A COMPARISON OF ENERGY RATING METHODOLOGIES USING FIELD TEST MEASUREMENTS

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1 Presented at the 3 rd Eurpean PV Slar Energy Cnference and Exhbtn, Valenca, Span, Sept A COMPARISON OF ENERY RATIN METHODOLOIES USIN FIELD TEST MEASUREMENTS Y. Pssant *, S. Pelland and D. Turctte CANMET Energy Center Varennes, Natural Resurces Canada 1615 Lnel-Bulet Blvd., Varennes, QC, J3X 1S6, Canada * Phne : +1 (45) Fax : +1 (45) eal : y.pssant@nrcan.gc.ca ABSTRACT: The a f ths wrk s t cpare tw types f energy ratng ethdlges n ters f ther accuracy and ther usefulness fr gudng dule selectn fr a gven lcatn. The ethdlgy currently under develpent was cpared t the spler ethdlgy prpsed by the Eurpean Unn Jnt Research Center (JRC). Fur PV dule technlges (trple junctn a-s, laser grved c-s, back cntact c-s and heterjunctn S) were characterzed n the feld t btan the nput paraeters requred by the tw energy ratng ethdlges. Lcal weather cndtns (drect, dffuse, glbal and n-plane rradances and PV dule and abent teperatures) were ntred ver a year at a test lcatn near Mntréal, Canada. These were cbned t PV dule nputs t calculate ther energy utput ver dfferent days and ver extended te perds, usng bth ethdlges. The tw ethdlges were fund t have cparable accuraces bth fr daly and fr extended perds. Whle the edan abslute errrs fr the re cplex ethd were generally lwer (% fr extended perds, as ppsed t.8% fr the JRC ethd), t s nt clear whether the gan n accuracy wuld justfy the added cst n cplexty f easureents and calculatns nvlved. Bth ethds were useful n predctng specfc yeld rankngs fr the fur dules under study. Hwever, dfferences between the dules were ften f the sae rder as the predctve errr f the ethds. Keywrds: Energy ratng, energy perfrance, PV dule 1 INTRODUCTION Many energy ratng ethdlges have been develped t calculate the energy utput f phtvltac (PV) dules under dfferent clatc cndtns and prvde a realstc estate f hw a dule wll perfr at varus lcatns. These energy ratng ethdlges cbne three basc eleents: PV dule characterstcs fr perfrance testng, standardzed weather data sets and a PV energy yeld predctn del. Se ethdlges use a cplex delng apprach that takes nt accunt all knwn effects that pact the perfrance f PV dules whle thers ake splfyng assuptns abut secndary effects such as angle f ncdence and spectral rradance t preserve the splcty and applcablty f the energy ratng ethdlgy. The prary a f ths wrk s t cpare bth types f ethdlges n ters f the accuracy f ther energy predctns by cparng these t easured data. T ths end, the standard n PV dule energy testng currently under develpent [1-3] was selected as representatve f cplex ethdlges. Meanwhle, the energy ratng ethdlgy prpsed by the Eurpean Unn Jnt Research Center (JRC) was selected as the spler apprach, snce t has already been cpared t the apprach elsewhere [4-5], and snce t has been fund t yeld accurate predctns ver perds rangng fr a few weeks t a full year [6]. Anther bjectve f ths wrk was t exane whether usng reference days as the standardzed weather data n energy ratngs was useful fr the pnt f vew f selectng a dule fr a gven lcatn. The specfc yeld (kwh/kw) rankngs f fur dules as predcted fr sx reference days was thus cpared t the rankngs f ther specfc yelds as easured n an utdr feld test ver an extended perd. ENERY RATIN METHODOLOIES.1 /JRC Kenny et al. have prpsed an energy ratng ethdlgy where PV energy prductn s predcted fr abent teperature and fr rradance n the plane f the PV dule [5]. It requres easurng a atrx r perfrance surface f axu pwer pnt (P ) r related paraeters versus abent teperature and glbal rradance n the dule plane. Ths perfrance surface s then ftted wth a sth, snglevalued functn wth a anageable nuber f ftted paraeters [5]. Here we cnsder the fllwng functn prpsed n [7], whch s a splfed versn f the eprcal equatns f Kng et al. [8]: P ( 1 + c 1, T ln ) = P, STC + c ln ( 1 + α ( T T )) + β v ( T T ) where P s PV dule pwer at the axu pwer pnt (MPP), T s PV dule teperature, s the rradance n the dule plane, T and are dule teperature and rradance at standard testng cndtns (STC), P,,STC s MPP pwer at STC, and the reanng paraeters (α, β v, c 1 and c ) need t be deterned thrugh curve fttng. Cnly avalable weather data ( and abent teperature) frng a standard data set can then be cbned wth a theral del f dule teperature as a functn f rradance, abent teperature (and pssbly wnd speed) t btan dule teperature. and T then serve as nputs t the functn n (1) t generate P fr each eleent f the weather data. Fnally, P values are sued ver the selected te perd t btan the crrespndng energy ratng. * (1)

2 Presented at the 3 rd Eurpean PV Slar Energy Cnference and Exhbtn, Valenca, Span, Sept draft standard The standard under develpent deals wth bth PV dule energy ratng and perfrance testng. Perfrance testng as t fully characterze the dependence f PV utput pwer n varus paraeters knwn t pact PV perfrance - naely rradance, dule teperature, the angle f ncdence f lght strkng the dule and ts spectral dstrbutn. The an dfference between the JRC apprach and the draft apprach s the nclusn f spectral and angle f ncdence effects by the latter, and the asscated addtnal requreents bth n ters f PV dule characterzatn and n ters f weather data cplexty. Essentally, fr any gven rradance cndtn, the IEC apprach calculates an effectve, equvalent rradance wth nral ( ) ncdence and AM1.5 spectru, snce these are the cndtns under whch the dependence f dule perfrance n rradance and dule teperature s characterzed. Fr a gven rradance, the ncdence equvalent rradance d s sply the rradance that enters the dule crrected fr csne and reflectn effects: d where τ(θ) s the relatve transssn f lght nt the dule at angle f ncdence θ, dr s the drect nral rradance and dff (θ) s the angular dstrbutn f ttal dffuse rradance, whch ncludes bth sky dffuse and reflected rradance [3]. Next, an effectve rradance wth AM 1.5 spectral dstrbutn s derved by requrng that t generate the sae shrt-crcut current as d. In ther wrds: ~ ~ ~ ~ = τ ( θ ) cs( θ ) + τ ( θ ) ( θ ) cs( θ ) dθ d A M 15 = dr d SR( E( d EAM E( dλ SR( E 1.5 AM () ( dλ (3) ( ) ) 1.5 λ dλ where SR( s the dule s spectral respnse at wavelength λ and at teperature T, E( s the relatve slar spectru f d and E AM1.5 s the relatve slar spectru fr AM 1.5 [3]. Once dam1.5 has been btaned, PV dule teperature s calculated usng a theral del, as n the case f the JRC ethd. These theral dels were nt evaluated here, snce easured dule teperatures were used whenever pssble. Fr dam1.5 and T, dule utput pwer can be btaned fr the easured P (and Isc) versus, T atrces. Here, the ethd prpses a dfferent apprach than JRC based n lnear and plynal nterplatns f these atrces [1]. Snce ths step s anly a chce abut hw t treat the sae nput data, the JRC ft n equatn (1) was used t derve P fr the case als; ths ade the cparsn between the tw appraches clearer, and n partcular the pact f usng dam1.5 nstead f sply usng easured glbal rradance n the dule plane. Mrever, when appraches based n lnear r splne nterplatns (r regressns) were tested n the present case, the result was fund t be senstve t the nterplatn ethd selected, and the energy yeld estates typcally had larger errrs than thse f dff estates derved usng the JRC ft n (1)..3 The Mdfed ethdlges Except n the case f the reference days prpsed by the draft standard, dff (θ) and E( were nt avalable fr the te perds cnsdered, snce these were nt easured. A splfed versn f the IEC ethdlgy was therefre adpted fr these perds. Snce nly the sky dffuse rradance n a hrzntal plane was easured, ttal dffuse rradance n the plane f the dule was btaned fr: = cs( ) (4) dff, dr θ As a splfyng assuptn, t was assued that dff, arse fr an strpc dstrbutn, n whch case equatn () beces: ~ ~ ~ d = τ ( θ ) dr cs( θ ) + dff, τ ( θ ) cs( θ ) dθ (5) Snce τ(θ) was nt easured drectly, t was taken fr each dule fr the Sanda database whch gves τ(θ) as a furth rder plynal wth dule-specfc ceffcents [8-9]. Meanwhle, snce n spectral data was avalable, equatn (3) was replaced by an ar-ass based spectral crrectn prpsed by Kng et al. where the spectral crrectn s a ffth rder plynal n ar ass wth dule specfc ceffcents avalable n the Sanda database [8-9]. Ar ass was estated fr zenth angle and fr the alttude f the PV dule lcatn accrdng t the equatns presented n [1]. 3 OUTDOOR MEASUREMENTS AND PV MODULE CHARACTERIZATION 3.1 Outdr easureents Fur PV dules ssued fr dfferent technlges - laser grved bured junctn c-s (c-s 1), back cntact c-s (c-s ), trple junctn a-s (a-s 3J), and heterjunctn S (HIT) were unted n an pen utdr rack n Varennes, Canada (near Mntreal). The dules were rented wth lattude tlt (45 degrees), facng Suth. They were cnnected t a ulttracer whch perated the dules at ther axu pwer pnt, and whch read PV utput pwer and back-fdule teperature every 5 secnds, recrdng 1 nute averaged values. IV curves were als traced fr all dules at 5 nute ntervals. In addtn, varus weather nputs requred by the JRC and ethdlges were als read every 5 secnds, wth 1 nute averages recrded. Measureent wth precsn pyraneters and pyrheleters ncluded glbal rradance n the dule plane, drect nral/bea rradance, sky dffuse rradance n a hrzntal plane and glbal hrzntal rradance. Abent teperature and wnd speed were als recrded. 3. PV dule characterzatn: Cnstructng atrces f P vs and T Matrces f MPP pwer as a functn f ncdent rradance and dule teperature were cnstructed fr

3 Presented at the 3 rd Eurpean PV Slar Energy Cnference and Exhbtn, Valenca, Span, Sept each dule usng the IV curve utdr easureents. Maxu pwer pnts fallng wthn ±1% f the selected rradance and wthn ±1 C f the selected teperature were averaged. Specal care was taken t use pnts that were free f the pact f large ncdence angles and spectral shfts by elnatng utlers befre averagng the pnts and by selectng hurs clse t slar nn whenever pssble. Three pnts were selected at rand fr averagng fr each atrx entry. The selected teperatures were 5, 15, 5, 35 and 45 C and rradance levels 1,, 4, 6, 8, 1 and 11 W/. 4 ENERY RATIN SIMULATION RESULTS 4.1 Standard days Part 4 f the draft standard descrbes standard te perds and cntans the weather data that can be used t sulate the perfrance f a gven dule ver these perds. The dcuent defnes sx reference days wth hurly datasets f abent teperature, drect and dffuse rradance, wnd speed, angle f ncdence and spectral dstrbutn: HIHT: Hgh Irradance, Hgh Teperature HILT: Hgh Irradance, Lw Teperature MIMT: Medu Irradance, Medu Teperature MIHT: Medu Irradance, Hgh Teperature LILT: Lw Irradance, Lw Teperature NICE: Nral Irradance, Cl Envrnent These reference days were used as nput t the and t bth the rgnal and dfed energy ratng ethdlges t cpare results n a case where nput data was avalable fr all three ethds. Fgure 1 cpares the results btaned fr the technlges under study fr the NICE day and shws the rankngs f each technlgy fr that reference day. The specfc yelds btaned usng all three ethdlges are wthn 3% f each ther fr all technlges under study fr ths reference day. Over all reference days, the abslute value f the dfference n specfc yelds between the rgnal and dfed ethdlges ranged fr. t 3%, wth a edan dfference f 1.%. Meanwhle, the JRC ethd dffered fr the rgnal ethd by t 4%, wth a edan f 1.8%. Table I lsts the rankngs btaned fr all reference days usng all three ethdlges. Technlges wth specfc yelds wthn 3% f each ther were attrbuted the sae rankng based n the edan errrs reprted n 4. and 4.3 Specfc Yeld (Wh/W) NICE Md. Fgure 1: Specfc yelds f the technlges under study fr the NICE reference day usng the and the energy ratng ethdlges Table I: PV dule rankngs fr the reference days f nterest as btaned fr the tw ethdlges Reference Day Rankngs fr energy ratng ethdlges, & Sp. HIHT a-s > HIT > c-s 1 = c-s HILT c-s 1= c-s = HIT < a-s MIMT a-s > c-s 1= HIT > c-s MIHT a-s > HIT = c-s 1 > c-s LILT c-s 1 > c-s = HIT = a-s NICE a-s > HIT = c-s 1 = c-s 4. days Specfc days bserved n the feld reseblng the descrptn f the sx reference days prpsed n the draft standard were used t cpare the accuracy f the energy ratng ethdlges and t deterne whether the rankngs n the prevus sectn fr reference days carred ver t easured days. Fgure cpares the specfc yelds easured n the feld fr August 19 th, 7, a day slar t the NICE reference day, t thse calculated usng the energy ratng ethdlges and the weather data easured n the feld fr that day. The energy ratng ethdlges were bth successful n predctng the rankng f the dules n the feld, wth the caveat that equal rankngs were assgned fr perfrance dfferences f 3% r less. Als, the rankng establshed fr the NICE reference day (see 4.1) was the sae as that btaned fr Aug. 19, 7 n the feld. Specfc Yeld (Wh/W) Aug. 19th 7 (NICE) Md. Fgure : Specfc yelds f the technlges under study fr August 19 th, 7 (a day slar t the NICE reference day) usng the dfed and the energy ratng ethdlges Table II: Percent devatns f deled specfc yelds fr easured yelds fr selected days Day c-s 1 (%) c-s (%) a-s 3J (%) HIT (%) ESTI IEC ESTI IEC ESTI IEC ESTI IEC 7/8/7 (HIHT), -,4,1,,7, 4, 1,9 8/3/17 (HILT) 4,1,7 3,1,3 4, -,6 4,7 4, 8/4/11 (MIMT),6 -,4,3 -,3, -3,3, -,3 7/8/4 (MIHT) 3,8 1, 4,4,1 6,1, 3,6 1,4 7/1/1 (LILT) 4,7 3,4 4,4 5, -1,4-19,7 9,6 1,8 7/8/19 (NICE) 4,9 1,9 5,5,8, -,7 4,8, Table II lsts the devatns f the calculated specfc yelds fr the easured values n the feld n selected

4 Presented at the 3 rd Eurpean PV Slar Energy Cnference and Exhbtn, Valenca, Span, Sept days reseblng the descrptn f reference days. Overall, the edan abslute devatns were 3.9% fr the ethdlgy and.1% fr the dfed ethdlgy. Larger devatns were btaned when calculatng the perfrance f the arphus slcn trple junctn dule as well as fr days where the rradatn was lw. 4.3 Lnger te perds It wuld be dffcult t apply the rgnal ethdlgy t calculate the energy ratng f PV dules ver a lng te perd as t requres the nput f paraeters that are nt cnly avalable. Hwever, the dfed apprach, detaled n sectn.3, akes t pssble t carry ut such calculatns. T Suer (Aug. 9-7) (A) Specfc Yeld (Wh/W) ) Specfc Yeld (Wh/W Specfc Yeld (Wh/W) Specfc Yeld (Wh/W) 1, 8, 6, 4,,,, 16, 1, 8, 4,,, 16, 1, 8, 4,,, 15, 1, 5,, Fall (Sept. 13- Oct. 13 7) Wnter (Jan Feb. 8) Sprng (Apr ) (B) (C) (D) Fgure 3: Specfc yelds easured and calculated fr lng te perds n (A) suer, (B) fall, (C) wnter, (D) sprng Mdelled hurly energy prductn (Wh) Mdelled hurly energy prductn (Wh) Mdelled vs easured hurly energy prductn, c-s ths end, fur te perds were selected: Aug. 9, 7 (suer), Sept. 13 Oct. 13, 7 (fall), Jan. 19 Feb, 8 (wnter) and Apr. 1 3, 8 (sprng). Fgure 3 cpares the specfc yelds easured n the feld and calculated ver these perds. The PV technlges under study were fund t have slar perfrance and bth the and the dfed IEC ethdlges successfully predcted the technlgy rankngs fr the chsen te perds. Table III lsts the dfference between the yelds easured n the feld and thse calculated. Overall, the edan abslute devatns were.8% fr the ethdlgy and.% fr the dfed ethdlgy. Table III: Percent devatns between deled and easured specfc yelds fr the chsen te perds Perd c-s 1 (%) c-s (%) a-s 3J (%) HIT (%) ESTI IEC ESTI IEC ESTI IEC ESTI IEC Suer 3,9 1, 4, 1,5 -, -,5 4, 1,6 Fall 1,7,3 1,9 1,1,1-4,5, 1,4 Wnter 3,5 3, 1,3,3, -8,4 1,5,9 Sprng 3,3 1, 3,7 1,6 5,4,5 5,8 3,6 5 DISCUSSION 5.1 Errr analyss and accuracy f the ethdlges The prevus analyss fcused n the bas errr f the energy yeld predctns fr the and JRC ethdlges, fr perds rangng fr a day t a nth. In rder t further assess the accuracy f the hurly energy prductn (Wh) Mdelled vs easured hurly energy prductn, a-s 3J hurly energy prductn (Wh) Fgure 4: Mdeled vs. easured hurly energy prductn fr c-s 1 and a-s 3J wth dfed IEC ethd

5 Presented at the 3 rd Eurpean PV Slar Energy Cnference and Exhbtn, Valenca, Span, Sept ethdlges, the rt-ean-squared errr (RMSE) was cputed ver the full perd cnsdered n 4.3. Fgure 4 shws scatter plts f easured vs. deled hurly energy prductn fr the c-s 1 and a-s 3J dules. As n Sectn 4.3, the tw ethds yeld very slar accuraces, wth RMSEs f abut 6-8% fr the c-s and HIT dules, and f 1-11% fr the a-s 3J dule. RMSEs fr the splfed ethd are lwer than thse fr the JRC ethd, but nly by 1%. The RMSEs btaned fr the c-si and HIT dules are cparable t thse f abut 6-7% reprted n [6] usng the JRC and ther ethds excludng spectral and anglef-ncdence effects. The reference day analyss n Sectn 4.1. ndcated that whether spectral and angle f ncdence effects are taken nt accunt can lead t dfferences n daly energy ratngs n the range f % t 4%. Fr lnger perds, the rgnal ethd culd nt be appled, but a splfed versn f t typcally lead t a slght prveent ver the JRC apprach whch des nt take these effects nt accunt (see Table II). A ntable exceptn t ths ccurred fr the a-si 3J dules, where attepted spectral and angle f ncdence crrectns usng the splfed versn f the apprach actually prved cunterprductve, leadng t a decrease n accuracy. Alng these lnes, feld test results such as thse f Kng et al. [11] have ndcated that spectral and angle-f-ncdence crrectns can have agntudes f -5% t % and -3% t 1%, respectvely ver extended perds. Thus, prperly accuntng fr such effects shuld lead t crrespndng prveents n accuracy. On the ther hand, as pnted ut by Kenny et al. [5], t s nt clear whether the benefts f ncludng such effects n an energy ratng ethdlgy wuld utwegh the csts, even assung that lcatn specfc, dule-t-dule varatns n spectral respnse (and angle-f-ncdence effects) culd be adequately captured usng synthetcally generated reference spectra. One ssue t bear n nd when tryng t deterne the degree f accuracy that an energy ratng ethdlgy shuld a fr s that f dule-t-dule varablty f energy prductn fr dules f the sae type (sae anufacturer and del). Fr nstance, Fresen et al. [6] fund that energy predctn errrs ncreased by rughly 1% when the characterzatn f ne dule was carred ver t anther dule f the sae type. Ths hghlghts the prtance f ltng and/r quantfyng such dule-t-dule varablty. It als suggests a related lt t the usefulness f tryng t ake energy ratngs arbtrarly accurate, f a slar accuracy cannt be expected fr dules ther than thse used n the characterzatn prcess, but f the sae type. A fnal reark s that the ethdlges are based n easured (and nterplated) values f P. Thus the specfc yelds reprted n ths paper were calculated usng the easured P f the PV dules and nt the rated values gven by the anufacturers. If such anufacturer values had been used (and unfrtunately, ths s the nly nfratn st cnsuers have access t), the specfc yelds and rankngs establshed here wuld have been qute dfferent as any dules were fund t underperfr ther STC ratng t a certan degree. 5. The case f the a-s 3J dule The case f the a-s 3J dule deserves specal attentn, snce ts bas and RMS errrs were ntably greater than fr the ther dules, as exeplfed by the greater dspersn f pnts fr the a-s 3J n Fgure 4. In the case f ths dule, there were at least tw sgnfcant and related cplcatns. Frst, the STC pwer (and ther pnts n the P vs., T atrx) experenced seasnal varatns, wth excursns fr the yearly ean f the rder f ±3% fr STC pwer. (Nte: The dule was expsed utdrs fr a prlnged perd befre easureent began and had thus reached a etastable state.) A related ssue was the qualty f the ft t the P vs., T atrx that was perfred usng equatn (1). Devatns between atrx values and values based n the ft were calculated fr each atrx pnt. Medan abslute errrs fr the c-s and HIT technlges were f the rder f 1%, whle the edan abslute errr fr the a-s 3J dule was rughly 4%. Fnally, whle the pact f spectral rradance n the a- S 3J dule culd nt be assessed drectly, Fgure 4 ndcates that the a-s 3J dspersn s greater than that f the ther dules at all rradance values, whle a spectrally dnated nfluence wuld prarly pact the lw rradance end f the scatter plt crrespndng t hurs at the begnnng and end f the day where spectral nfluence s usually greatest. 5.3 Applcablty n the feld The a f the part 3 PV dule energy ratng standard under develpent s t defne a ratng ethdlgy, whch prvdes the PV dule energy (watt-hurs) and the perfrance rat at axu pwer peratn fr a set f defned abent cndtns [3]. Ths energy ratng syste, and a spler ne where PV energy prductn s predcted fr abent teperature and fr rradance n the plane f the PV dule, have been appled t a nuber f dfferent PV dule types peratng under standard days (as defned n part 4 f the standard), real actual days easured n the feld and lnger te perds t verfy hw useful the ratng syste s when selectng a PV dule type fr a gven lcatn. Fr real days reseblng the descrptn f the reference days n the standard, bth the and ethdlges predcted an energy ratng that atched what was bserved n the feld. The rankngs establshed based n reference days were the sae as thse bserved fr easured days n st cases. The ratng systes were thus useful fr the selectn f apprprate PV dules n ths cntext, althugh predcted dfferences between dules were ften f the sae rder as edan errrs. Fr cases where the user s nterested n selectng a technlgy accrdng t ts seasnal r annual perfrance, relyng n reference days culd prvde an educated guess at best. Fgure 5 presents the 365 days f the typcal eterlgcal year (TMY) f the test lcatn as a functn f axu drect nral rradance and axu abent teperatures. Based n ths representatn, t ght be suppsed that the NICE day wuld be the best predctr ang reference days f lng ter specfc yeld dfferences between dules, snce t

6 Presented at the 3 rd Eurpean PV Slar Energy Cnference and Exhbtn, Valenca, Span, Sept Max Abent Teperature (deg C) LILT MIHT MIMT Lcal TMY NICE Maxu Drect Nral Irradance (W/ ) HIHT HILT Fgure 5: Lcal TMY dsplayed as a functn f axu abent teperature and axu drect nral rradance has the hghest densty f pnts arund t and snce ts rradance s greater than fr the LILT, MIMT and MIHT days. One culd thus use the NICE day t derve tentatve perfrance rankngs fr the lcatn under study. In ths case, annual perfrance rankngs wuld have been crrect. Hwever, ths need nt have been the case, and t wuld be very dffcult t deterne hw t wegh dfferent reference days n general. Instead, re accurate energy ratngs wuld be btaned by usng datasets representng these lnger te perds. 6 CONCLUSIONS The and JRC/ energy ratng ethdlges currently under develpent were cpared n ters f ther accuracy and f ther usefulness fr gudng dule selectn fr a gven lcatn. The tw ethdlges were fund t have cparable accuraces when used t predct specfc yelds fr easured days and fr extended perds. Whle the edan abslute errrs fr the re cplex IEC ethd were generally lwer (.% fr extended perds, as ppsed t.8% fr the JRC ethd), t s nt clear whether the gan n accuracy wuld justfy the cst n cplexty f easureents and calculatns nvlved. Bth ethds were useful n predctng specfc yeld rankngs fr the fur dules under study. Hwever, dfferences between the dules were ften f the sae rder as the predctve errr f the ethds, n whch case rankngs were cnsdered equal. Als, the usefulness f the ratngs culd be lted by the ssue entned prevusly that there are currently sgnfcant dule-tdule perfrance varatns fr dules f the sae type (anufacturer and del). The usefulness f reference days fr predctng perfrance ver easured days and lnger te perds was als exaned. The NICE reference day was judged t be the st representatve f yearly average cndtns at the test ste. Rankngs based n ths day were ndeed fund t be the sae as thse easured n the feld, althugh the prcedure used ay nt wrk n ther cases, and s dffcult t systeatze. Fnally, as ndcated n., attepts t use lnear r splne nterplatns f the P vs., T atrces rather than the JRC ft ndcated that results were senstve t the nterplatn ethd used. Ths ay be an aspect f the draft standard that wuld deserve clser study. 7 ACKNOWLEDEMENTS Fnancal supprt fr ths research prject was prvded by Natural Resurces Canada thrugh the Prgra n Energy Research and Develpent. 8 REFERENCES [1] Phtvltac (PV) dule perfrance testng and energy ratng Part 1: Irradance and teperature perfrance easureents and Pwer Ratng, Draft H (W wrkng draft) [] Phtvltac (PV) dule perfrance testng and energy ratng Part : Spectral respnse, ncdence angle and dule peratng teperature easureents, Draft E (W wrkng draft) [3] Phtvltac (PV) dule perfrance testng and energy ratng Part 3: Energy ratng f PV dules, Draft C (W wrkng draft) [4] S. Mau, S. Zan, B. Bergar, E. Ruppert, S. R. Wllas, J. Ry, T. R. Betts, R. ttschalg, H. Müllejans, Quantfyng envrnental effects fr dfferent devce technlges based n prpsed energy ratng standard, Prceedngs f the nd EPVSEC, Mlan, Italy, Septeber 7. [5] R. P. Kenny, E. D. Dunlp, H. A. Ossenbrnk, H. Müllejans, A practcal ethd fr the energy ratng f c-s phtvltac dules based n standard tests, Prg. Phtvlt: Res. Appl. 6; 14: [6]. Fresen, R. ttschalg, H.. Beyer, A. uern de Mntgareul, N. van der Brg, W.. J. H. M. van Sark, T. Huld, B. Müller, A. C. de Kezer, Y. Nu, Intercparsn f dfferent energy predctn ethds wthn the Eurpean prject PERFORMANCE Results f the 1 st rund rbn, Prceedngs f the the nd EPVSEC, Mlan, Italy, Septeber 7. [7] R. P. Kenny,. Fresen, D. Chanese, A. Bernascn, E. D. Dunlp, Energy ratng f PV dules: cparsn f ethds and apprach, Prceedngs f the 3 rd Wrld Cnference n PVEC, May 3, Osaka, Japan. [8] D. L. Kng, W. E. Bysn, J. A. Kratchvll, Phtvltac array perfrance del, Sanda reprt SAND4-3535, Deceber 4. [9] Sanda Natnal Labratres, August 7, 8. [1] D. L. Kng, J. A. Kratchvl, W. E. Bysn, W. Bwer, Feld experence wth a new perfrance characterzatn prcedure fr phtvltac arrays, Prceedngs f the nd Wrld PVSEC, July 1998, Venna, Austra. [11] D. L. Kng, W. E. Bysn, J. A. Kartchvl, Analyss f factrs nfluencng the annual energy prductn f phtvltac systes, Cnference Recrd f the IEEE PVSC,, Pages