太阳能利用领域论文.docx
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太阳能利用领域论文.docx
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太阳能利用领域论文
AppliedEnergy79(2004)239–248
APPLIED
ENERGY
Optimaltilt-anglesforsolarcollectors
usedinChina
RunshengTang*,1,TongWu1
SolarEnergyResearchInstitute,YunnanNormalUniversity,Kunming650092,PRChina
Accepted17January2004
Availableonline11March2004
Abstract
Areasonableestimationoftheoptimaltiltangleofafixedcollectorformaximizingits
energycollectionmustbedonebasedonthemonthlyglobalanddiffuseradiationonahor-
izontalsurface.However,themonthlydiffuseradiationisnotalwaysavailableinmanyplaces.
Inthispaper,asimplemathematicalprocedurefortheestimationoftheoptimaltiltangleofa
collectorispresentedbasedonthemonthlyhorizontalradiation.Acomparisonoftheoptimal
tiltanglesofcollectorsobtainedfromexpectedmonthlydiffuseradiationandthatfromthe
actualmonthlydiffuseradiationshowedthatthismethodgivesagoodestimationofthe
optimaltiltangle,exceptforplaceswithaconsiderablylowerclearnessindex.Acontourmap
oftheoptimaltiltangleofthesouth-facingcollectorsusedfortheentireyearinChinaisalso
outlined,basedonmonthlyhorizontalradiationof152placesaroundthecountry,combing
theoptimaltiltangleofanother30citiesbasedontheactualmonthlydiffuseradiation.
Ó2004ElsevierLtd.Allrightsreserved.
Keywords:
Optimaltiltangle;Solarcollectors;China
1.Introduction
Forthepracticalapplicationofsolarpanels,suchassolarcollectorsandsolar
cells,thetiltangle,definedastheangleofcollectorswithrespecttohorizontal,isa
*Correspondingauthor.Tel.:
+86-871-5518598;fax:
+86-871-5151719.
E-mailaddress:
kingtang@(R.Tang).
1Thisworkisequallysharedbybothauthors.
0306-2619/$-seefrontmatterÓ2004ElsevierLtd.Allrightsreserved.
doi:
10.1016/j.apenergy.2004.01.003
240
Nomenclature
R.Tang,T.Wu/AppliedEnergy79(2004)239–248
H
H0
I0
Kt
N
n
R
d
/
k
h
q
sday
x0
monthlycollectibleradiation(J/m2)
monthlyradiationonanextraterrestrialhorizontalsurface(J/m2)
solarintensityonanextraterrestrialsurfacenormaltotheradiation
direction(W/m2)
monthlyaverageatmosphericclearness-index
daysofagivenmonth
numberofdayscountedfromthefirstdayofJanuary
ratioofmonthlycollectibleradiationonatiltedsurfacetothatona
horizontalsurface
declinationofthesun(°)
azimuthangleofcollector(°)
locallatitude(°)
tiltangleofcollectorwithrespecttohorizontal(°)
albedooftheground
daylengthofaday(86,400s)
hourangleofthesunset(rad)
xc;s;xc;rapparenthouranglesofthesunsetandsunriseonatiltsurface,
respectively(rad)
Subscripts
a,eactualmonthlydiffuseradiationandexpectedones,respectively
b,d,hbeam,diffuseandhorizontalradiation,respectively
t
opt
tiltsurface
optimalangle
y,w,scollectorsusedfortheentireyear,wintermonthsandsummermonths,
respectively
dominantparameteraffectingthecollectibleradiationofafixedcollector.Ingeneral,
theoptimaltiltangleofafixedcollectorisrelatedtothelocalclimaticcondition,
geographiclatitudeandtheperiodofitsuse.Hence,differentplaceswillhavedif-
ferentoptimaltiltanglesforayearly-usedsolarcollector.Todate,anumberof
studiesontheoptimaltiltangleofcollectorshavebeenconducted[1–8],andalotof
empiricalcorrelationsforestimatingtheoptimaltilt-angleareavailableinthelit-
erature[2,5–8].Asexamples,Heywood[8]suggestedthattheoptimaltiltangleofa
yearlyusedcollectorshouldbeequaltolatitudeminus10°;Chinnery[5]suggested
thattheoptimaltiltangleofcollectorsusedinSouthAfricawaslatitudeplus10°;
andintheUS,theoptimaltiltangleofcollectorsusedforspaceheatingshouldbe
latitudeplus20°[6].
Chinaisoneofthebiggestcountriesintheworldwithcomplexclimaticand
topographicalconditions.Thus,differentplacesinthecountryshouldhavedifferent
R.Tang,T.Wu/AppliedEnergy79(2004)239–248
241
optimaltiltangles.Areasonableestimationoftheoptimaltiltangleofayearly-used
collectorshouldbebasedonthemonthlyglobalanddiffuseradiationofeachmonth
obtainedfromtheobservationsovermanyyears.However,themonthlydiffuse
radiationisnotalwaysavailableinmanyplacesofthecountry.In1989,Lin[7]
suggestedanempiricalcorrelationfortheestimationoftheoptimaltiltangleof
ayearly-usedcollectorbasedonanempiricalcorrelation,obtainedfromsolar
radiationdataof30citiesaroundthecountry,forthecalculationofmonthlydiffuse-
radiation.Butthiscorrelationcannotgiveanyestimationoftheoptimaltiltangleof
collectorsusedinplaceswherethemonthlydiffuseradiationisnotavailable.
Inthisarticle,asimplemathematical
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