4 The extraction of energy from Wind, especially in the form of Electricity, has enjoyedRenewed interest amongBoth utilities and governments.Wind energy is the fastest growingForm of energy today, up to400% increase in the past 20 years.
5 Wind turbines worldwide, with An installed capacity of Over 40,000 MW. Today, there are over 30,000Wind turbines worldwide, withAn installed capacity ofOver 40,000 MW.Wind power’s environmentalImpact is almost insignificant,Its main problem being visual“pollution,” although concernsAbout noise, communicationsInterference have been expressed.
7 With current wind construction, Bird mortality has fallen Substantially.Infact, bird collisions withAutomobiles and windows in highBuildings cause more birdDeaths, by a factor of a million!
8 US wind power estimate map Favorable California tax incentives resulted in major U.S. wind farmsAltamonte PassTehachapiSan Gorgonio PassOther turbines are located in Dakotas, Iowa, OR, Texas, Minnesota, NY, WA, Wyoming, Iowa, PA, VA, Vermont, etc.
10 Wind Statistics and Assessment Wind speed and direction are measured by an anemometerSpeed is derived from rotating cups or a spinning propeller driving an interrupter device or a small electric generatorData are logged electronically for later processingThe mean (average) and peak (gust) speeds are of the greatest importanceTurbulence may affect turbine efficiency, but yawing points the turbine into the average windTen-minute averages are used for power assessment, while gust studies may require two to ten points per second
11 Wind resources vary greatly with latitude, season, and surrounding terrain Extensive data and wind maps exist for wind prospectingAt the mesoscale level, topographic information is being used to create predictions of wind speed from scattered real dataAnemometers can be erected to obtain wind speeds in a likely locale for comparison to NWS long-term recordsAn alternative is to erect a small wind turbine to sample the energy and help determine where a large turbine should be placedWind resources may be excellent, but there is much more to installing a turbine
12 AnemometersAnemometers measure the speed and direction of the wind as a function of timeSpinning cups or propellerUltrasonic reflection (Doppler)Sodar (Sound detection and ranging with a large horn)RadarDrift balloonsEtc.Wind data are usually collected at ten-minute rate and averaged for recordingGust studies are occasionally used, and require fast sampling at a higher rate to avoid significant information loss (4 pts/gust)Spectral analysis indicates the frequency components of the wind structure and permits sampling frequency selection to minimize loss
13 Power Is Proportional to Wind Speed Cubed Recall that the average wind power is based upon the average of the speed cubed for each occurrenceDon’t average the speed and cube it!Cube the various speeds and average those cubes to estimate the powerThe Bergey wind turbine curve below indicates the energy output in nonturbulent flowRef.: Bergey
14 How to find the Wind Power A turbine power curve is cubic to start, but becomes intentionally less efficient at very high wind speeds to avoid damageAt very high winds, the power output may fall to zero, usually by design to prevent damage
15 Wind Energy Derivation Equations (also applies to water turbines)Assume a “tube” of air the diameter, D, of the rotorA = π D2/4 (could be rectangular for a VAWT)A length, L, of air moves through the turbine in t secondsL = u·t, where u is the wind speedThe tube volume is V = A·L = A·u·tAir density, ρ, is kg/m3 (water density ~1000 kg/m3, or 832 times more than air)Mass, m = ρ·V = ρ·A·u·t, where V is volumeKinetic energy = KE = ½ mu2
16 Wind Energy Equations (continued) Substituting ρ·A·u·t for mass, and A = π D2/4 , KE = ½·π/4·ρ·D2·u3·tTheoretical power, Pt = ½·π/4·ρ·D2·u3·t/t = ·ρa·D2·u3, ρ (rho) is the density, D is the diameter swept by the rotor blades, and u is the speed parallel to the rotor axisBetz Law shows 59.3% of power can be extractedPe = Pt·59.3%·ήr·ήt·ήg, where Pe is the extracted power, ήr is rotor efficiency, ήt is mechanical transmission efficiency, and ήg is generator efficiencyFor example, 59.3%·90%·98%·80% = 42% extraction of theoretical power
18 Advantages and Disadvantages of Wind Systems Wind systems, more than solar, provide variable energy as the weather changes rapidlyStorage is required to have energy available when the wind isn’t blowing and smooth it somewhat; batteries now exist for thisThis highly variable wind sends variable power to lines; each turbine has different outputs, reducing electrical line variability by the square root of the number of turbinesLarge utility size turbines now produce energy at a cost competitive with fossil fuels, but it takes a lot of them to get comparable energyA typical utility plant may have nearly 1000 MW or 1 GW peak power, while a “large” turbine might be rated at 4 MW at 25 mph wind --- that’s 250 turbines for rated wind speed!Largest now is the Enercon E-126: 126 m diameter and 7+ MW nameplate rating at Emden, Germany10 MW to come:
19 Overview: Wind Turbine Systems Wind energy turbines stem from early Persian panemones – a vertical axis spinner for grinding grainNot all power (59.3% max) can be extracted from the wind, but the turbines are relatively simple technologyThis presentation discusses the types and construction of wind turbinesWind turbine is a generic term, and it generally denotes an electrical power generator; windmills are specifically for grinding corn, wheat, or other grainsNASA used term “WECS” for Wind Energy Convertor SystemThere are also wind pumps for water; wind mills are for grinding grain
20 Early History5000 BCE (before common era): Sailing ships on the Nile River were likely the first use of wind powerHammurabi, ruler of Babylonia, used wind power for irrigationHero (Heron) created a wind-pumped organPersians created a Vertical Axis WT (VAWT) in the mid 7th Century1191 AD: The English used wind turbines1270: Post-mill used in Holland1439: Corn-grinding in Holland1600: Tower mill with rotating top or cap1750: Dutch mill imported to America1850: American multiblade wind pump development; 6.5 million until 1930; was produced in Heller-Allen Co., Napoleon, Ohio1890: Danish 23-meter diameter turbine produced electricity
21 Later History1920: Early Twentieth Century saw wind-driven water-pumps commonly used in rural America, but the spread of electricity lines in 1930s (Rural Electrification Act) caused their decline1925: Windcharger and Jacobs turbines popular for battery charging at 32V; 32Vdc appliances common for gas generators1940: 1250kW Rutland Vermont (Putnam) 53m system (center): 200kW Danish Gedser mill (right)1972: NASA/NSF wind turbine research1979: 2MW NASA/DOE 61m diameter turbine in NCNow, many windfarms are in use worldwide
22 Types of Turbines: HAWT & VAWT HAWT (Horizontal Axis Wind Turbines) have the rotor spinning around a horizontal axisThe rotor vertical axis must turn to track the windGyroscopic precession forces occur as the turbine turns to track the windVAWT (Vertical Axis Wind Turbines) have the rotor spinning around a vertical axisThis Savonius rotor will instantly extract energy regardless of the wind directionThe wind forces on the blades reverse each half-turn causing fatigue of the mountingsThe two-phase design with the two sections at right angles to each other starts more easilyThis is available in parts for experimenterPhoto by F. Leslie, 2001
23 HAWT Examples Charles Brush (arc light) home turbine of 1888 (center) 17 m, 1:50 step-up to drive 500 rpm generatorNASA Mod 0, 1, 2 turbinesThe Mod-0A at Clayton NM produced 200kW (below left)projects/Nybroe%20Home/l
24 Horizontal Axis Wind Turbines (HAWT) Sailwing, 1300 A.D.ExperimentalWind farmAmerican Farm, 1854Dutch with fantail1.8 mModern TurbinesDutch post mill75 mRef.: WTC
25 Darrieus troposkein blades (jump rope) Savonius rotor ~1925 VAWT ExamplesDarrieus troposkein blades (jump rope)Savonius rotor ~1925Madaras rotor using the Magnus EffectRotors placed on train cars to push them around a circular trackVortex TurbineThe SANDIA Darrieus turbine was destroyed when left unbraked overnight
26 Location of Turbines: USA States If wind projects are measured by commercial success, the Southeast USA isn’t the best area to use!2003showing MW in each state9/30/2007
27 The wind energy varies from trivial to useful to disastrous! Power Is Proportional to Wind Speed CubedRecall that the average wind power is based upon the average of the speed cubed for each occurrenceThe wind energy varies from trivial to useful to disastrous!Precautions are needed to protect the turbineEnergy is power times the time of energy persistenceRef.: Bergey
28 Turbine Power CurvesSince power is negligible at low speeds of 6 mph or less, it doesn’t matter that the turbine won’t start thenThe distribution of wind speeds indicates the relative probability that wind will exceed a given valueMuch of the power occurs in the top 30% of the wind speeds, so these speeds set the design parametersFor this reason, it is desirable to keep the turbine extracting power in strong winds while still protecting it from damageLarge turbines are turned out of the wind at approximately 30 to 35 mph or their blades are turned (rotated) into the wind to produce less torque
29 Rotor hub is high above turbulent ground wind layer Large Systems: Size and NumbersRotor hub is high above turbulent ground wind layerProduction line assembly660kW to 7 MW power modelsGroups of 10 to 1000s of turbinesAttractive, modern appearance
30 Large Systems: Examples & Locations WA: FPL Stateline and Vansycle Ridge Wind FarmsHI: Honolulu, OR: Wasco, TX: McCamey, AmarilloNM: Clayton; near House NMMany others in IL, NY, OH, PA, CO, WV, WY, IA, PA, MN; see AWEA websiteNACELLE 1 MWThe nacelle is the enclosure at the top of the tower
31 State Line Wind Farm, WA & OR This telephoto from the anti-Cape Wind Project group, “Save Our Sound”, shows a string of turbines from the end to emphasize ugliest visual effectWindfarm companies usually show a side view of the string, which looks less crowded and interesting
32 Offshore Wind FarmsWind farms are often placed offshore a few miles because the winds are unimpeded (have a good “fetch”, or upwind distance, of the wind)Depths of less than 60 feet are preferableUndersea cables carry power to shore terminalsThe turbines are clearly visible if close and often are attacked by NIMBYs who want their “viewscape” unblemishedThe proposed Cape Wind farm would appear a finger-width high at arm’s lengthNIMBYs want only things found in nature like ships, yachts and windsurfers (John Kerry) in view
33 Cape Wind PoliticsThe Cape Wind Project of 170 turbines has many detractors who don’t want to see wind turbines on Horseshoe Shoal offshore of Cape Cod MAEnvironmentalist organizations are divided as to lower GHGs with clean wind power instead of coal or possible bird/bat strikes or other disturbancesGreenpeace is supporting the project; Audubon and Humane Society protest it; Sierra Club waffles on itRobert Kennedy, Jr. opposes the windfarm although the Natural Resources Defense League organization that employs him as their lawyer endorses windfarmsA heavily funded, posh website by protests the project
34 From the “Save Our Sound” Website Area is within view of nearby islands with expensive homes
35 From the “Save Our Sound” Website I presume this family is looking in horror at the simulation?
36 Cape Wind Construction Plan Pile-climbing barges are used to support the lift cranes and transport the rotorThe barge is jacked up to get a steady platformA tall crane lifts the rotor to be pulled into place and bolted onNot good for a windy day!
37 Large Turbine Components sgroup.cms.schunk-group.comLarge Turbine ComponentsNote railingRef.: windfarm/index.asp?i=2
38 Rotor AerodynamicsThe blades of an airplane propeller are curved on the front and flatter on the back towards the planeThe blades not only pull the plane forward by their angle, but the airflow over the curve develops lift or pulling forces that move the plane forwardTurbine rotors are reversed with the curve at the downwind side and with the angle of the blade reversed; wind hits the flatter sideA model airplane propeller can’t be used as a turbine blade since the key dimensions are backwards from a wind rotorPossibly a propeller manufacturer could be persuaded to make a “standard” profile blade that could be used in 2s, 3s, or 4sModel helicopter blades can be used since they are just one bolt-on blade instead of a double-sided propeller; hub sets the angle
39 Airfoils and their Design Propellers pull the rotor into the air, which is why the British call them “airscrews”Rotors for wind turbines are pushed by the wind, and use lift on the downwind side of the blades to pull them around the shaft fasterBlade numbers vary from 2 to perhaps 5Blade solidity is the percent of the disk area that is solid with bladesThrust force is the force of the wind pressing back on the rotor that the tower must resistStall occurs when the airstream over the blade separates due to an excessive angle of attack
40 Turbine Installation Turbine installations consist of many steps Land acquisitionLocal permittingPossibly provide living quarters for crewsBuild a control and operations centerProvide maintenance shopsInstall the turbine(s)Build a switchyardConnect the turbines through underground wiring to the distribution switchyard
41 Large TurbinesLarge turbine installations usually require new road access for trucks to bring the partsMonopod towers may be in long sectionsTurbine blades are in one piece and may require special long trucks and long-radius-turn roadsDeep (~20 ft) concrete foundations are poured, the tower assembled, and the complete nacelle mounted on topThe blades are hoisted by crane and bolted to the rotor hub on the nacelleSometimes, the blades and hub are hoisted together
42 Small Turbines Small turbines weigh from 10 to 1000 pounds Manual or crane lifting may be usedA “gin pole” may be clamped to a tower to hold a hoisting pulley overhead to lift tower sections or the generatorSome turbines are light enough that the turbine and tower may be erected as a unitTowers may also be designed to tilt over for turbine maintenance
43 Turbine Power Control Turbine States Stop Slow rotor, feather blades (turn into wind), apply brakesStartRelease brakes, set blade attack angle, continually yaw nacelle to wind direction, at speed engage power contactorsStorm ProtectionYaw to 90° from wind, feather blades, apply rotor brakes, continue to yaw to avoid wind on turbine rotor diskMaintenanceLock out to “Stop” state to protect workers from backfeed from wiring, engage interlocks, set warning indicators
44 Wind modeling provides energy density mapping Wind Turbine Siting and InstallationTurbine siting is somewhat of an art, but science is providing tools that speed the selectionWind modeling provides energy density mappingAccurate siting strongly determines the economic and energy success of the systemEnergy storage is likely to be in batteries for the foreseeable future; more exotic methods are slow in reaching a cost-effective market entrySince wind energy is the fastest developing energy source, the economic fall of prices will speed its adoption in areas where the wind is powerfulWind energy is about $2.50/W and comparable with a new coal power plant
45 Grants and AssistanceIn some cases, grants and/or anemometer loans from a state or the US Federal government may be approved to stimulate interest in wind energy systemsSome states provide a rebate of up to 50% of the costAnemometers for energy testing might consist only of a wind distance indicator with a digital readout of miles of wind (difference the readings & divide by time elapsed)The tower used should approximate the height of the turbine rotor, but the tower may be a temporary mast like a television antenna would be mounted onSome experts advise that it is better to simply put up a substantial tower and mount a small wind turbine on itWind energy can be used from the small turbine before buying a larger size070212
47 Conclusion: Wind Theory The theory of wind energy is based upon fluid flow, so it also applies to water turbines (water has 832 times the density)While anemometers provide wind speed and usually direction, data processing converts the raw data into usable informationBecause of the surface drag layer of the atmosphere, placing the anemometer at a “standard” height of 10 meters above the ground is important; airport anemometer heights often historically differ from 10 metersFor turbine placement, the anemometer should be at turbine hub heightThe average of the speeds is not the same as the correct average of the speed cubes!The energy extracted by a turbine is the summation of each speed cubed times the time that it persisted070212
48 Conclusion: Wind Turbine Theory The rotor must be matched to the generator or alternator to obtain the maximum extracted energy over a yearAlthough most turbines won’t rotate until the wind speed reaches 6 mph; there is no significant energy lost below this speed; power is proportional to the cube of speedIf turbine placement can increase the wind speed by 10%, the power increases by 33%All parts must be designed to survive high winds, say 130 mph; this is important to survive a hurricaneWe lowered our 10-ft diameter turbine on Roberts Hall and removed the blades for Hurricane JeanneThe anemometer remains on the WFIT tower during hurricanes so speed can be read or logged