I E C TS 62 446-3 ® Edition 201 7-06 TE C H N I C AL S P E C I F I C ATI ON colour i n sid e P h oto vol tai c (P V) s ys tem s – Re q u i rem en ts for te s ti n g , d ocu m en tati on an d m n te n an ce – IEC TS 62446-3:201 7-06(en) P art 3: P h otovol tai c m od u l e s an d pl an ts – O u td oor i n frared th erm og raph y 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 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 - webstore i ec ch /catal og u e The stand-alone application for consulting the entire bibliographical information on IEC International Standards, Technical Specifications, Technical Reports and other documents Available for PC, Mac OS, Android Tablets and iPad I E C pu bl i cati on s s earch - www i ec ch /search pu b The advanced search enables to find IEC publications by a variety of criteria (reference number, text, technical committee,…) It also gives information on projects, replaced and withdrawn publications E l ectroped i a - www el ectroped i a org The world's leading online dictionary of electronic and electrical terms containing 20 000 terms and definitions in English and French, with equivalent terms in additional languages Also known as the International Electrotechnical Vocabulary (IEV) online I E C G l os sary - s td i ec ch /g l oss ary 65 000 electrotechnical terminology entries in English and French extracted from the Terms and Definitions clause of IEC publications issued since 2002 Some entries have been collected from earlier publications of IEC TC 37, 77, 86 and CISPR I E C J u st Pu bl i s h ed - webstore i ec ch /j u stpu bl i sh ed Stay up to date on all new IEC publications Just Published details all new publications released Available online and also once a month by email I E C C u stom er S ervi ce C en tre - webstore i ec ch /csc If you wish to give us your feedback on this publication or need further assistance, please contact the Customer Service Centre: csc@iec.ch I E C TS 62 446-3 ® Edition 201 7-06 TE C H N I C AL S P E C I F I C ATI ON colour i n sid e P h otovol tai c (P V) s ys te m s – Req u i rem en ts for tes ti n g , d ocu m e n tati on an d m n ten an ce – P art 3: P h otovol tai c m od u l es an d pl an ts – Ou td oor i n frared th erm og raph y INTERNATIONAL ELECTROTECHNICAL COMMISSION ICS 27.1 60 ISBN 978-2-8322-4290-2 Warn i n g ! M ake s u re th a t you ob tai n ed th i s p u b l i cati on from an au th ori zed d i stri b u tor ® Registered trademark of the International Electrotechnical Commission –2– I EC TS 62446-3:201 © I EC 201 CONTENTS FOREWORD Scope Norm ative references Term s and definitions Requirements of inspection equipment General M inimum requirements for I R-cameras used for inspecting PV plants Requirements for photo cameras for docum entation of the findings 4 Requirements for equipment to record the am bient conditions I nspection procedure 1 General 1 Visual inspection Environmental conditions I maging procedure General Using fast carriers for I R-cam era, e g aerial drones Emissivity Software for evaluation Evaluation General Evaluation of I R images Therm al abnorm alities 7 General 7 Classes of abnormalities (CoA) 7 3 Abnormalities of PV m odules 7 Abnormalities of other BOS components 7 Projection of tem perature differences to nom inal irradiance General Modules 20 Other BOS components 21 I nspection report 21 Annex A (norm ative) I nspection procedure explanations 24 Geom etric resolution of the cam era 24 A A Angle of view 24 A Matrix for cell identification 25 Annex B (norm ative) Qualification of personnel 27 Annex C (normative) Matrix for thermal abnormalities of PV m odules 28 Annex D (informative) Pol ygon m easurement as a method of evaluation 32 Annex E (inform ative) Beaufort scale 34 Bibliograph y 36 Figure – I m pact of camera m oving speed Figure – Dependence of the em issivity of glass on the angle of view [1 0] Figure – Examples of influence of wind (left) and cloud m ovement (right) on observed temperature pattern I EC TS 62446-3: 201 © I EC 201 –3– Figure – Exam ple infrared thermogram s of a PV string com biner box with cables, contacts, fuses and switches before (left) and after (right) m aintenance on a faulty contact Figure – Graphic representation of the correction factor for tem perature differences to nom inal irradiance/load conditions as a function of the relative irradiance/load Figure – Example of image reporting 23 Figure A – Geom etric resolution of the I R cam era 24 Figure A – Angle of view 25 Figure A – View for the designation of cell position, viewed from the front of a 60cell m odule, with the j unction box at the top (rear side) 26 Figure D.1 – Arithmetic mean value by pol ygon measurement 32 Figure D.2 – Arithmetic mean and spot value by pol ygon measurement 33 Table – Minimum requirem ents for I R-cam eras Table – Requirements for equipm ent to record the ambient conditions 1 Table – Required inspection conditions Table – Allocation in classes of abnorm alities Table – Example correction factors for tem perature differences to nom inal load conditions based on formula above and Figure 20 Table E – Beaufort scale taken form World Meteorolgical Organization (www wmo.int) and Royal M eteorological Society (www.rm ets.org) 34 –4– I EC TS 62446-3:201 © I EC 201 INTERNATI ONAL ELECTROTECHNI CAL COMMISSI ON P H O T O VO L T AI C ( P V) S YS T E M S – RE Q U I RE M E N T S F O R T E S T I N G , D O C U M E N T AT I O N P a rt : AN D M AI N T E N AN C E – P h o t o vo l ta i c m o d u l e s a n d p l a n t s – O u t d o o r i n fra re d th e rm o g p h y FOREWORD ) The I nternati on al Electrotech ni cal Comm ission (I EC) is a worl d wid e organization for stand ardization com prisin g all nati on al el ectrotechnical comm ittees (I EC Nation al Comm ittees) The object of I EC is to prom ote internati onal co-operation on all qu estions concerni ng standardi zati on in the electrical and electronic fields To this en d and in ad dition to other activities, I EC pu blish es I nternational Stan dards, Techn ical Specificati ons, Technical Reports, Publicly Avail abl e Specificati ons (PAS) an d Gui des (hereafter referred to as “I EC Publication(s)”) Th eir preparation is entrusted to technical comm ittees; any I EC N ation al Comm ittee interested in the subj ect dealt with m ay participate i n this 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internati onal u niform ity, I EC Nation al Com m ittees undertake to apply I EC Publ ications transparentl y to th e m axim um extent possibl e in thei r n ational an d regi onal pu blicati ons Any di vergence between an y I EC Publ ication and the correspondi ng n ational or regi on al pu blicati on shall be clearl y in dicated in the latter 5) I EC itself d oes n ot provid e an y attestati on of conform ity I ndepend ent certificati on bod ies provi de conform ity assessm ent services an d, in som e areas, access to I EC m arks of conform ity I EC is not responsi ble for an y services carri ed out by ind ependent certification bodi es 6) All users shou ld ensure that th ey h ave the l atest editi on of thi s publicati on 7) No liability shall attach to I EC or its directors, em ployees, servants or ag ents includ ing i n divi du al experts and m em bers of its tech nical com m ittees and I EC Nati on al Com m ittees for an y person al i nju ry, property dam ag e or other dam age of an y nature whatsoever, wheth er di rect or indirect, or for costs (includi ng leg al fees) an d expenses arisi ng out of th e publ ication, use of, or rel ian ce upon, this I EC Publicati on or an y other I EC Publications 8) Attention is drawn to the Norm ative references cited i n this publ ication Use of the referenced publications is indispensable for the correct applicati on of this publication 9) Attention is drawn to th e possibility that som e of the elem ents of this I EC Publication m ay be the subject of patent rig hts I EC shall not be held responsibl e for identifyi ng any or al l such patent ri ghts The m ain task of I EC technical com mittees is to prepare I nternational Standards I n exceptional circum stances, a technical com mittee may propose the publication of a technical specification when • • the required support cannot be obtained for the publication of an I nternational Standard, despite repeated efforts, or the subject is still under technical development or where, for an y other reason, there is the future but no immediate possibility of an agreem ent on an I nternational Standard Technical specifications are subj ect to review within three years of publ ication to decide whether they can be transform ed into I nternational Standards I EC TS 62446-3, which is a technical specification, has been prepared by I EC technical committee 82: Solar photovoltaic energ y systems I EC TS 62446-3: 201 © I EC 201 –5– The text of this technical specification is based on the following documents: Enqui ry draft Report on votin g 82/1 88/DTS 82/1 242A/RVDTS Full inform ation on the voting for the approval of this technical specification can be found in the report on voting indicated in the above table This docum ent has been drafted in accordance with the I SO/I EC Directives, Part A list of all parts in the I EC 62446 series, published under the general title Photovoltaic (PV) systems – Requirements for testing, documentation and maintenance , can be found on the I EC website The committee has decided that the contents of this publication will rem ain unchanged until the stability date indicated on the I EC website under "http: //webstore iec.ch" in the data related to the specific publication At this date, the publication will be • • • • • transform ed into an I nternational standard, reconfirmed, withdrawn, replaced by a revised edition, or am ended A bilingual version of this publication m ay be issued at a later date I M P O RT AN T – T h e ' c o l o u r i n s i d e ' th at it co n tai n s u n d e rs t a n d i n g c o l o u r p ri n t e r of c o l o u rs i ts wh i c h c o n te n ts l og o a re U s e rs on th e co ve r p ag e o f th i s c o n s i d e re d sh ou l d to t h e re fo re be p u b l i c ati o n u s e fu l p ri n t th i s fo r i n d i c ate s th e d o cu m en t c o rre c t u si n g a –6– I EC TS 62446-3:201 © I EC 201 P H O T O VO L T AI C ( P V) S YS T E M S – RE Q U I RE M E N T S F O R T E S T I N G , D O C U M E N T AT I O N P a rt : AN D M AI N T E N AN C E – P h o t o vo l ta i c m o d u l e s a n d p l a n t s – O u t d o o r i n fra re d th e rm o g p h y S cop e This part of I EC 62446 defines outdoor thermographic (infrared) inspection of PV m odules and plants in operation The inspection can include cables, contacts, fuses, switches, inverters, and batteries This inspection supports the preventive m aintenance for fire protection, the availability of the system for power production , and the inspection of the quality of the PV m odules I ncluded in this document are the requirem ents for the measurem ent equipm ent, am bient conditions, inspection procedure, inspection report, personnel qualification and a m atrix for therm al abnorm alities as a guideline for the inspection This document defines outdoor thermograph y on photovoltaic (PV) m odules and Balance-ofsystem (BOS) com ponents of PV power plants in operation, using passive techniques (standard system operating conditions under natural sunlight, without an y external power or irradiation sources) I EC 60904-1 2-1 covers general m ethods for laboratory or production -line PV module thermographic im aging but not the specific details that are most relevant to outdoor im aging of operational power plants including BOS components Two different levels of inspections are currentl y used: a) A sim plified therm ographic inspection This is a lim ited inspection to verify that the PV m odules and BOS components are functioning, with reduced requirem ents for the qualification of personnel For exam ple, during a basic commissioning of a PV plant Authoritative conclusions regarding module quality are not possible with this inspection, and exam ples of abnormalities are provided to aid the inspector b) A detailed thermographic inspection and anal ysis This may include thermal signatures which differ from the exam ples provided, and therefore requires a deeper understanding of the therm al abnormalities For exam ple, it m ay be used for periodic inspections according to the I EC 62446 series and for trouble-shooting the cause of underperform ing system s Absolute tem perature measurem ents m ay be made An authorized expert in PV plants, together with therm ograph y experts can perform the inspection N o rm a t i ve re fe re n c e s The following docum ents are referred to in the text in such a way that some or all of their content constitutes requirem ents of this docum ent For dated references, onl y the edition cited applies For undated references, the latest edition of the referenced document (including an y amendments) applies I EC 60050-1 31 , International Electrotechnical Vocabulary – Part 131: Circuit theory I EC 6021 6-2, Electrical insulating materials – Thermal endurance properties – Part 2: Determination of thermal endurance properties of electrical insulating materials – Choice of test criteria I EC 6021 6-5, Electrical insulating materials – Thermal endurance properties – Part 5: Determination of relative thermal endurance index (RTE) of an insulating material I EC TS 62446-3: 201 © I EC 201 –7– I EC 60269-1 , Low-voltage fuses – Part 1: General requirements I EC 61 095, Electromechanical contactors for household and similar purposes IEC 61 21 5-1 , Terrestrial photovoltaic (PV) modules – Design qualification and type approval – Part 1: Test requirements IEC 61 439-1 , Low-voltage switchgear and controlgear assemblies – Part 1: General rules IEC 61 724-1 , Photovoltaic system performance – Part 1: Monitorin g IEC 61 730-1 , Photovoltaic (PV) module safety qualification –Part 1: Requirements for construction IEC 61 730-2, Photovoltaic (PV) module safety qualification –Part 1: Requirements for testing IEC TS 61 836, Solar photovoltaic energy systems – Terms, definitions and symbols I EC 621 09-1 , Safety of power converters for use in photovoltaic power systems – Part 1: General requirements IEC 62446-1 , Photovoltaic (PV) systems – Requirements for testing, documentation and maintenance – Part 1: Grid connected systems – Documentation, commissioning tests and inspection IEC 62446-2: –, Photovoltaic (PV) systems – Requirements for testing, documentation and maintenance – Part 2: Grid connected photovoltaic (PV) systems – Maintenance of PV systems I EC 62930: –, Electric cables for photovoltaic systems with a voltage rating of 1, kV d.c I SO 9488, Solar energy – Vocabulary I SO 971 2, Non-destructive testing — Qualification and certification of NDT Personnel VATh- Directive, Electrical Infrared Inspections – Low Voltage Planning, execution and documentation of infrared surveys on electrical sys te ms a n d com p on e nts ≤1 kV (http: //www vath de/docs/richtlinien/VATh-Richtlinie_Elektro_N S+PV_engl_web pdf) EN 671 4-3, Non-destructive testing – Thermographic testing of electric installations EN 501 0-1 , Operation of electrical installations – Part 1: General requirements DGU V BGV/GU V-V A3 E, Accident prevention regulations, Electrical installations and equipment Terms and definitions For the purposes of this docum ent, the term s and definitions given in I EC TS 61 836, I SO 9488, I EC 60050-1 31 and the following appl y _ To be publ ished –8– I EC TS 62446-3:201 © I EC 201 I SO and I EC maintain term inological databases for use in standardization at the following addresses: I EC Electropedia: available at http://www electropedia.org/ I SO Online browsing platform : available at http: //www iso org/obp • • a b n o rm a l t h e rm a l b e h a v i o r thermal signature of an element that cannot be explained by its operating condition or its technical design, e g position of load resistors [SOU RCE:I EC 60050-903: 201 3, Am endment : 201 4, 903-01 -22; m odified: adapted to therm al behavior] re fl e c t e d T t e m p e t u re m ean apparent tem perature of the am bient that is reflected by the object towards the I Rcamera re fl Note to entry: Measured i n Celsius (° C) Note to entry: Som e m anufactures of I R cam eras use the term : am bient tem perature 3 a t m o s p h e ri c a i r t e m p e t u re defined in Celsius (°C) for the geographic installation location as measured and documented by meteorological services for this geographic location B e a u fo rt ( s c a l e ) B ft quantifies wind speed by phenomenological criteria, e g movem ent of branches and trees SEE: Annex E cl o u d c o v e g e for the inspection two types of clouds are to differ: Cumulus and Cirrus The cloud coverage should be given in okta (part of eight of cloud coverage) SEE: I SO 5469:2004[1 8] e m i s s i v i t y o f th e o b j e ct ε ratio of the thermal radiation that is em itted by the surface of an object compared to a black bod y radiator both at the sam e tem perature I n s tan tan eo u s F i e l d o f Vi e w IFOV field of view of one pixel of an I R-cam era-lens com bination Note to entry: Measured i n m illiradian (m rad ) _ Num bers in sq uare brackets refer to the Bi bliography – 26 – I EC TS 62446-3:201 © I EC 201 IEC Fig u re A – Vi ew for th e d esi gn ation of cell positi on , viewed from th e fron t of a 60-cel l m odu l e, with th e j u n ction box at th e top (rear si d e) I EC TS 62446-3:201 © I EC 201 – 27 – Annex B (normative) Qualification of personnel The testing personnel shall have sufficient knowledge in electrical installations, PV plants and also therm ograph y including the anal ysis of the therm ographic findings in electrical systems, in particular: a) sufficient knowledge to be able to work in electrical installations has to be proven, b) sufficient knowledge to document PV power plant related findings in accordance to requirem ents stated in Clause and to relevant standards (e g I EC 62446 series), c) knowledge and skill in electro thermograph y has to be assured by the proof of a qualification and a certification A certificate according to I SO 971 can serve as confirmation For the simplified thermographic inspection during the commissioning of a PV plant, the technician shall have the knowledge of the basic functionality of a PV plant Furtherm ore, sufficient knowledge regarding the therm ographic m easurements shall be present I t is recomm ended that an education, like a l evel certification according to I SO 971 2, or equivalent should be proven Access to the electrical installation, like opening enclosures with access to electricall y li ve parts shall be restricted to electricall y qualified persons Onl y in the case that the personnel has appropriate knowledge of the functionality of a PV plant, a two days training session of the basics of thermograph y and the thermographic characteristics of PV plants will be adequate for the comm issioning of the PV system Training on the I R cam era, provided by the m anufacturer, is not sufficient For the detailed thermographic inspection, the authorized expert for PV plants shall have indepth understanding of the PV system , related failure m odes, and therm ographic im aging The thermographic expert should have a qualification equal to level electro therm ograph y according to I SO 971 2, and m inim um shall have level certification In case the purpose of the planned inspection of the system is the prevention of fire hazards, the testing personnel should be independent (no personnel of the owner or operator) The proof of eyesight m ay be done non-recurring according to I SO 971 Annex C (normative) Matrix for thermal abnormalities of PV modules Example – 3: Strings and modules Category CoA Temperature difference to normal operating devi ce at 000 W/m ( Δ T2 ) Th ermal pattern, definition and additional information of abnorm ality M odules in open circuit 2 K to K Assessable by therm al pattern and classified as a extend ed area abnorm ality (at % m odule- efficiency typically K to K) (crystalline Si and thin film) The m odule su rface is h om ogeneously h eated ∆ T of the j unction box is sim ilar to operational state Recom m ended: check m odule, state of operati on of inverter, and condition of cablin g, connectors, and fuses IEC Averag ed K to K over m odule surface (at % m odule- efficiency typically K to K) (crystalline Si) Assessable by th erm al pattern, visual im age an d classified as a exten ded area abnorm ality Sim ilar pattern as with broken front g lass (check isolation resistance), PI D, cell defects and m ism atch – 28 – M odule in short circuit Recom m ended: check m odule and cablin g Crystalline Si module with broken fron t glass (crystalline Si) IEC Averag ed K – K over m odul e surface Assessable by th erm al pattern and visual im age (at % m odule- efficiency typically K – K) Beware of h igh voltag e as isol ation resistance is lost Sim ilar pattern as m odules in short circuit, with PI D, cell defects and m ism atch Som etim es just single broken cell s are h eated I n the first weeks after th e breakage, a m odul e with broken g lass can show alm ost norm al therm al behaviour I EC TS 62446-3: 201 © I EC 201 IEC Category CoA Temperature difference to normal operating devi ce at 000 W/m ( Δ T2 ) Th ermal pattern, definition and additional information of abnorm ality Substring in short circuit Averag ed K to K hi gh er th an substrin g Assessable by th erm al pattern and classified as a extend ed area abnorm ality (at % m odule- efficiency typically K to K) (crystalline Si) At one or m ore substri ngs, easily m istaken for cel l breakage or cell d efects, Potenti al ind uced deg radation (PI D) or m ism atch Recom m ended: check m odule and bypass diod es for proper function un d er reverse biasi ng IEC 2-3 K to K (at % m odule- efficiency typically K to K) (crystalline Si and thin film) Assessable by th erm al pattern and classified as a extend ed area abnorm ality Part of the m odul e surface is h om ogeneousl y heated u p an d heat dissipati on by the bypass diod e, which is operati ng, is vi sible Tem perature difference of th e gl ass on top of the junction box containi ng th e operatin g bypass diode differs with construction Loss of contact at a cell nection m ight lead to a serial arc visibl e on th e m odule backside surface=> CoA: IEC 2x substring s in open circui t, loss of connection s within module junction box (crystalline Si and thin film) 2-3 K to K (at % m odule- efficiency typically K to K) Assessable by th erm al pattern and classified as a extend ed area abnorm ality Part of the m odul e surface is h om ogeneousl y heated u p an d heat dissipati on by the bypass diodes, that are operatin g, is vi sible Tem peratu re difference of the glass on top of the junction box differs with construction Loss of contact at a cell nection (or fail ure of a bypass diode) m ight lead to a serial arc visibl e on the m odul e backside surface=> CoA: IEC – 29 – x substring in open circui t, loss of connection within module junction box or cell connector I EC TS 62446-3:201 © I EC 201 Example – 6: Substrings within module Example – 9: Local abnormalities Category CoA Temperature difference to normal operating devi ce at 000 W/m ( Δ T2 ) Th ermal pattern, definition and additional information of abnorm ality Single cell with differen ce in temperatu re a) a) K – 40 K average val ue over the cell area Assessable by th erm al pattern, visual im age an d classified as an extend ed area abn orm ality b) > 40 K average valu e over the cell area Difference i n tem perature increases with load, cell efficiency an d num ber of cells in a substring High tem peratu res m ostly caused by broken cells b) (crystalline Si) Mig ht lead to i rreversible d am age of cell, encapsu lation an d bypass diod es Recom m ended: Ch eck that there is no sh adi ng or severe soili ng IEC M odule with cells shaded by dirt b) a) if location with lots of rai n an d ∆ T a few K b) if location with basicall y no rai n an d ∆ T > 40 K Assessable by th erm al pattern, visual im age an d classified typicall y as an extended area abn orm ality a) Norm al di rt, e g d ust or bi rd droppi ngs on m odul es will be washed by rai n No further imm ediate action requi red b) Cl eaning of PV m odules is hig hly recom m ended in near futu re to avoi d dam age of PV m odule Thin film module with broken front glass Averag ed K – K over m odul e surface Assessable by th erm al pattern and visual im age (at % m odule- efficiency typically K – K) Beware of d an gerous voltage(s) as isolati on resistance is lost Sim ilar pattern as m odules in short circuit, with PI D, cell defects and m ism atch Som etim es just single broken cel ls are h eated I n the first weeks after th e break a m odul e with broken glass can show n orm al therm al beh avi ou r IEC I EC TS 62446-3: 201 © I EC 201 IEC – 30 – (crystalline Si and thin film) a) Category CoA Transfer 2-3 resistan ce at cross-connections of a thin film module Temperature difference to normal operating devi ce at 000 W/m ( Δ T2 ) Th ermal pattern, definition and additional information of abnorm ality >1 K Assessable by th erm al pattern, visual im age an d classified as a point abnorm ality Difference i n tem perature increases with load, caused by increased contact resistance e g du e to bad sol derin g Person al revi ew by a PV expert or therm ographer level or equ ivalent is recom m ended I EC TS 62446-3:201 © I EC 201 Example – Local abnormalities; Evaluation onl y by experi enced PV – thermographers IEC 2-3 >1 K Assessable by th erm al pattern, visual im age an d classified typicall y as a point abnorm ality Difference i n tem perature increases with load, caused by increased contact resistance e g du e to bad or n o sold eri ng Coul d al so be caused by a broken ribbon or a m issed solder poi nt between ribbon an d cross conn ector Person al revi ew by a PV expert or therm ograph level or equi val ent is recommend ed IEC Heated module junction box (crystalline Si and thin film) 2-3 ≥ K high er tem peratu re com pared to nearby junction box Assessable by th erm al pattern, visual im age and classified typicall y as a point abnorm ality Tem peratu re difference i ncreases with load caused by increased contact resistance withi n the ju nction box Altern ativel y i t could be caused by low resistive bypass diodes that carry a significant cu rrent althou gh th ey shou ld be biased i n reverse direction Person al revi ew by a PV expert or therm ographer level or equ ivalent is recom m ended Be aware of hi g h voltag es Source: H aWe Engineerin g Gm bH IEC – 31 – Transfer resistan ce at cell connections of a crystallin e Si module – 32 – I EC TS 62446-3:201 © I EC 201 Annex D (informative) Polygon measurement as a method of evaluation For classification and plausibility check of abnorm alities, tem peratures can be compared by using pol ygon measurem ent areas with arithmetic mean tem peratures or spot-m axim um tem peratures Exam ple : Figu re D shows a m ean ∆ T of + , K at the g iven am bien t param eters This is a hint th at the m odul e is n ot in open circuit Different backsheets with different heat dissipati on m ay be th e reason IEC I m age inform ation: Fil en am e: BU081 700; Date: 08 201 4; Tim e: 3: 55: 02; Em issivity: 0, 83; Trefl : -30 °C; Tai r: 20 °C; Wind speed: to bft, east; I rradiance: 980 W/m ² ; Module efficiency: % Figure D.1 – Arithmetic mean value by polygon measurement Exam ple 2: Figu re D shows a m ean ∆ T of + 4, K at the given am bien t param eters This is the expectation in case of open circuit Additi onally the spot ∆ T of 6, K (- 4, K) at the j un ction box i ndicates active bypass diod es Probabl y all substrin gs are i n open ci rcuit I EC TS 62446-3:201 © I EC 201 – 33 – IEC I m age inform ation: Fil en am e: BD081 773; Date: 08 201 4; Tim e: 3: 00: 48; Em issivity: 0, 80; Trefl : -30 °C; Ta i r: °C; Wind speed: to bft, east; I rradiance: 980 W/m ; Module efficiency: % Fi g u re D – Ari th m eti c m ean an d spot val u e by pol yg on m easu rem en t For long term com parision, e g between two inspections, the tem perature difference ∆ T of both inspections shall be norm alized to 000 W/m per Relative power loss can often be estimated on areas with a homogenous temperature distribution using arithmetic mean tem peratures on m odules or cells The environm ental conditions (air tem perature Tai r, wind speed in Bft or m /s and direction, cloud coverage in okta and type, irradiance in plane of m odule in W/m , efficiency of module) shall be taken into account – 34 – I EC TS 62446-3:201 © I EC 201 Annex E (informative) Beaufort scale Table E shows the Beaufort Scale (wind force) with a description and wind speeds in km per hour For easier understanding a description is given All given values are mean wind speeds, typically over a period by convention, and not by gusts The given wind speeds are typicall y m easured m above ground Ground wind speed is typicall y onl y 50 % to 70 % of the given wind speeds I nfrared im aging should be done with maximum bft With up to 28 km /h this is alread y a significant wind speed that will effect the absolute measured temperatures I t may also change thermal gradients and edge effects Table E.1 – Beaufort scale taken form World M eteorolgical Organization (www.wmo.int) and Royal M eteorological Society (www.rmets.org) Wind force in bft Wind description Wind speed km/h Calm 1 Devastation; The r is fil led with foam and spray; sea com pletel y white with d ri ving spray; visibility very seri ousl y affected – 36 – I EC TS 62446-3:201 © I EC 201 Bibliography [1 ] Perch-N ielsen T., Sørensen J C., “Guidelines to thermographic inspection of electrical installations“, Danish Technological Institute / Department of Energy Technology, Taastrup, 994 [2] C Buerhop, “Quality Control of PV-Modules in the Field Using I nfrared Thermograph y” EUPVSEC, 2011 (I SBN 3-93-6338-27-2; p 3894) [3] Buerhop C , Schlegel, Nieß, Vodermayer, Weißmann, Brabec, “Reliability of I R I m aging of PV Plant under operating conditions” Solmat, Vol 07; 201 2; pp 54-1 64 [4] Weinreich B , Schauer B , 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Using Therm ograph y And Thermal Modelling” , 31th EUPVSEC, Hamburg, Germany, 2015 [1 ] Köntges M , Kurtz S , Packard C , Jahn U , Berger K A , Kato K , Friesen T., Liu H , Van I seghem M , “I EA-PVPS T1 01 -201 4, Review of Failures of Photovoltaic Modules External final report, M arch 201 4, (I SBN 978-3-906042-1 8-3); link for download: http: //iea-pvps org/index php?id=275&eI D=dam _frontend_push&docI D=2064 [1 2] VATh – Richtlinie, “Electrical therm al imaging” (Part B: Low voltage and Photovoltaics); 2014 German available: “VATh- Richtlinie: Elektrothermografie” [1 3] Sunspec Alliance, “Commissioning for PV Performance” (Part Thermography) [1 4] NEPA 70B, Recommended Practice for Electrical Equipment Maintenance, NFPA National Fire Protection Association (U SA), August 998 [1 5] Infrarot – Thermografie Überwachung elektrischer Anlagen, CN N P Enterprise (Frankreich), Februar 2003 I EC TS 62446-3: 201 © I EC 201 [1 6] – 37 – Jaeckel B., Weinreich B , Buerhop C , Jahn U., “Outdoor non-destructive infrared therm ograph y of photovoltaic modules and plants for inspection: I EC 62446-3“, 32nd EUPVSEC, Munich, Germany, 2016 [1 7] I EA-PVPS Task1 3, “Data Collection Docs”, see http://iea-pvps org/index php?id=344, 501 21 _Docum entation_of_module_condition xlsx [1 8] I SO 5469: 2004, Spatial distribution of skylight – CIE standard general sky _ INTERNATIONAL ELECTROTECHNICAL COMMISSI ON 3, rue de Varembé PO Box 31 CH-1 21 Geneva 20 Switzerland Tel: + 41 22 91 02 1 Fax: + 41 22 91 03 00 info@iec.ch www.iec.ch