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HomeMy WebLinkAboutRenewable Hydrogen Stationary Power Systems June 21-26, 1998AN EXAMINATION OF THE CRITERIA NECESSARY FOR SUCCESSFUL WORLDWIDE DEPLOYMENT OF ISOLATED,RENEWABLE HYDROGEN STATIONARY POWER SYSTEMS G.D.Rambach and J.D.Snyder Energy and Environmental Engineering Center Desert Research Institute 5625 Fox Avenue Reno,NV 89506 USA Presented at the XII World Hydrogen Energy Conference Buenos Aires,Argentina June 21 -26,1998 Abstract: This paper examines the top-down rationale and methods for using hydrogen as an energycarrierinisolated,stationary power systems.Such an examination can be useful because it provides a framework for detailed research on subsystems and helps clarify why,when andwherelarge-scale hydrogen use would be beneficial.It also helps define the pathway foranevolvinghydrogenstationarypowermarketworldwide.Remote,stationary powersystemsareanidealmarketentryopportunityforhydrogen.For example,if it issufficientlydifficultforconventionalfuelstoreachacommunity,and indigenousrenewablesourcesarepresent,then on-site clean energy production becomes economicallycompetitive. Relying heavily on intermittent sources of energy requires an energy carrier system that isefficientoverlongperiodsoftime.In addition,the energy carrier must not defeat the reasons for initially switching to the clean sources of energy,and must be economicallyfeasible.Hydrogen is an elegant solution to all of these needs.Choices exist for the methods of producing hydrogen,storing and transporting it,and converting it back tousefulenergy.There is considerable debate about how best to increase the use of renewable hydrogen because it is not yet economically competitive with conventional energy Carriers in most applications. The deployment of isolated power systems relying on hydrogen as the energy storagemediumrequirescomplexandcomprehensiveplanninganddesignconsiderationstoprovidesuccessfulmarketentrystrategiesaswellasappropriatesystemengineering.Thispaperwilldiscussthecriteriaandframeworknecessarytodeterminehowtosuccessfullydeployanyspecificsystemortoplanaglobalmarketingstrategy. The objectives of this project go beyond simple design,purchase and installation of autilityenergystoragesystembasedonhydrogen.Simply providing such a system does notgeneratethecommercializationtoolsandopportunitiesforhydrogenuseinthenear-term. 1.INTRODUCTION: Over the past two decades many of the technologies needed for a sustainable energyeconomyhaveevolvedconsiderably,and are at the brink of large-scale commercialization.Renewable technologies such as wind and solar have proven to be technically viablesourcesofpower.Wind power production costs are competitive with conventionalsources,while solar power is expected to be competitive within a decade.There arecertainmarketswherethevalueofelectricityisseveraltimeshigherthantheelectricitypriceinlargepowergridmarkets.For example,dozens of communities in Alaska pay$.25 to $.70/kWh for diesel-powered electricity,where the national average is less than$.10/kWh.Many regions having high-value electricity also have abundant,quality windresources.This model is repeated,and often exceeded throughout the world.The keyingredientsforcommercializationofrenewable-based utility systems are:high cost (orvalue)electricity,need for electricity,adequate renewable resource and access to investment capital or other financing.These high-value power markets are whererenewabletechnologiesaremakingtheircommercialentry. Increased use of renewables in these markets will accelerate economy-of-scale costreductions,and broaden the market base.About 1/3 of the world's six-billion populationhaveyettobenefitfromtheuseofutilityelectricity,and it is prudent to foster thedevelopmentofanintegratedrenewableenergyindustrytoacceleratetheuseofrenewablesindevelopingregions. In order for any renewable hydrogen stationary power system to be competitive,a numberofcomplex,intelligent decisions must be accomplished to provide a power system that isoptimizedforanyarbitraryrenewableenergysourceandanyarbitrarypowerload.Unlikesimplebattery,flywheel or pumped hydroelectric storage systems,a hydrogen storagesystememploysfiveindependent,principal components.They are necessary for hydrogenproduction,pressurization,storage and utilization,and for power logic control.Systemsintegratedwithcommunitiesorotherenduserscanalsorequireintegratedthermalmanagementaswellashydrogenfuelandpowermanagement. There is a large range of applications where renewable;hydrogen utility power systemscanbedeployed.Throughout that range,the differences in any of the components orconfigurationofasystemcanbeeithersubtleorlarge.Likewise,there can be subtle orlargedifferencesinthecriteriaforperformanceofasysteminstallation.For example,arenewableenergysourcecoupledtoanenergystoragesystemcanbedeployedinanisolatedenvironmenttoprovidecontinuouselectricityservicefromalocal,intermittent, renewable energy source.However,the system design and system controls can varyconsiderablyfromsitetosite,resulting from subtle difference in the way the source profiles or load profiles vary. Additionally,isolated communities have a requirement for vehicle transportation as well asutilityelectricity.As hydrogen powered vehicles enter the niche marketplace,they can beintroducedintotheseenclosedcommunitiesinafleet-like manor.Fleet introduction of hydrogen-powered vehicles in niche applications is a favorable way to bring them into thegeneralmarketplace,and in isolated communities,the hydrogen production and storageelementscanbeincreasedincrementallytoallowrenewablehydrogentoprovideboth utility electricity and transportation. 2.MODELS FOR SYSTEM DESIGNS AND CONTROLS: Two critical aspects of successful deployment of stationary,renewable hydrogen energysystemsare1)designing the best system for a given location and 2)controlling that system ot& to provide the lowest cost electricity to the customer.The satisfaction of these two requirements can be accomplished employing two computer-based coupled optimizationalgorithms.The first would be a design optimization algorithm that would select theoptimumcomponentsforastoragesystemforagivenlocation.The inputs to this designoptimizationalgorithmwillincludealoadtime-profile,a renewable resource time-profile,size limitations,noise restrictions,operations and maintenance restrictions,and needed reliability.The algorithm will determine the system design providing the lowest cost of electricity. The second would be a control optimization algorithm,which would determine the best strategy for the power logic controller to use.This algorithm would be used to control the power system with the objective of providing the lowest cost of electricity at apredeterminedlevelofreliability.In this case the algorithm will ensure the highestreliabilitypossible.Also,as a part of the control strategy,the use of weather forecast mesoscale models to aid in the system operation and variable electricity pricing withcustomerfeedbackbothhavethepotentialtolowercostsandincreasereliability. The design and operational models that perform in this way can be valuable tools to improve the confidence of market niche identification and validation.They can show boththeexpectedeconomicandtechnicalperformanceofanyanticipated,integrated systemconsideredforanarbitrarylocationworldwide.The inputs to such models are the indigenous renewable source and load characteristics,methods of financing at and theperformanceandcostcharacteristicsofallcomponentsconsideredforanydesignconfiguration.The outputs are the expected cost of electricity,power quality,power reliably and installation costs. There are numerous ways in which hydrogen renewable systems can be integrated,bysimplyconnectingcomponentstogetherinafunctionalform.Figure 1 shows the genericelementsforanyofthesesystems.As shown,the elliptical figures symbolize any arbitraryrenewableresourceorarbitraryvariableload.The rectangular figures show the component options for each specific function:renewable energy conversion to electricity,power logiccontrolandenergystorage.Within the energy storage list of options the hydrogen systemsrequirefiveindependentcomponentsintegratedinasystemwhiletheotherstorageoptionsonlyrequireoneortwocomponents.The generic form of these options is shown in Figure Each element in a renewable hydrogen power system can be defined by specific criteria that dictate its performance and also by specific relationships to the other elements in thesystem.Figure 3 gives an example of some of relationships that would be considered intheoptimizationofthedesignforagivensystem.There would also be a similar figure thatwoulddescribethecriteriaandrelationshipswithinandamongthesystemelementsfor optimization of the system operation. 3.SUMMARY DESCRIPTION OF A RENEWABLE,HYDROGEN STATIONARY POWER SYSTEMS: One very important combination of the system elements selected from Figure 1 isdescribedinFigure4.The configuration includes power production from wind turbines,hydrogen production from an electrolyzer,medium-pressure gaseous hydrogen storage,and a fuel cell to provide the return of electricity.Such a configuration can be employed innumerousapplicationsaroundtheworldtoday.Wind turbines can provide low costrenewableelectricity,and electrolyzers,compressors,medium-pressure hydrogen storagetanksandhydrogenfuelcellsareavailableinsizesforsmall,remote communities andsmall,remote utility applications such as telecommunication repeater stations. In order for any renewable utility power system that employs energy storage to be bothtechnicallyandcommerciallyviable,four primary criteria must be satisfied.First,theregionorlocationwhereasystemistobedeployedneedstohaveareasonablyabundant,intermittent renewable resource.Second,the location must require a new electricity supplywhosevaluesupportsthecostsassociatedwithsystemsofthiscomplexityorcapitalcost.Third,other forms of energy storage are not available,or do not economically competewithhydrogen.Finally,the financing or capital necessary to the job must be available.We have found numerous locations worldwide word these four conditions hold. Moreover,some locations where the value of electricity is high,and there is abundant,quality wind at capacity factors greater than 50 percent.A major advantage that large-scale electricity storage,such as offered by hydrogen provides for the renewable industry isthepossibilityofpenetrationupto100%of the local grid load,which is not possible withtherenewableresourcealone. DESCRIPTION OF SYSTEM AND COMPONENT OPTIONS: A.Primary Power Production: The primary power production installation must be "overbuilt"in peak capacity to permitsimultaneousloadfollowingandstoredenergyproduction.The principal criteria thatdefinetheprimary,renewable power source,require: 1)the source to be intermittent. 2)the average source power to be adequate enough to technically andeconomicallyjustifyinstallationofanautonomoussystem. 3)the maximum credible quiescent period to be within a range that permits theuseofarealistic,economically viable energy storage system. Wind turbines -The most mature renewable technology that permits small-scale,and incremental installation.The current,and expected capital and installation costs for wind turbines make them the most attractive choice for most potential sites.Quiescent periodsmaylastfordaystoweeks.Wind turbines rated for arctic use are currently available commercially. Solar photovoltaic -A maturing renewable technology whose capital costs are severaltimeshigherthanwindturbines.However,such costs are expected to fall to a competitive range in 5 -10 years.Under certain conditions of regional power value and resource,solarPVcanbethetechnologyofchoice.Quiescent periods would generally follow a diurnal cycle. Micro-hydroelectric -Under the conditions where an adequate flowing water resource isavailable,and where it is intermittent (regularly spaced rain or monsoon episodes),and where topography,or other constraints prohibit the use of pumped,or other reservoirhydroelectricstorage,micro-hydroelectric power production with the type of energystoragesystemsconsideredherecanbeappropriate. Low-dynamic-pressure (q)water turbines:-Given the conditions in the section above,and intermittent,low-gradient river flows,submerged water turbines with the type ofenergystoragesystemsconsideredherecanbeappropriate. B.Energy storage:Energy storage capacity,to first order should be sized for the maximum credible period ofquiescencefortheprimarypowerproductionsystem,and for the average load.Whilethereareseveraldifferentpossibleenergystoragetechnologies,with varying degrees of et»bibdbeind maturity,cost and scalability,this presentation will be confined to hydrogen based energystoragemethods.As such,all hydrogen energy storage posses three basic elements: 1)a primary power-to-hydrogen conversion system (hydrogen production),2)a hydrogen storage system (storage),and 3)a hydrogen-to-electricity conversion system (electricity production). i,HYDROGEN PRODUCTION-electrolysisPotassiumhydroxide(KOH)electrolyzers are commercially available in two basicconfigurations;low-pressure,unipolar and intermediate-pressure bipolar.Both types areattractivemethodsofhydrogenproductionforremotepowersystems.Under certainconditions,the bipolar system may provide hydrogen elevated pressure,potentially up tothestoragepressure,reducing or removing the requirement for a compressor.The currentcapitalcostforKOHelectrolysissystemsishigh,but the potential for economy of scaleimprovementsispromising. Solid polymer electrolysis is an emerging,solid state method of hydrogen production thatshouldhavecapitalcoststhatevolvesimilartoPEMfuelcells.As the costs decline,thiswillbeanattractivemethodofhydrogenproduction. ii.HYDROGEN STORAGE: The scale of the hydrogen storage system in remote,renewable power systems is directlyproportionaltothemaximumcrediblequiescentperiodoftherenewableresourceandthe average load.It is this property that makes flowing electrochemical storage methods moreattractivethanbatteriesinremoteapplicationsofrenewableenergywithlongperiodsofstoredenergyconversion.In these systems,the power conversion and energy storagehardwareareseparate,requiring only the size of the storage hardware (generally leastcostly)to fit the quiescent power production conditions. Intermediate-pressure,100 -500 psi,gas vessels are a good choice for most small community power systems.The expected costs and required system volumes are reasonable.Where space is premium,or where the storage system is also supplyinghydrogenfortransportationapplications,high pressure,500 -3000 psi,or low-pressurehydridesystemsmayberequired. iii.RETURN ELECTRICITY PRODUCTION:a)Hydrogen-ICE-generator set-An electrical generator driven by an internalcombustion,reciprocating engine (ICE),with a high compression ratio and lean operationcanprovideelectricityproductionwithefficienciessimilartoafuelcell.The productionsystemwouldhavetohaveanefficientturn-down ratio that matches well with thetemporalloadprofile.The key advantage to a hydrogen-ICE genset is the very low near-term capital cost relative to the current cost of fuel cells.This leaves a cost "window ofopportunity"while fuel cell costs decline.The primary environmental concern would bethesmallNOxemissionfromnitrogenfixation.However,the chances that this type of power system would be used in a NOx nonattainment area are slight. b)Hydrogen fuel cell:Phosphoric acid fuel cell (PAFC)-Currently available in 200 kW units integrated with anaturalgasreformer.The reformer is not necessary for remote hydrogen stored energyapplications.The PAFC operating temperature in excess of 150C in a 200 kW unit permitscogenerationofutilityheat,but also requires long start up times.Long start up times meanthatthePAFCwouldhaveto"idle"even while stored electricity is not necessary. Proton exchange membrane fuel cell (PEMFC)-Currently 205 kW units have beenintegratedintobusesforusewithneathydrogen.A hydrogen PEMFC could operate withshort(several seconds)start up and shut down times.The primary issue for including aPEMEFCinaremote,stationary power application 1s the capital cost. Regenerative fuel cell (RFC)-Solid polymer regenerative fuel cells are electrochemicaldevicesthatperformelectrolysiselectrochemistrywhencurrentisappliedtoitselectrodes, and perform electricity production when hydrogen and air are applied to its electrodes.Current cost are high and system sizes are small,but if RFCs can be manufactured at a lower combined cost than electrolyzers and conventional fuel cells,then this would be the preferred technology. 5.SUMMARY AND CONCLUSIONS: The necessary technology is available to deploy renewable,hydrogen,utility power systems to isolated communities worldwide.However,the integration of the technologyelementsrequiresmethodsofoptimizationforboththedesignofthesystems,as well astheircontrol.Careful attention must be paid to all of the design,operation and deploymentdecisionsthatmustbemadewheneverahydrogen,renewable energy system is considered for any location. REFERENCES [1]Rambach,G and Haberman,D,(1997)Uninterruptable,Renewable,Hydrogen-BasedEnergyforIsolatedCommunitiesWorldwide,Advocate of the National HydrogenAssociation,2,2,6-7.Presented to 8th Annual U.S.Hydrogen Meeting,Washington, DC,March 1997. Source,process and load options *Community °Mine ¢Military post ¢Autonom ous device ¢Grid or microgrid e Wind *Sunlight *Water flow ¢Hydrogen-fuel cell °Hydrogen-ICE gen *Halogen fuel ceil ¢Wind turbine :°Zn-Air fuel cell*Solar PV Hydro |---»v»em=J|_--Power topic [yd 7 n-FeCN fuel cell *Low-q water turbine controller °Flywheelqy *Compressed air ¢Pum ped hydro ¢Battery Figure 1.Block diagram of stationary,renewable power system,showing the options for renewable sources,power conversion devices,power control,energy storage and load. Block diagram of hydrogen storage element options Power logic p-|Com presso Power logic Compressor]controller |>”|Electrolyzer (if needed)controller ||Electrolyzer-”|(it needed) Electrical |,|Hydrogen Fuel |_o|generator ICE cell v Hydrogen b Hyarrogen|storage Cogenerated|g Cogenerat heat (high-Theat{fuel cell Power logic |9q--_gp-|Regenerativd |Com pressor}controller fuel cell (if needed) |®Hydrogenstorage Figure 2.Possible configurations for hydrogen energy storage systems. Intermittent,renewable Intermittent P(the=KCOE(tpser) Pren =FRoad-peate Nero,TEH2,NicompCEPteCoan)”|- Power logic Costic =KPricupeat) Fuel cell Pre =KRoad-pea Entec.sto) y Cogenerated H =fra DG.)YvElectrolyzePein=A Bowi-peab Pea)Pant200 =KCostar,Typex) Vv ier (eal (ifQ=AQw)Pe-out =P.)Pea =KPen2-0=) Vv HydrogenE,=KQuse oadevg)AE,=fity.,vehicles) P.=KCoStesa,Site Figure 3.Examples of the relationships that must be considered in the optimization of the design ofa stationary,renewable power system with energy storage. Power grid Power -tara |)Electricity } Wind turbines Electrolyzer t-0)| <9)Hydrogen storage 2 Figure 4.Wind,hydrogen utility power system using a fuel cell for the return electricity.