ASTM_E_2481_-_12.pdf

Designation:E248112Standard Test Method forHot Spot Protection Testing of Photovoltaic Modules1This standard is issued under the fixed designation E2481;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method provides a procedure to determine theability of a photovoltaic(PV)module to endure the long-termeffects of periodic“hot spot”heating associated with commonfault conditions such as severely cracked or mismatched cells,single-point open circuit failures(for example,interconnectfailures),partial(or non-uniform)shadowing or soiling.Sucheffects typically include solder melting or deterioration of theencapsulation,but in severe cases could progress to combus-tion of the PV module and surrounding materials.1.2 There are two ways that cells can cause a hot spotproblem;either by having a high resistance so that there is alarge resistance in the circuit,or by having a low resistancearea(shunt)such that there is a high-current flow in a localizedregion.This test method selects cells of both types to bestressed.1.3 This test method does not establish pass or fail levels.The determination of acceptable or unacceptable results isbeyond the scope of this test method.1.4 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2E772 Terminology of Solar Energy ConversionE927 Specification for Solar Simulation for PhotovoltaicTestingE1036 Test Methods for Electrical Performance of Noncon-centrator Terrestrial Photovoltaic Modules and ArraysUsing Reference CellsE1799 Practice for Visual Inspections of Photovoltaic Mod-ulesE1802 Test Methods for Wet Insulation Integrity Testing ofPhotovoltaic Modules3.Terminology3.1 Definitionsdefinitions of terms used in this testmethod may be found in Terminology E772.3.2 Definitions of Terms Specific to This Standard:3.2.1 hot spota condition that occurs,usually as a result ofshadowing,when a solar cell or group of cells is forced intoreverse bias and must dissipate power,which can result inabnormally high cell temperatures.4.Significance and Use4.1 The design of a photovoltaic module or system intendedto provide safe conversion of the suns radiant energy intouseful electricity must take into consideration the possibility ofpartial shadowing of the module(s)during operation.This testmethod describes a procedure for verifying that the design andconstruction of the module provides adequate protectionagainst the potential harmful effects of hot spots during normalinstallation and use.4.2 This test method describes a procedure for determiningthe ability of the module to provide protection from internaldefects which could cause loss of electrical insulation orcombustion hazards.4.3 Hot-spot heating occurs in a module when its operatingcurrent exceeds the reduced short-circuit current(Isc)of ashadowed or faulty cell or group of cells.When such acondition occurs,the affected cell or group of cells is forcedinto reverse bias and must dissipate power,which can causeoverheating.NOTE1The correct use of bypass diodes can prevent hot spot damagefrom occurring.4.4 Fig.1 illustrates the hot-spot effect in a module of aseries string of cells,one of which,cell Y,is partiallyshadowed.The amount of electrical power dissipated in Y isequal to the product of the module current and the reversevoltage developed across Y.For any irradiance level,when the1This test method is under the jurisdiction of ASTM Committee E44 on Solar,Geothermal and OtherAlternative Energy Sources and is the direct responsibility ofSubcommittee E44.09 on Photovoltaic Electric Power Conversion.Current edition approved Dec.1,2012.Published December 2012.Originallyapproved in 2006.Last previous edition approved in 2008 as E2481-08.DOI:10.1520/E2481-12.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 reverse voltage across Y is equal to the voltage generated by theremaining(s-1)cells in the module,power dissipation is at amaximum when the module is short-circuited.This is shown inFig.1 by the shaded rectangle constructed at the intersection ofthe reverse I-V characteristic of Y with the image of theforward I-V