FINAL-A Zero-Emissions City in the Desertcushman/courses/engs44-old/Zero...Energy surplus: Masdar...
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March/April 2009 ‐ Technology Review ‐ Published by MIT since 1899 A Zero-Emissions City in the Desert Oil‐rich Abu Dhabi is building a green metropolis. Should the rest of the world care? By Kevin Bullis The first hints of the project are visible. A white wall stretches through the desert, like a chalk line on a dusty playing field. A bus with darkened windows stirs a low cloud, ferrying workers past a cluster of steel cranes, two portable drilling rigs, and a stand of concrete columns sprouting rust‐colored rebar. A tall wire fence guards rows of solar panels mounted on concrete pads. The construction is the start of a vast experiment, an attempt to create the world's first car‐free, zero‐carbon‐dioxide‐emissions, zero‐waste city. Due to be completed in 2016, the city is the center‐piece of the Masdar Initiative, a $15 billion investment by the government of Abu Dhabi, which is part of the United Arab Emirates. The new development, being built on the outskirts of Abu Dhabi city, will run almost entirely on energy from the sun and will use just 20 percent as much power as a conventional city of similar size. Garbage will be sorted and recycled or used for compost; sewage will be processed into fuel. Concrete columns will lift the city seven meters off the ground, creating space underneath for a network of automated electric transports that will replace cars. Planners predict that the development will attract 1,500 clean‐tech businesses, ranging from large international corporations to startups, and‐‐eventually‐‐some 50,000 residents. The city will be an oasis of renewable energy in a country of five million, made rich by oil, that consumes the most natural resources per capita in the world. Seen one way, it's just the latest ostentatious project in a country that's been defined by them. Indeed, the UAE is already home to the world's tallest building and an enormous indoor ski facility that features a 200‐meter‐long black‐diamond slope. Real‐estate developers have dredged coral and sand from the sea floor, piling it up in the Persian Gulf to create islands in the shape of palm trees and a map of the world. Yet many experts are optimistic that the city can become a test bed for new approaches to the engineering and architectural problems involved in creating environmentally sustainable cities. Although architects have already designed and builders constructed many small zero‐emissions residences and commercial buildings, projects involving large, multi‐use commercial buildings have fallen short of expectations, using too much energy or failing to generate enough. Part of the problem is the growing complexity that comes with scale, says J. Michael McQuade, senior vice president of science and technology at United Technologies in Hartford, CT; today's design software hasn't been able to handle it. But Masdar City, itself developed with the help of
Transcript of FINAL-A Zero-Emissions City in the Desertcushman/courses/engs44-old/Zero...Energy surplus: Masdar...
March/April2009‐TechnologyReview‐PublishedbyMITsince1899AZeroEmissionsCityintheDesertOil‐richAbuDhabiisbuildingagreenmetropolis.Shouldtherestoftheworldcare?ByKevinBullis
Thefirsthintsoftheprojectarevisible.Awhitewallstretchesthroughthedesert,likeachalklineonadustyplayingfield.Abuswithdarkenedwindowsstirsalowcloud,ferryingworkerspastaclusterofsteelcranes,twoportabledrillingrigs,andastandofconcretecolumnssproutingrust‐coloredrebar.Atallwirefenceguardsrowsofsolarpanelsmountedonconcretepads.Theconstructionisthestartofavastexperiment,anattempttocreatetheworld'sfirstcar‐free,zero‐carbon‐dioxide‐emissions,zero‐wastecity.Duetobecompletedin2016,thecityisthecenter‐pieceoftheMasdarInitiative,a$15billioninvestmentbythegovernmentofAbuDhabi,whichispartoftheUnitedArabEmirates.Thenewdevelopment,beingbuiltontheoutskirtsofAbuDhabicity,willrunalmostentirelyonenergyfromthesunandwillusejust20percentasmuchpowerasaconventionalcityofsimilarsize.Garbagewillbesortedandrecycledorusedforcompost;sewagewillbeprocessedintofuel.Concretecolumnswillliftthecitysevenmetersofftheground,creatingspaceunderneathforanetworkofautomatedelectrictransportsthatwillreplacecars.Plannerspredictthatthedevelopmentwillattract1,500clean‐techbusinesses,rangingfromlargeinternationalcorporationstostartups,and‐‐eventually‐‐some50,000residents.Thecitywillbeanoasisofrenewableenergyinacountryoffivemillion,maderichbyoil,thatconsumesthemostnaturalresourcespercapitaintheworld.Seenoneway,it'sjustthelatestostentatiousprojectinacountrythat'sbeendefinedbythem.Indeed,theUAEisalreadyhometotheworld'stallestbuildingandanenormousindoorskifacilitythatfeaturesa200‐meter‐longblack‐diamondslope.Real‐estatedevelopershavedredgedcoralandsandfromtheseafloor,pilingitupinthePersianGulftocreateislandsintheshapeofpalmtreesandamapoftheworld.
Yetmanyexpertsareoptimisticthatthecitycanbecomeatestbedfornewapproachestotheengineeringandarchitecturalproblemsinvolvedincreatingenvironmentallysustainablecities.Althougharchitectshavealreadydesignedandbuildersconstructedmanysmallzero‐emissionsresidencesandcommercialbuildings,projectsinvolvinglarge,multi‐usecommercialbuildingshavefallenshortofexpectations,usingtoomuchenergyorfailingtogenerateenough.Partoftheproblemisthegrowingcomplexitythatcomeswithscale,saysJ.MichaelMcQuade,seniorvicepresidentofscienceandtechnologyatUnitedTechnologiesinHartford,CT;today'sdesignsoftwarehasn'tbeenabletohandleit.ButMasdarCity,itselfdevelopedwiththehelpof
extensivemodeling,willbewiredfromthebeginningtocollectdatathatcouldprovevaluablefordevelopingbettermodels.Thatinformationcouldmakefuturezero‐emissionscitiescheaperandeasiertobuild.
Andthedevelopmentismeanttomakemoney,notjustintroducenewtechnology."WewantMasdarCitytobeprofitable,notjustasunkcost,"saidKhaledAwad,theproject'sdirectorofpropertydevelopment,atahugereal‐estateexhibitioninDubailastfall."Ifitisnotprofitableasareal‐estatedevelopment,itisnotsustainable."Yetifitis,itmaybereplicable.
"Ifenvironmentalengineers,bygainingexperiencefrombuildingthiswildcity,becomemuchmoreproductiveatbuildingthenextcity,thisstartstomovefrombeingsciencefictiontosomethingHoustonwouldadopt,"saysMatthewKahn,aprofessorofeconomicsattheUniversityofCalifornia,LosAngeles.GilFriend,CEOofNaturalLogic,asustainable‐designcompanybasedinBerkeley,CA,agrees."IseeMasdarontheonehandasaplaygroundfortherich,"hesays,"andontheotherhandasanR&Dopportunitytodeployandtestouttechnologythat,ifthingsgowell,willshowupinothercities."
Ofcourse,muchofwhat'slearnedfromMasdarwon'tapplyoutsidetheincrediblyhotandsunnycoastofthePersianGulf.AsiteinGermany,whichwouldn'tgetasmuchsunlight,couldn'trelyasheavilyonsolarenergy.AsiteinSanFranciscomightnotneedairconditioning,makinginformationaboutadvancedcoolingsystemslessrelevant.Butiftheprojectreachesitsenvironmentalgoals,itwillattheveryleastshowthatsuchcitiescanbebuilt."Peoplesay,'Gee,thatwouldbegreat.Thatwouldbeagoodidea,butobviouslyit'snotpossible,'"Friendsays."Onceyoucanpointatsomething,ittakesawayalotofthosearguments."
Energysurplus:Masdarheadquarters,showninanarchitecturalrendering,isdesignedtogeneratemorerenewableelectricitythanitconsumes;itwouldbethefirstlarge‐scale,multi‐usebuildingtodoso.Credit:©AdrianSmith+GordonGillArchitecture
BreakingGroundTheMasdarInitiativeispartofanambitiousplantotransformaresource‐basedeconomy‐‐thethird‐largestexporterofoilintheworld‐‐intoonebasedonknowledgeandexpertise.ThenameMasdarcomesfromtheArabicwordfor"source,"andtheplanistomakeAbuDhabitheSiliconValleyofalternativeenergy:asourceoftalent,patents,andstartupsintheveryindustrythatcouldonedaychallengethesupremacyofoil.It'sadauntingchallengetosaytheleast,especiallyforaregionthat,accordingtoAwad,"hasn'tbeenknownforinnovationforathousandyears."
Thecitywasconceivedasatax‐freezonemeanttoattractclean‐technologycompanies,largelyfromothercountries.(Thefirsttenant,GeneralElectric,planstobuilda4,000‐square‐meterfacility.)TheMasdarInstitute,thefirstpartofthecitytobebuilt,ismeanttobewhatStanfordUniversityistoSiliconValley.DevelopedincollaborationwithMIT,whichorganizedthecurriculumandishelpingtoselectandtrainthefaculty,theinstitutewillbeagraduateresearchschool,offeringmaster'sdegreesand,eventually,PhDs.Itsfirstclassof100studentswillstartcoursesthisfall.Andifgraduatesdeveloppromisingideasandstartcompanies,theycanlooktotheMasdarInitiativeforcapital.Ofthe$15billionthegovernmenthassetasidesofarfortheinitiative,onlyabout$4billionisdesignatedasseedmoneyforbuildingthecity's
infrastructure.(Thecityisexpectedtocostatotalof$22billion,theresttocomefromoutsideinvestors.)Theremaining$11billionisearmarkedforarangeofinvestments;projectssofarincludeasolar‐cellfactoryinGermany,anoffshorewindfarmintheUnitedKingdom,andeffortstoreducecarbonemissionsinNigeria.
Still,thecityisthemostvisiblepartoftheinitiative.Itisbyfarthelargestzero‐emissionsandzero‐wasteprojectintheworld,accordingtoseveralexperts.(Alarger"eco‐city"developmentnearShanghaidoesn'taspiretozeroemissions.)Effortselsewherehavesofarbeenlimitedtosmalltomoderate‐sizedbuildingsandsmallcommunities,likeaseriesofefficientrowhousesfor250peopleinWallington,SouthLondon.Oneofthemostambitiouszero‐emissionsbuildingstodate,theLewisCenteratOberlinCollegeinOhio,has1,263squaremetersoffloorspace.MasdarCitywillcoversixsquarekilometers.Itsheadquartersalone,whichwillincludeofficesaswellasretailandculturalspace,willoccupyan89,500‐square‐meterstructure.
Adetailedmasterplanforthecityiscomplete,asareplansforthefirstbuildings:theMasdarInstituteandtheheadquarters.Thecity‐‐whichwillincludeapartmentsandlaboratories,butalsofactories,movietheaters,cafés,schools,firestations,andsoon‐‐isintendedtogenerateasmuchelectricityasituses.Itswaterwillberecycledtosavetheenergycostsofdesalination.Vacuumtubesunderthecitywilltransportgarbagetoacentrallocation,whereitwillbesorted,andasmuchaspossiblewillberecycled.Trashthatcan'tberecycledwillbeconvertedtoenergythroughagasificationprocessandtheleftoversincorporatedintobuildingmaterials.Sewagewillbetreatedandsomeofitprocessedintoadryrenewablefuelforgeneratingelectricity.Thetransportationsystemwillincludealight‐raillinelinkingthedevelopmenttodowntownAbuDhabiandtheairport,aswellasapersonalrapid‐transit(PRT)systemwithstationsthroughoutthecity.ThePRT,asystemofautomatedelectricvehicles,willconnectpeopletotheraillineordeliverthemtoparkinggaragesoutsidethecity.
Asistypicalforzero‐emissionsprojectstodate,thecitywillneedtorelyinpartonfossilfuels‐‐bothduringconstructionandforpoweratnight,whenitssolarpanelswon'tbeproducinganyelectricity.Thegoalisactuallybestdescribedaszeronetcarbondioxideemissions:toreachthezero‐emissionstarget,thedeveloperswillturntoasystemofcarboncredits.Asthecityisbeingbuilt,a10‐megawattarrayofsolarpanelswilldeliverpowertonearbyAbuDhabicity,reducingdemandforelectricityfromlocalnatural‐gas‐firedpowerplantsduringtheday.Thecarbonemissionssavedwilloffsettheemissionsproducedatnight,whenMasdardrawspowerfromthosesamenatural‐gasplants.Thissolararray,andadditionalpanelsthatwillbeinstalledasconstructioncontinuesandelectricitydemandgrows,willalsooffsetthecarbonemissionsfromconstructionequipment,fromtheprocessesusedtomakebuildingmaterialssuchasconcrete,andevenfromconsultants'flightsintoAbuDhabifromcitiesaroundtheworld.
Sofar,thedevelopershavebeenaccountingfor"justabouteverything,"saysPooranDesai,cofounderofBioRegional,aBritishcompanythathelpeddevelopthezero‐emissionsprojectinLondonandhasconsultedforMasdar."Idon'tknowofanyotherprojectthathasbeenasthoroughintermsofitscarbonmonitoring,"saysDesai."They'rehuntingdowneverymoleculeofcarbondioxide."
Thebuilding’sstructuralcones,whichsupportaroofladenwithsolarpanels,willprovidelightandventilation.Thepondhelpscooltheair.Credit:©AdrianSmith+GordonGillArchitecture
TheMasterPlanDubaiisasprawling,car‐dominatedcityaboutanhour'sdrivefromAbuDhabicity.Skyscrapersstretchalonga12‐lanehighway,SheikhZayedRoad.Sunlightheatstheunshadedareasto46°Cinthesummer.ButthereareafewplacesinDubaiwhereapersoncanwalkoutdoorsinthemiddleofthedaywithoutriskingheatstroke,andallareartifactsofthepast.Therearethecoveredsouks,shadedmarketplaces.AndthereisahistoricdistrictcalledtheBastakiya,whichpreservessomeofthearchitecturethatprotectedlocalsfromtheheatandhumiditybeforethearrivalofairconditioning.Thehousesandshopshavethickwallsmadeofdriedcoralandgypsumthatabsorbheatduringtheday,releasingitslowlyatnight.Becausethebuildingsarepackedcloselytogether,theyshadebotheachotherandthenarrowpassagesbetweenthem.Thepassagesfunnelbreezes,coolingthebuildingsfurther.WhenGerardEvenden,aseniorpartnerattheBritishfirmFosterandPartners,begantomakethemasterplanforMasdarCity,helookedtosuchtraditionaldesignsforwaystosaveenergy.Sincethecitywilldependalmostentirelyonelectricityfromsolarpower,whichisfivetimesthepriceofelectricityfromthelocalgrid,thecityneedstoberoughlyfivetimesasenergyefficientascompetingdevelopmentsnearby.OneofthefirstthingsEvendendidwassubtractcars:withthehighwaysgone,thecity'sbuildingscouldbeseparatedbypassagesjust7to12meterswide,closeenoughtoshadeeachotheryetfarenoughaparttoletinindirectlight.That'sacheapwaytoreducetheneedfornotonlyairconditioningbutelectriclighting,thelargestdrainonelectricityincommercialbuildings.Insulationischeap,too:intheMasdarInstitute,Evendenplanstouse30‐centimeter‐thickinsulationtokeepouttheheat.He'salsoincorporating"skins"ofcopperfoilthatreflectlightandconductheatawayfromthebuildings.Thefoilwillbeprotectedfromthedesertdustbyaself‐cleaningTeflon‐likeplastic.Toreducetheneedforenergy‐intensivedesalination,Evenden'sdesignwillcutwaterconsumptionby75percentthroughrecycling,low‐flowfixtures,andwaterlessurinals.
Asmallfractionoftheenergythat'sstillneededtorunthecitywillcomefromwaste‐basedfuelandperhapsgeothermalpower.Therestwillcomefromthesun‐‐butnotallofitthroughexpensivephotovoltaics,whichconvertsunlightintoelectricity.Muchcheaperdevicesthatconcentrateheatfromthesunwillheatwaterandrunatypeofairconditionercalledanabsorptionchiller.(Thisisthesamekindoftechnologythatisusednowinpropane‐poweredrefrigerators.)
Intheory,itshouldallwork.Butinpractice,evenmuchlessambitiousprojectshavefailed.OberlinCollege'sLewisCenterfeaturesmanyofthesameelementsofenergy‐efficientdesign:thickinsulation,naturalventilationwithheatexchangers,plentyofwindowstooffsettheneedforelectriclighting,andheatpumpsratherthanconventionalfurnaces.A60‐kilowattarrayofsolarpanelsonitsroofwassupposedtoproduceasmuchelectricityoverthecourseofayearasthebuildingconsumes.Yetthebuildinginitiallyusedtoomuchenergy,andthesolarpanelswerenotadequate.Toachievezeronetenergy,thecollegehadtoinstallanextrasolararraynearby,morethantriplingthetotalpowerproduction.Itaddedoveramilliondollarstoanalreadyexpensivebuilding,estimatesJohnScofield,aphysicsprofessoratOberlinwhohaspublishedadetailedanalysisofthebuilding'sperformance.
Ingeneral,architectsfindthatpredictinghowenergy‐efficientsystemswillinteractgetsmuchharderasbuildingsgetbigger.Inbuildingsdesignedtotakeadvantageofnaturallight,forexample,designerscaninstallsensorstoautomaticallyswitchbulbsoffwhenenoughlightcomesinfromoutside.Butlights
turningonoroffinonesensingzonemayaffectthesensorsinanother.Insomebuildingsthishascreatedafeedbackloopthatmakeslightscycleonandoffannoyingly.
Neighboringheatingandcoolingzonescanalsoaffectoneanothertocreatecomplexandunpredictablefeedbackloops,especiallyasthenumberofzonesincreases.UnitedTechnologies'J.MichaelMcQuaderecallswhathappenedwhenhiscompanydesignedwhatwassupposedtobeanintelligentheating,ventilation,andair‐conditioningmanagementsystemforanewbuildinginParis.Thesystemwasdesignedtocoördinate3,000differentzones."Whenthatbuildingwasfirstputtogether,itwasasignificantenergyconsumer,andittookarevampoftheintegratedcontrolsystemstogetitright,"McQuadesays.
Ifzero‐emissionsbuildingsaretobeeconomical,Scofieldsays,thedesignswillhaveworkfromthestart."Ifyoudon'tgetitright,"hesays,pointingtothefiascoatOberlin,"everycorrectionyoumakeissomuchmorecostlythangettingitrightthefirsttime."
PersonalTransitMasdarCitywillberaisedonconcretestiltstomakeroomforapersonalrapid‐transit(PRT)systemthatwillreplacebusesandtrainswithsmallervehiclesdesignedforfourpeople.Masdar'splannersexpectthesystemtouselessenergythanconventionalmasstransit,andtheysayitwillbemoreconvenient,too.
InaPRTsystem,severalsmallvehicles,oftencalledpods,arekeptwaitingateachstation.Anindividualorasmallgroupboardsoneandselectsadestination;thepodproceedsautomaticallytothedestinationwithoutstopping.Inatypicaldesign,eachvehicleresemblesabattery‐poweredgolfcart,onlyit'scompletelyenclosedandsomewhatbigger‐‐anditlacksasteeringwheel.Thevehiclefollowsatrack,whichisconnectedtostationsbyon‐rampsandoff‐ramps,andacomputercontrolshowthepodsenterandexitthestations:therampsallowindividualpodstomakestopswhileotherscontinuealongthemaintrackattopspeeds.Simulationssuggestthatthesystemscouldrunwithaslittleashalfasecondbetweenvehicles.
ButalthoughPRTslookpromising,theyhaven'tcaughton.That'sinpartbecauseanearlyPRT‐likesystembuiltinthe1970sinMorgantown,WV,gavetheideaabadname,saysJerrySchneider,anemeritusprofessorofurbanplanningandcivilengineeringattheUniversityofWashingtoninSeattleandalongtimeadvocateofPRTs."Peoplewouldgetonthevehiclesandtheywouldn'tstop,"Schneidersaysofthesystem,atransitlinewithautomatedcarsforabout20people.Technologyhasimprovedsincethen,hesays,buttherehasn'tbeenasignificantreal‐worlddemonstrationoftheupdatedsystems.
Twodemonstrationprogramsareontheway.Thefirst,whichwilltransportpassengerstoanewterminalatHeathrowInternationalAirportnearLondon,willopenlaterthisyear.Testsofthatsystemarealreadyunderway.AndthefirststageofthesystematMasdarCity,tobebuiltbytheDutchfirm2GetThere,isscheduledtobeinplacefortheopeningoftheMasdarInstitutethisfall.
Shadylane:Solarpanelsontheroofsprovidesunprotectioninpublicspacesbetweenbuildings.Credit:©AdrianSmith+GordonGillArchitecture
TheTestBedSameerAbu‐Zaidisn'tbreakingasweat.It's39°Cwith74percenthumidity,buthesaysit'saniceday‐‐muchcoolerthanthesummerinAbuDhabi,whentemperaturescanreach49°C.Abu‐Zaid,who'soriginallyfromJordanandwasmostrecentlyamanageratasemiconductorequipmentmanufacturerinSiliconValley,willmanageMasdarCity'spoweranddistributioninfrastructure."Allofthesemoduleshavebeentestedatthefactories,"hesaysashegivesatourofoneofthefirstvisiblesignsofthecity,atestsitewherehe'sputting41arraysofsolarpanelsfromvariousmanufacturersthroughtheirpaces."Buttheyhavebeentestedunderstandardtestconditions:1,000wattspermetersquared,25°C.Niceair‐conditionedspace.Itistotallydifferenthere."
Dustfromthedesertquicklycoatsthepanels,effectivelydimmingthelightthatreachesthem.Abu‐Zaidhaslearnedthatjustfourmonthsofdustreducestheoutputofthesolararraysbymorethan20percent‐‐informationhe'llusetodecidehowoftentowashthepanels,balancingpowerlossagainstwaterconsumption.
Anotherproblemistheheat.Solarpanels'darksurfacesabsorbsunlight,raisingtheirtemperaturetoasmuchas80°C.Theheataffectssomesolar‐celltechnologiesmorethanothers.Someofthemostefficientsolarpanelsalsoproducelesspowerwhentheygethot.Becauseofthesetrade‐offs,it'snotobviouswhichpanelswillworkbestattheMasdarsite,Abu‐Zaidsays.Atthetestplot,sensorstrackhowmuchvariouspanelsheatup,howeffectivedifferentcoolingstrategiesare,andhowpoweroutputchangeswithtemperature,amongotherfactors.
Suchdatagatheringwillcontinueasthecitygrows.Itsdesignersandengineerswillmeasurebothenergyconsumptionandenergyproduction.Theywilltrackwaterconsumptiondowntotheindividualfixture.AtMasdarheadquarters,designersmayuseRFIDtagsinsecuritybadgestogatherinformationontheway‐peopleusewaterandenergy.Suchmeasurementswillallowdesignersandengineerstocomparetherealperformanceofthecitywiththeperformancepredictedbylaboratorytestsandsimulations.RealityCheckIntheearly1960s,whiletheUnitedStateswasrushingtoputamanonthemoon,electricfansandlightswerestillunheard‐ofinAbuDhabi,accordingtoMohammedAlFahim,anativeoftheemiratewhohaswrittenararehistoryoftheplace.Thatwasnotlongafteroilwasdiscoveredthere,andwellbeforethemoneystartedflowing.AlFahimisfromoneofthewealthiestfamiliesinthearea,yetbothhissisterandlaterhismotherdiedbecauseofalackofbasichealthcare.NowlifeexpectancyinAbuDhabiisvirtuallythesameasintheUnitedStates.Before,thelocalssurvivedonwaterfrombrackishwells;nowtheydrinkfreshwaterfromnewdesalinationplants.Thefragileandhighlyflammablepalm‐frondhutsthathousedmostpeoplehavebeenreplacedbygleamingglass‐and‐steelskyscrapers.Inmanyways,thedevelopmentofAbuDhabioverthelastfewdecadeshasreflectedafreneticefforttocatchupwiththedevelopedworld.Now,becauseofprojectssuchasMasdarCity,theemiratehasachancetoraceahead.Butintermsofurbandevelopment,itappearstobeverymuchatacrossroads.Inafewyears,whilethecitizensofMasdarCitywillbepinchingkilowatt‐hoursandusingwaterlessurinals,go‐cartswillbescreamingaroundanewtrackataFerrarithemeparknearby,kidswillbeshriekingas
theyplummetdownwaterslidesatanewwaterpark,andmassiveairconditionerswillberoaringastheycoolanew700‐storesupermall.It'sallpartofa2,500‐hectaredevelopmentthatwilldwarfthe640‐hectareMasdarCity.ThetwodevelopmentsarecompetingvisionsforthefutureofAbuDhabi.IftheMasdarprojectdoesn'tjustifyitselffinancially,itcouldindeedbejustagreenplaygroundfortherich,anenvironmentalthemeparkthatislargelyirrelevantforthedevelopmentofsustainabletechnologyonabroaderscale.Butifitisprofitable,itcouldbeadrivingforceforsustainableurbandesign.Thentheoil‐richdevelopersintheUAEandelsewheremighthaveareasontobuildmoregreencitiesandskipconstructinganotherskislopeinthedesert.Anddevelopersworldwidewillfollow.KevinBullisisTechnologyReview'sEnergyEditor.
