公路可再生能源光伏噪声屏障

HighwayRenewableEnergy:

PhotovoltaicNoiseBarriers

Photosource:TNCConsulting

August2017FHWA-HEP-17-088

OfficeofNaturalEnvironmentWashington,D.C.

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1.AGENCYUSEONLY(Leaveblank)

2.REPORTDATE

July2017

3.REPORTTYPEANDDATESCOVEREDFinalReport

4.TITLEANDSUBTITLE

HighwayRenewableEnergy:PhotovoltaicNoiseBarriers

5a.FUNDINGNUMBERS

HW9HA2QD169and

HW9HA2QC749

6.AUTHOR(S)

CarsonPoe,AmyPlovnick,TinaHodges,AaronHastings,SueDresley

5b.CONTRACTNUMBER

7.PERFORMINGORGANIZATIONNAME(S)ANDADDRESS(ES)U.S.DepartmentofTransportation

JohnAVolpeNationalTransportationSystemsCenter

55Broadway

Cambridge,MA02142-1093

8.PERFORMINGORGANIZATIONREPORTNUMBER

DOT-VNTSC-FHWA-17-20

9.SPONSORING/MONITORINGAGENCYNAME(S)ANDADDRESS(ES)

USDepartmentofTransportationFederalHighwayAdministrationOfficeofNaturalEnvironment

1200NewJerseyAvenue,SEWashington,DC20590

10.SPONSORING/MONITORINGAGENCYREPORTNUMBER

FHWA-HEP-17-088

11.SUPPLEMENTARYNOTES

12a.DISTRIBUTION/AVAILABILITYSTATEMENT

ThisdocumentisavailabletothepublicontheFHWAwebsiteat

/environment/sustainability/energy/publications/photovoltaic/

12b.DISTRIBUTIONCODE

13.ABSTRACT(Maximum200words)

Highwayphotovoltaicnoisebarriers(PVNBs)representthecombinationofnoisebarriersystemsandphotovoltaicsystemsinordertomitigatetrafficnoisewhilesimultaneouslyproducingrenewableenergy.FirstdeployedinSwitzerlandin1989,PVNBsarenowfoundinseveralcountrieswheretransportationagencieshavesoughtwaystofindmultipleusesoftheirinfrastructure.ThePVNBexperiencedocumentedinliteratureandsupplementedthroughaseriesofinterviewsprovidesevidencesuggestingthatnoisebarrierscanbe

designedtoproducerenewableenergywithoutcompromisingtheirabilitiestoreducenoise,anddososafely.ThebusinesscaseforaPVNBoftenhingesontheavailabilityofsubsidiesorotherincentivesthatpromotetherenewableenergymarket.Althoughthefirst

highwayPVNBisyettobeconstructeddomestically,atleasttwoStateDepartmentsofTransportationarecurrentlyworkingwith

partnerstopursuePVNBpilotsintheUnitedStates.Giventhesubstantialextentofnoisebarriersinthecountry,thepotentialforsolarenergyproductiononAmericannoisebarriersislikelyatleast400Gigawatthoursannually,roughlyequivalenttotheannualelectricityuseof37,000homes,andperhapsmuchhigher.

14.SUBJECTTERMS

Renewableenergy,noisebarrier,photovoltaicnoisebarrier,solarnoisebarrier,PVNB,sustainability

15.NUMBEROFPAGES

16.PRICECODE

17.SECURITYCLASSIFICATIONOFREPORT

Unclassified

18.SECURITYCLASSIFICATIONOFTHISPAGE

Unclassified

19.SECURITYCLASSIFICATIONOFABSTRACT

Unclassified

20.LIMITATIONOFABSTRACTUnlimited

NSN7540-01-280-5500StandardForm298(Rev.2-89)

PrescribedbyANSIStd.239-18298-102

ACKNOWLEDGMENTS

Theprojectteamwouldliketothankthepractitionerswhosharedtheirtime,expertise,and

respectiveorganization’sexperiencesviainterviewandemailcorrespondence.Thisreportcouldnothavebeendevelopedwithouttheinputandreviewfromspecialistsattheseagencies:

•BundesanstaltfürStraßenwesen(FederalHighwayResearchInstitute),Germany

•BundesamtfürStrassen(FederalRoadsOffice),Switzerland

•InnoviaTechnology,England

•MassachusettsDepartmentofTransportation

•Rijkswaterstaat(MinistryofInfrastructureandtheEnvironment),theNetherlands

•SolarEnergyApplicationCenter,theNetherlands

•TheRayC.AndersonFoundation

•TNCConsulting

•VicRoads,Victoria,Australia

AppendixAprovidesafulllist.

CONTENTS

ExecutiveSummary 2

1.Introduction 3

1.1PhotovoltaicNoiseBarriers:TheConcept 4

2.LiteratureReview 7

3.ExamplesfromtheInternationalExperience 11

3.1Switzerland 11

3.2Germany 12

3.3TheNetherlands 15

3.4Australia 17

4.PotentialPVNBProjectsintheUnitedStates 20

4.1HighwayNoiseGovernance 20

4.2MassachusettsDOT’sLexingtonSolarRetrofitPilotProgram 21

4.3TheRay:APotentialTestingGroundforPrototypeSolarNoiseBarriers 23

5.Conclusions 25

5.1LessonsLearnedSummary 25

Bibliography 27

AppendixA:PointsofContact 30

AppendixB:Interviewguide 31

AppendixC:Calculations 33

1

ACRONYMSANDABBREVIATIONS

BASt

BundesanstaltfürStraßenwesen(FederalHighwayResearchInstitute)

CFR

CodeofFederalRegulation

CoRTN

CalculationofRoadTrafficNoise

dB

Decibel

dBA

A-weightedDecibels

ECN

EnergyResearchCentreoftheNetherlands

EEG

Erneuerbare-Energien-Gesetz(RenewableEnergySourcesAct)

FEDRO

SwissFederalRoadsOffice

FHWA

FederalHighwayAdministration

FIT

Feed-inTariff

Foundation

TheRayC.AndersonFoundation

GDOT

GeorgiaDepartmentofTransportation

GWh

Gigawatthour

I-85

Interstate85

ITC

InvestmentTaxCredit

kWh

kilowatt-hour

kWp

Kilowatt-peak

LSC

LuminescentSolarConcentrator

MassDOT

MassachusettsDepartmentofTransportation

MW

Megawatt

MWp

Megawatt-peak

PV

Photovoltaic

PVNB

PhotovoltaicNoiseBarrier

RFP

RequestforProposals

ROW

Right-of-way

RWS

Rijkswaterstaat(MinistryofInfrastructureandtheEnvironment)

SDOT

StateDepartmentofTransportation

SEAC

SolarEnergyApplicationCentre

SMART

SolarMassachusettsRenewableTarget

TheRay

SectionofInterstate85inGeorgia

TNM

TrafficNoiseModel

U.K.

UnitedKingdom

VicRoads

RoadsCorporationofAustralia

2

EXECUTIVESUMMARY

Photovoltaicnoisebarriers(PVNBs)representthecombinationofnoisebarriersystemsand

photovoltaic(PV)systems.Noisebarriersarephysicalobstructionsdesignedtolowernoiselevelsbetweennoisesourcesandsensitivereceptors,suchashospitals,schools,andresidentialareas.

Photovoltaicsystemsusesolarcellstoconvertlightenergydirectlyintoelectricity.FirstdeployedinSwitzerlandin1989,PVNBsarenowfoundinseveralcountrieswheretransportationagencieshavesoughttoabatenoiseandproducerenewableenergysimultaneously.

TheliteratureonPVNBs,mostofwhichisseveralyearsold,generallyagreesthatthereisgreat

potentialtousebothexistingandplannednewnoisebarrierstoproducesolarpower.Professionalsfromselecttransportationagencieswhoprovidedinformationtotheprojectteamechoedthese

views,especiallywhentheintegrationofsolartechnologiesispartofaholisticapproachtodesignandconstruction.Accordingtoinformationcollected,noisebarrierscanbedesignedtoproduce

powerwithoutcompromisingtheirabilitiestosafelyreducenoise,andinsomecasesmayimprovetheirperformance.ThebusinesscaseforaPVNBisoftencontingentonthedifferencebetween

marginalcostsofconstructingtheinfrastructurewithandwithoutenergygeneratingcapacity.

Transportationagenciesincountrieswithattractivesubsidiesorotherincentivesavailableto

promotetherenewableenergymarketwilllikelyfindPVNBimplementationmorefeasibleand

economicallyself-sustainingthanagenciesincountrieswheretheregulatoryenvironmentisnotasfavorabletorenewableenergydevelopers.

AlthoughthefirsthighwayPVNBisyettobeconstructedintheUnitedStates,atleasttwoState

DepartmentsofTransportationarecurrentlyworkingwithpartnerstopursuePVNBpilotson

highwaysintheUnitedStates.GiventhesubstantialextentofnoisebarriersintheU.S.(nearly

3,000linearmiles),coarseestimatesdoneasapartofthisstudysuggestthatthepotentialforsolarenergyproductiononAmericannoisebarriersisatleast400Gigawatthours(GWh)annually,

roughlyequivalenttotheannualelectricityuseof37,000homes,andperhapsmuchhigher.

3

1.INTRODUCTION

AsdefinedbytheFederalHighwayAdministration(FHWA),noiseisanyunwantedsound.1

Althoughitcanoriginatefrommanydifferentsources,highwaytrafficnoiseisamongthemost

pervasiveanddifficulttoavoid.2IntheU.S.,highwaytrafficnoisehasbeenaconcernamong

communitiesandalllevelsofgovernmentsincetheearly1960swhenthefirstnoisebarrierwasbuiltinWashingtonState.Now,48statesandtheCommonwealthofPuertoRicohaveconstructedapproximately3,000linearmilesofhighwaytrafficnoisebarriers.3

Ahighwaynoisebarrierisaphysicalobstructionconstructedbetweenthehighwaynoisesource

andthenoisesensitivereceptor(s)thatattenuatesthenoiselevelnearthereceptor,asmeasuredindecibels(dB).Noisebarriersincludestand-alonewalls,berms,andcombinationberm/wallsystemsandareconstructedfromdiversematerials,suchasearth,wood,concrete,andmetal,among

others.Theyreducenoisebyreflectingitbackacrossthehighwayorforcingittotakealongerpathoverandaroundthebarrier.Althoughtheydonotblockallnoisecompletely,noisebarriers

typicallyreduceoverallnoiselevelsby5to10dB,effectivelycuttingtheloudnessoftrafficnoisebyuptoonehalf.4

Inmostcases,noisebarrierconstructioninvolvesthemultidisciplinaryinputoftransportation

planners,architects,landscapearchitects,androadway,acoustical,andstructuralengineers.A

generalgoalamongnoisebarrierteamsistodesigncost-effectivenoisebarriersthatfitwiththesurroundings,whileperformingtheintendednoiseabatementfunctions.Inrecentyears,thisgoalhasevolvedtoincludefindinginnovativewaystomergenoiseabatementwithsustainability

concepts,suchasstormwaterretention,5airpollutionreduction,6andelectricitygeneration.

1FHWANoiseBarrierDesignHandbook.

/environment/noise/noise_barriers/design_construction/design/design02.cfm

2Sullivan,J.WallsofFame.PublicRoads.May/June2003.

/publications/publicroads/03may/03.cfm

3FHWANoiseBarrierInventory:

/environment/noise/noise_barriers/inventory/

4Ibid.

5PersonalconversationwithRijkswaterstaatstaffduringFHWA,WashingtonStateDOT,andRWSpeerexchange.April10,2017.

6Kotzen,B.andEnglish,C.(2009).

4

1.1PhotovoltaicNoiseBarriers:TheConcept

Thephotovoltaicnoisebarrier(PVNB),orsolarnoisebarrier,representsthecombinationofnoisebarriersystemswithphotovoltaic(PV)systemsthatusesolarcellstoconvertlightenergydirectlyintoelectricity.PVNBscaneitherentailtheretrofittingofexistingnoisebarrierswithPVmodules

(i.e.,solarpanels)ortheintegrationofthePVmodulesintothedesignofnewnoisebarriers.Inbothcases,thenoisebarrierservesasasubstructureforPVmodules.Top-mounted,retrofitdesignsthatprovideadditionalareatoanexistingnoisebarrierstructurearecurrentlythemostcommonPVNBapproach.

Figure1

showssomepossibleconfigurationsofPVNBstructures.

Top-mounted

Integrated

CassetteZigzag

designdesign

Figure1.DifferentPossiblePVNBConfigurations.

Source:Adaptedfrom

Goetzbergeretal.(1999)

andAuerbachpresentation

Fully-integrateddesign

ArtificialorEarthenBerm-mounted

Generally,thedegreetowhichPVNBsattenuatenoiselevelshingesontheproportionofthesolarpanels’glasssurfacestothenoisebarrier’sothermaterials,astheglasssurfaceofaPVmodulecanonlybeappliedforsoundreflection.Inmanycases,soundabsorptionisnotrequiredforthenoisebarriertoachieveitsintendedacousticalfunction.Materialssuchassolidconcrete,wood,ormetaldonotprovidesoundabsorption,andPVpanelsareacousticallynolesssatisfactoryprovidedthattheyaresufficientlydense.Thetop-mounteddesignoffersgreaterPVsurfaceareaperlinearmeterofbarrierwall,especiallywhenconfiguredinseveralrowsas“shingles,”butcanonlybeusedin

situationswherenoiseabsorptionisnotnecessary.Wherenoiseabsorptionisrequired,an

integratedcassetteorzigzagdesignhastobeapplied,enablingacombinationofsoundreflection(offthePVglass)andsoundabsorption(viaabsorptivematerialinthenon-PVareas);adrawback

5

ofthecassetteorzigzagconfigurationsfromanenergyperspective,however,isthattheshapeofthebarriersencourageshadingofthesolarpanels.7

Figure2.ThePVNBrepresentsthe

combinationofnoisebarriersystemswithPVsystemsthatusesolarcellstoconvertlight

energydirectlyintoelectricity.

Photosource:TNCConsulting

Recently,technologiessuchasPVglass,thinfilmPV,semi-transparentPV,andluminescentsolar

concentrators(LSCs)8havebeentrialedinnoisebarrierapplicationsinordertofindnewwaysthatsolarPVmightbecombinedwiththebuiltenvironmentonalargerscale.Thesetechnologiesare

increasingfreedomincolorsandshapespossiblebecausetheyaremadeofdifferentmaterialsthanconventionalPVcells.TheycanalsobelighterinweightthanconventionalPVcells,potentially

loweringinstallationcosts.

PVNBsproducemuchlesspowerthanlarge-scalesolarfarms.Forexample,thecurrentworld’s

largestPVpowerstation,completedinChinain2015,covers14km2andhasan850megawatt-

peakcapacity(MWp).9Incomparison,aPVNBlocatednearTöging,Germany,oneofthelargest

PVNBsintheworld,isapproximately1kmlongand6,000m2inarea,andhasnearlya2MWp

capacity.Nevertheless,since1989whentheSwissfirstretrofittedahighwaynoisebarrierwithPVmodules,PVNBshavebeeninstalledinleast14countries

(Table1)

andareplannedinothers.

7NordmannandClavadetscher(2004).

8LSCsaretechnologiesthatguidesunlightinaconcentratedformtotraditionalsolarcells.Theymaycomeinavarietyofcolors,shapes,andtransparencies.LSCsarenotyetcommercialized.Formoreinformation,seeDebije,M.Renewableenergy:Betterluminescentsolarpanelsinprospect.Nature519.298-299.March19,2015.Doi:

10.1038/519298aandthefouruniversitiesoftechnologyintheNetherlandsat

www.4tu.nl/bouw/en/PDEng/Luminescent%20Solar%20Concentrator/.

9

/environment/2017/jan/19/china-builds-worlds-biggest-solar-farm-in-journey-to-become-

green-superpower

6

Table1.CompiledHighwayPVNBCounts*

Country

Earliest

Implementation

Count(atleast)

Australia

2007

2

Austria

1992

3

Croatia

2010

1

Denmark

1991

2

France

1999

2

Italy

2006

2

Germany

1992

18

TheNetherlandsa

1995

4

Slovenia

2012

1

Sweden

2014

1

Switzerland

1989

9

UnitedKingdom(U.K.)

2006

3

*Confirmedbyavailabledocumentation;plannednotincluded

aIncludesluminescentsolarconcentratorpilotSources

10

TransportationagenciesinthesecountrieshavedocumentedanumberofbenefitsofusingPVNBs.First,thePVNBsallowformultipleusesofthesameroadspaceandthusconsumealimitedamountofland,avoidingacommondrawbackofsolararraysnotmountedonroofsorintegratedwith

buildings.TrialshaveshownPVNBstobesafeandrelativelylow-maintenance.Thepotentialforrenewableenergygeneration,especiallywhenconsideredcumulativelyacrossacountry,isoftenhigh.Furthermore,thecoststoinstallsolarPVintheresidential,commercial,andutility-scale

sectorshavecontinuedtodeclineoverrecentyearsmakingnovelapplicationspotentiallymorefeasible.11

10Datasourcesare:

http://sunenergysite.eu/,

.pl/wp-

content/uploads/I.Kacafura_GOLEA_Slovenia.pdf

,

www.noisun.se/,

/awards/noise-barrier-

integrated-photovoltaic-plant,

www.vdpsrl.it/public/files//noise-barriers-2007.pdf,

Literaturereview(see

Bibliography),andelectroniccorrespondence.

11U.S.DepartmentofEnergy,NationalRenewableEnergyLaboratory

/news/press/2016/37745

7

2.LITERATUREREVIEW

TheearliestliteratureonPVNBsevaluatedthepotentialofalargegrid-connectedPVinstallation

alongmotorwaysandrailwaysinSwitzerland,includingananalysisoftheeconomicparameters

thatwouldmakePVNBsviableinthefuture(Nordmannetal.1989).Nearly10yearspassedbeforeadditionalliteratureonPVNBswaspublished.Inthelate1990s,researchersbeganreportingontheperformanceofPVNBtechnologyoptionsavailableatthetime,aswellastherenewableenergy

potentialofsuchsystemswhenconsideredatanationallevel.Nordmannetal.(1998)compared

thenoisedampeningandelectricitygenerationcharacteristicsofsixdifferentconceptsdeployedaspartofaninternationalcompetitiononPVNBs.Theresearcherspresenteddetailedfindingsfrom

theconstruction,operations,andmonitoringphasesofthreedemonstrationprojectsinSwitzerlandandthreeinGermany,includinglaborhoursrequiredtoinstallthePVmodulesandelectricity

outputbyseason.

Resultsindicatedthatitwaspossibletodesignbarriersas“highabsorbing”systemsbyGerman

standards,whilealsoproducingelectricity.Otherearlystudiesthatcalculatedtherenewable

energypotentialfromPVNBsforEuropeanUnioncountriesreportedPVNBstorepresentoneoftheleastexpensivewaystoimplementlargescalegrid-connectedPVinstallations(Goetzbergeretal.

[1999]andNordmannetal.[2000]).Thesestudiesalsodiscussedtheattitudesofvarious

stakeholders,includingroadauthorities,towardPVNBs.Atthetime,roadauthoritiesexpressedconcernsaboutthecostsandqualityofthewalls.

LaterresearchhasprovidedadditionalresultsonsubsequentyearsofmonitoringPVNBs(e.g.,

Grottke,Voigt,andHartl2010)orrefinedcountry-specificestimatesforPVNBfeasibility,withbothgenerallyfindingthatnoisebarriersoffergoodopportunitiesforelectricityproduction(e.g.,

Belluccietal.2003,deSchepperetal.2012,andNordmann,Vontobel,andLingel2012)eveninlocationswithregularcloudcover(Meppelink2015).ForthcomingresearchfromMichigan

TechnologicalUniversityestimatesthetotalU.S.energypotentialfromPVmodulesonexistingnoisebarrierstobeapproximately815GWh/yr(WadhawanandPearce2017).

SolarEfficiency

Intermsofsolarefficiency,monitoringhasshownthataccumulatedtrafficdust(VanderBorgandJansen2001)orgraffitionmodulescancauseenergylosses,especiallyifthemodulesaremountedtoolow,nearthesurfaceoftheroad(NordmannandClavadetscher2004).Self-shadingcanalso

reducePVmoduleperformance.However,rainhasbeenobservedtobeeffectiveatcleaningPVNBs(CarderandBarker2006),andthesystemscanbedesignedtominimizeshading(DeJongetal.

2016).

Sinceroadorientationdictatesnoisebarrierorientation,italsocanalsoaffectthesolarefficiencyofPVNBs.East-westorientedroadswereinitiallyviewedastheonlyroadssuitableforPNVBs,buttheemergenceofbifacialpaneltechnologyhaspresentedapotentiallyattractiveoptiongiventheir

abilitytoproduceelectricityinanyorientation—particularlyonnorth-southorientedhighways

8

(Figure3)

.BifacialPNVBs,whichallowlighttoenterfrombothsides,werefirstdeployedina

highwaysettinginAubrugg,nearZürichAirportinSwitzerlandin1997;thatsystemwaslater

expandedin2005,andseveralothershavebeenconstructedsince,withthetechnologyhaving

shownsubstantialimprovementsfromstandpointsofphysicalsizeandcellefficiency(Nordmannetal.2012).ThenoisebarriersupportstructuresforbifacialPVNBsystemslikelyneedtobelargerthantheidealsizeforthesolarmodulessincethenoisebarriersmustbedesignedtomaintaintheirnoiseblockingfunctionality(i.e.,belargeandofacertainmass)andtowithstandhighwindloads

(DeJongetal.2016).

TheangleofthePVpanelsonthenoisebarrierisalsoimportant.A30°PVpaneltiltpositionand

east-westorientationhasbeenshowntobeidealintermsofcapturingsolarirradiation

(WadhawanandPearce2017),althoughoptimaltiltanglesdependsonlatitudeandlocalweatherconditions.Thesameresearchnotes,however,thatpanelstiltedat90°–whichissuboptimalfromanenergyproductionperspective–arelesssusceptibletosoilingalonghighways,lessexpensivetoinstall,andgenerallyhavemoreareaavailableforPVcells.ThissuggestsalargepotentialforPVNBregardlessofroadorientation(WadhawanandPearce2017).12

Figure3.BifacialPNVBsallowlighttoenterfrombothsides.

Photosource:TNCConsulting

NoiseAttenuation

12MeasurementsinSwitzerlandhaveshownthatthecombinedannualsolarirradiationoftwoverticalplanes,onefacingeastandonefacingwest(bifacial),is108percentoftheannualirradiationofasouth-facingplaneata45

degreeorientation(GoetzbergerandNordmannetal.).

9

Fromanoiseperspective,researchresultssuggestthatPVNBsproduceaquietzone,ornoise

shadow,similarindepthandeffecttothatofasolidnoisebarrierofsimilarheight(Highways

Agency2013).APVNBpilotprojectintheU.K.thatincludedsimultaneoussoundmeasurementsatacontrolsitefoundthattheminimalincreaseinnoiselevelsoppositethePVNBsite(0.3dBA)13

wouldnotbeexpectedtocauseanychangeinthedisturbancefromroadtrafficnoise(CarderandBarker2006).OtherstudieshaveobservedthataPNVBcanresultinaslightincreaseinnoiseonthesideoftheroadoppositethePVinstallation,butonethatislikelyunnoticeabletoabutters,andpotentiallyminimizedbythecarefulpositioningofthePVmodulesoruseofselectvegetation

behindoroppositethebarrier(Corfield2012).

SafetyPerformance

ThecurrentliteraturedoesnotoftenspeaktothesafetyperformanceofPVNBsspecifically.One

exception(CarderandBarker2006)describesastudythattheHighwaysAgency(now“HighwaysEngland”)conductedinordertoaddressaconcernthatthePVNBmightbeasourceofdistractionfordriversandasaresultleadtoareductioninsafedrivingatthesite.Thestudyinvolvedtwo

camerasthatfilmedvehiclesfromthefrontandrearastheyapproachedthePVNBsite.Theteam

didnotseeanydifferencesinvehiclespeed,brakeapplication,orlateraldisplacementbetweenthesitebeforeandafterinstallationofthearrayundersimilarroadandweatherconditions,norwas

anydriverbehaviorthatmightindicatedriverdistractionobserved.ItwasnotedthatanunusedaccessroadseparatedthePVNBfromthehighwayandthatthearraymayhavebeenmore

distractingifclosertothehighway.

InformationontheAustralianexperiencethatwasprovidedtotheprojectteamindicatedthatPVpanelsinclinedatapproximately60degreesfromhorizontalcausedcomplaintsfromdriversaboutglare.ComplaintsweresufficientenoughtopromptthecoatingofthosePVpanelswithnon-

reflectivefilm,whichslightlycompromisedtheirperformancegeneratingelectricity.

EconomicFeasibility

FindingsregardingeconomicfeasibilityofPVNBsaremixed.OneimportanteconomicfactoristhattheefficiencyofsolarcellsisincreasingwhilethecostforPVsystemsisdecreasing.Now,paybackhorizonslargelydependingonfactorssuchasPVNBsize,noisebarriermaintenanceschedules,theavailabilityofrenewableenergyincentives,andelectricityprices—thelatterofwhichhave

continuedtodeclinesincemuchoftheliteraturewaspublished.Forexample,adecadeago

researchersestimatedthatelectricitygeneratedover30yearsbyaprojectintheU.K.wouldnotpayforthecostofinstallationunlessthepriceofelectricitywasmanytimesitscurrentvalue

(CarderandBarker2006).Thatanalysiscouldnotaccountforthefeed-intariffs(FIT)thattheU.K.’sEnergyActof2008introducedandthattookeffectinApril2010.IntheU.K.,FITsarepaymentsto

13dBAisshorthandforA-weightednoisemeasurements.Itdenotestheuseofaweightingfiltertoapproximatetherelativeloudnessofsoundstothehumanear.

10

peopleandorganizationsthatgeneraterenewableenergyupto5Megawatts(MW).14MorerecentstudieshaveestimatedthattheinstallationcostsofaseriesofproposedPVNBsintheU.K.could

possiblybeoffsetbytheirelectricitygenerationrevenueover20to25years(Highways2013andGiles2015).Finally,researchersinBelgiumwhomonetizedtheecologicalbenefitsofPVNBsfoundthataPVNBinvestmentinthatcountrycouldberecuperatedafter12years(Schepperetal.

2012).15

Mostrecently,researchersintheNetherlandshavemonitoredthefirsttwoyearsofperformanceoftwoLSCnoisebarriersatatestsiteinDenBosch,theNetherlands—thelargestdeploymentoftheprototypetechnologytodate(Kanellisetal.[2017]andSloofetal.[2016]).AlthoughtheLSC

technologymaynotcurrentlybereadyforwidespreaduseinnoisebarriersettings,researchershavemadeobservationsthatmayhelptransportationagenciesdeployfutureLSCnoisebarriersystems,suchaswaystodesignLSCstructureframestoavoidself-shading.

14Curre