Energy‐Water Nexus in Texas

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THEUNIVERSITYOFTEXASATAUSTIN|ENVIRONMENTALDEFENSEFUND



Energy‐WaterNexusinTexas



AshlynnS.Stillwell

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CareyW.King



MichaelE.Webber



IanJ.Duncan



AmyHardberger

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

THEUNIVERSITYOFTEXASATAUSTIN|ENVIRONMENTALDEFENSEFUND



Energy‐WaterNexusinTexas



AshlynnS.Stillwell



CareyW.King

1



MichaelE.Webber

1



IanJ.Duncan

1



AmyHardberger



April2009



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Affiliations

TheUniversityofTexasatAustin

EnvironmentalDefenseFund

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Acknowledgements

TheauthorswouldliketoacknowledgethecontributionsofEliotMeyerandDesmondLawleratthe

UniversityofTexasatAustin.ThisworkwassponsoredbytheEnergyFoundationandtheTexasState

EnergyConservationOffice.

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TableofContents

ExecutiveSummary ............................................................................................................................. 1

Introduction ...................................................................................................................................... 3

Chapter1. WaterforEnergy ........................................................................................................... 5

ElectricityGenerationandUse ................................................................................................................. 5

CoolingTechnologies ................................................................................................................................ 6

TypesofPowerPlants............................................................................................................................. 13

Chapter2. EnergyforWater ......................................................................................................... 20

PublicWaterSupplySystems.................................................................................................................. 20

SourceCollectionandConveyance..................................................................................................... 20

Treatment ........................................................................................................................................... 21

Distribution ......................................................................................................................................... 22

ResidentialWaterUse......................................................................................................................... 23

WastewaterSystems .............................................................................................................................. 24

CollectionandConveyance................................................................................................................. 24

Treatment ........................................................................................................................................... 24

Discharge............................................................................................................................................. 25

Chapter

3. Energy‐WaterNexusinTexas ...................................................................................... 26

ElectricityGenerationfromTexasPowerPlants .................................................................................... 26

WaterConsumptionandWithdrawalsofTexasPowerPlants ............................................................... 26

EnergyforWaterandWastewaterTreatmentSystemsinTexas........................................................... 27

Chapter4. FutureEnergyandWaterUseinTexas......................................................................... 30

ElectricityDemandProjections............................................................................................................... 30

WaterDemandProjections.....................................................................................................................33

ConservationofEnergyandWater......................................................................................................... 33

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ii

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Chapter5. PolicyDiscussion ......................................................................................................... 36

Carbon,Water,andEnergy:TensionsandPolicyTradeoffs..................................................................36

EnergyPoliciesHaveMixedWaterImpacts .......................................................................................36

WaterPoliciesMightHaveDetrimentalCarbonImpacts ...................................................................37

CarbonPoliciesMightHaveDetrimentalWaterImpacts ................................................................... 37

ClimateChangeImpactsonWaterResources.................................................................................... 38

Conclusions .................................................................................................................................... 40

FutureWork ............................................................................................................................................ 41

References .................................................................................................................................... 42

AppendixA:Glossary 

ofTerms.......................................................................................................... 47

Energyterms ...........................................................................................................................................47

Waterterms............................................................................................................................................ 47

Generalterms .........................................................................................................................................48

AppendixB:TypicalWaterBalancesforPowerPlants....................................................................... 49 

AmericanElectricPower .........................................................................................................................49

SouthTexasProject................................................................................................................................. 51

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1



ExecutiveSummary

Asweconfrontthechallengesposedbyclimatechange,decisionsonsupplyingenergyandwatertothe

world’sgrowingpopulationshouldnolongerbemadeinisolation.ThechallengesfacingTexasandthe

restofthegloberequirethatwerecognizethedeepinter‐connections andtrade‐offsinvolvedin

deciding

howtomeetpowerandwaterneedsinanincreasinglyresource‐

constrainedworld.

Thisreportisthefirstinaseriesdesignedtoexploreaspectsoftheenergy‐

waternexusinTexas.Itexaminesthewaterrequirementsforvarioustypes

ofelectricitygeneratingfa cilities,bothfortypicalsystemsnationwideand

hereinTexas.Italsoaddressestheuseofenergybywatersupplyand

wastewatertreatmentsystems,comparingnationalaverageswithTexas‐

specificvalues.

Futureinstallmentsinthisreportserieswillincludecasestudiesofthe

implicationsforenergyoffuturewatersupplystrategiesforTexasandmore

place‐specificwatersupplyimplicationsofthefuturefuelmixforelectricity

production.Thereareseveralotheraspectsoftheenergy‐waternexusthat

arebeinginvestigatedbyseveralotherentitiesbutarenotcontemplatedin

thisseries,includinghydroelectricpowergeneration,unconventionalfossil

fuelproduction,andthedevelopmentofbiofuelssuchas

ethanol.

AnalysisofavailabledataforTexasrevealsthatapproximately157,000

milliongallons(482,100acre‐feet)ofwaterannually–enoughwaterforover

3millionpeopleforayear,eachusing140gallonsperpersonperday–are

consumedforcoolingthestate’s thermoelectricpowerplantswhile

generatingapproximately

400terawatt‐hours(TWh)ofelectricity.Atthe

sametime,eachyearTexasusesanestimated2.1to2.7TWhofelectricity

forwatersystemsand1.1to2.2TWhforwastewatersystemseachyear–

enoughelectricityforabout100,000peopleforayear.Theseestimatesfor

waterand

wastewatercombinedrepresentapproximately0.8to1.3%of

totalTexaselectricityand2.2 to3.4%ofindustrialelectricityuseannually.

Thereportpresentsageographicdistributionofthecurrentwaterusefor

electricitygenerationandelectricityuseforwatersupplyandwastewater

treatment,whichmaybeusefulaspolicymakersbeginto

examinethese

aspectsoftheenergy‐waternexus.

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2

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Inpreparingthereport,however,itbecameclearthat

substantiallymoresite‐specificdataarenecessaryforafull

understandingofthenatureoftheenergy‐waternexusinTexas.

Thus,werecommendthatthestateincreaseeffortstocollect

accuratedataonthewithdrawalandconsumptionofcoolingand

process

wateratpowerplants,aswellasdataonelectricity

consumptionforpublicwatersupplyandwastewatertreatment

plantsanddistributionsystems.Thesedatawillalsobeusefulin

planningforthefuture.

Inthefuture,wateruseforelectricitygenerationwilldependonseveralfactors,includingthefuelmix

fornewgeneratingcapacity,thetypeofpowerplantandthetypeofpowerplantcoolingsystemsthat

aredeployed.Likewise,theamountofelectricityusedtopump,treatanddeliverpublicwatersupply

andtotreatwastewaterwilldependonchoicesaboutwatersourceandtreatmenttechnology.These

trends,and

trade‐offsstillneedtobebetterunderstood,butitisundeniablethattherewillbe

importantimplicationsforwaterandenergypolicyatthestate andlocallevel.

Somestepscanbetakennowtobuildthebasicsofaframeworkformoreintegratedenergyandwater

planning,including:

• Amendstatelawtorequirethatapplica tionsfornewpowerplantsincludeananalysisofthe

waterandefficiencyimplicationsofvarioustypesofcoolingoptionsapplicabletotheproposed

plant.Theanalysisshouldincludefactorsrelatingtolocalclimateandairquality,regionalair

quality,wateravailability,includinginstream

flowrequirements,fueltypeandplantefficiency.

• Requireacleardemonstra tionofwateravailabilityinthesitingofnewfossil‐fueledpower

plantsorconcentratedsolar(thisanalysisshouldconsideraveragerainfallyearsaswellas

availabilityduringextremedroughtevents).

• Providestatestatutoryandregulatoryincentivesfor

implementationofpowerplantcooling

technologiesthatarelesswater‐intensivethantraditionalsystems,suchasair‐coolingorhybrid

wet‐drycooling.

• Providestate‐approvedg uidance(fromtheTexasWaterDevelopmentBoardand/ortheState

EnergyConservationOffice)towatersuppliersandwastewatertreatmentproviderstohelp

quantifyenergy

useandcostsavingsassociatedwithwaterconservation.

Theover‐archingmessageisthatimplementingadvancedefficiencyisthekeytothesustainableuseof

bothenergyandwater.Improvingwaterefficiencywillreducepowerdemandandimprovingenergy

efficiencywillreducewaterdemand.Greaterefficiencyinusageofeither

energyorwaterwillhelpto

stretchourfinitesuppliesofboth,aswellasreducecoststowaterandpowerconsumers.Thestateand

localgovernmentsshouldcontinue,andwhereverpossible,increasefundingandtechnicalsupportfor

waterandenergyconservationandefficiencyprograms.

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3



Introduction

Energyandwaterareintimatelyinterrelated:weuseenergyforwaterandweusewaterforenergy.

Weusewaterforelectricityproductiondirectlythroughhydroelectricpowergenerationatmajordams

andindirectlyasacoolantforthermoelectricpowerplants.Ther moelectricpowerplants—comprisedof

powerplantsthatuseheattogenerate

power,suchasnuclear,coal,naturalgas,solarthermalor

biomassfuels—arethesinglelargestuserofwaterintheUnitedStates.Wealsousewaterasacritical

inputforthegrowthandproductionofbiofuels,suchascornethanol.

Inadditiontousingwaterforenergy,wealso

useenergyforwater.Specifically,weuseasignificant

amountofelectricitytoproduce,deliver,heatandtreatwatersuppliesandtotreatwastewater.

Despitetheinterconnections,historicallythesetwosectorshavebeenregulatedandmanaged

independentlyofoneanother.Planningforenergysupplytraditionallygavescantconsiderationto

watersupply

issuesandplanningforwatersupplyoftenneglectedtofullyconsiderassociatedenergy

requirements.[1]

Failuretoconsidertheinte rdependenciesofenergyandwaterintroducesvul nerabilitieswhereby

constraintsofoneresourceintroduceconstraintsintheother.Thatis,droughtsandheatwavescreate

waterconstraintsthatcanbecomeenergyconstraints,

andgridoutagesorotherfailuresintheenergy

systemcanbecomeconstraintsinthewaterandwastewatersectors.

AseveredroughtinthesoutheastUnitedStatesin2007‐2008broughtpowerplantswithindaysofbeing

forcedtoshutdownduetoalackofwaterforcooling.[2‐6]

Todayinthewest,amulti‐yeardroughthas

loweredwaterlevelsbehindHooverDam,introducingtheriskthatLasVegaswillloseasubstantial

portionofitsdrinkingwateratthesametimethedam’shydroelectricturbinesquitspinning,which

wouldcutoffasignificantsourceofpowerfor

LosAngeles.[7,8]Heatwavescanalsointroduce

problems.Duringthe2003heatwaveinFrancethatwasresponsibleforapproximately15,000deaths,

nuclearpowerplantshadtoreducetheirpoweroutputbecauseofthehighinlettemperaturesofthe

coolingwater.[9]EnvironmentalregulationsinFrance(andtheUnited

States)limittherejection

temperatureofpowerplantcoolingwatertoavoidecosystemdamagefromthermalpollution.When

theheatwaveraisedrivertemperatures,thenuclearpowerplantscouldnotachievesufficientcooling

withintheenvironmentallimits,andsotheyreducedtheirpoweroutputatatimewhenelectricity

demand

wasspikingbyresidentsturningontheirairconditioners.Inaddition,thecorollaryistrue:

poweroutageshampertheabilityforthewater/wastewatersectortotreatanddistributewater.These

poweroutagescanoccurforavarietyofreasons,includinggridfailuresthatarecommon after

hurricanes.Forexample,hurricanesIke

andGustavinducedsustainedpoweroutages,whichcanaffect

theabilitytogetsafe,cleandrinkingwatertothepublic.

Droughts,heatwavesandhurricanesarenotunusualexperiencesforTexas,andbecauseoftheenergy‐

waternexus,theyintroduceacoupledcross‐sectoralvulnerability.Thesevulnerabilitiesmightonlyget

morepronouncedasresourcesbecomemoreconstrainedduetopopulationgrowthandaswaterand

energysuppliersconfrontnewchallengesassociatedwithclimatechange.[10]Understandingand



4



accountingfortheenergy‐waternexusisbecomingincreasinglyimportanttoensurethatnatural

resourcepoliciesandplansleadtosustainableandaffordableresults.Usingan integratedpolicymaking

approachtomakethesystemmoreresilientandsustainablewouldbeasignificantstepforward.

Thisisthefirstina

seriesofreportsdesignedtoexplorecertainaspectsoftheenergy‐waternexus.This

reportexaminestheaveragewaterrequirementsforvarioustypesofelectricitygeneratingfacilities,

bothnationwideandhereinTexas.Italsoaddressestheuseofenergybywatersupplyandwastewater

treatmentsystems,againfroma

nationalaverageandTexas‐specificperspectives.

Futureinstallmentsinthisreportserieswillincludecasestudiesofenergyimplicationsoffuturewater

supplystrategiesforTexasandmoreplace‐specificwatersupplyimplicationsofthefuturefuelmixfor

electricityproduction.Thereareseveralotheraspectsoftheenergy‐waternexus

thatarenot

contemplatedinthisseries,butbeinginvestigatedbyseveralotherentities,includingproductionof

hydropowerforelectricitygenerationandwateruseinproducingvariousfossilfuelsandalternative

transportationfuels,suchasethanolorotherbiofuels.



Texas Electricity Consump on by Sector

(Total: 380 billion kWh)

Transporta on

Commercial

29%

Reside

33%

Industrial

38%

U.S. Electricity Consump on by Sector

(Total: 3,700 billion kWh)

Transporta on

Industrial

28%

Reside

37%

Commercial

35%

Chapter 1. Water for Energy

A number of primary energy sources such as coal, uranium, natural gas, biomass, sun, water, or wind,

can be used to generate electricity, which distributes energy to

commercial, and industrial

customers. Using diﬀerent processes, energy within these fuel sources (chemical, kine

c, or radiant

energy) is converted into electrical energy. Based on the laws of thermodynamics, energy is neither

created nor destroyed when converted into electrical energy. However, the conversion processes are

inherently ineﬃcient, which generates waste heat that is typically dissipated by use of cooling water.

The typical thermoelectric power plants use nuclear or fossil fuels to heat

high purity water into steam,

which then turns a turbine connected to a generator, producing electricity. The steam is then

condensed back into water to con

nue the process again in a closed loop. This conde requires

cooling either by use of water, air, or both. The energy eﬃciency of the turbine in

ng steam into

electric energy depends in part on the eﬀ

of the steam conde process. That is, the

eﬃciency of the power plant depends on its ability to cool its steam loop. The

ty of water

required for cooling depends on the type of fuel, power gen

on technology, and cooling technology.

Even some power plants that do not operate with a steam cycle (i.e. gas turbines) require a small

amount of cooling for various components. In the case of fuels that must be mined (including coal,

natural gas, and uranium), the mining process also requires water.

Electricity Generation and Use

Electricity is used for many diﬀerent aspects of society, including l ng homes and businesses and

running industrial machinery and processes. As shown in Figure 1.1, electricity consump

on for

purposes – ligh ng and hea ng homes, as well as powering appliances – is 37% of the total

electricity use in the U.S. and a similar 33% in Texas. Though e

lectricity powers some transp

the

amount used is negligible for both the U.S. and Texas. Since Texas is home to many energy-intensive

reﬁning, chemical and manufacturing fa

industrial electricity use is higher, as a percentage of

total use, than in the country as a whole.

Figure 1.1. U.S. ) and Texas (right) electricity consum in percent, by sector for 2006. Texas uses a larger

percentage of electricity for industrial purposes than does the U.S. as a whole. [11, 12]

Residen al

Commercial

Industrial

Transporta on



6



U.S.ElectricityGenerationbySource

(Total:4,100billionkWh)

Petroleum

Other

Renewable

Nuclear

19%

Coal

49%

NaturalGas

20%



TexasElectricityGenerationbySource

(Total:400billionkWh)

Petroleum

Other

Renew able

Nuclear

10%

Coal

37%

NaturalGas

49%

Coal

NaturalGas

Nuclear

Renewable

Petroleum

Other

Differentprimaryenergysourcesareusedtogenera teelectricity.Figure1.2below showsthe

percentagesofelectricitygenerationbysourceforboththeU.S.andTexas.Thediscrepanciesintotal

electricitybetweenFigure1.1andFigure1.2areduetoenergylossesduringdistribution.TheTexasfuel

mixdiffersfromthatoftheU.S.withtwomajorpri

maryenergysources:coalandnaturalgas.Though

coalproducesnearlyhalfoftheelectricitygeneratednationwide,coalaccountsfor37%ofelectricity

generatedinTexas.NearlyhalfoftheelectricitygeneratedinTexasisfromnaturalgas,comparedto

thenationalaverageof20%.

Figure1.2.U.S.(left)andTexas(right)electricitygeneration,inpercent,byprimaryenergysourcefor2006.While

nearlyhalfoftheelectricitygeneratednationwideisfromcoal,nearlyhalfoftheelectricitygeneratedinTexasis

fromnaturalgas.Here,renewableincludestraditionalhydropower,solar,andwindpower.[11,12]

Thismixofsourcesforelectricitygenerationchangesgraduallyasnewpowerplantsandnewpower

generationtechnologiescomeon‐line.Forexample,therenewablesourceinFigure1.2from2006

includeswindpower,alongwithothersourceslikehydropowerandsolarpower.In2008,Texaswind

turbinesgeneratedover12terawatt‐hou

rs(TWh)ofelectricity–morethanthetotalrenewable

generationin2006.[13]

ManyoftheelectricitygenerationsourcesinFigure1.2requirewaterforcoolingtocondensesteam.

Thewaterneededforcoolingvarieswithtypeoffuel,powergenerationtechnology,andcooling

technology.Thesecoolingtechnologiesarediscussedinth

efollowingsection.

CoolingTechnologies

Coolingtechnologiesforthermoelectricpowergenerationusewaterorairtocondensesteamfroma

steamturbine.Acloserlookateachofthedifferenttypesoftechnologiesused forcoolingreveals

advantagesanddisadvantagesofeach.Forwatercoolingtechnologies,aterminologydistinctionis

madebetweenwaterwithdrawal,removingwaterfr

omasurfaceorgroundwatersourceforuse,and

waterconsumption,evaporatingwatersuchthatisitnotdirectlyreusableinthesamelocation.Using



7



thisterminology,waterwithdrawalisalwaysgreaterthanorequaltoconsumption.TheTexasWater

DevelopmentBoardusesthetermdemand,whichisconsideredhereequaltoconsumption.Althougha

largepercentageofwithdrawnwateristypicallyreturnedtothelakeorriver,themagnitudeof

withdrawal

isimportantbecauseifthosequantitiesofwaterarenotavailablethepowerplantwill have

toshutdown.Similarly,whenwateriswithdrawnforplantuseitisnolongeravailableforotherusers

suchasmunicipalwatersupplyandenvironmentalneeds.Toassureadequatesupplyforwithdrawal,

powerplants

areoftenlocatedonwaterreservoirs.

Open‐loopcooling,showninFigure1.3,condensessteamusingaheatexchangerandawatersource.

Largevolumesofwaterarewithdrawnfromthewatersource(reservoir,lakeorriver),flowingthrough

theheatexchangertocondensesteaminasinglepass.Consequently,

open‐loopcoolingisalsoknown

asonce‐throughcooling–wateriswithdrawnandpassesoncethro ugh theheatexchangerbeforemost

isreturnedtothesource.



Figure1.3.Schematicofopen‐loopcoolingforthermoelectricpowergeneration.Mostwaterthatiswithdrawnis

subsequentlyreturned,albeitatahighertemperature.

Sincewaterisonlycycledonceanddoesnotsignificantlyevaporateinthecoolingsystem,wateras

salineasseawatercanbeusedwithopen‐loopcooling.Open‐loopcoolingalsoconsumes le ss water

perMWhwithinthepowerplant comparedtocoolingtowersorcoolingreservoirs,typically100to

400

gal/MWh.Consumptionasapercentofwithdrawalrangesfrom1to2% .However,thispercentage

doesnottellthefullstory,sinceopen‐loopcoolingwithdrawsmuchlargervolumesofwater–40to80

timesmore—thanothercoolingtechnologies.Thislargewaterwithdrawalcanhavesevereimpactson

nearbyusers,asitwillnotbeavailableforotherneeds.Additionally,waterintakestructurescankillfish

andthermalpollutionofreceivingwaterwaysispossiblewiththeelevatedtemperatureofthereturn

water.[14]Thermalpollutionfromhightemperaturewaterdecre asesthesolubilityofoxygeninwater,

therebyreducingdissolved

oxygen,whichisnecessaryforaquaticspeciessurvival.[15]

Closed‐loopcoolingisanalternativetoopen‐loopcooling.Insteadofwithdrawingwaterandusingit

once,closed‐loopcoolingrecycleswaterforadditionalsteamcond ensation.Twomaintechnologiesfor



8



implementingclosed‐loopcoolingexist:coolingtowers,withanaccompanyingsupplyreservoirorriver,

andcoolingreservoirs.Acoolingtower,showninFigure1.4,withdrawswaterfromasource,usuallya

coolingwatersupplyreservoir,condensessteaminaheatexchanger,andthenrecyclescoolingwater

withinthecooling

tower.Coolingtowersdissipateheatthroughevaporationofthecoolingwater.[14]



Figure1.4.Schematicofclosed‐loopcoolingwithacoolingtowerforthermoelectricpowergeneration.Most

waterthatiswithdrawnisconsumed.

Closed‐loopcoolingwithacoolingreservoiraloneoperatessimilarly,butthereservoiritselfisusedto

dissipatetheheatviabothevaporationandlossofradiantheatduringthecoolereveninghours.[16]

Waterconsumptionreported(i.e.fortheU.S.EnergyInformationAdministration)forclosed‐loop

coolingtypicallydoesnot

includelossesthroughforcedevaporationincoolingreservoirsandcertainly

doesnotincludenaturalevaporation–evaporationfromthewatersurfacedrivenbysolarenergyand

wind.However,thepowerplantwaterreporting methodsusedbytheTexasWaterDevelopmentBoard

andTexasCommissiononEnvironmentalQualityinherentlyaccountfor

forcedevaporationfromcooling

reservoirs.

Closed‐loopcoolinghastheadvantageofrequiringmuchlesscontinuouswaterwithdrawalfroma

stream,river,oraquiferthanopen‐loopcoolingbecausewaterisrecycledwithinthecoolingsystem.On

theotherhand,80%ormoreofthewatercycledthroughthesystemis

consumedthroughevaporation,

typicallyattherateof110to850gal/MWh.Manytimes,thewaterthatisnotconsumedincooling

towers(knownasblowdown)isofalowerqualitythanthewithdrawnwaterbecauseevaporationhas

concentratedpollutantsandparticlesintheblowdown.[17]Additionally,watervaporleaving

cooling

towerscancreateaplume,whichmayreducevisibilityorcauseicingonnearbystructures.[18]While



9



manypeopleassociatecoolingtowerswithnuclearpower,theyarealsousedbysomecoalandnatural

gaspowerplants.

Thermoelectricpowerplantcoolingispossiblewithoutwaterbyuseofair‐cooling,oftenreferredtoas

dry‐cooling,showninFigure1.5.Forthisconfiguration,air‐cooledcondensers collectsteam

inmany

smalltubes,blowairacrossthetubesusingfans,andcollectthecondensedwateratthetubeoutlet.

[19]Theoverallair‐coolingprocessissimilartoacarradiator.

Figure1.5.Schematicofair‐coolingforthermoelectric

powergeneration,whichdoesnotrequirewater.

Air‐coolingeliminatestheneedforwater,which

openspossibilitiesforplantstobesitedinarid

locations.[19]However,air‐coolinghasalower

coolingefficiencythanwatercooling.Thatis,a

cubicfootofairhasalowerabilitytodissipate

heatthanacubicfootofwater.Consequently,



largercoolingstructuresarerequired,andthese

largerstructuresrepresenthighercapitalcosts

thatvarysubjecttolocalclimate,weather,and

plantdesign.

Additionally,apowerplantcanexperiencea1%

lossinefficiencyofpowergeneration–the

conversionofprimaryfuelenergyintoelectricity–foreach1

°Fincreaseintemperatureofthe

condenser,whichislimitedby ambient temperature.[20]Thoughair‐coolingusesnowater,the

tradeoffislowerpowerplantefficiency,creatingadditionalairemissionsforeachunitofelectricitythat

isgenerated.Additionally,forequivalentcoolingcapacity,capitalcostsarehigherforair‐cooled



systems.

Asacompromisebetweenwaterandair‐coolingofthermoelectricpowerplants,somehave

implementedhybridwet‐drycoolingtechnologies,shownonthenextpageinFigure1.6.Hybridcooling

combinesacoolingtowerwithanair‐cooledcondenser,increasingcoolingefficiencyoverair‐cooling

duringthecriticalhot

summerdayswhiledecreasingtheoverallannualwaterconsumptionfromusing

coolingtowers.Thewatervaporexitingthewetcoolingtowerportionmixeswithheatedairfromthe

air‐cooledcondensertocombinethebenefitsofwaterandair‐co oling.Inaddition,hybridsystemscan

bebuiltinparallelconfigurationsmaking

themsomewhatredundant,thuscreatingsomeresiliency for

thepowerplants.



10



Figure1.6.Schematicofhybridwet‐drycoolingforthermoelectricpowergeneration.

Hybridwet‐drycoolingtechnologiesimprovethepowerplantefficiencyoverpureofair‐cooling,while

alsoreducingthewaterco nsumptionofpureclosed‐loopcooling.However,thesehybridsystemsare

expensiveandgenerallyoperatewithonlythewetcoolingtowerportionduringhotsummers,saving

waterformostofthe

yearwithrelativelylowpowerefficiencyreduction.[21]Unfortunately,summeris

oftenwhenwaterresourcesarethemoststrained.Currently,hybridwet‐drycoolingtechnologiesarein

operationforpowerplantsinTheNetherlands,GreatBritain,Austria,andGermany.[22]

Onereasonwhyhybridtechnologiesarereceivingincreasedfocusis

fortheirusewithconcentrating

solarplants.Concentratingsolarpower(CSP)plantsarebestsuitedfordesertenvironmentsthathave

highdirectsolarinsolationbutfewwaterresources.Figure1.7onthenextpageshowsresultsofan

analysisofaparticularhybridwet‐drycoolingdesignforaCSPplant

locatedinBarstow,California–a

locationwithaverygoodsolarresource.[23,24]FortheCSPandhybridcoolingdesignanalyzedfor

Figure1.7thewaterconsumptionvariesfrom80to800gal/MWhfrom100%dryto100%wetcooling.

The100%drycoolingdesignproducesapproximately4.5

to5%lesselectricitywhereasthehybrid

designwouldproduceanywherefrom96to99%oftheelectricityofthe100%wetcoolingdesign.

Thegeneraltrendshownforhybridcoolingholdsforanythermalpowerplan tusingasteamcycle,but

willvaryaccordingtosite‐specificparameters.Thecooling

towercanbedesignedfrom100%wet

coolingto100%drycooling,andinbetweenarangeofhybridizationexists.Asahigherpercentageof

air‐coolingisused,theefficiencyimpactsandreductioninwaterconsumptionincrease.Thus,hybrid

systemsrepresentinherenttradeoffsamongplantefficiency, infrastructurecosts,and

watercosts.



11



0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.94

0.95

0.96

0.97

0.98

0.99

1.00

Fractionofwetcoolingtowerwaterconsumption

Fractionofwetcoolingtowernetplantoutput

100%wet

coolingtower

100%air

coolingtower



Figure1.7.Dependinguponthedegreeofhybridizationandtechnologicaldesign,hybridcoolingtowerscanvary

inwaterconsumptionfromthatofwetcoolingtowertodrycoolingtower,alongwiththeconcomitantenergy

efficiency.(Modifiedfrom[23])

Waterrequirementsforcoolingdependonfuel,powergenerationtechnology,andcoolingtechnology.

ThesewaterrequirementsaresummarizedonthenextpageinTable1.1andTable2.2anddiscussed

furtherinthefollowingsection.Thesetablesillustratethatthereareawiderangeofpowerplantwater

usageconditionsdepending

uponthecombinationofpowerandcooling technology.



12



Table1.1.Waterwithdrawalreportedvolumesfordifferentfuelsandcoolingtechnologies.Air‐coolingrequires

negligiblewaterandiscompatiblewithallofthetechnologieslisted.[17,25‐27]

 CoolingTechnologies–WaterWithdrawal(gal/MWh)



Open‐

Loop

Closed‐Loop

Reservoir

Closed‐

Loop

Cooling

Tower

Hybrid

Cooling

Air‐Cooling

Coal 35,000

(±15,000)

450

(±150)

550

(±50)

between <100

Nuclear 42,500

(±17,500)

800

(±300)

950

(±150)

between <100

NaturalGasCombustion

Turbine

negligible negligible negligible negligible negligible

NaturalGasCombined‐

Cycle

13,750

(±6,250)

155

†



(±25)

230 between <100

†



IntegratedGasification

Combined‐Cycle

notused notused

400

†



(±110)

between <100

†



Thermal

ConcentratedSolar

Power

notused notused

840

†



(±80)

between <100

†



Wind none none none none none

FuelTechnology

Non‐

Thermal

PhotovoltaicSolar none none none none none

†

Estimatedbasedonwithdrawalandconsumptionratios



Table1.2.Waterconsumptionreportedvolumesfordifferentfuelsandcoolingtechnologies.Air‐coolingrequires

negligiblewaterandiscompatiblewithallofthetechnologieslisted[17,25‐27]

 CoolingTechnologies–WaterConsumption(gal/MWh)



Open‐

Loop

Closed‐Loop

Reservoir

Closed‐

Loop

Cooling

Tower

Hybrid

Cooling

Air‐Cooling

Coal

300

385

(±115)

480 between

60

(±10)

Nuclear

400

625

(±225)

720 between

60

(±10)

NaturalGasCombustion

Turbine

negligible negligible negligible negligible negligible

NaturalGasCombined‐

Cycle

100

130

†



(±20)

180 between

†



(±10)

IntegratedGasification

Combined‐Cycle

notused notused

350

†



(±100)

between

†



(±10)

Thermal

ConcentratedSolar

Power

notused notused

840

(±80)

between

†



(±10)

Wind none none none none none

FuelTechnology

Non‐

Thermal

PhotovoltaicSolar none none none none none

†

Estimatedbasedonwithdrawalandconsumptionratios



13



TypesofPowerPlants

Powerplantsuseavarietyofdifferentfuelsandtechnologiesforgenerationofelectricity.Thesefuels

andtechnologiescombinetoproduceelectricitywithdifferingefficiencies,asshowninTable1.3.The

observedpowerplantefficienciesinTexasarelowerthanthetheoreticaleffi ciencyvaluesduetoenergy

lossesinthepower

generationsystem(particularlytheoperationofpollutioncontrolsystems)and

start‐up/shut‐downperiods.

Table1.3.Actu aloperatingefficienciesforpowerplantsusingdifferentfuelsandpowergenerationtechnologies.

[27‐29]

FuelType TexasGenerationEfficiency(%) MaximumReportedEfficiency

(%)

Coal Lignite:26‐34%

Subbituminous:27‐35%

IntegratedGasification

Combined‐Cycle:50%

NaturalGas SteamTurbine:28%

GasTurbine:26%

Combined‐Cycle:39%

Combined‐Cycle:50%

Nuclear 33%



ApproximatelyhalfoftheelectricitygeneratedintheUnitedStatescomesfromcoal‐firedpowerplants,

asshowninFigure1.2.[12]Coal‐firedthermoelectricpowerplantsconvertchemicalenergyfromcoal

intoelectricalenergywithanaverageoverallefficiencyof33%(26to35%inTexasduetovarious

plant

designandoperationalpatterns),asillustratedinFigure1.8onthenextpage.There mainderofthe

energyleavesthesystemasheatembodiedinexitingcoolingwaterorfluegas.Intheseplantscoal‐fired

boilersproducesteamthatdrivesteamturbines.Condensingthesteam(viaacoolingsystem)

asitexits

theturbineisakeytomaximizingtheenergyefficiencyoftheplant.Whenthesteamcondenses,a

rapidloweringofvapor‐to‐liquidspecificvolumesresultsinasustainedvacuumattheoutletofthe

turbineoutlet,referredtoasturbinebackpressure.Thecoolingsystemis

anintegralpartofpower

generationprocessandgreatlyinfluence s onplantperformance.



14



Figure1.8.Basicschematicofapulverizedcoal‐firedpowerplantwithpercentageofenergyflowandmedian

waterwithdrawalandconsumptionforcoolingperMWhofelectricitygenerated.Only33%oftheincomingfuelis

convertedtoelectricity.[17,30]

Nuclearpowerplantsgenerateroughlyone‐fifthoftheelectricityusedintheUnitedStates.[12]Much

likecoal‐firedthermoelectricpowerplants,nuclearpowerplantsconvertatomicenergypresentin

nuclearfuelintoelectricalenergybyusingheattomakesteamtodrivesteamturbines.Theseplants

haveoverallthermal

energyefficienciesaveraging33%,showninFigure1.9onthenextpage.However,

unlikecoal‐firedutilities,nuclearpowerplantsdonotemitfluegases,thusreleasingmorethermal

energyviathecoolingwater.Nuclearpowerplantstypicallydissipatetwiceasmuchoftheprimary

energysourceintheform

ofwasteheattocoolingwaterascomparedwithcoal(67%fornuclearin

Figure1.9comparedto33%forcoalinFigure1.8).However,thecoolingwaterrequirementsforsteam

condensationareonlyone‐fifthtoone‐third(20to35 %)higher(seeTables1.1and1.2)becausenuclear

reactor

temperaturesarenotashighascoalcombustiontemperatures(300°Cfornuclearversus over

1,500°Cforcoal).[31,32]Thisadditionalwaterconsumptionisatradeoffforthelackofairemissions

fromnuclearpowerplants.



15



Figure1.9.Basicschematicofanuclearpowerplantwithpercentagesofenergyflowandmedianwater

withdrawalandconsumptionforcoolingperMWhofelectricitygenerated.[17,30]

Roundingoutthemajorelectricitygenerationfuelsisnaturalgas,whichproducesapproximately20%of

UnitedStateselectricityand49%inTexas.[11,12]Naturalgashasflexibilityasafuelasitcanbeused

togeneratesteamforasteamturbine,usedtofuelacombustionturbine,orused

inacombined‐cycle

systemforelectricitygeneration.Acombustionturbine(orgasturbine)powerplant,showninFigure

1.10,isbasedoncombustionofgasinaturbineandtheresultinghightemperature,highpressuregas

spinstheturbinedirectly.[33]Thisprocessrequiresnegligibleamountsofcoolingwater

(otherthanthe

smallamountsneedfortheturbinebla desandothercomponents),sincetheturbineusesgasinsteadof

steam,andisapproximately33%efficient.

Figure1.10.Basic

schematicofanatural

gasturbinepowerplant

withpercentagesof

energyflow.[30]

Toincreasethe

efficiencyof

electricitygeneration

usingagasturbine,

newtechnology

knownasaheat

recoverysteam

generator(HRSG)has

beenincorporated,



16



resultinginnaturalgascombined‐cyclepowerplantslikethatshowninFigure1.11.UsingtheHRSG,

wasteheatfromtheturbineexhaustgeneratessteamthatspinsasteamturbine,boostingoverall

powerplantefficiencytoapossibleefficiencyof50%.[30,34]Coolingwaterisrequiredtocondense



steamfromtheHRSG,yetthiscoolingwaterrequirementislowerperMWhgeneratedthanthatof

nuclearandcoal‐firedpowerplantsusingonlyasteamturbine.



Figure1.11.Basicschematicofacombinedcyclepowerplantwithpercentagesofenergyflowandmedianwater

withdrawalandconsumptionforcoolingperMWhofelectricitygenerated.[17,28,30]

Anadditionaluseofthecombined‐cyclepowerplantistheIntegratedGasificationCombined‐Cycle

(IGCC)powerplant,depicted onthenextpageinFigure1.12.IGCCpowerplantsusecoal,petroleum

coke,orpossiblybiomassasafuelsources.InIGCCplants,thefuelisnotdirectlycombusted,but

instead

isgasifiedwithsteamandcontrolledoxygenlevelsathightemperatureandpressure.Syngas,

theproductofgasification,iscomposedofcarbonmonoxideandhydrogen.Thissyngasisthen

convertedtocarbondioxideandhydrogenbysteamreformingoveracatalyst.Theresultinggasisthen

usedtofuela

combustionturbinethatgenerateselectricity.AnHRSGisalsoincorporatedintotheIGCC

process,generatingadditionalelectricitywithasteamturbine(makingitacombined‐cycle),bringing

overallefficiencyto50%.[29]

Sincecoalisnotcombusted(andthehydrogengasiscleaneduppriortoitscombustion)intheIGCC



process,fewerairpollutantsareemittedwiththefluegas.Forexample,essentiallyallofthesulfur

presentinthecoalisremovedpriortocombustion,therebyavoidingtheformationofsulfurdioxide.



17



[29]IGCCdoeshaveaninherentprocesswateruseofapproximately30to60gal/MWhforthe

productionofsyngas,whichisapproximately10to20%ofthepowerplantwaterconsumptio n.[27]

Figure1.12.Basicschematicofan

integratedgasificationcombined

cycle(IGCC)powerplantswith

percentagesofenergyflowand

medianwaterwithdrawaland

consumptionforcoolingperMWh

ofelectricitygenerated.[27,29,

35]

Themarketsharefor

renewableenergysourcesfor

electricitygenerationis

growing.Amongthese

renewableenergy

technologiesiswind‐

generatedelectricity,shownin

Figure1.13.Thekineticenergy

ofblowingwindisconverted

intomechanicalenergyof

turningblades,mountedon

topofatalltower.Mechanicalenergyfromtherotating

turbinebladesisthenconvertedintoelectrical

energyusingagenerator.Sincetheprocessdoesnotuseasteamturbine,nocoolingwaterisrequired.

Windturbinesdonotconvertallthekineticenergyofthewindintomechanicalenergy,thusacertain

amountofwindisleftunconverted

.Thisunconvertedwind,alongwithgeneratorefficien cy,resultsin

atypicaloverallwind‐generatedelectricityefficiencyof50%.Verylittlewasteheatiscreatedinthe

generator,andsodedicatedcoolingis

notrequired.

Figure1.13.Basicschematicofwind‐

generatedelectricitywithpercentagesof

energyflow.[30]

Anotherrenewabletechnologyfor

electricitygenerationisthe

photovoltaic(PV)solarpanel,shown

onthenextpageinFigure1.14.Two

maintypesofPVsolarpanelsare





Themaximumtheoreticalefficiencyofhorizontalaxiswindturbinesis59%.



18



currentlyinuse:wafer‐basedsiliconpanelsand thin‐filmpanels.Wafer‐basedsiliconPVpanelsusea

crystallineorpolycrystallinesiliconstructurecontainingphosphorusandboronatoms.Whensunlight

hitsthephosphorusandboronatoms,radiantenergyisconvertedintoelectricalenergy.[36,37]Thin‐

filmPVpanelsuseamorphous

silicon,cadmiumtelluride,orcopperindiumgalliumdiselenideasa

semiconductorlayeronathinstructure,alsoconvertingradiantenergyintoelectricalenergy.[38,39]

PVpanelefficiencyrangesfrom10to20%,withcommercialsystemsatthelowendofthisr ange.[30]

Thoughnocoolingwaterisneeded

duringsolarelectricitygeneration,thesurfaceofPVpanels mustbe

keptcleantomaintainefficiency.Processcleaningwaterconsumptionisapproximately 30gal/MWh,

minimalcomparedtothermoelectricpowerplants. [26]



Figure1.14.Basicschematicofphotovoltaicsolar‐generatedelectricitywithpercentagesofenergy.[26,30]

AnalternativetoPVsolar‐generatedelectricityisconcentratingsolarpower(CSP)orsolarthermal‐

generatedelectricity–collectingandconcentratingsolarenergyasapowerplantfuelsource.CSP

plants,ofthetypeshowninFigure1.15,generateelectricityinamannersimilartootherthermoelectric

powerplants.Usingconcentrating

mirrors,sunlightisconcentratedtoheatafluidthatinturncreated

steamviaaheatexchanger.Thesteamisconvertedtoelectricityviaasteamturbineasinother

thermalpowerplants.Steamisthencondensedusingacoolingtoweroraircooling.[25]

Figure1.15.Basicschematicof

CSP‐generatedelectricitywith

percentagesofenergyflowand

medianwaterwithdrawaland

consumptionforcoolingper

MWhofelectricitygenerated.

[25,30]

Eachofthepowergeneration

technologiespresentedabove

useswaterforprocesses,

coolingtocondenseprocess

steam,orcleaning.Notethat

allthermoelectricpower

plantsmaybecooledusing



19



air‐cooling,whichdoesnotrequirewater.Forinstance,theproposedTrailblazerEnergyCenter,near

Sweetwater,Texas,isapulverizedcoalfacilityforwhichTenaskais consideringair‐coolingtoreduce

waterconsumption.[40]Currentlytwothermalpowerplants inTexas,bothnaturalgas‐powered

combined‐cycleplants,use

air‐coolingtosomedegree.Thesepowerplantshaveoperatedatover45%

powerefficiencyin2006.[28]



20



Chapter2. EnergyforWater

Freshwaterisessentialforhumansurvivalandprosperity,whetherfordrinking,sanitation,industrial

use,irrigation,orpowergenerationandeverystageofthewatersupplyprocess hasenergy

requirements.Developing,pumping,andtreatingwaterforpublicwatersupplysystemsis acomplex

andresource‐intensiveactivityrequiringsignificantamountsofenergy.

Aspressureonwaterresources

growswithpopulationgrowth, publicwatersuppliersareoftenlookingfurtherfromhomefornew

suppliesortotechnologies likedesalination.Waterisalsoamediumfortransportingwastes.Inorder

toprotectwaterquality,wastewaterdischargestosurfaceandgroundwatermustmeetvariousfederal

andstatetreatmentrequirementsandthosetreatmentprocessesrequireenergy.

PublicWaterSupplySystems

Publicwatersuppliesnotonlyprovidedrinkingwater,theyalsoarecriticalforarangeofcommercial

andindustrialactivity.Providingpublicwatersupplyrequirescollectionandconveyanceofsource

water,treatmentanddisinfection,thendistributiontoresidential,commercialandsometimesindustrial

customers.Manyendusesofwateralsorequirethat

thewaterbeheated.Eachofthesestepsrequires

energyinputs,typicallyintheformofelectricity.

SourceCollectionandConveyance

PublicwatersupplyintheUnitedStatescomesfromtwomainsources:surfacewater(streams,rivers,

lakes)andgroundwater(aquifers,wells).In2000,63%ofU.S.publicwater(27.3

billiongallonsperday)

originatedfromsurfacewatersources.[41]Movingrawwaterthroughpipelinesorcanalstothe

treatmentplantrequirespumping,exceptwheregravity‐drivenflowispossible.

Groundwatersupplied37%ofsourcewaterforpublicwatersys temsin2000(16billion gallonsperday),

whiledomesticwateruse

–self‐suppliedwater,usuallyinruralareas–was98%groundwaterthrough

theuseofwells.[42]Collectionandconveyanceofgroundwatertypicallyusesmoreelectricitythan

surfacewatersourcesinthesamelocationduetotheenergyrequirements ofpumpingwaterfrom

undergroundaquifers.Theseenergyrequirementsfor

pumpingvarywithwaterdepth:pumpingfroma

depthof120feet(ft)requires540kilowatt‐hourspermilliongallons(kWh/Mgal),whilepumpingfrom

400ftrequires2000kWh/Mgal.[14]AveragegroundwaterwelldepthinTexasisnearly700feet.[43]

Generally,one‐thirdofthetotalenergyrequiredforcollecting,

treating,anddistributinggroundwateris

forwellpumping.[44]

Theenergyrequirementsforconveyingsourcewatertothetreatmentplantvarywithgeography;long‐

haulanduphillwaterpipelinesrequiremoreenergyforpumping,whilepartiallygravity‐fedsystems 

requireless.Forexample,California,whichmoveswaterhundredsofmiles

overtwomountainranges,

requires1,330to9,930kWh/Mgal.[45]

Brackishgroundwaterandseawaterarebecomingmorecommonsourcesofrawwaterinareaswhere

freshwatersuppliesarenotreadilyavailable.Seawaterdesalinationplants areusually locatedcloseto

thecoastandsothereislittleenergyrequiredtoconvey

thewatertothetreatmentplant.Energy



21



requirementsforpumpingandconveyingbrackishgroundwateraresimilartothoseforfreshwater

aquifersources.

Treatment

Afterrawsourcewateriscollected,itistreatedtomeetdrinkingwaterqualitystandards (eventhough

onlyasmallfractionofthewaterisusedfordrinking).Atypicalsurfacewatertreatment

plant,shownin

Figure2.1,usesacombinationofphysicalandchemicaltreatmentprocessestoremovecontaminants

fromwater.Ofthetreatmentprocessesshownin Figure2.1,pumpingbetween processesrequires

nearlythree‐fourthsofthetotalelectricityusedforwatertreatment.Theactualtreatmentprocesses–

flocculation,sedimentation,filtration,

anddisinfection–usetheremainingfourthofthetotalelectricity.

[44]



Figure2.1.Typicalwatertreatmentplantoperationsforconvertingsurfacewatersourcesintodrinkingwater

suppliesincludemanystepsandrequiresignificantenergyinputs.[44]

GroundwatertreatmentissimilartothatofsurfacewatertreatmentinFigure2.1.Dependingonraw

groundwaterquality,littletreatmentmayberequired:insomecasesonlytasteandodorremovaland

disinfectionareneeded.[44]

Desalinationdiffersfromtraditionaltreatmentforsurfacewaterorgroundwater.Thoughmany

desalinationtechniquesexist,

includingmulti‐effectdistillationandmulti‐stageflash,themostcommon

technologyinusetodayisbasedonpermeablemembranetechnologyandisreferredtoasreverse

osmosis.[46]Reverseosmosistrainsaregenerallyassembledinacascadefashion,showninFigure2.2

onthenextpage,toimproveoverall

waterrecovery.Duringreverseosmosisdesalination,highpressure

pumpsarerequiredonthefeedsideofthemembranetoovercomeosmoticpressureandproduce

permeate,whichisthedesalinatedwater.Reverseosmosistrainsalsocreateawastestream,knownas

theconcentrate.[46]Forseawaterdesalinationsystems,theconcentratewastestream

canrangefrom

40to65%oftheincomingseawater,whilebrackishgroundwaterdesalinationconcentratestreams

rangefrom15to40%.[47]



22



Figure2.2.Reverseosmosis

cascadetrainforwater

desalination.[48]

Electricityrequirementsfor

publicwatersupplytreatment,

therefore,varywiththelevel

andtypeoftreatment,as

showninTable2.1.Notethat

theelectricityrequirementper

unitwater(inkWh/Mgal)listed

inTable2.1includesonly

sourcecollectionand

treatment,notpotablewater

distribution.Generally,the

electricityuseper unit

ofwater

treatedremainsrelativelyconstantwithwatertreatmentplantsize,soenergyefficiencydoesnot

improvemuchwithscale.[44]

Table2.1.Nationalaverageelectricityusefor

watercollectionandtreatmentusing

differentwatertreatmenttechnologies.

Distributionrepresentsadditionalenergyuse.

[44,45]

Pharmaceuticals,personalcareproducts,

andendocrine‐disruptingcompoundsare

estimatedtobepresentindrinkingwatersuppliesforatleast41millionAmericans.[49]WhiletheEPA

regulatesthelevelsofmanyorganiccompoundsindrinkingwater,nostandardscurrentlye x istforlevels

ofsuchcontaminants.[50]Removingpharmaceuticals,personalcare

products,andendocrine‐

disruptingcompoundsfromwatersupplies,however,isanenergy‐intensiveprocess.Researchshows

thattherangeofremovalvariesamongstcontaminantswithdifferentlevelsoftreatment,spanning

fromnegligibletoover90%.[51]Higherlevelsofcontaminantremovalrequirecost‐andenergy‐

intensivetreatmentproces ses,suchas

activatedcarbonadsorptionandadvancedoxidationprocesses.

[51,52]Aswaterregulationsandstandardsbecomestricter,additionalenergyandinvestmentwill

likelybeneededtomaintaindrinkingwaterquality.

Distribution

Oncewaterhasbeencollectedandtreatedtoapplicablestandards,itmustbedistributedtoendusers.

Distributionrequirespumping,the

mostenergy‐intensiveaspectofwatersystems.AsshowninFigure

2.3,waterdistributionrepresents85%oftheenergyusefortypicalsurfacewatertreatment.[44]

WaterCollectionandTreatment kWh/Mgal

SurfaceWaterTreatment

220

GroundwaterTreatment

620

BrackishGroundwaterTreatment

3,900‐9,700

SeawaterDesalination

9,700‐16,500

Energy Use for Drinking

Water Treatment (kWh/Mgal)

Treatment

15%

Distribuon

85%

Figure 2.3. Naonal average percentage of energy consumed for

treatment (15%) and distribuon (85%) for typical freshwater

treatment. [44]

The energy requirements for water distribuon vary with the

distribuon of end users in relaonship to the treatment plant.

Addionally, aging infrastructure with old pipelines has leaks and

creates more fricon, requiring more electricity for water

distribuon. [44]

Residential Water Use

Residenal water end use also requires energy. In some

geographic areas of the U.S., water use in the home is one of the most energy-intensive aspects of the

water sector. [45] This energy comes in the form of electricity and somemes natural gas. Figure 2.4

shows the average uses of water for U.S. households.

Figure 2.4. Distribuon of average water use for U.S. homes. For indoor purposes, over half of the water used is

commonly heated, requiring energy. [53]

Of the common household water uses shown in Figure 2.4, over half – including clothes washers,

showers, faucets, baths, and dishwashers – generally draw a poron of heated water, which requires

energy for heang. In most households, energy use for heang water is second only to use of energy for

heang and cooling the home itself. [54] New, more eﬃcient appliances, including low ﬂow

showerheads and high eﬃciency clothes and dishwashers, can reduce heated water use, and also

Bath

Dishwasher

Clothes

Washer

25%

Toilet

31%

Shower

19%

Faucet

18%

Other

domesc

Indoor

35%

Leak

Unknown

Outdoor

58%

U.S. Residenal Water Use



24



therebyreduceenergyconsumption.Ifresidentialconsumptionofheatedwaterisreducedbyathird,

thenelectricityconsumptioninthestatewouldbereducedby1to3billionkWh.[55]

Afterresidentialuse,nearlyallofthewaterusedindoorsleavesaswastewater,eventhoughmuchofit

issuitableforre‐useforirrigationorotherapplications.Treatingthiswastewateralsorequiresenergy,

asdiscussedinthefollowingsection.

WastewaterSystems

Likewatersystems,wastewatersystemsmustalsoabidebyfederalandstateenvironmental

regulations.Treatingrawsewagetowastewatereffluentstandardsrequireselectricityforcollection

andconveyance,treatment,anddischarge.

CollectionandConveyance

Municipalwastewatertreatmentplantsutilizegravityforrawsewagecollectionandconveyance

wheneverpossible,reducingtheelectri cityrequired

forpumps.Thoughwastewaterconveyancemay

requirefewerpumpsthanwaterdistributioninsomeareas,wastewaterpumpsarelessefficientdueto

pumpingbothsolidsandliquids.[45]

Treatment

Wastewatertreatmentisbasedonphysicalsteps(suchassettlingandscreening)aswellasbiological

processes,suchasusingbacteria

tobreakdownorganicmaterialinthesewageandchemicalreaction

stepstoremovenutrientssuchasnitrogenandphosphorus.Atypicaladvancedwastewatertreatment

plant,whichisgenerallyrequiredtomeetcurrentwaterqualityregulationsisshowninFigure2.5.



Figure2.5.Typicalplantoperationsforadvancedwastewatertreatment.[44]

OftheprocessesshowninFigure2.5,overthree‐fourthsofthetotalelectricityrequiredforisusedfor

solidsprocessing–diffusedairaeration,nitrification,gravityandflotationsettling,anaerobicdigestion,



25



anddewatering.Over30%oftheelectricityrequiredgoestowardaerationaloneduetotheuseof

energy‐intensiveblowers.[44]

Asthelevelofwastewatertreatmentadvances,theelectricityrequirementsperunitofwastewater

increaseaswell,asshowninTable2.2.Thelargeenergy‐intensityincreasefrom

tricklingfilterto

activatedsludgetreatmentreflectsthelargeelectricityrequirementforblowersusedduringaeration.

Table2.2.Generalelectricityusefor

differentwastewatertreatment

technologies.Moreadvancedtreatment

thatmeetsstricterenvironmentalstandards

requiresmoreenergy.[44]

Unlikewatertreatmentplants,

electricityrequiredperunitofvolume

treatedvarieswithwastewater

treatmentplantsize,reflectedinTable

2.3.Largerwastewatertreatment

plantsprovidesignificanteconomiesofscaleandrecenttrendsreflectamovetowardlargercapacity

wastewatertreatmentplantsforthatreason.[44]

Table2.3.Variationinunitelectricityconsumptionfordifferentsizesofwastewatertreatmentplants.Larger

wastewatertreatmentplantsexhibiteconomiesofscalewithlowerenergyrequirementspervolumeof

wastewatertreated.[44]

 ElectricityConsumption(kWh/Mgal)

Wastewater

TreatmentPlant

Size

(MGD) TricklingFilter

Activated

Sludge

Advanced

Wastewater

Treatment

Advanced

Wastewater

Treatment

with

Nitrification

1 1,811 2,236 2,596 2,951

5 978 1,369 1,573 1,926

10 852 1,203 1,408 1,791

20 750 1,114 1,303 1,676

50 687 1,051 1,216 1,588

100 673 1,028 1,188 1,558



Discharge

Followingtreatment,effluentisdischargedintoreceivingwaterbodies.Manycitieslocatewastewater

treatmentplantssoastominimizetheenergycostsofpumpingtreatedeffluent.

WastewaterTreatment kWh/milliongal

TricklingFilter

950

ActivatedSludge

1,300

AdvancedTreatmentwithout

Nitrification

1,500

AdvancedTreatmentwith

Nitrification

1,900



26



Chapter3. EnergyWaterNexusinTexas

Asahighly‐populated,industry‐intensivestate,Texasrequiressignificantamountsofbothenergyand

water.Thischapterexaminescurrentresourceuseandenergy‐waternexusissues.FutureTexastrends

arediscussedinChapter4.

ElectricityGenerationfromTexasPowerPlants

Texas’258powerplantshavethecapacity

toproduceover110Gigawatts(GW)of

power.Actualgenerationtotalsabout400

terawatt‐hours(TWh),or400x10

kWh,

annually.[28]Thesepowerplants,shownin

Figure3.1,arelocatedmostlyineastTexas,

withafewlargeplantsinwestTexas.

Figure3.1.Electricitygenerationcapacity(kW)

fromTexaspowerplants.Totalelectricity

generationcapacitystatewideisover110GW

(110,000,000kW).[28]

Mostpowerplantsarelocatedinthe

easternhalfofthestatetobecloseto

populationcenters,ligniteresources,and

coolingwater.Texasriversgenerallyflowto

thesoutheast,andeastTexasreceivesmore

rainfallthanwestTexas,resultingin

additionalsurfacewateravailabilityinthe

easternhalfofthe

state.OfTexaspower

plants,22plantswithgenerationcapacities

totaling9,400MW–approximately8%of

totalTexasgenerationcapacity–usegroundwaterforcoolingwithcoolingtowers,mostofthosebeing

locatedinthewestTexaspanhandleregion.Therestusesurfacewatersourcesorair‐cooling.

WaterConsumptionandWithdrawalsofTexasPowerPlants

ThermoelectricpowerplantsinTexasconsumewaterforcooling,asshownonthenextpageinFigure

3.2.WaterconsumptionbyTe xaspowerplantstotalsover157,000milliongallons(482,100acre‐feet)

annually–enoughwaterforthemunicipaluseofover3millionpeopleforayear,eachusing140

gallons

perpersonperday.Thistotalwasestimatedbasedondataregardingwaterintake,diversion,and

returnflowsfromtheTexasWaterDevelopmentBoard(TWDB)andTexasCommissionon

EnvironmentalQuality(TCEQ).[28]Asexpected,highvaluesofwaterconsumptionperkWhinFigure

3.2correspondtoclosed‐loop

coolingsystems,whichconsumealargepercentageofwaterwithdrawn,

asdiscussedinChapter1.



27



Figure3.2.Waterconsumptionfor

thermoelectricpowergenerationinTexas.

Totalwaterconsumptionforelectricity

generationstatewideisover157,000million

gallons(482,100acre‐feet)annually–enough

waterforover3millionpeopleforayear,each

using140gallonsperpersonperday.[28]

Powerplantsareresponsibleforan

estimated2.5%ofthetotalwater

consumptionforTexas.[56]This

percentagereflectswaterconsumption

onlyanddoesnotincludewaterwithdrawn

foropen‐loopcooling.Waterwithdrawal

forcoolingismuchlargerthanwater

consumption,especiallywithopen‐loop

cooling.Understandingandaccountingfor



thedifferencesbetweenconsumptionand

withdrawalisimportantforaccurate

planningandmanagement.Specifically,

thelargeamountsofwaterthatneedtobe

withdrawnforcoolingintroduceavulnerabilityintothesystem:ifdroughtcreatesawatershortage,

thenpowerplantsmightbeforcedtoshutdown.Furthermore,reservoirsused

forclosed‐loopcooling

confinewaterthatotherwisecouldbeusedforotherpurposesdownstream.

EnergyforWaterandWastewaterTreatmentSystemsinTexas

SurfacewaterpermitsforpublicwatersupplyareconcentratedineastTexas,asshownonthenextpage

inFigure3.3,asaresultofavailabilityandpopulation.Theseallocationsrepresentrightstodivertor

storesurfacewater,whichisthentreatedtoapplica blestandardsinawatertreatmentplantand



distributedforuseinresidential,commercialandsometimesindustrialestablis hments. 



28



Figure3.3.Surfacewaterpermitsfor

municipalwatersupply.Decreasingrainfall

fromeasttowestTexasalsodecreasessurface

wateravailability.[57]

Largecitiesandriverauthoritiesgenerally

holdthelargestmunicipalsupplyrights.

Riverauthorities,quasi‐governmental

entities,generallysellwaterwholesaleto

citiesfortreatmentanddistributionas

publicwatersupply.Some,suchasLower

ColoradoRiverAuthority,alsotreatand

distributewaterforpublicsupply

themselves.

AccordingtotheState

WaterPlan,public

watersupplyinTexascurrentlyaccounts

forapproximately1,470,000million

gallons(4.5millionacre‐feet)ofwater

eachyear.[56]ElectricityuseforTexas

waterandwastewatersystems,however,

isnotcurrentlymeasureddirectly.Consequently,electricityconsumptionforTexaswatersystemsmust

beestimatedbasedonnational

averageelectricityusepervolumeofwatertreated,asshowninTable

2.1.UsingcurrentwaterflowratesfromtheStateWaterPlanandnationalaveragevaluesforenergy

perwatervolumetreated,Texasusesan estimated2.1to2.7TWh/yrforpublicwatersupplysystems,

accountingforabout1.5to

1.9%ofTexasindustrialelectricityuseand0.5to0.7%oftotalelectricityuse

annually.Thisislowerthanthenationalpercentagesforelectricityuseforwatersystemsduetothe

overallhigherelectricityconsumptioninTexasindustries.[11]Directlymeasuringelectricity

consumptionofTexaswatertreatmentplants,aswell

astheelectricityneededforsourcewater

collectionandconveyance,wouldprovideamorereliablepictureofenergyrequirementsforwater

treatment.

Municipalwastewatertreatmentplantsaregenerallydistributedaccordingtopopulationandarethus

concentratedineasternandcentralTexas,asshownonthenextpageinFigure3.4.

Over76%ofthe

municipalwastewatertreatmentplantsinTexaseachtreatflowsof1milliongallonsperday(mgd)or

less.LargerwastewatertreatmentplantsservingcitiessuchasDallas,Houston,SanAntonioandAustin,

however,treatflowsupto200mgd.



29



Figure3.4.Municipalwastewatertreatmentflow

forTexaswastewatertreatmentplants.Over

76%ofthewastewatertreatmentplantsinTexas

aresmall–lessthan1mgd.[58,59]

Similarlytowatertreatmentplants,

informationonenergyuseatTexas

wastewatertreatmentplantsisnotreadily

available.Thus,electricityforwastewater

treatmentmustbeestimatedbasedon

nationalaveragevaluesforenergyper

volumeofwastewatertreatment,givenin

Table2.2.However,asdiscussedinChapter

2,energyrequiredper

volumeof

wastewatertreatedvarieswithwastewater

treatmentplantcapacity,asshowninTable

2.3.Usingenergypervolumeofwastewater

treatedforspecificplantcapacities,total

energyforwastewaterwasestimatedfor

technologiesrangingfromtricklingfiltertreatmentatthelowendtoadvancedtreatmentwith

nitrificationatthe

highend.Usingthisapproach itisestimatedthat1.1to2.2TWh/yrisrequiredfor

wastewatersystemsinTexas,amountingto0.8to1.5%ofTexasindustrialelectricityuseand0.3to

0.5%oftotalelectricityuse.

Combiningtheseestimatesforwaterandwastewatertreatment,Texaswaterandwastewater

systems

require3.2to4.9TWhofelectricityannually.Withcurrentelectricitygenerationof400TWh/yr,water

andwastewatersystemsuse0.8to1.2%oftotalTexaselectricityand2.2to3.4%ofindustrialelectricity

use.[44].DirectmeasurementandreportingofelectricityuseinTexaswaterandwastewater

treatmentplants

wouldprovideamoreappropriatebasisforplanning,management,andpolicy.



30



Chapter4. FutureEnergyandWaterUseinTexas

ThepopulationofTexasispredictedtodoubleby2060,fromthecurrent23milliontoabout46million

by2060.[56]PopulationinTexashasexperienceddramaticgrowthsince1850,showninFigure4.1.

U.S.CensusprojectionsinFigure4.1suggestnearlyexponentialpopulationgrowthbetween2000and

2030.[60]

Withoutimplementationofsignificantenergyandwaterconservationandefficiency

increases,energyandwaterconsumptionarelikelytogrow.



Figure4.1.Texascensuspopulation

withprojectionsto2030.[60]

Undera“businessasusual”

scenario,thispopulation

increasewilltranslateinto

greatlyincreaseddemandfor

bothpowerandwater.The

centralchallengeforTexas

policymakersishowtobalance

thisprojectednewdemandwith

theneedtoensuresustainable

useoflimitedwaterresources

andprovidepowerina

manner

thatprotectsairqualityandmeetsthelikelyrequirementsofnewfederallegislationtoaddressclimate

change.Thischallengeismademoredifficultbytheinterconne ctionsbetweenwaterandenergyand

thetradeoffsinvolvedinselectingvariouspowerandwatersupply options.

ElectricityDemandProjections

UsingthecurrentfuelmixforpowergenerationinTexas,a“businessasusual”powerdemandscenario 

wasprojectedto2018(Figure4.2).Thisscenariodoesnotaccountforsignificantreductionsindemand

thatcouldbeattainedwiththeimplementationofadvancedefficiencymeasures, nordoesitreflect

changesinfuel

mixthatwouldlikelyresultfromacarboncap‐and‐tradeorcarbontaxsystem.



31



100

150

200

250

300

350

400

450

500

2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018

TWh

Texas Total Electricity Generation by Fuel - BAU

Nuclear Coal NGCC NG-ST NG-GT Wind Non-wind Renewable On-site industrial

Figure4.2.ProjectionsforTexaselectricitygenerationunderabusinessasusual(BAU)scenarioshowgrownto490

TWhby2018.[61]

Inthebusinessasusual(BAU)scenarioincludingcurrentpowergenerationandannouncedfuture

powerplants,totalelectricitygenerationincreasestonearly490TWhannuallyby2018.Thefuelmix

forthisscenarioassumesnuclearpowerplantscurrentlypursuingpermittingwillbebuilt.Italso

assumesrapidlyexpandingwind‐generatedelectricity.

Sincenaturalgaspowerplantsprimarily

representpeakelectricityloadgenerati ngpotential,electricitygenerationfromtheseplantsremains

relativelyconstantthroughouttheprojectedscenario.Severalnewpowerplantsareproposedfor

constructioninTexasby2015.The“On‐siteindustrial”categoryisthatelectricitythatisgeneratedat

industrialfacilities

fortheirownuse,buttheindustrialsectoradditionallybuyselectricityfromthe

electricgrid.

Figure4.3onthenextpageprojectsfuelmixunderanalternative“highrenewables”scenario.Ahigh

renewablescaseispossiblethroughlegislationthatpromotesahigherrenewablefuelsstandardor

implementationofacarbontax

orcap‐and‐tradesystem.Thesetypesoflegislationpromotesources

suchaswind,solar,biomassandnuclear.ThescenarioinFigure4.3doesnotaccountforsignificant

reductionsindemandthatcouldbeattainedwiththeimplementationofadvancedefficiencymeasures,

nordoesitaccountforotherregulatory,economic

orotherfactorsthatmightaffectfuelmix(e.g.the

availabilityoffinancingorwastedisposalfornuclearplants).Coal‐generatedelectricityisprojectedto

decreasesomewhatunderthehighrenewablesscenarioifacaponcarbonisestablishedthrough

federallegislation,whilebothwindandnuclearpowerareprojectedto

increasedramatically.



32



100

150

200

250

300

350

400

450

500

2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018

TWh

Texas Total Electricity Sales by Fuel -

High Renewables Projection

Nuclear Coal NGCC NG-ST NG-GT Wind Non-wind Renew On-site Industrial



Figure4.3.ProjectionsofTexaselectricitygenerationwithalargeincreaseinrenewableenergy‐generated

electricityisshownabove.[61]

Itisdifficulttoprojecthowthevariouselectricityge nerationscenariosinFigures4.2and4.3might

affectwaterdemand,sincesuchdemandishighlydependentnotonlyonthefuelmix,butalsoonthe

typeofcoolingtechnologyselectedforparticularplants.Whatisclear,however,isthatwithout



implementationofadvancedenergyefficiencymeasures,electricitydemandinTexaswillgrowrapidly

andtherewillbepressuretosupplypartofthatnewdemandthroughnuclearplants,evenundera

“highrenewables”scenario.Thisscenariocouldhavesignificantimplicationsforwatersupplysince

nuclearplantsconsumemorewaterthan

similarly‐sizedfossilfuelplants. Whilenonuclearpower

plantscurrentlyuseair‐cooling,thePaloVerdenuclearpowerplantsinArizonausereclaimedwater.

Carboncaptureandstorage(CCS)systemsareapossibilityforthefuture,especi allyinresponseto

potentialcarbonlegislationasataxorcapandtradescenario.Carbondioxide(CO

)canbecaptured

fromfluegasesinexistingpulverizedcoalpowerplantsbyretrofittingCO

scrubbers.Suchscrubbers

captureCO

usingchemicalsolvents,afterwhichthesolventthenundergoesthermalcyclingtoremove

,whichisthentransportedandstored.[29]CCSsystemsallowforpowergenerationusingcoal

whileconcurrentlyreducingcarbonemissionstotheatmosphere.TheseCCSsystemsdo,however,

increasewaterconsumptionratesofpowerplants,intermsofgallonspernetgeneration,dueto:1)

theparasiticpowerlossfrom

theuseofsteamtoregeneratethesolvent;2)thepowerrequiredto

compressCO

toasupercriticalstateforpipelinetransport;3)additionalcoolingrequirementsofthe



33



carbonstrippingprocess;and4)additionalelectricityforpumpingcollectedCO

intostorage.[28]These

tradeoffsbetweenairqualityandwaterconsumptionmayplayanincreasinglyimportantroleinthe

future.

WaterDemandProjections

The2007StateWaterPlanprojectsthatmunicipalwatersupplydemandwillgrowto8.3millionac‐

ft/yearby2060,fromacurrentlevelofabout4.5millionac‐ft/year.[56]Whilesomeimplementationof

increasedmunicipalwateruseefficiencyisincludedinthisprojection, muchmoreadvanced

conservationispossible

andwouldgreatlyreducedemand.Forexample, arecentanalysisbytheTexas

StateComptrollershowsthatseveralcitiesprojectonlyminorornoreductioninpercapitawater

demandby2060.[62]

Figure4.4.ProjectionsfromtheStateWater

Planshowalargeincreaseinmunicipal

waterdemandfrom2000to2060.[56]

TheStateWaterPlanproposesthat

muchoftheprojecteddemandbemet

throughconstructionofnewreservoirs

thatwouldmovewaterfromeastTexas

toDallasandothercentralTexascities.

Italsoenvisionsseveralnewmajor

pipelineprojectstobringwaterfrom

ruralareastocities.

Newsupplyproposals

basedonmovingwaterlongdistancescreatepotentiallysignificantenergy

demands,thoughinsufficientinformationexistsatthistimetoquantifytheincreasedelectrical

generationcapacityrequiredforspecificprojects

.Inaddition,increasedpublicwatersupplyuse

(howeverthewaterissupplied)willresultinincreasedelectricityusefortreatmentanddistributionand

forwastewatertreatment.

ConservationofEnergyandWater

Giventheenergy‐waterinterrelationships,waterconservationandenergyconservationaresynonymous

andareagoodstartingpointforrobustpolicyformulation.Specifically,conservingwaterreducesthe

electricityneededtocollect,treat,anddistributewater,aswellastoconvey,treat,and discharge

wastewater,inmanysituations.Conservingelectricitysavesenergy

andalsothewaterneededtocool

powerplantswhilethatelectricitywasgenerated.





Thesecondvolumeofthisreportwillexamineseveralproposedwatersupplycasestudiesinmoredetail,

includingquantificationofenergydemands.

1990 2000 2010 2020 2030 2040 2050 2060 2070

Muncipal Water (million ac‐ft/yr)

Year

MunicipalWaterDemandProjections



34



Thesecondvolumeofthisreportwillhavemoredetailedanalysisonthemutualbenefitsofwaterand

energyconservation,howeversomepreliminaryresults aresharedhere.Becauseelectricity

consumptionislinearwiththeamountofwaterandwastewaterthataretreated,distributedand

collected,itcanbeseen

thatreducingwaterflowsthroughtheseenergy‐intensivestepsreducesthe

amountofelectricitythatis required.Ifmunicipalwateruseandwastewaterflowsarereducedby10%,

thestate’sdemandforelectricitywouldgodownby320to490millionkWhatthewater/wastewater

sectorsalone.Inaddition,if

theresidentialsectorreducesitsuseofheatedwaterbyathird,thenthat

wouldsaveapproximately1to3billionkWhofelectricityannually.[55]Reducingenergydemandalso

reducesdemandforcoolingwateratpowerplants:reducingoverallelectricitygenerationinTexasby

10%couldreducewaterconsumptionby

asmuchas15,000milliongallonsofwaterperyear,depending

onwhichpowerplantsreducetheiroutputtoaccommodatethelowerdemand.

Inadditiontoincreasedwaterefficiency,waterreuseisanoptionforsavingwaterandenergy.Some

wateruses,suchaslandscapeirrigationandtoiletflushing,do

notrequirewatertobetreatedto

drinkingwaterstandards.Onealternativetowateringlawnsandflushingtoiletswithdrinkingwateris

usingreclaimedwater.Reclaimedwateriseffluentfromawastewatertreatmentplant,trea tedwitha

processlikethatshowninFigure2.5withadditionaltertiaryfiltrationbeforereuse.Though

reclaimed

waterisnotnecessarilysafefordrinking,additionalfiltrationremovescontaminantsthatposethreatsto

humanhealthduringunintendedexposure.[63]Whilethisadditionalwastewatertreatmentrequires

approximately120kWhpermilliongallonsfortertiaryfiltration,useofreclaimedwatersaves

approximately1,400to1,800kWhofelectricityper

milliongallonsneededforcollecting,treating,

disinfecting,anddistributingdrinkingwaterfornon‐potablesuses.[44]

Inadditiontosavingenergy,waterreusecanaugmentexistingwatersuppliesandisgenerallyamore

cost‐effectiveoptionthanacquiringnewwatersupplies.[64]Varyinglevelsofadditionaltreatmentare

necessary,dependingon

thewaterreuseapplication.

Reclaimedwatercanalsobeusedtoartificiallyrechargegroundwateraquifersthroughsurface

spreadinganddirectinjection.Surfacespreading–applyingreclaimedwatertothelandsurfaceto

promotewaterseepageandpercolationintotheaquifer–requireslittletonoadditionaltreatmentor

energydue

tothenaturalfiltrationofsoil.Directinjection–usingwellstointroducereclaimedwater

intotheaquiferwatertable–however,requiresadditionaltreatm entbeyondadvancedwastewater

treatment,usuallyenergy‐i ntensivemembranewatertreatmenttoremovepotentialpathogens.[63]

Reclaimedwatercanalsobereusedtosupplementpublicdrinkingwater

supply.Followingadvanced

wastewatertreatment,reclaimedwateristreatedusingmembranesorotheradvancedtechnologyto

removepathogensandtracecontaminantsandisthenaddedtoanexistingsurfacewatersource,such

asareservoir,orfeddirectlytoawatertreatmentplant.Thoughthistypeofwaterreusehas

sometimesignitedadversepublicperceptionregardingquality–the“toilet‐to‐tap”idea–reclaimed

waterhasahigherqualityaftermembranetreatmentthanmanyrawwatersources.[63]Infact,

drinkingwatersourcesforover26millionpeopleintheUnitedStatescontainbetween5and100%

treatedwastewatereffluent

fromupstreamdischargeduringlowflowperiods.[64]Somewater‐



35



strainedsocietiessuchasSingaporealsousereclaimedwaterasapublicsupplywithoutadversehealth

effects.

Waterreuseconserveswaterand,insomeapplications,conservesenergybynottreatingwaterfornon‐

potableusestodrinkingwaterstandards.Inotherapplications,additionalenergy‐intensivetreatment,

suchasmembrane

filtration,isnecessarytoprotecthumanhealthduringwaterreuse,requiringupto

4,000kWhpermilliongallons.[45]Yetthisenergyinvestmentforwaterreuseisstilllessthanthe

energyneededforseawaterdesalinationat9,700to16,500kWhpermilliongallonsorlong‐haulwater

transferwhen

watersuppliesaredepleted,over6,100kWhpermillion gallonsfortheColoradoRiver

AqueducttransfersysteminCalifornia.[45]



36



Chapter5. PolicyDiscussion

AsTexasconfrontsthechallengesposedbyclimatechange,decisionsabouthowtosupplyenergyand

watertoourstate’sgrowingpopulationshould nolongerbemadein isolationfromeachother.The

challengeswouldbenefitfromrecognizingthedeepinter‐connectionsandtrade‐offsinvolvedin

decidinghowtomeet

powerandwaterneedsinamoreresource‐constrained21

century.

Carbon,Water,andEnergy:TensionsandPolicyTradeoffs

Becauseenergyandwaterareinextricablylinked,limitsorincreasingdemandsononeresourcecan

affecttheother.Furthermore,becauseofthepowersector’scarbonemissions,increasingtheenergy

efficiencyofelectricpowergenerationbothlowerstheseemissionsandreduceswaterconsumption.

Sincecarbonemissionsinpartdriveclimatechange,which

impactsthehydrologicalcycle,itisanother

linkagebetweenenergyandwater.Implementationofnextgenerationpowerplanttechnologiessuch

asultra‐supercriticalcoalandintegratedgasificationcombined‐cycleplants(aswellascombined‐cycle

naturalgastechnology)hasthepotentialtoincreaseenergyefficienciesby25to50%over

thosefor

traditionalpulverizedcoalplantswithpollutioncontrols.Subsequently,thecarbonemissionsandwater

useperMWhofgeneratedelectricitywouldgodown.

Increasedefficiencyinwaterusagealsocanplayaroleinreducingcarbonemissions.Providingwater

fordomestic,agriculturalandindustrialconsumptionrequiresenergy,whichemitscarbon.

Traditionally

loweringwaterusagesimultaneouslylowersenergyconsumption,whichlowerscarbonemissions

(thoughsuchreductionshavealwaysbeenoverwhelmedbyoverallgrowthintheusageofbothwater

andenergy).Forexampleoverthelast50yearsthewaterefficiencyofpowerproductionhassteadily

increasedwhileatthesame

timebothelectricpowerproductionandthewaterusedforpower

productionhassteadilyincreased.

Despitethesynergiesofconservation,weareenteringanerainwhichpublicpoliciesdesignedtoreduce

wateruseforenergymayleadtoincreasesincarbonemissions.Conversely,policiestoreducecarbon

emissionsmightincrease

wateruse.And,energypolicies,suchaspromotionofalternativebiofuelsfor

transportationhavecompetingeffectsonwateruse.

Movingforward,theseinterrelationshipsmustbeidentifiedandunderstoodbeforeimplementingpublic

policyproscriptionsthatbenefitonecomponentofthiscomplicatedcarbon‐water‐energyrelationship

whileaccidentallyundermininganother.(Issuesrelated

tothelinkagesbetweentransportationfuels

andwaterwillbediscussedinaforthcomingreport.)

EnergyPoliciesHaveMixedWaterImpacts

Analysisofcurrentlong‐termprioritiesinU.S.energypolicysuggestsamixedoutlookforfutureimpacts

oftheenergysectoronwaterresources.TheEnergyPolicyActof2005

(EPACT2005)andtheEnergy

IndependenceandSecurityActof2007(EISA2007)bothprioritizeddevelopmentofdomesticsourcesof

energy,includingrenewablepower,nuclearpower,andunconventionaltransportationfuels.



37



BecausetheelectricpowersectorisresponsibleforthelargestwithdrawalsofwaterintheU.S.,changes

tothepowersectorcanhaveasignificantimpactontheavailabilityofwaterresources.Specifically,

increasingthemarketpenetrationofrenewabletechnologiessuchassolarphotovoltaics(PV)andwind 

turbineswill

lowertheuseofwaterbythepowersectorbecausethosetechnologiesdonotrequire

cooling.Concentratedsolarpower(CSP)systemsaremorecompatibleforlarge‐scale,centralized

powergenerationthansolarPVsystemsandtheycurrentlyareconsiderablylo wer incostperunitof

electricpower.Thethermalconversion

ofradiantenergyfirsttosteamandthentoelectricityviaa

steamturbine,however,canrequirecoolingwateratrates(gallonsperkWh)higherthan coaland

nuclearpowerplantsifusingpurewetcoolingtowers.However,air‐andhybridcoolingsystemsforCSP

couldbeimplementedinTexas.

The

positivewatereffectsofrenewablepowermightalsopossiblybeoffsetbyprojectedincreasesin

nuclearpowerinstallationsdrivenbycarbonlimits.Nuclearpoweristhemostwater‐intensiveformof

conventionalpowergeneration,andair‐cooling isveryunlikelytoeverbeusedfornuclearpowerplants.

Furthermore,the

economicenvironmentthatisconducivetorenewablesources,namelyhighpricesfor

carbonemissionsandnaturalgas,isalsogoodfornuclearpower.Thus,itispossiblethattheseformsof

powerwillgrowintandem.Consequently,theneteffectonwaterresourcesfromfuturechangesinthe

electricpowersector

duetocarboncontrolpoliciesaredifficulttopredict.

WaterPoliciesMightHaveDetrimentalCarbonImpacts

Althoughtheimpactoflong‐termenergypoliciesonwaterconsumptionisnotclear,somewater

policiesunderconsideration mayhavedetrimentalimpactsoncarbonemissions.Thesepoliciesinclude:

1)apushfornew

watersupplyfromdistant,low‐qualitysources,and2)strictertreatmentstandardsfor

waterandwastewater.

Somecommunitiesmayturntodesalinationtomeetnewwaterdemand.Desalinationofseawaterisa

drought‐resistantwatersupply,howeverwithcurrenttechnologiesthisstabil itycomeswithalarge

energycost.InTexasdesalination

ofbrackishwaterisalreadyunderwayorisbeingimplementedasa

portionofthepublicwatersuppliesforthecitiesofSanAntonio,ElPaso,andLubbock.

Finally,morestringenttreatmentstandardsfordrinkingwaterqualityandwastewatermaybecome

addedtofederalregulations,inparticulartoremediatethe

presenceofpharmaceuticalsandother

contaminantsforwhichtherearenocurrentstandards.Watertreatmenttoremovelowconcentration

pollutantsistypicallyanenergy‐intensiveprocess.Thus,raisingthetreatmentstandardsleadsto

increasedenergyconsumptionbywaterandwastewatertreatmentplants,whichnominallyyields

increasedcarbonemissions.

CarbonPoliciesMight

HaveDetrimentalWaterImpacts

Thereisageneralconsensusamongelectricpowercompaniesthatimplementationofanationalcap‐

and‐tradeprogramoracarbontaxisinevitableintheU.S.inthenearfuture.Althoughsomeoutcomes

fromimplementationofnewcarbonpolicieswillreducewaterusage(suchas

greaterpenetrationof

windpower,anddeploymentofphoto‐voltaicgeneration)atleastforthefirstfewdecadesitispossible



38



thesewatersavingswillbe

counteractedbyincreasesinwater

consumptionrelatedtocarbon

capture,deploymentofconcentrated

solarandincreasednuclear

generation.Asnotedbefore,carbon

policieswillfavorexpansionof

existingnuclearpowerinstallationsas

wellasthepermittingand

constructionofnewones.Because

nuclearpower

plantsarewater‐

intensive,anincreaseinthecapacity

ofnuclearplantswilllikely leadto

greaterwaterusebythepower

sector.

Carboncaptureandsequestration

(CCS)willalsohavedirectimpactson

waterwithdrawalandconsumption

bytheelectricpowerindustry.If

carboncaptureisimplementedata

large‐scalethroughretrofitting

existingfossilfueledpowerplants,the

waterdemandsbythepowersector

couldincreasedramatically.Post

combustioncarboncapturesystems

basedonaminesreducenetpower

plantefficiencies,possiblybyasmuch

as25to30%,suchthatinmakingthe

sameamountofelectricityavailable

for

thegrid,moregrosspowerand

heatmustbegeneratedthus

increasingtheamountofwaterused

proportionally.Inthiscase,itis

possibleadditionalpowerplant

capacitywouldbebuilttomakeupfor

lostcapacity.Ifimplementationof

CCSleadstoconstructionofnew

powerplants,theymight

bebasedon

moreenergyefficientpowerplant

technologiessuchassupercriticalcoal

ClimateChangeImpactsonWaterResources

Manyunknownsstillexistregardingtheimpactofclimatechangeonwater

resources.Applyingpredictionsofrisingglobaltemperaturetoregional

climateandweathermodelsisarelativelynewfield,andmanyregionshave

yettohaveanyresearchdirectlyfocuseduponthem.Furtherapplyingthese

predictionsaboutlocalimpactsto

waterresourcesissuesrequiresonemore

stepofprediction.Havingsaidthis,thereareseveralfactorsthatscientists

agreewillshapeboththequalityandquantityofwaterresourcesoflocal

governments.

Climatechangemayactasaforcingfunctionthatfurtherintertwinesand

strainstheenergy‐waternexus.Specifically,

greenhousegas(GHG)

emissionsfromenergyusearealeadingcauseofclimatechange.One

importantaspectofclimatechangeisitspotentialfornegativeimpactonthe

watercycle.Discussionofclimateeffectsoftenfocusesontherisksofrising

sealevels,butitistheriskofchangesto

thehydrologicalcyclethatshouldbe

ofequalorgreaterconcern.Theseeffectsarehardtopredict,butitis

expectedthathighertemperaturescouldinduceseveralconsequences,

includingmoreprecipitationasrainratherthansnowfall,movingthe

snowmeltseasonearlier(andtherebyaffectingspringwaterflowsforrivers

like

theRioGrandeortheRedRiver),increasingintermittencyandintensity

ofprecipitation,andraisingtherisksoffloodsanddroughts.[10]Whilemost

ofTexasisnotveryvulnerabletochangesinsnowpatterns,thesealevel

risescancausecontaminationofgroundwateraquifersfromsalinewater

intrusionnearthe

coasts.Thesechallengescanbemitigatedbyutilizing

deeperaquifers,movingwaterfartherwithlong‐haultransfersystems,or

treating/desalinatinglower‐qualitywatertomakeitdrinkable.Eachofthese

approachesinvolvesgreaterenergyexpendituresforeachgallonofwater.

Withatypicalenergymixoverthenextfewdecades,

theseenergy

expendituresforwatertreatmentandconveyancewillreleaseadditional

greenhousegases,whichintensifythehydrologicalcyclefurther,potentially

compoundingtheprobleminaself‐reinforcingfeedbackloop.

Figure5.1.

Theenergy‐climate‐

watercyclecreatesaself‐

reinforcingchallenge.Energyuse

releasedgreenhousegases

contributetoclimatechange,which

intensifiesthehydrologicalcycle,

whichleadstogreaterenergyuse

forwater,whichleadstoadditional

greenhousegasemissions.





39



andintegratedgasificationcombinedcycle(IGCC)plantsallofwhichrequirelesswaterthanatypical

pulverizedcoalpowerplant.ForIGCCplantsbasedonGERadiant‐Convective(452gallonsperMWh),

GE‐Quench(510gallonsperMWh),Conoco‐Phillips(433gallons perMWh)orShell(443gallonsper



MWh)gasifiers,thewateruseissubstantiallylessperunitofproducedelectricitythanthatofatypical

pulverizedcoalpowerplant.[65]

Anadditional10to20%morewaterisrequiredforaddingcarboncapturetotheseIGCCreference

plants,whichissmallrelativetothatforpulverizedcoal

plants.[66]AsaresultanIGCCplantwith

carboncapturehasawaterusageonethirdlessthanatraditionalpulverizedcoalplantwithoutcapture .



[27]

Ifclimatechangedrivenpublicpolicyresultsinnew‐buildpowerplantsbeingamixofnewpowerplant

designssuchasIGCCthathavebothhigherwaterandenergyefficiencies,evenwithcarboncapture

thenclearlytheeffectonwaterresourceswillbepositive.



40



Conclusions

Aslongasthermoelectricpowerplantsusewatercooling technologiesandwaterandwastewater

treatmentplantsuseelectricityforprocesses,itwillbeimportanttoconsidertheenergy‐waternexusin

planningandresourcemanagement.Withpopulati ongrowth,theeffectsofclimatechangealready

impactingthehydrologicalcycle,andnewcarbon

‐pricingpolici esunderconsideration,understanding

thetradeoffsbetweenenergyandwaterbecomesevenmorevitalthaneverforresourceplanningand

management.

Inpreparingthereport,however,itbecameclearthatsubstantiallymoresite‐specificdataare

necessaryforafullunderstandingofthenatureoftheenergy‐waternexus

inTexas.Thus,we

recommendthatthestateincreaseeffortstocollectaccuratedataonthewithdrawalandconsumption

ofcoolingandprocesswateratpowerplants,aswellasdataonelectricityconsumptionforpublicwater

supplyandwastewatertreatmentplantsanddistributionsystems.Thesedatawillalsobeuseful

in

planningforthefuture.

Inthefuture,wateruseforelectricitygenerationwilldependonseveralfactors,includingthefuelmix

fornewgeneratingcapacity,thetypeofpowerplantandthetypeofpowerplantcoolingsystemsthat

aredeployed.Likewise,theamountofelectricityusedtopump,

treatanddeliverpublicwatersupply

andtotreatwastewaterwilldependonchoicesaboutwatersourceandtreatmenttechnology.These

trends,andtrade‐offs,stillneedtobebetterunderstood, butitisundeniablethattherewillbe

importantimplicationsforwaterandenergypolicyatthestate andlocal

level.

Thefollowingpolicyrecommendationsarestepsthatcanbetakennowtobuildthebasicsofa

frameworkformoreintegratedenergyandwaterplanning:

• Requirethatapplicationsfornewpowerplantsincludeananalysisofthewaterandefficiency

implicationsofvarioustypesofcoolingoptionsapplicable

totheproposedplant.Theanalysis

shouldincludefactorsrelatingtolocalclimateandairquality,regionalairquality,water

availability,includinginstreamflowrequirements,fueltypeandplantefficiency. 

• Requireacleardemonstra tionofwateravailabilityinthesitingofnewfossil‐fueledpower

plantsorconcentratedsolar(this

analysisshouldconsideraveragerainfallyearsaswellas

availabilityduringextremedroughtevents).

• Providestatestatutoryandregulatoryincentivesforimplementationofpowerplantcooling

technologiesthatarelesswater‐intensivethantraditionalsystems,suchasair‐coolingorhybrid

wet‐drycooling.

• Providestate‐approvedg uidance

(fromtheTexasWaterDevelopmentBoardand/ortheState

EnergyConservationOffice)towatersuppliersandwastewatertreatmentproviderstohelp

quantifyenergyuseandcostsavingsassociatedwithwaterconservation.



41



Theover‐archingmessageisthatimplementingadvancedefficiencyisthekeytothesustainableuseof

bothenergyandwater.Improvingwaterefficiencywillreducepowerdemandandimprovingenergy

efficiencywillreducewaterdemand.Greaterefficiencyinusageofeitherenergyorwaterwillhelpto

stretch

ourfinitesuppliesofboth,aswellasreducecoststowaterandpowerconsumers.Thestateand

localgovernmentsshouldcontinue,andwhereverpossible,increasefundingandtechnicalsupportfor

waterandenergyconservationandefficiencyprograms.



FutureWork

Futureinstallmentsinthisreportserieswillincludecasestudiesofenergyimplicationsoffuturewater

supplystrategiesforTexasandmoreplace‐specificwatersupplyimplicationsofthefuturefuelmixfor

electricityproduction.Thereareseveralotheraspectsoftheenergy‐waternexusthatarenot

contemplatedinthis

series,butbeinginvestigatedbyseveralotherentities,includingproductionof

hydropowerforelectricitygeneration,wateruseinproducing variousfossilfuelsandalternative

transportationfuels,suchasethanolorotherbiofuels.



42



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

47



AppendixA:GlossaryofTerms



Energyterms

capacity Theelectricalpowerthatapowerplantiscapableofproducing,generally

measuredinkilowattsormegawatts

CCS Carboncaptureandstorage;systemstocollect,transport,andstoreCO



frompowerplants

 carbondioxide

consumption Evaporatingwatersuchthatitisnotdirectlyreusableinthesamelocation

CSP Concentratingsolarpower;typeofsolarcellsthatconvertthermalenergy

fromthesunintoelectricalenergy

generation Theamountofelectricalenergythatapowerplantproduces,generally

measuredinkilowatt‐hours

ormegawatt‐hours

GHG greenhousegas

GW Gigawatt

HRSG Heatrecoverysteamgenerator;usedwithcombined‐cyclepowerplants

IGCC Integratedgasificationcombined‐cycle

kW kilowatt,unitsofpower

kWh kilowatt‐hour,unitsofenergy

MW Megawatt,10

kW,unitsofpower

MWh Megawatt‐hour,10

kWh,unitsofenergy

PV Photovoltaic;typeofsolarcellsthatconvertradiantenergyfromthesun

intoelectricalenergy

TWh Terrawatt‐hour,10

kWh,unitsofenergy

withdrawal Removingwaterfromasurfaceorgroundwatersource



Waterterms

ac‐ft acre‐feet.(325,851gallons)

capacity Theflowratethatawaterorwastewatertreatmentplantiscapableof

treating,generallymeasuredingallonsperday

demand Consumption;termprimarilyusedbyTWDB

gal gallon



48



Mgal milliongallons

mgd milliongallonsperday

permitteddischarge Themaximumflowratethatawaterorwastewatertreatmentplantcan

legallyreturntoareceivingwaterbody



Generalterms

EISA2007 EnergyIndependenceandSecurityActof2007

EPA EnvironmentalProtectionAgency

EPACT2005 EnergyPolicyActof2005

TCEQ TexasCommissiononEnvironmentalQuality

TWDB TexasWaterDevelopmentBoard



49



AppendixB:TypicalWaterBalancesforPowerPlants

AmericanElectricPower



50



51



SouthTexasProject