83781057 Flying Windmills or Flying Electric Generator Feg Technology

7/29/2019 83781057 Flying Windmills or Flying Electric Generator Feg Technology

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ADHIPARASAKTHI ENGINEERING COLLEGE

MELMARUVATHUR-603319

Department of

ELECTRICAL AND ELCTRONICS ENGINEERING

Paper on

FLYING WINDMILLS (OR) FLYING ELECTRICGENERATOR (FEG) TECHNOLOGY

Submitted by

A.Narendran

[email protected] Ph: +918124220089s

T.A.DHEVA BARATH

[email protected] Ph :+918608406713

R.KATHIRESAN

[email protected] Ph: +918124432425

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A BSTRACT

High Altitude Wind Power uses

flying electric generator (FEG)technology in the form ofwhat have been more popularlycalled flying windmills, is a

proposed renewable energyproject over rural or low -populated areas, to producearound 12,000 MW of electricitywith only 600 well clusteredrotorcraft kites that use onlysimple auto gyro physics to

generate far more kinetic energythan a nuclear plant .

According to Sky Wind Power;the overuse of fossil fuels and theoverabundance of radioactivewaste from nuclear energy plantsare taking our planet once againdown a path of destruction, forsomething that is more expensiveand far more dangerous in the

long run. FEG technology is justcheaper, cleaner and can providemore energy than thoseenvironmentally unhealthymethods of the past, making it adesirable substitute/alternative.

The secret to functioning HighAltitude Wind Power is efficienttether technology that reaches15,000 feet in the air, far higher

than birds will fly, but creatingrestricted airspace for planes andother aircraft.

The same materials used in thetethers that hold these balloons in

place can also hold flyingwindmills in place; and withenergy cable technology gettingever lighter and stronger. Flyingwindmills appear to be 90

percent more energy efficient inwind tunnel tests than their land-

based counterparts; that is threetimes more efficiency due tosimple yet constantly abundant

and effective high altitude windpower, available only 15,000 feetin the air by way of clusteredrotor craft kites tethered withexisting anti-terroristtechnologies like those used onthe Mexican/American borderradar balloons.

High Altitude wind power offersitself as a clean and more

powerful source of powergeneration than anythingavailable on-the grid at presentand if sky wind power corp. hastheir way, FEG technology andflying windmills will take thelead of a more sustainable futurewithin the decade.

Flying electric generators (FEGs)are proposed to harness kinetic

energy in the Powerful, persistenthigh altitude winds. Average

power density can be as high as20 kW/m2 in approximately 1000km wide band around latitude 300 in both Earth hemispheres. At15,000 feet (4600 m) and above,tethered rotorcraft, with four ormore rotors mounted on eachunit, could give individual ratedoutputs of up to 40 MW. These

aircraft would be highlycontrollable and could be flownin arrays, making them a large-scale source of reliable wind

power. The aerodynamics,electrics, and control of thesecraft are described in detail,along with a description of thetether mechanics. A 240 kW crafthas been designed to demonstratethe concept at altitude. It isanticipated that large-scale unitswould make low cost electricity

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available for grid supply, forhydrogen production, or forhydro-storage from large-scalegenerating facilities.

INTRODUCTION

Two major jet streams, the Sub-Tropical Jet and the Polar FrontJet exist in both Earthhemispheres. These enormousenergy streams are formed by thecombination of tropical regionsunlight falling and Earthrotation. This wind resource isinvariably available wherever the

sun shines and the Earth rotates.These jet stream winds offer anenergy benefit between one andtwo orders of magnitude greaterthan equal rotor-area, groundmounted wind turbines operatingin the lowest regions of theEarths boundary layer. In theUSA,Caldeira and ODohertyand Roberts have shown thataverage power densities ofaround 17 kW/m2 are available.In Australia, Atkinson et al showthat 19 kW/m2 isachievable.These winds areavailable in northern India,China, Japan,Africa, theMediterranean, and elsewhere.

Various systems havebeen examined to capture thisenergy, and these include

tethered balloons, tethered fixed-winged craft, tether climbing anddescending kites, and rotorcraft.

Our preferred option is atethered rotorcraft & tethered

balloons, tethered rotor craft -variant of the gyroplane, whereconventional rotors generate

power and simultaneouslyproduce sufficient lift to keep the

system aloft. This arrangement,using a twin-rotor configuration,has been described and flown atlow altitude by Roberts andBlackler (Fig. 1). More recentdevelopments have produced aquadruple rotor arrangement(Fig. 2). Commercialization ofthe quad-rotor technology couldsignificantly contribute togreenhouse gas reductions.

Tethered rotorcraft, withfour or more rotors in each unit,could harness the powerful,

persistent jet streams, and shouldbe able to compete effectivelywith all other energy productionmethods. Generators at altitudealso avoid community concernassociated with ground-basedwind turbine appearance andnoise. Bird strike problems arealso less. However, tetheredgenerators would need to be

placed in dedicated airspace,which would restrict otheraircraft. Arrays of tetheredgenerators would not be flownnear population centers unlessand until operating experienceassured the safety of such aconfiguration.

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Fig. 1. Photograph of early

two-rotor prototype in flight.

At this time, the besttether for the rotorcraft appearsto be a single, composite electro-mechanical cable made ofinsulated aluminium conductorsand high strength fiber. Whenoperating as a power source, two,four, or more rotors are inclinedat anadjustable angle to the on-coming wind, generally a 40degree angle. The wind on theinclined rotors generates lift,gyroplane-style, and forcesrotation, which generateselectricity, windmill-style.

Electricity is conducted down thetether to a ground station.

The craft simultaneouslygenerates lift and electricity.However, it can also function asan elementary poweredhelicopter with ground-suppliedelectrical energy, and with thegenerators then functioning asmotors. The craft can thus ascendor descend from altitude as anelementary, tethered helicopter.During any lull periods aloft,

power may be supplied tomaintain altitude, or to land on asmall groundbase. A groundwinch to reel the tether could beused to retrieve the craft in anemergency.

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Fig. 2. Rendering of Sky

WindPower Corp.s planned

240 kW, four-rotor

demonstration craft.

THE BEST SPOTS TO

PLACE FEGs

Based on the ERA-15reanalysis of the EuropeanCentre for Medium-RangeWeather Forecasts, we calculatedthe seasonal-mean, climate-zonewind power density fromDecember 1978 to February 1994.Computed power densities inhigh altitude winds exceed a 10kW/m2 seasonal average at the

jet streams typical latitudes andaltitudes. This is the highestpower density for a largerenewable energy resourceanywhere on Earth. It exceedsthe power densities of sunlight,near surface winds, oceancurrents, hydropower, tides,geothermal, and other large-scalerenewable resources. Forcomparison, Earth surface solar

energy is typically about 0.24kW/m2, and photovoltaic cell

conversion of energy intoelectricity has an efficiencyseveral times less than that ofwind power. High powerdensities would be uninterestingif only a small amount of

total power wereavailable. However, wind poweris roughly 100 times the powerused by all human civilization.Total power dissipated in windsis about 15 times 10W. TotalHuman thermal power consumption is about 13 times 10W. Removing 1% of highaltitude winds available energyis not expected to have adverseenvironmental consequences.

High altitude winds are avery attractive potential source of

power, because this vast energyis high density and persistent.Furthermore, high altitude windsare typically just a fewkilometres away from energyusers. No other energy sourcecombines potential resource size,density, and proximity so

attractively.

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The wind speed data from acrossthe globe is recorded at heightsfrom 263 feet to almost 40,000feet over the last 30 years, andcalculated which regions would

generate the most power.According to the study, Tokyo,Seoul, Sydney and New YorkCity all sit on a goldmine ofstratospheric wind power.

During the summer months,Delhi and Mumbai could also

benefit from sky high turbines.But unfortunately for India, thegusts die down in the fall and

spring, reducing the energydensity in the atmosphere.

DESCRIPTION OF THE

PREFERRED ENERGY

CONVERSION SYSTEM

The currently proposednew tethered craft consists offour identical rotors mounted inan airframe which flies in the

powerful and persistent winds.The tethers insulated aluminumconductors bring power toground, and are wound withstrong Kevlar-family cords. Theconductor weight is a criticalcompromise between power lossand heat generation. We proposeemploying aluminum conductorswith tether transmission voltages

of 15 kV and higher, becausethey are light weight for theenergy transmitted. To minimizetotal per kWh system cost andreduce tether costs, the designallows higher per meter lossesand higher conductor heatingthan doestraditional utility powertransmission. Depending onflight altitude, electrical losses

between the tether and theconverted powers insertion into

the commercial grid are expectedto be as much as 20%, and areincluded in energy cost estimatesdescribed in detail below.

The flying electric

generator units (FEGs)envisioned for commercial power

production have a rated capacityin the 3 to 30 MW range.Generators arrays arecontemplated for wind farms inairspace restricted fromcommercial and private aircraftuse. To supply all U.S. energyneeds, airspace for powergeneration is calculated to restrict

far less airspace than is alreadyrestricted from civil aviation forother purposes. While similar inconcept to current wind farms, inmost casesflying generator arrays may belocated much closer to demandload centers.

When operating as anelectrical power source, four ormore rotors are inclined at anadjustable, controllable angle tothe on-coming wind. In generalthe rotors have their open faces atan angle of up to 50 degree tothis wind. This disk incidence isreduced in various windconditions to hold the poweroutput at the rated value withoutexceeding the design tetherload.Rotorcraft can also function

as an elementary poweredhelicopter as described.The capacity, or

generating factor calculationsaccount for wind lulls or stormsduring which the generators must

be landed. However, theprojected capacity for flyingelectric generators is far higherthan for the best ground-basedwind turbine sites because of the

persistent winds at high altitudes.

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High altitude wind speeds andother conditions are measured at12 A.M. and P.M. at majorairports worldwide by radiosondeweather balloons, and are

reported on NOAA and othergovernment websites. It is thus

possible to calculate what thepast capacity of flying generatorsat those locations would have

been.The U.S. average

capacity factor would have beenabout 80% for craft flying at10,000 meters. At Detroitslatitude, the capacity factor was

calculated at 90%, at SanDiegos, 71%. This compares tocapacity factors of about 35

percentage for ground-basedwind turbines operating at the

best sites.Fig. 2 above and Fig. 3

below show the four-rotorassembly with four identicalrotors arranged, two forward, andtwo aft. The plan-form of therotor centerlines is approximatelysquare. Adjacent rotors rotate inopposite directions; diagonallyopposite rotors rotate in the samedirection.

In this particular fourrotor assembly, craft attitude in

pitch, roll, and yaw can becontrolled by collective rotor

pitch change. No cyclic pitch

control is needed to modify theblades pitch as they rotate, as isneeded in helicopter technology.This should help reducemaintenance costs. Rotorcollective pitch variation thenvaries the thrust developed byeach rotor in the formatdescribed below using GPS/Gyrosupplied error signal data.(1) Total craft thrust (and total

power output) is controlled by

simultaneously equal, collectivepitch action on all rotors.(2) Roll control is by differential,

but equal, collective pitch actionbetween the port and starboard

pair of rotors.(3) Pitch control is bydifferential, but equal, collective

pitch action between the fore andaft pair of rotors.(4) Yaw control, via differentialtorque reaction, is by differential,

but equal, collective pitchchanges on pairs of opposingrotors.

Ground-based windturbines experience surfacefeature turbulence not present athigh altitude. In addition,turbulence reaction is differentfor a FEG. Ground-basedturbines are, more or less, rigidlymounted on support towers. Evenwhen flexible units and

procedures are used, direct andgust-induced moment loads aresignificant for these ground-

based facilities. ConsiderableEuropean and US research anddevelopment has been directedtowards relieving load excursionsfrom nearsurfacewind gusts.

Flying electric generatorshave a great, inherent advantageover equivalent ground-based

facilities in their ability to reducegust loads. This is due to tethercable flexibility, both as built-inelasticity and as changeableshape (drape) under gustconditions. This flexibility verysignificantly alleviates gust loadsand torques applied to the rotors,gearboxes, etc. This means thatgust loads in flying units arereduced by more than an order of

magnitude compared to ground-based turbine gust loads. Sky

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WindPower Corp. has developedprograms that demonstrate thisgust alleviation process. SectionV details the flight performanceof these flying generators.

ELECTRODYNAMICTETHER

Tether is the connecting mediabetween the turbines up in the airto the grid on the surface.Electrodynamic tethers are longconducting wires, such as the onedeployed from the tether satellite,which can operate onelectromagnetic principles as

generators, by converting theirkinetic energy to electricalenergy, or as motors, convertingelectrical energy to kineticenergy. Electric potential isgenerated across a conductivetether by its motion through theEarth's magnetic field. Thechoice of the metal conductorto

be used in an electrodynamictether is determined by a varietyof factors. Primary factorsusually include high electricalconductivity, and low density.Secondary factors, depending onthe application, include cost,strength, and melting point.

An electrodynamic tetheris attached to an object, the tether

being oriented at an angle to thelocal vertical between the object

and a planet with a magneticfield. When the tether cuts theplanet's magnetic field, itgenerates a current, and therebyconverts some of the orbiting

body's kinetic energy to electricalenergy. As a result of this

process, an electrodynamic forceacts on the tether and attachedobject, slowing their orbitalmotion. The tether's far end can

be left bare, making electricalcontact with the ionosphere via

the phantom loop. Functionally,electrons flow from the space

plasma into the conductivetether, are passed through aresistive load in a control unit

and are emitted into the spaceplasma by an electron emitter asfree electrons. In principle,compact high-current tether

power generators are possibleand, with basic hardware, 10 to25 kilowatts appears to beattainable.

ELECTRICAL SYSTEM

DETAILS

Flying electric generatorsneed to ascend and remain aloftfor short periods on grid-sourcedenergy. In low-wind conditions,only a small proportion of outputrating as grid sourced energy isrequired to raise or maintain thecraft aloft. Voltages at theterminals of both thegenerator/motor and at the gridinterface need to be kept withindesigned tolerances and/or beadjusted by timely voltageregulation.

In a national regulatedelectricity market, such as thatfound in Europe and elsewhere, aSystem Impact Study (SIS) isrequired to connect a newgenerator to the grid if the

generators capacity is above aminimum level, e.g. 5 MW. Evennon-dispatchable embeddedgenerators require Grid SystemImpact Assessments. Thegenerator proponent usually paysfor the generator-to-grid networkconnection. Land and sealocations for generation fromrenewable energy sources,especially wind energy, are often

remote from the existing grid,hence, connection costs are often

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http://en.wikipedia.org/wiki/Tether_satellitehttp://en.wikipedia.org/wiki/Electrical_generatorhttp://en.wikipedia.org/wiki/Kinetic_energyhttp://en.wikipedia.org/wiki/Electrical_energyhttp://en.wikipedia.org/wiki/Electrical_energyhttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Electrical_conductorhttp://en.wikipedia.org/wiki/Electrical_conductivityhttp://en.wikipedia.org/wiki/Electrical_conductivityhttp://en.wikipedia.org/wiki/Densityhttp://en.wikipedia.org/wiki/Magnetospherehttp://en.wikipedia.org/wiki/Ionospherehttp://en.wikipedia.org/wiki/Phantom_loophttp://en.wikipedia.org/wiki/Tether_satellitehttp://en.wikipedia.org/wiki/Electrical_generatorhttp://en.wikipedia.org/wiki/Kinetic_energyhttp://en.wikipedia.org/wiki/Electrical_energyhttp://en.wikipedia.org/wiki/Electrical_energyhttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Electrical_conductorhttp://en.wikipedia.org/wiki/Electrical_conductivityhttp://en.wikipedia.org/wiki/Electrical_conductivityhttp://en.wikipedia.org/wiki/Densityhttp://en.wikipedia.org/wiki/Magnetospherehttp://en.wikipedia.org/wiki/Ionospherehttp://en.wikipedia.org/wiki/Phantom_loop


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50% of the total investment fornew generating capacity. Alsowhere a renewable energy sourcegenerator is not n-1 reliable foravailability, the Network

Connection Contracts usuallyinclude the costs of back-upsupply contingencies. Theserelate to network charges whenthe renewable generator is notsupplying.

Flying electric generatorsat altitude will have a relativelyhigh availability, around 80%.Reliability and peak premiumsales could be enhanced by a link

to a pumped storage facility foroff-peak filling/storage and peak-release energy sales anddelivery. Energy could be storedas hydrogen gas produced fromelectrolysis, or as water pumped-

back and re-released forhydroelectric generation.

Conventional ground-based wind energy systemsharvest only about 30%availability. Flying electricgenerators, in single units of 20MW or more, can achieve about80% availability with suitablesitting at land or sea locations.These generators at altitudeinvolve power transmission overlengths of between 4 and 8 km.Flying generator/tether voltages

between 11 kV and 25 kV ac

could be used on units of 30 MWat the most extreme altitudes.Also there are recent moderninnovations, which use

powerformers/motorformers. Thelatter, being developed byequipment suppliers such asABB, Siemens, Mitsubishi, etc.,would allow polymeric cablestators and tether voltages at say33 kVac or more. Grid

interfacing would then be easierat bulk energy levels.

The jet-stream locationcan drift north and south, soseasonal mobility from one

prepared site to another could bea feature of flying generators

grid utilization and optimization.This could be advantageous inseasonal summer/winterdemand-side managementthrough peak-matching generator

placement or relocations. Thiswould include matching seasonal

peaks for rural industries, such asgrape processing, cottonharvesting, and irrigation tourban air-conditioning etc.

Because arrays of flyinggenerators could move north orsouth to follow seasonal shifts inwind patterns or power demand,it could be advantageous to haveplug-in flying generators at

pre-arranged sites along anexisting grid 33 kV, or more,overhead feeder with minimalinterfacing. This would use, forexample, a HV Live Line HVBypass cable, sometimes calledTemporary cable, with a mobileor transportable High VoltageGenerator switchyard circuitBreaker /metering unit.

If the tether arrangementwere to contain three conductors,two could form the single-phasecircuit, while the third could bethe ground wire and control

cabling function. Three-phasebalance is then achieved byadding other nearby generatoroutputs to form single-phasecombinations for gridconnection. Alternatively, ifnecessary, a transformer withOLTC could be used, similar tothat used for monoplex or 50kVac duplex rail electric tractionsupply. This would be similar to

a rail traction supply transformerof 50 MVA and 132 kV three

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phase to 25 kV ac positive and25 kV ac negative to centre tapearth.

When using a shipboardsite, fixed ocean site, or a site

adjacent to a water-reservoirwhich is remote from the desiredFEG ground-surface connectionlocation, then the use of HVDCon tethers, withsurface/submarine cabling,should be considered incombination with a HVDCvoltagemotorformer/powerformerTMdesign. In addition, a units DC

motor/generator commutation byconventional brushes might befacilitated by more modernelectronic switching or bytriggered Vacuum Gaps (TVG).

Where an AC interfacingtransformer, or a HV AC /DCConverter Station (usually withan included transformer) isrequired for grid interfacingconnectivity, the economics ofscale would encourage moremultiple-unit connections.

A 60 MW to 150 MWgrid connection composed ofthree 20 to 50 MW airborne unitswith a powerformerTM, orHVDC AC/DC connection, can

perform as a synchronouscondenser, thereby adding ACgrid stability advantages in the

SIS. This will depend on gridsiting.Starting and retrieval

characteristics of flying units atspecific grid connections could

be an important SIS review item.A higher fault level at theconnection site is desirable for alarge motor start up. Generatorand tether performance dependon a good lightning storm

detection system. Surgeprotection schemes and

hardening of the control systemsare also under examination.

FLIGHT CONTROL USING

GPS AND GYRO DATA

Very accurate control is neededto precisely maintain a desired

position in the sky. GPS withgyroscopes is an ideal way to

provide the reference datanecessary to provide this control.

The Global PositioningSystem (GPS) consists of aconstellation of 24 satellites that

provide a continuous navigation

capability to users at any locationon (or near) Earth in all weatherconditions. With this system,currently operating with 29satellites, real-time, threedimensional position informationwith accuracies on the order of 5-10 m can be achieved.

Main error sources for thesystem include signal

propagation effects through theatmosphere, satellite orbit andtiming errors, and GPS receivernoise and signal reflection(multipath). When used indifferential mode, wheremeasurement corrections arecomputed at a GPS referencestation sited on a known location,accuracies can be improved quiteeasily to within a few meters

(DGPS).Although generally usedfor positioning and navigation,GPS can also be used for

platform attitude determinationand control. If three or more GPSreceivers and antennas aremounted on a platform, such asan FEG, the GPS carrier phasedata can be used to directlyestimate the roll, pitch, and

heading of the platform in real-time at a rate of 1-20 Hz [18].

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The attitude parameteraccuracy is primarily a functionof the signal multipath, andantenna separation (widerspacing yields higher attitude

accuracies Fig. 5). For theFEG, multipath could occurthrough the reflection of the

signals off the structure itself.However, when antennas areseparated by over 5 m on theFEG, attitude accuracy should be

better than 0.25 degree with

multipath present, which is wellwithin the required attitudecontrol specifications.

Fig.5. Relationship between the

achievable GPS-derived

heading and pitch accuracy andantenna separation

Two other factors mustbe considered when using GPSfor attitude determination andcontrol on the FEG. One is therigidity of the structure itself.Antennas with maximumseparation increase theachievable accuracy, but function

best with antennas located on a

rigid frame. A second factor issystem performance duringsignificant FEG nose-up angles.These angles range from 0degree when hovering up to 45degree when generating. Whilehovering, some GPS satellitesmay be obscured since the FEGmay block reception signalsalong the line-of-sight. Testsshow that attitude parameters can

still be estimated up to at least a

45 degree tilt, however, agyroscope used asan auxiliary attitude sensor,augments GPS availability andreduces noise. This has beenimplemented for manyapplications, and overallaccuracy is a function of the gyrosensor characteristics.

DETAILS OF A 240 KW

DEMONSTRATION CRAFT

Sky WindPower Corp.has completed the design for a

240 kW demonstration craft. Fig.2 is an isometric view of thiscraft.

Two units willdemonstrate the commercialviability, or otherwise, of theflying generator concept. Thesecraft have four, two-bladed rotorsturning in paired counter-rotationas described above. The rotorsare 10.7 m in diameter with

solidity of 5%, and the un-twisted blades are of

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conventional construction.Collective pitch control on therotors will be via electricactuators. The craft is designedfor operations up to 15,000 feet

(4600 m).The rotors are connected

to four separate gearboxes, whichdrive four motor/generator unitssupplied by AC Propulsion.These electrical machines are ofhigh armature speed to ensure asatisfactory power-to-weightratio. They are also electricallylinked to ensure that rotor speedsdo not vary with one another.

Typical armature speeds are24,000 rpm. The four powerunits are mounted in anelementary, low-drag fuselage offiber composite construction. Theall-up weight of each craft isestimated at around 1140 lbs(520 kg).

The electro-mechanicaltether is designed to transmit240kW at a voltage of 15kV. Theelectrical transmission efficiencyis 90%. The tether has twoinsulated aluminium conductorsembedded in a Vectran fibercomposite. The tethers specificweight is around 115 kg/km at adiameter of 10mm. A sample has

been constructed. The electricalground facility is configured fora DC supply to and from the

platform. The motor/generatorsare series connected.The crafts rated output is

developed at an 18.4 m/s windspeed at an altitude of 15,000feet (4600 m). The 11.5 m/sautorotation speed is at the samealtitude. The power consumptionin no wind (hover) at 15,000 feet(4600 m) is estimated to bearound 75 kW. Rotor speeds are

in the range of 130 to 300 rpm.The craft in this demonstrator is

designed to withstand a wind of35 m/s at 15,000 feet (4600 m).Throughout the operatingenvelope the crafts nose-upattitude varies in the range 10

and 45 degree. At no time duringthese operations does the bladeincidence on the retreating bladeexceed acceptable values at theconventional reference station,while tip Mach numbers neverexceed about 0.6.

Finally, there is somemerit in the view that the bestreturn on investment of thesecraft will be dependent on an

optimal, operating altitude. Atlow altitudes the average windvelocity wanes, while at higheraltitudes, adjacent to the jetstream core, the costs produce aless than beneficial return,

because of the need for a highertransmission voltage as thealtitude increases. Thus it will benecessary to find the best returnfrom an investment as a functionof the maximum operatingaltitude.This aspect will be developedand confirmed over 12 months offlights planned during thedemonstration program.

COST AND PERFORMANCE

PROJECTIONS AT THE

LARGE SCALE

A. Scalability Considerations

As discussed in sectionIV. , the tethered rotorcraft isinherently scalable in size andoutput, from small prototypeconfigurations of below 240 kW,through commercially viablesystems with competitive costs ofenergy, in the range of 3MW to30 MW per craft. Larger sizes

are more economical and mayutilize more than four rotors to

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maintain economy andmanageability of materials.

In this section we analyzecost and performance of a fourrotor, 3.4 MW (platform-rated)

configurations as might bedeployed in an array over varioussites in the U.S. Because oflosses described earlier, theactual output after conditioningwould be about 20% lower. The3.4 MW size was chosen becauseit is large enough to providecompetitive economics in a four-rotor configuration, and a rotordesign that is within the scope of

currently available methods andmaterials.

B. Weights and Costs

For cost illustrationpurposes, we use a 100 MWarray, comprised of 3.4 MWFEGs. The cost estimates are

based on 250 FEGs/yearproduction rate assuming priorproduction of 150 FEGs, inaccordance with NRELguidelines. A 3.4 MW platform-rated craft is estimated to weigh21,000 lbs (9500 kg) and cost$1,360,000. Adding groundsystems and production profits

brings the total to $2,260,000 per3.4 MW. The balance of stationcosts for the 100 MW array,including site preparation,

facilities and equipment, spareparts and construction is$4,210,000. Taken together theseinitial capital costs come to$71,200,000 per 100 MW.

C. Performance and Net

Annual Energy Production

Three design sites werechosen for analyzing the outputof the 100 MW array, Topeka,

Kansas, Detroit, Michigan andSan Diego, California. Topeka is

a "Great Plains" site, Detroit is asite where a great deal of energyis used, and San Diego isa site where capturing powerfrom the wind is not normally

thought to be practical.Net Annual Energy

Production kWh/yr is determinedby multiplying rated power by asite capacity factor. Capacityfactors for FEGs of the proposeddesign are based on windstatistics provided by NOAAradiosonde readings for majorairports near the design sites,normally taken daily at noon and

midnight. FEGs are to be flownat the most efficient altitude for

prevailing wind conditions, andcapacity factor is calculated inthe normal manner.

In making thesecalculations we have taken intoaccount the projected operatingcharacteristics of the 3.4 MWdesign through the range ofaltitudes up to 9,000 meters.Over the current range of interestthe rated wind speed has beenapproximated to the linearvariation (4), while the airdensity varies according to

NACA Standard Atmospherevalues.

Capacity factors havebeen computed for the threedesign sites using software we

developed, from datadownloaded from NOAA. Thedata is for the year startingSeptember 20,2000 and ending September 21,2001.V = 14m/s + 5.7m/s * H/10000m

Where,V Required wind speed in meters

per second to operate at rated

capacity, andH is Altitude in meters.

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Capacity factors forTopeka, Detroit, and San Diegoare 91%, 90% and 70%,respectively. As a reserve against

storms, maintenance andmechanical problems, we assume10% downtime. This gives NetAnnual Energy Productionfigures of 581 GWh/yr, 575GWh/yr and 447 GWh/yr,respectively for a 100 MW arrayat each of the three sites.

D. Projected Cost of Energy

Annual OperatingExpenses (AOE) include LandLease Costs (LLC), Operations& Maintenance (O&M) andLevelized Replacement/OverhaulCosts (LRC). AOE projectionsare necessarily subjective, sinceno plant like thiscurrently exists. O&M costs arederived from an $82,000/yrestimate for a 3.4 MW FEG,multiplied by 29.4 FEGs/100MW plant. Life-limitedcomponents are anticipated torequire replacement at 10 yearsand 20 years. Tether longevity isarisk. Replacement cost isestimated at 80% of the initialcapital cost for the whole system.Expressed in per kWh terms, the

AOE for the Topeka, Detroit, andSan Diego sites are estimated at$0.0102/kWh, $0.0103/kWh, and$0.0129/kWh,respectively.

TETHERED BALLOONS

AIRBORNE WIND

TURBINE

Airborne wind generator

An airborne wind turbine is adesign concept for a wind turbinethat is supported in the airwithout a tower. Airborne windturbines may operate in low orhigh altitudes; they are part of a

wider class of airborne windenergy systems (AWE)addressed by high altitude wind

power. When the generator is onthe ground, then the tetheredaircraft need not carry thegenerator mass or have aconductive tether. When thegenerator is aloft, then aconductive tether would be usedto transmit energy to the ground

or used aloft or beamed toreceivers using microwave orlaser. Airborne turbine systemswould have the advantage oftapping an almost constant wind,without requirements forsliprings oryaw mechanism, andwithout the expense of towerconstruction. Kites and'helicopters' come down whenthere is insufficient wind;kytoons and blimps resolve thematter. Also, bad weather such as

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lightning orthunderstorms, couldtemporarily suspend use of themachines, probably requiringthem to be brought back down tothe ground and covered. Some

schemes require a long powercable.and, if the turbine is highenough, an aircraft exclusionzone. As of 2008, no commercialairborne wind turbines are inregular operation.

Magenn Power Inc. is takingorders for their first commercial

product, a 100kW device with aprice tag of $500,000. (MARS-Magnenn Air RotorSystem(Tethered Balloons))

The Magenn machines arelarge ridged dirigibles that rotateon their tethers. The machinesrequire lots of helium to stayaloft and they are designed towork between 500 - 1000 ft.elevation.

Fig: Magenn Air Rotor System

(MARS)

(Tethered Balloon technology

based FEG)

Magenn is targeting the device asan alternative to diesel generatorsets for remote and emergency

power applications. Relativelylow-level operation of this

systems means that it can operatejust about anywhere withoutregard to airspace restrictions.

ESTIMATED COSTS:

Sky Windpower estimate thattheir technology will be capableof producing electricity for $0.02

per KWh, while a system ofraising a kite to a high altitude

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while turning a generator on theground, and then changing itsshape so that it can be drawn

back down with less energy thanit produced on the way up, has

been estimated to be capable ofproducing electricity for $0.01per KWh- both numbers beingsignificantly lower than thecurrent price of non-subsidizedelectricity.

ADVANTAGES &

DISADVANTAGES OF FEG

ADVANTAGES

Environment friendly

FEG technology is justcheaper , cleaner andhave more efficiency.

Low cost availability ofelectricity.

FEGs are unaffected bysurface featureturbulence.

The environment impactat high altitude areminimal with virtually novisual or noise intrusionand no bird strikes.

FEG wind farms wouldgive capacity (generating)factors around three times

greater than that fromconventional wind farms.

DISADVANTAGES

Restricted airspace forairplanes to fly.

Not suitable for highlypopulated areas, unless

there are adequate safetymeasures provided.

Seasonal variations in jetstreams speed across theglobe can create dull

periods for electricityproduction by FEG.

CONCLUSION

It has been shown that flyingelectric generators can harnessthe powerful and persistent windsaloft to supply electricity for gridconnection, for hydrogen

production or for hydro-storage.

Globally, upper atmosphericwinds provide an enormousresource for this application. Theenvironmental impacts at altitudeare minimal with virtually novisual, or noise intrusion and no

bird strikes. The proposedsystems lead logically torural/remote area installations inregions of restricted airspace.Full-scale facilities, usingindividual FEG units of rated

power around 30 MW, couldeasily form wind-farmsequivalent in output to regularcoal, gas and nuclear facilities.These wind-farms would givecapacity (generating) factorsaround three times greater thanthat from conventional wind-farms. The estimated bulk

electricity cost for the power soproduced is estimated to be of theorder of $20/MWh. High altitudewind power is not science fiction.It depends on currently availabletechnologies and engineeringknowhow, building on decadesof experience with wind turbineand gyroplane technologies.Harnessing high altitude windenergy, using a combination of

essentially existing technologies,appears to be thoroughly

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practical and suggests that thisenergy source can play animportant part in addressing theworld's energy and globalwarming problems.

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83781057 Flying Windmills or Flying Electric Generator Feg Technology

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