IEC 61 829 Edition 2 0 201 5 1 0 INTERNATIONAL STANDARD NORME INTERNATIONALE Photovoltaic (PV) array – On site measurement of current voltage characteristics Champ de modules photovoltaïques (PV) – Me[.]
I E C 61 ® Edition 2.0 201 5-1 I N TE RN ATI ON AL S TAN D ARD N ORM E I N TE RN ATI ON ALE P h oto vol tai c (P V) arra y – On -s i te m eas u rem en t of cu rren t-vol tag e ch aracteri s ti cs C h am p d e m od u l es ph oto vol taïq u e s (P V) – M es u rag e s u r s i te d es caracté ri s ti q u es IEC 61 829:201 5-1 0(en-fr) cou ran t-te n s i on T H I S P U B L I C AT I O N I S C O P YRI G H T P RO T E C T E D C o p yri g h t © I E C , G e n e v a , S wi tz e rl a n d All rights reserved Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either IEC or IEC's member National Committee in the country of the requester If you have any questions about I EC copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or your local I EC member National Committee for further information Droits de reproduction réservés Sauf indication contraire, aucune partie de cette publication ne peut être reproduite ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie et les microfilms, sans l'accord écrit de l'IEC ou du Comité national de l'IEC du pays du demandeur Si vous avez des questions sur le copyright de l'IEC ou si vous désirez obtenir des droits supplémentaires sur cette publication, utilisez les coordonnées ci-après ou contactez le Comité national de l'IEC de votre pays de résidence IEC Central Office 3, rue de Varembé CH-1 21 Geneva 20 Switzerland Tel.: +41 22 91 02 1 Fax: +41 22 91 03 00 info@iec.ch www.iec.ch Ab ou t th e I E C The I nternational Electrotechnical Commission (I EC) is the leading global organization that prepares and publishes I nternational Standards for all electrical, electronic and related technologies Ab o u t I E C p u b l i ca ti o n s The technical content of IEC publications is kept under constant review by the IEC Please make sure that you have the latest edition, a corrigenda or an amendment might have been published I E C Catal og u e - 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webstore i ec ch /csc Si vous désirez nous donner des commentaires sur cette publication ou si vous avez des questions contactez-nous: csc@iec.ch I E C 61 ® Edition 2.0 201 5-1 I N TE RN ATI ON AL S TAN D ARD N ORM E I N TE RN ATI ON ALE P h otovol tai c (P V) arra y – On -s i te m eas u rem e n t of cu rre n t-vol tag e ch aracte ri s ti cs C h am p d e m od u l es ph oto vol taïq u es (P V) – M e s u rag e s u r s i te d es caractéri s ti q u e s cou ran t-ten s i on INTERNATIONAL ELECTROTECHNICAL COMMISSION COMMISSION ELECTROTECHNIQUE INTERNATIONALE ICS 27.1 60 ISBN 978-2-8322-2966-8 Warn i n g ! M ake s u re th at you obtai n ed th i s pu bl i ca ti on from an au th ori zed d i s tri bu tor Atten ti on ! Veu i l l ez vou s ass u rer q u e vou s avez obten u cette pu bl i cati on vi a u n d i stri b u teu r ag ré é ® Registered trademark of the International Electrotechnical Commission –2– I EC 61 829: 201 © I EC 201 CONTENTS FOREWORD I NTRODUCTI ON Scope Norm ative references Terms and definitions Apparatus I rradiance measurem ents in natural sunlight Module tem perature m easurem ents Electrical measurements Measurem ent procedure Choose and record appropriate conditions for measurement Clean the m odules Check for shading Confirm uniform ity of irradiance over the test array 5 Mount the reference device Prepare to m easure the array temperature Disconnect the array 1 Connect the measurem ent system to the array to be m easured 1 Record electrical data and measurem ent conditions 1 Record spectral data 1 Typical and extreme module selection Analysis Adjust the measured irradiance for an y deviation from reference conditions Compute the average temperature of the array under test Compute the j unction tem perature Translate the measurem ent to the desired test condition Correct for soiling losses Test report Annex A (informative) Reference values and reference device A Reference test conditions (RTC) A Standard test conditions (STC) A Reference device Bibliograph y Figure – Exam ples of extreme and central modules I EC 61 829: 201 © I EC 201 –3– INTERNATI ONAL ELECTROTECHNI CAL COMMISSI ON P H O T O VO L T AI C ( P V) ARR AY – O N -S I T E M E AS U RE M E N T O F C U RRE N T -VO L T AG E C H AR AC T E RI S T I C S FOREWORD ) The I nternati on al Electrotechni cal Comm ission (I EC) is a worl d wid e organization for stan dardization com prisin g all n ation al el ectrotechnical comm ittees (I EC National Comm ittees) The object of I EC is to prom ote internati onal co-operation on all q uestions concerni ng stand ardi zati on in the el ectrical an d electronic fi elds To this en d and in additi on to other acti vities, I EC pu blish es I nternational Stan dards, Techn ical Specificati ons, Technical Reports, Publicl y Avail abl e Specificati ons (PAS) and Gu ides (h ereafter referred to as “I EC Publication(s)”) Th ei r preparation is entrusted to tech nical comm ittees; any I EC N ational Comm ittee interested in the subj ect dealt with m ay partici pate in this preparatory work I nternational, governm ental an d n on governm ental organ izations l iaising with th e I EC also participate i n this preparation I EC collaborates closel y with the I nternational Organi zation for Stand ardization (I SO) in accordance with ditions determ ined by agreem ent between th e two organi zati ons 2) The form al decisions or ag reem ents of I EC on tech nical m atters express, as n early as possible, an i nternati onal consensus of opi nion on the rel evant subjects since each technical com m ittee has representati on from all interested I EC N ational Com m ittees 3) I EC Publications have the form of recom m endations for intern ational use an d are accepted by I EC National Com m ittees in that sense While all reasonable efforts are m ade to ensure that th e tech nical content of I EC Publications is accu rate, I EC cann ot be h eld responsi ble for th e way in which th ey are used or for an y m isinterpretation by an y en d u ser 4) I n order to prom ote intern ational u niform ity, I EC National Com m ittees und ertake to apply I EC Publications transparentl y to the m axim um extent possible i n their national an d regi on al publicati ons Any d ivergence between an y I EC Publication and the correspondi ng national or regi on al publicati on sh all be clearl y in dicated in the latter 5) I EC itself d oes n ot provi de an y attestation of conform ity I n depend ent certificati on bodies provi de conform ity assessm ent services and, in som e areas, access to I EC m arks of conform ity I EC is not responsi ble for any services carri ed out by ind ependent certification bodi es 6) All users shou ld ensure that they h ave the l atest editi on of thi s publicati on 7) No liability shal l attach to I EC or its directors, em ployees, servants or ag ents inclu din g in divi dual experts an d m em bers of its tech nical com m ittees and I EC Nati on al Com m ittees for any person al i nju ry, property d am age or other dam age of any n ature whatsoever, wheth er di rect or indirect, or for costs (includ i ng leg al fees) and expenses arisi ng out of the publ ication, use of, or relian ce upon, this I EC Publicati on or any other I EC Publications 8) Attention is drawn to th e N orm ative references cited in th is publ ication Use of the referenced publ ications is indispensable for the correct applicati on of this publication 9) Attention is drawn to the possibility that som e of the elem ents of this I EC Publication m ay be the su bject of patent rig hts I EC shall not be held responsibl e for identifyi ng any or all such patent ri ghts I nternational Standard I EC 61 829 has been prepared by I EC technical committee 82: Solar photovoltaic energ y systems This second edition cancels and replaces the first edition published in 995 This edition constitutes a technical revision This edition includes the following significant technical changes with respect to the previous edition: a) b) c) d) it addresses man y outdated procedures; it accom modates com monl y used com mercial I- V curve tracers; it provides a m ore practical approach for addressing field uncertainties; it removes and replaces procedures with references to other updated and pertinent standards, including the I EC 60904 series, and I EC 60891 –4– I EC 61 829: 201 © I EC 201 The result is a m uch m ore practical and useful stand ard The text of this standard is based on the following documents: FDI S Report on votin g 82/1 008/FDI S 82/1 041 /RVD Full information on the voting for the approval of this standard can be found in the report on voting indicated in the above table This publication has been drafted in accordance with the I SO/I EC Directives, Part The comm ittee has decided that the contents of this publication will remain unchanged until the stability date indicated on the I EC website under "http: //webstore iec.ch" in th e data related to the specific publication At this date, the publication will be • • • • reconfirmed, withdrawn, replaced by a revised edition, or amended I EC 61 829: 201 © I EC 201 –5– INTRODUCTION The performance of photovoltaic (PV) system s over their decades-long life tim e is determined by com paring measured power production with the expected production as estim ated from recorded weather conditions Continuous m easurements of system - or subsystem -level operating output can detect underperform ing arrays but are not well suited for tracking degradation with an y accuracy, or for identifying the weaknesses or failure m odes th at may exist within the array Field I- V curve m easurem ents offer a practical m ethod of in situ benchm arking or troubleshooting for modules, strings and arrays This I nternational Standard specifies methods and approaches for field I- V curve measurem ents and calculations, and includes guidance for addressing the uncertainties associated with m easurement devices and array configurations Consistent and proper application of I- V curve m easurem ent procedures helps to ensure that a PV system’s perform ance is adequatel y characterized over time –6– I EC 61 829: 201 © I EC 201 P H O T O VO L T AI C ( P V) ARR AY – O N -S I T E M E AS U RE M E N T O F C U RRE N T -VO L T AG E C H AR AC T E RI S T I C S S cop e This I nternational Standard specifies procedures for on-site measurement of flat-plate photovoltaic (PV) array characteristics, the accompan ying m eteorological conditions, and use of these for translating to standard test conditions (STC) or other selected conditions Measurements of PV array current-voltage ( I- V) characteristics under actual on-site conditions and their translation to reference test conditions (RTC) can provide: • • • • • data for power rating or capacity testing; verification of installed array power perform ance relative to design specifications; detection of possible differences between on-site m odule characteristics and laboratory or factory m easurements; detection of possible performance degradation of m odules and arrays with respect to onsite initial data; detection of possible m odule or array failures or poor perform ance For a particular m odule, on-site m easurements translated to STC can be directl y com pared with results previousl y obtained in a laboratory or factory for that module Corrections for differences in the spectral or spatial response of the reference devices m ay need to be assessed as specified in I EC 60904 On-site array m easurements are affected by diode, cable, and mism atch losses, soiling and shading, degradation due to aging, and other uncontrolled effects Therefore, they are not expected to be equal to the product of the number of modules and the respective m odule data I f a PV array is form ed with sub-arrays of different tilt, orientation, technolog y, or electrical configuration, the procedure specified in this I nternational Standard is applied to each unique PV sub-array of interest N o rm a t i ve re fe re n c e s The following docum ents, in whole or in part, are normativel y referenced in this docum ent and are indispensable for its application For dated references, onl y the edition cited applies For undated references, the latest edition of the referenced docum ent (including an y amendments) applies I EC 60891 , Ph o tovo lta ic de vice s – Pro ce dure s fo r te m p e ture a n d irra dia n ce co rre ctio n s to m e a s ure d I- V ch a cte ris tics I EC 60904-1 , Ph otovolta ic de vice s – Pa rt 1: Me a sure m e n t o f p h o to vo lta ic curre n t-vo lta ge ch a cte ris tics I EC 60904-2, I EC 60904-3, Ph otovo lta ic de vice s – Pa rt 2: Re quire m e n ts fo r p h otovolta ic re fe re n ce de vice s Ph o tovo lta ic de vice s – Pa rt 3: Me a s ure m e n t p rin cip le s p h o tovo lta ic (PV) so la r de vice s with re fe re n ce s p e ctra l irra dia n ce da ta for te rre s tria l I EC 61 829: 201 © I EC 201 IEC 60904-4, Ph o to vo lta ic –7– de vice s – Pa rt 4: Re fe re n ce so la r de vice s – Proce dure s for e sta b lis h in g ca lib tio n tra ce a b ility I EC60904-7, Ph o tovolta ic de vice s – Pa rt 7: Co m p uta tio n of th e sp e ctra l m ism a tch corre ction for m e a s ure m e n ts o f p h o tovo lta ic de vice s IEC 60904-1 0, Ph otovo lta ic de vice s – Pa rt 0: Me th o ds for lin e a rity m e a sure m e n ts T e rm s a n d d e fi n i t i o n s For the purposes of this docum ent, the following terms and definitions apply p y n o m e t e r radiometer normall y used to m easure global irradiance on a horizontal plane Note to entry: A pyranom eter can also be used to m easure diffuse irradiance when used with a shade ri ng or disc Note to entry: A pyranom eter can also be used to m easu re total i rradiance on an inclin ed plane, which would includ e radiati on reflected from the foreg rou nd [SOU RCE: I EC TS 61 836:2007, 5.7 b)] d i o m e t e r instrum ent for m easuring the intensity of solar irradiance Note to entry: See also I EC 60050-845: 987, 845-05-06 Note to entry: Comm only, a radiom eter is a th erm al i nstrum ent using therm ocoupl es or th erm opil es an d is independent of wavelength [SOU RCE: I EC TS 61 836: 2007, 5.7] 3 s p e c t ro d i o m e t e r instrument used to m easure spectral irradiance distribution of an incident radiation as a function of wavelength [SOU RCE: I EC TS 61 836:2007, 5.7 d)] 4 Ap p a t u s I rra d i a n c e m e a s u re m e n t s i n n a t u l su n li gh t The irradiance measurem ents shall be made using a PV reference device packaged and calibrated in conformance with I EC 60904-2 or with a pyranometer PV reference devices shall have spectral matching addressed by one of the following m ethods a) The reference device is spectrally m atched to the modules in the array under test b) A spectral mism atch correction should be perform ed in conformance with I EC 60904-7 The reference device shall be linear in short-circuit current as defined in I EC 60904-1 over the irradiance range of interest c) I f spectral m easurements are not practical, uncertainties associated with the irradiance m easurement and specific sensors used should be reported as part of the anal ysis Measurem ents should be completed under clear-sky conditions with the nearest clouds at –8– I EC 61 829: 201 © I EC 201 least 5° from the sun and the sensor mounted in the plane of the items under test as discussed elsewhere To be considered spectrall y matched, a reference device shall be constructed using the sam e cell technology and encapsulation package as the m odules in the array under test I f this is not the case, the spectral m ismatch shall be reported or an estimate of the uncertainty shall be made as part of the anal ysis Spectral m ismatch is of particular concern with thin film modules For m odules that concentrate sunlight with an optical concentration ratio of greater than 3: , at least one radiometer shall provide a collimated measure of direct norm al irradiance (I EC 60904-4) The tem perature of the reference device shall be measured using instrumentation with an accuracy of ± °C with repeatability of ± 0, °C I f the reference device has internal correction for temperature or if the reference device is a pyranom eter with a tem perature coefficient < 0,02 %/°C, temperature measurem ent is not required H owever, the m ounting of a therm opile shall be consistent with the conditions used for calibrating it A suitable means is required to check that the reference device and the m odules are coplanar within ± 2° accuracy NOTE A digital l evel or oth er calibrated device can be used to confirm coplan ar m odul es An additional pyranom eter is required for checking the uniformity of the in-plane radiance This radiometer shall provide a stable output, but need not be calibrated since it is onl y used for relative measurements I f spectral corrections will be made, a spectroradiometer is required that is capable of measuring the spectral irradiance of the sunlight in the range of the spectral response of the test specimen and the reference device 4.2 M odule temperature measurements The tem perature of the m odule backsheets of the array under test sh all be measured using instrumentation with an accuracy of ± °C with repeatability of ± 0, °C I t is recomm ended to mechanicall y attach a flat therm al sensor with fine leads directl y to the backsheet in the middle of a m odule and at least cm from an y junction box, but opposite an active part of the module The attachm ent m ethod should not change the temperature of the module, as may be identified by infrared im aging from the front of the module An optical thermom eter may be used onl y if the backsheet em issivity has been calibrated well enough that the optical therm om eter accuracy is within °C A handheld contact thermom eter m ay be used onl y if it has been verified that the accuracy is within °C NOTE Most h an dhel d therm om eters conduct h eat into th e handle of the th erm om eter causing a tem peratu re readin g that is less than the actual backsheet tem perature 4.3 Electrical measu rements A self-contained I- V curve tracing unit shall be able to accom modate the anticipated array voltage, current, and power levels The rate at which the unit sweeps the curve should be fast enough to avoid changes in irradiance during the curve but slow enough to ensure that the PV modules are achieving stead y state conditions Other equipment suitable for sweeping the array through a significant portion of its I- V curve may be used though an y limitations with respect to the above requirements shall be clearly stated in the measurem ent report The I- V curve tracing unit shall be able to measure voltages and currents with an accuracy of ± % of the open-circuit voltage and short-circuit current using independent leads from the terminals of the array under test and keeping all wires that would add series resistance as short as possible I f only two leads are used, the error introduced shall be included in the