Page - 97 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2016,9, 86 4.3. ChargingNetworks IssuesofEVs Onemajorbarrier to thesuccessofEVs is the limitednumberof refuelingstations.Dueto the restrictedrangeofbatteries, theestablishmentofan infrastructure to facilitate recharging isapressing concern. Twocritical factorsdetermine theneedfor infrastructureservicessuchasbatteryswapping and recharging: dailydrivingdistance andbattery range. Due to the large capital costs involved in infrastructure investment, economic factors arevery important indetermining thenumberand locationofstations. Therefore, studiesmustworktoprovidea theoreticalbasis forstationdeployment, suchaswitha facility locationmodel, toeconomicallyandefficiently serveEVtrips [33]. Location problems ingeneralarespatial resourceallocationproblemsdealingwithoneormoreservice facilities servingaspatiallydistributedsetofdemands. Theobjective is to locate facilities tooptimizeaspatially dependentobjectivesuchas theminimizationofaverage traveling timeordistancebetweendemands andfacilities. Themoststudiedpracticalprobleminthiscontextconcernshydrogenstation location. Generalcriteriaareproposedfor identifyingeffective locations forearlyhydrogenstations: (i) close toareaswithhightrafficvolume; (ii) inplaces toprovide fuelduring longdistance trips; (iii) athigh profile locations to increasepublicawareness;and(iv) inplaces thatareaccessible to individualswho arebuyingtheirfirst fuel-cellvehicle. Thesecriteriaarealsoneededtobe taken intoaccount inEVM inorder toensureconsumerconfidence in thereliabilityof therefuelingnetwork[33]. 4.4. Routing IssuesofEVs RoutingofEVs is a critical aspect ofEVM, it consists ofdesigning routes formaximizing the autonomyofvehicles. EfficientEVroutingplaysamajor role for encouragingEVuse. Theenergy shortestpathproblemandtheenergyroutingproblemandsomerelationshipsbetweentheseemerge as new challenges to face in the EVM. Restricted driving distance between battery charges is a fundamental impediment to increase consumer adoption of EVs. In the small-package shipping industry, several big companies, such asDHL,UPS andDPDhave already startedusingEVs for last-mile deliveries, particularly inurban areas. Moreover, governments in all parts of theworld promote the electrification trend and plan to provide the required infrastructure. Asmentioned earlier,asuccessful transitionfromconventionalvehicles toEVsrequires thedevelopmentofnovel efficient route-planning techniques that take into account the specific features of EVs. Currently, themaximumdriving rangeofmostEVs is estimated tobeabout100–150miles [16], but it canbe decreasedsignificantlybycoldtemperaturesandso-calledrangeanxiety [94,95]. Thus, theavailable range ispotentiallynotsufficient toperformthe typicaldelivery tourofa logistics serviceprovider in onerunor toreachcustomers locatedfar fromthedepot. Becausereducingthenumberofdeliveries performedbyonevehicle isclearlynotaprofitableoption,visits torechargingstationsalongtheroutes arerequired. Theserechargingvisitshavetobeexplicitlyconsideredintherouteplanningtoavoid inefficientvehicle routeswith longdetours, especially if thenumberofavailable rechargingstations is scarce. Inarecentwork,Hung et al. [96]proposeaqueuingmodelingframeworktodevelopefficient routing strategies for EVs requesting charging at available stations. These authors show that the proposedroutingstrategiescontribute to improvingthe throughputof thequeuingsystemandalso to reducingstopover times. Inaddition,Liu et al. [97]analyzeaheterogeneousfleetversionof theVRPin whichthegoal is tofindaroutingsolutionminimizingthecarbonfootprint. Similarly,Fang et al. [98] try tominimize thecarbonfootprintgeneratedbybirdwatchingtouristactivities throughoutoptimal routingdesignsupportedbygeographic informationsystems. Table 2 summarizes someof themaindecisionvariables, constraints, andobjective functions relatedto thenewVRPvariants thatemergewhenconsideringheterogeneousfleetsof ICEVsandEVs. 97