in battery banks and utilized. Initial careful evaluation and implementation involves capital investment that may give good pay back in power.

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Renewable Energy Research Lab: wind technology_1

  1. 1. This introduction to wind power technology ismeant to help communities begin considering orplanning wind power. It focuses on commercial andmedium-scale wind turbine technology available inthe United States.We also recommend a visit to a modern wind powerinstallation – it will answer many of your initialquestions, including size, noise levels, footprint, andlocal impact. Some possible field trips are listed onthe back page.Wind Power Technology forCommunitiesWind power can be divided into three size ranges,which are used for different applications. The focusof this series of fact sheets is medium and commer-cial-scale wind power. The size is chosen differentlydepending on the turbine’s purpose. Typical sizes inthe three ranges available in the US are:Residential: below 30 kWChoose a size based on electrical loadDiameter: 1 - 13 m (4 - 43 ft)Height: 18 - 37 m (60 - 120 ft)Example: 20,000 kWh/yearMedium: 30 - 500 kWMay be sized to a load. Typically used whenthere is a large electrical load.Diameter: 13 - 30 m (43 - 100 ft)••••••Height: 35 - 50 m (115 - 164 ft)Example: 600,000 kWh/yearCommercial scale: 500 kW - 2 MWUsually fed into the grid, not sized to a singleloadDiameter: 47 - 90 m (155 - 300 ft)Height: 50 - 80 m (164 - 262 ft)Example: 4,000,000 kWh/yearFor comparison, an average Massachusetts householduses 7,200 kWh/year••••••Wind Power:Wind Technology TodayWind Power on the Community ScaleRenewable Energy Research Laboratory, University of Massachusetts at AmherstCommunityWind PowerFact Sheet #RERL—MTCCommunity WindFact Sheet SeriesIn collaboration with the Mas-sachusetts Technology Collabor-ative’s Renewable Energy TrustFund, the Renewable Energy Re-search Laboratory brings you thisseries of fact sheets about WindPower on the community scale:TechnologyPerformanceImpacts & IssuesSitingResource AssessmentWind DataPermittingCase Studies1. Power Today1Inside this Edition:TechnologyIntroduction p. 1Wind Power Today p. 1Size ranges p. 1Vocabulary p. 2Power & Energy p. 3Sources for Teachers &Kidsp. 4Nearby Wind Installations p. 4For More Info p. 4Wind power is a growing industry, and the technologyhas changed considerably in recent decades. Whatwould a typical commercial-scale* turbine installedtoday look like?Design: - 3 blades- Tubular towerHub-height: - 164 - 262 ft (50 - 80 m)Diameter: - 154 - 262 ft (47 - 80 m)Power ratings available in the US:- 660 kW - 1.8 MW* Other scales are discussed below.Size RangesWhat do we mean here when we say “community-scale wind power”?A wind turbine’s height is usuallydescribed as the height of the cen-ter of the rotor, or hub.Example annual production is for comparison only. Basedon sea-level mean winds of 7m/s (15.6 mph); manufactur-er’s data for the following turbines: Residential: BergeyXL-S (7.5kW); Medium: Fuhrländer FL 250 (250 kW);Commercial: GE 1.5 SL (1500 kW) .The focus ofthis series offact sheets ismedium- andcommercial-scale wind.
  2. 2. Page 2CommunityWind Power Fact Sheet #1The Vocabulary of Wind PowerRenewable Energy Research Laboratory, University of Massachusetts at AmherstTurbine: a turbine is a device that converts the kinet-ic energy of a moving fluid into rotational energy(engineers call both liquids and gases “fluids” –i.e. things that flow). A wind turbine’s blades useaerodynamic lift and drag to capture some of thewind’s energy and turn the generator’s shaft.The main parts of a typical wind turbine are:- Rotor: a wind turbine’s blades and the hub to whichthey attach form the rotor.- Nacelle: the frame andhousing at the top of thetower. It protects the gear-box and the generatorfrom weather, and helpscontrol the mechanicalnoise level.-Tower: a steel structure,typically tubular, with aladder up the inside formaintenance access.-Base or foundation: made ofconcrete reinforced withsteel bars. Typically eithera shallow flat disk or adeeper cylinder.Other useful terms are:Yaw: commercial-scale tur-bines have a motor toyaw, or turn the rotor toface into the wind.At highwind-speeds, they yawout of the wind to protectthemselves.Up-wind turbines: Moderncommercial turbines yawthemselves so the rotor isfacing into the wind, i.e.upwind of the tower.Cut-in speed: the wind speedat which a wind turbinebegins to generate elec-tricity. Typically 4 m/s(9 mph) for commercialwind turbines.Cut-out wind speed: the highwind speed at which theturbine must shut downand turn perpendicular to the wind to protect it-self from being overpowered. Typically 25 m/s(56 mph)Variable-speed turbines: Some turbines incorporatepower electronics that allow them to optimizetheir power output by varying their speed, for in-stance, from 10 to 20 rpm. Other types vary theirspeed little or not at all. Variable speed turbinesincrease their rotation speed in higher winds inorder to optimize the aerodynamic efficiency.Constant speed turbines keep their rotation speedmore or less constant while the power and thetorque change.Variable bladepitch: many tur-bines can changethe angle of theirblades to optimizeperformance.Horizontal axis:All commercial-scale turbines to-day have the rotorturn around a hor-izontal axis. His-torically, verticalaxis turbines havebeen tested, suchas the “Darrieus”egg-beater design,but have not beenas efficient or ableto survive highwinds.Penetration: Theamount of windenergy in a givenarea of the grid,as a percentage oftotal production.In the US, windpenetration is un-der 1%. North-ern Germany andparts of Denmarkhave penetrationsof around 20%(2003 figures).If you come acrossother unfamiliarterms or ideas,the Danish WindIndustry Asso-ciation offers clear technical information in their“Guided Tour on Wind Energy”:
  3. 3. Wind Technology Today Page 3The Power in WindThe first law of thermodynamics tells us that energycan neither be created nor destroyed, but it can changeforms. Anything that is in motion – such as movingair – contains a form of energy we refer to as kineticenergy. Slow-ing air down re-duces its kineticenergy and thatenergy has togo somewhere.Wind turbiness l o w w i n ddown and con-vert some of theenergy to mechanical and electrical energy.Kinetic energy is:KE = ½ mV2where m stands for mass (in kg) and V stands for ve-locity (in m/s). This allows us to calculate the amountof power in moving air. The power of the wind pass-ing perpendicularly through a circular area is:P = ½ ρV3AWhere:P = the power of the wind (in Watts).ρ = rho = the density of the air (in kg/m3)(1.225 kg/m3for dry air at sea level)V = the velocity of the wind measured in m/sA = π r2= the area swept by the circular rotor,in square meters, andπ = pi = 3.1416...r = the radius (half the diameter) of the rotor(in meters)Betz’s Limit on what we can extractA wind turbine slows air down, but it cannot re-move 100% of the air’s kinetic energy – obviouslythe air cannot stop completely, or else it would pileup behind the turbine. In 1919, German physicistAlbert Betz figured out that the upper limit to theamount of energy you can capture from the wind is16/27 or about 59%. In practice, all real wind tur-bines extract less than this hypothetical maximum.The Power from a Wind TurbineThe power a turbine actually gets from the wind is:P = Cpη ½ ρV3AYou can see that we have added two things to theoriginal equation of the power in the wind:Cp= the turbine’s power coefficientη = eta = the turbine’s mechanical & electricalefficiencies.Cpmust be less than the Betz limit. In practice, itvaries with wind speed, turbulence and operatingcharacteristics; for example it could be around 44%for a commercial-scale turbine, in winds of 10 m/s.A typical overall efficiency, η, would be in the rangeof 90%.To estimate the power output of a given commercialturbine, we do not have to use the power equation;rather we use power curves supplied by the manu-facturer.What does the power equation tell us?Even though we do not use the power equation tocalculate power output of a particular turbine, thepower equation tells us useful information aboutsignificant factors that determine what we can getfrom a wind turbine:V3: The power available in the wind is proportionalto the cube of the wind speed. There is much moreenergy in high-speed winds than in slow winds. Smallchanges in wind speed make big changes in power.A : Power is proportional to the swept area, and tothe square of the diameter. Doubling the diameterquadruples the available power.ρ : Air density matters too. The lower density ofwarmer air, and air at higher altitudes somewhatreduces the power available in the wind.The Power & Energy in WindRenewable Energy Research Laboratory, University of Massachusetts at AmherstEnergyis the ability tochange oneself orone’s surroundingsPoweris a rate of using orproducing energy.Power = energy / timeUnits of MeasureA kilowatt-hour (kWh)is a unit of EnergyA kilowatt (kW)is a unit of Power.So are watts,megawatts, andhorsepower.Wind Turbine Power Curve-2004006008001,0001,2001,4001,6000 5 10 15 20 25 30Wind Speed (m/s)Power(kW)
  4. 4. Mass. Technology CollaborativeMass. Renewable Energy Trust75 North DriveWestborough, MA 01581508–870– Governors DriveAmherst, MA 01003413–545– ofMassachusettsat AmherstRenewableEnergyResearchLaboratoryCommunity Wind Power Fact Sheet #1Page 4For More InformationWind Energy Explained: Theory, Design andApplication, Manwell, McGowan, & Rogers,Wiley, 2002• RERL’s website: includesthis and other fact sheets,• The Danish Wind Industry Association’s websitehas thorough and very accessible technical infor-mation:• American Wind Energy Association:• Renewable Energy Policy Project:• Case studies of community wind:• The Database of State Incentives for RenewableEnergy (DSIRE) has a thorough list of Mas-sachusetts incentives for wind power: Lake, Iowa, has 2 wind turbines on their schoolgrounds. The schools use the generators in their cur-ricula: Danish Wind Industry Association includes asection for kids: has curricula and links to otherresources. So do and has curricula, as well as a kids’ link page: books offers wind energy activities foryoung children in their Magic School Bus website,, includes introductions to wind energy on vari-ous levels.See RERL’s website,, for a more complete list of teacher resources.Sources for Teachers & KidsRenewable Energy Research Laboratory, University of Massachusetts at AmherstA field trip to an installation is one of the bestintroductions to modern wind power.▪ Hull, MA, 660 kW turbine at the high school,accessible any time.▪ Searsburg, VT, tours in summer, (802)▪ Madison, NY, 11.5 MW,▪ Harbec Plastics, Ontario, NY, 250 kW turbine▪ Fenner project in Madison County, NY, 30 MW, & www.madisontourism.comNearby Wind InstallationsFuhrländerFL250,29.5mdiameter,photocourtesyLoraxEnergyCommunity-owned wind turbine in Spirit Lake, IA