Energy&Sustainability

Lecture12:Hydroelectricity

February19,2009

EstimatingthePowerBeforeDecisiontoBuild

•  Empiricalrelationshipsbetweenflowrateandeitherwaterdepthorspeed(inparticularfordevelopedcountriessuchdatahasbeenaccumulatedforyears)

•  Alternativemethod:determinationofannualprecipitation,particularlysuitableforlargesystems,needtotakeintoaccountlossesduetoevaporation,leakage,vegetation(asmuchasthreequarters)

•  Timevariations•  Protectionagainst‘100yearflood’

Francisturbine

•  Picture:GrandCouleedam

•  Byfarthemostcommontypeinpresent‐daymediumorlarge‐scaleplants

•  Usedininstallationswhereheadisaslowas2morashighas300m

•  Radialflowturbines,waterflowisinwardstowardsthecenter

Francisturbine•  Picture:Threegorgesdam•  Completelysubmerged

•  Runsequallywellwithhorizontalorverticalaxis

•  Inmedium‐orhigh‐headturbines:flowischanneledthoughascrollcase(volute),curvedtubeofdiminishingsize(snailshell)withtheguidevanessetinitsinnersurface

•  Guidevanesguidewatertowardstherunner

Francisturbine •  Picture:Threegorgesdam•  Completelysubmerged

•  Runsequallywellwithhorizontalorverticalaxis

•  Shapeoftheguidevanes,runnerblades,andthespeedofthewaterarecritical:runmostefficientlywhenbladespeedonlyslightlylessthanwaterspeed

•  Aswatercrossesthecurvedbladesitisdeflectedsideways,losingitswhirlmotion

•  Wateralsodeflectedtotheturbineaxiswhereitfinallyflowsoutofthecentraldrafttube(seesketchonlastslide)

•  Pushesbladesintheoppositedirection:thisreactionforcetransfersenergyandmaintainstherotation

•  Waterarrivesattherunnerunderpressure‐>pressuredropthroughtheturbineaccountsforlargepartofthedeliveredenergy

Maximizingefficiency•  Efficienciesashighas95%,butonlyunderoptimum

conditions•  Maintainingtherightspeedanddirectionofthewater

relativetotherunnerbladesisimportant•  But:supposethedemandfalls

–  Outputpowercanbereducedbyreducingthewaterflow–  InFrancisturbinesthisisdonebyturningtheguidevanes,but‐>changestheangelatwhichthewaterhitsthemovingblades

‐>efficiencyfalls

•  Otherefficiencyloss:flowingwatercarriesawaykineticenergy–  ‐>partialremedy:flarethedrafttube+volumeflowstaysthe

same‐>speedofwaterdecreases‐>pressurebackattheexitofthetubeisreduced‐>pressuredropacrossitincreases

‐>energyextractedincreases

LimitsoftheFrancisTurbine•  Low‐headsituationsandhigh‐headsituations•  High‐head:meanhighwaterspeeds‐>highrotationspeeds‐>forsiteswithveryhigh‐headsFrancisturbinebecomesunsuitable‐>impulseturbine

•  Low‐head:lowwaterspeeds,largevolume‐>largerinputarearequiredandadaptationofbladestothereducedspeed‐>wideturbineentryandincreasinglytwistedblades‐>propellerturbine

Propellerturbine

•  Axial‐flowturbine•  Areathroughwhichwaterentersaslargeascanbe:itistheareasweptbytheblades

•  Suitableforverylargevolumeflowsandpropellershavethereforebecomeusualforverylowheadsofafewmeters

PropellerTurbine

Propellerturbine

•  Technicallysimplertoimproveefficiencybyvaryingtheangleofthebladeswhenpowerdemandchanges=>Kaplanturbines

•  Bladespeedis>>waterspeed(asmuchastwiceasfast)

•  Bladeangleneedstoincreasewithdistancefromcenterbecauseouterpartsmovefaster=>twistedshape

•  Semi‐Kaplan:guidevanesarenotadjustable

Impulseturbines •  Forsideswithheads>~250m:Peltonwheels

•  Asetofdoublecupsorbucketsmountedaroundtherim

•  Ahighspeedjetofwater,formedunderthepressureofahighhead,hitsthesplittingedgebetweeneachpairofcupsandinturnasthewheelspins

•  Thewaterpassesroundthecurvedbowlsandgivesupalmostallitskineticenergy

•  Powercanbevariedbyadjustingthejetsizeorbydeflectingtheentirejetawayfromthewheel

Impulseturbines

•  EfficiencyofaPeltonwheelisgreatestwhenthespeedofthecupsishalfthespeedofthewater

•  Cupspeeddependsonthewaterspeedandthewheeldiameterandthewaterspeeddependsonthehead

‐>optimumrelationshipbetweenthosethreefactors

•  Differencetoreactionturbinesbefore:isnotsubmergedanddoesn’tworkbasedonthepressuredifference,operatesinairatnormalatmosphericpressure,drivenbytheimpulseofthewaterfromthejet

PeltonWheelInputPower•  PotentialenergyofwatermassMandheightH:MgH,gaccelerationduetoGravity

•  Ifallpotentialenergyisconvertedintokineticenergy:MgH=½Mv2=>v=√(2gH),sothevolumeflowofaneffectiveheadHis

Q=A×√(2gH)

•  sotheinputpowerisP(kW)=1000×A×√(2gH)×g×H

=45A√H3

•  Numberofjetsisj:P(kW)=45jA√H3

PeltonWheelInputPower

RangesofApplication

SpecificSpeed

€

NS = n × PH 2 × H

TypeofTurbine Rangeofspecificspeeds

Francis 70‐500

PropellerorKaplan 350‐1000

Pelton 10‐80

n: rotation rate in rpm P: available power in kW H: effective head in m

Small‐ScaleHydroelectricity(SSH)•  Prevailingview:<~10MW,intheUS:<30MW•  Canalsobeclassifiedbytheavailablehead•  ManySSHplantsarerun‐of‐riverwithheadsofonlyafew

meters•  Nowadays:500‐1000MWarethenormforpower

stations(large‐scale)•  RenewedinterestinSSHdifferentreasonindifferent

regions:–  Industrializedcountries:Environmentalissues–  Developingcountries:stepwiseelectrification(localgridsystems)

•  Renewedinterestleadtotechnicalimprovements(standardizationofcomponents,electroniccontrols=>off‐the‐shelfsystemsatreducedcostsandmorereliable)

WorldSSHData•  SSHcapacityandoutputisrising•  Buthowrapidlynoteasytoestimate•  Noreliabledataespeciallyfromremoteareas•  China’s100000SSHplants(reportedintheearly1990s)havebecome43000(2003)

•  WECsurvey:bytheendof1999installedcapacityofSSH(<10MW)is18GWin38selectedcountries,includesAmericasandEurope,butnotChina

•  World‐wideincreaseestimates:1‐2GW/year•  Estimatedoperationalcapacityin2003:50‐60GW,about1%oftheworldelectricitygeneration

SSHinChina•  300millionpeoplederivetheirelectricityfromSSH(heredefinedas<25MWcapacity)

•  Intenseprogramoflocalelectrificationoverthepastfewdecades,inearly2002:totalinstalledcapacity>26GW

•  Chinadistinguishesmicro(<100kW),mini(100‐500kW),andsmall(0.5‐25MW)plants

•  Ofthe43000plants:90%microormini

•  but¾ofthetotaloutputcomesfromthe10%ofsmallinstallations‐>raisingconcernbecauseofenvironmentalimpactsofthese

SSHintheRestoftheWorld

•  >26GWfrominstallationwith<10MW,10GWinwesternEurope,3.5GWinJapan

•  SSHinmostcontextsismorecostlythanelectricityfromconventionalsources

•  IEA2003:itisclaimedthattechnicalimprovementswillbringthecoststoalevelwhichmakesSSHcompetitiveinsuitablelocations

•  StillmanyEuropeancountriesconcentrateonotherrenewableslikewindpowerandsolarPV

SSHintheRestoftheWorld

•  Elsewhereintheworld:considerableSSHpotentialremainsunused

•  Conceptofcompletewater‐to‐wiresystemsatremotesitesisestimatedtorepresentaworld‐widemarketofupto$5billionandhasattractedmanufacturersinEurope,theU.S.etc

SSHintheRestoftheWorld

•  Localmanufacturershavebeenencouragedaswell:ex.Nepal:–  manymountainstreamsaresuitableforhigh‐headplants

–  ‐>developmentoflocalindustryproducingextremelysmall‐scalesystems,transportablebyasinglepersononfoot

–  Peltricturbo‐generatorset:•  tinyPeltonwheeldrivingasimplegenerator

•  Operatesunderheadsof50‐70m,output:~1kW

•  Copiedinothercountries–  Unfortunatelyencouragingdevelopmentcametoahalt,

becauseofsocialunrestandtotaloperationalcapacityhasfallenbelow13MWrecordedin2000(WEC)

EnvironmentalConsiderations

•  Firstquote:

“Theenvironmentalimpactsofahydroelectricprojectmustbethoroughlyanalyzedsince,afteritiscompleted,theyareessentiallyirreversible”

EnergyResourcesandPolicy,R.C.Dorf,1978

EnvironmentalConsiderations

•  Secondquote:

“Theecologicaldamageperunitofenergyproducedisprobablygreaterforhydroelectricitythanforanyotherenergysource”

FinalReportoftheCommitteeonNuclearandAlternativeEnergySystems(CONEAS),1979

EnvironmentalConsiderations•  Thirdquote:“…carefullyplannedhydropowerdevelopmentcan,anddoes,makeagreatcontributiontoimprovingelectricalsystemreliabilityandstabilitythroughouttheworld.[It]willplayanimportantroleintheimprovementoflivingstandardsinthedevelopingworld,[and]makeasubstantialcontributiontotheavoidanceofgreenhousegasemissionandtherelatedclimatechangeissues”

SurveyofEnergyResources,Hydropower,WEC,2003

BenefitsofHydro‐electricity•  NoCO2

•  Noparticulatesorchemicalcompoundssuchasdioxinsthatareharmfultohumanhealth

•  Noemissionofradioactivity•  Nomajorexplosionsorfire•  Oftenassociatedwithpositiveenvironmentaleffectssuchasfloodcontrolorirrigation

•  Valuedamenityorevenavisualimprovementoflandscape

DeleteriousEffects

•  Hydrologicaleffects–waterflows,groundwater,watersupply,irrigationetc.

•  Othereffectsoflargedamsandreservoirs

•  Socialeffects

HydrologicalEffects

•  Divertingrivers:TheGabcikovo‐NagymarosProject

TheGabcikovo‐NagymarosProject•  Danubeisalreadyusedforhydroelectricitybutthisprojecton

theSlovak‐Hungarianborderhasbeencontroversial

•  1977:Agreementona880MWschemeincludingareservoirandacanaltocarrydivertedwatertoapowerplantinGabcikovoandasecondbarrageandplantatNagymaros

•  Workproceededforadecade•  Late1980s:politicalchanges,increasinglyvocaloppositionon

environmentalgrounds

•  1989:constructionstoppedonHungarianside

•  May1992:cancellation•  NewlyestablishedSlovak

statedeclaredcancellationillegal

TheGabcikovo‐NagymarosProject•  October1992:Slovakengineerscompletedthediversioninto

thenewchannel(18kmlong,withwallsrising15mabovethesurroundings)

•  Effects:–  fallinthewatertable–  Wellsdryingup

–  Vegetationdying–  Uniqueformsofwild‐lifeindanger

•  Reaction:-  Callsforlegallimitstodiversion

-  Artificialirrigationscheme-  1995:Slovakiaagreedto

reducediversion

TheGabcikovo‐NagymarosProject•  September1997:InternationalCourtofJustice

–  ruledthatbothcountriesactedillegally–  demandedthattheyshouldjointlynegotiateanewsolution–  demandedthatthissolutionmust‘accommodateboththeeconomic

operationofthesystemofelectricitygenerationandthesatisfactionofessentialenvironmentalconcerns’

•  StatusasofOctober2007:–  negotiationsbetweenthetwocountriesareongoing–  Presenthalfschemewithonlyonepowerstationfinancialdisaster

See also: http://en.wikipedia.org/wiki/Gab%C4%8D%C3%ADkovo_-_Nagymaros_Dams http://www.icpdr.org/icpdr-files/14200

OtherHydrologicalEffects

•  Evaporationfromexposedsurfaceofalargereservoirmaysignificantlyreducetheavailabilityofwatersupply

DamsandReservoirs

•  Constructionprocessitself:widespreaddisturbanceifonlyforafewyears

•  Effectsonafragileeco‐system:long‐lasting

•  Inanycase:Significantenvironmentalchanges

•  Viewdependsonthesituation•  DOEsurvey2001:primarypurposeorbenefitof– 35%ofdamsintheUSisrecreation– 2%ishydroelectricity

Catastrophes–  ‘Duringthe20thcentury,some200damsfailuresoutsideChinaarethoughttohaveresultedinthedeathsofmorethantenthousandpeople.AndwithinChina,inoneyearalone,1975,itisestimatedthatalmostaquarterofamillionpeopleperishedinaseriesofhydroelectricdamfailures’(L.Sullivan,1995,TheThreeGorgesProject…)

–  1971earthquakenearLosAngeles:LowerSanFernandoDamdamaged,hadthewallbeenatitsmaximumheight15milliontonnesofwatercouldhavebeenreleasedonthe80000inhabitantsinthevalleybelow

Silt

•  AswanDaminEgypt,builtinthe1960s– LanddownstreamnolongerreceivesthesoilsandnutrientspreviouslycarriedbytheannualNilefloods‐>agriculturalsystemlargelybeendestroyed

– Siltreducesitsusefulvolumeandhydropotential

•  HooverDam:70yearsold–  lostabout1/6thofitsusefulstorageinitsfirst30years

– LossratefellwhenGlenCanyonwasbuilt

MethaneCH4•  MorepotentgreenhousegasthanCO2•  VegetablesmatterdecaysinairtoCO2,butcandecay

anaerobically,producingmethane,whenlargeareaisflooded

•  WorldCommissiononDams(WCD)2000:‘Alllargedamsandnaturallakesintheborealandtropicalregionsthathavebeenmeasuredemitgreenhousegases[…]somevaluesforgrossemissionsareextremelylow,andmaybetentimeslessthanthethermaloption.Yetinsomecasesthegrossemissioncanbeconsiderable,andpossiblygreaterthanthethermalalternatives’

•  Tropicalclimates(e.g.Brazil):largescalehydromayemitasmuchgreenhousegasesannuallyasthermalalternativealthoughdatastillpatchy

Socialeffects

•  AswanandKaribadamsinEgypt:140000peoplerelocated

•  InallofChinaoverthesecondofthe20thcentury:10millionpeople

Economics

•  Relevantfactors:–  Initialcapitalcosts– Operationandmaintenancecosts– Predictedlifetime– Loadfactor– Discountrates– Costsofborrowingmoney

Economics•  Expectedlifetimeofmachinery25‐50years•  Expectedlifetimeofstructures50‐100years

•  Dominantfactorhowevercivilengineeringcostswhichcanvarygreatlyfromsitetosite:accountsfor65%to75%ofthetotalcosts

•  Environmentalandothercriteriaforalicense:15‐20%

•  So85‐95%aresitecosts•  Remaining:turbogeneratorsandcontrol‐systems(~10%)andoperationandmaintenance(1‐2%)

Economics•  Capitalcostsbetween$1200and$4000perkW,dependonwhere(‘green‐field’)

•  Refurbishingabouthalfthat•  Buthydroelectricplantshavelonglives,costsforaelectricityproducedbyaplantseveraldecadesagoisverysmallincomparison‐>investinginhydroelectricityseemslikeaprofitableinvestment

•  Whyaregasturbineplantspreferredinmanycountries?

Economics•  CompareCCGTplantandhydroplant(exactlythesameannualoutputandsametotallifetimecosts:construction,maintenance,operationfuel)

•  Hydroplanthasgreaterlifetimeoutput

•  Butfuturecostsandearningsarebothsubjecttodiscounting

•  ReducesfuelcostsforCCGTandreducesoutputearningsforboth

•  Hydroappearstohavehigherlifetimecostlater,netearningshigherforCCGT

Thearticles/talks

•  Article:4pagesexcludingfigures,doublespacing,withreferences

•  Talks:10to15minutes,about10slotsavailable

•  ExtraCredit:Youmayhandinanarticleinadditiontoyourtalk

Thearticles/talks

•  Introduction:Whatisthequestion/problemdiscussed?Whatisthecontext?

•  Scientificbackground•  Economicalbackground

•  Politicalbackground•  Prosandcons•  Conclusion•  Baseyourargumentationonsolidnumbersforwhichyoucangivereferences