1、Designation: E2481 12 (Reapproved 2018)Standard 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
2、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-term
3、effects 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 deteriorat
4、ion 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
5、 (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 s
6、tated 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,
7、 health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of Int
8、ernational Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E772 Terminology of Solar Energy ConversionE927 Specification for Solar Simulation for PhotovoltaicTestingE1036 Test Methods
9、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
10、 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
11、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 des
12、cribes 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 fr
13、om 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 a1This test method is under the jurisdict
14、ion of ASTM Committee E44 on Solar,Geothermal and Other Alternative Energy Sources and is the direct responsibility ofSubcommittee E44.09 on Photovoltaic Electric Power Conversion.Current edition approved May 1, 2018. Published May 2018. Originallyapproved in 2006. Last previous edition approved in
15、2012 as E2481-12. DOI:10.1520/E2481-12R18.2For 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 Inte
16、rnational, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards,
17、 Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1condition occurs, the affected cell or group of cells is forcedinto reverse bias and must dissipate power, which can causeoverheating.NOTE 1The correct use of bypass diodes can prevent hot
18、 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 irr
19、adiance level, when thereverse 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 character
20、istic of Y with the image of theforward I-V characteristic of the (s-1) cells.4.5 By-pass diodes, if present, as shown in Fig. 2, beginconducting when a series-connected string in a module is inreverse bias, thereby limiting the power dissipation in thereduced-output cell.NOTE 2If the module does no
21、t contain bypass diodes, check themanufacturers instructions to see if a maximum number of series modulesis recommended before installing bypass diodes. If the maximum numberof modules recommended is greater than one, the hot spot test should bepreformed with that number of modules in series. For co
22、nvenience, aconstant current power supply may be substituted for the additionalmodules to maintain the specified current.4.6 The reverse characteristics of solar cells can varyconsiderably. Cells can have either high shunt resistance wherethe reverse performance is voltage-limited or have low shuntr
23、esistance where the reverse performance is current-limited.Each of these types of cells can suffer hot spot problems, but indifferent ways.4.6.1 Low-Shunt Resistance Cells:4.6.1.1 The worst case shadowing conditions occur whenthe whole cell (or a large fraction) is shadowed.4.6.1.2 Often low shunt r
24、esistance cells are this way becauseof localized shunts. In this case hot spot heating occurs becausea large amount of current flows in a small area. Because this isa localized phenomenon, there is a great deal of scatter inperformance of this type of cell. Cells with the lowest shuntresistance have
25、 a high likelihood of operating at excessivelyhigh temperatures when reverse biased.4.6.1.3 Because the heating is localized, hot spot failures oflow shunt resistance cells occur quickly.4.6.2 High Shunt Resistance Cells:4.6.2.1 The worst case shadowing conditions occur when asmall fraction of the c
26、ell is shadowed.4.6.2.2 High shunt resistance cells limit the reverse currentflow of the circuit and therefore heat up. The cell with thehighest shunt resistance will have the highest power dissipa-tion.4.6.2.3 Because the heating is uniform over the whole areaof the cell, it can take a long time fo
27、r the cell to heat to thepoint of causing damage.4.6.2.4 High shunt resistance cells define the need forbypass diodes in the modules circuit, and their performancecharacteristics determine the number of cells that can beprotected by each diode.4.7 The major technical issue is how to identify the hig
28、hestand lowest shunt resistance cells and then how to determine theworst case shadowing for those cells. If the bypass diodes areremovable, cells with localized shunts can be identified byreverse biasing the cell string and using an IR camera toobserve hot spots. If the module circuit is accessible
29、the currentflow through the shadowed cell can be monitored directly.However, many PV modules do not have removable diodes oraccessible electric circuits. Therefore a non-intrusive method isneeded that can be utilized on those modules.4.8 The selected approach is based on taking a set of I-Vcurves fo
30、r a module with each cell shadowed in turn. Fig. 3shows the resultant set of I-V curves for a sample module. Thecurve with the highest leakage current at the point where thediode turns on was taken when the cell with the lowest shuntresistance was shadowed. The curve with the lowest leakagecurrent a
31、t the point where the diode turns on was taken whenthe cell with the highest shunt resistance was shadowed.4.9 If the module to be tested has parallel strings, each stringmust be tested separately.4.10 This test method may be specified as part of a series ofqualification tests including performance
32、measurements andFIG. 1 Hot Spot EffectE2481 12 (2018)2demonstration of functional requirements. It is the responsibil-ity of the user of this test method to specify the minimumacceptance criteria for physical or electrical degradation.5. Apparatus5.1 In addition to the apparatus required for the ele
33、ctricalperformance (I-V) measurements of Test Methods E1036, thefollowing apparatus is required:5.1.1 Illumination Sourcenatural sunlight or Class C (orbetter) steady-state solar simulator as defined in SpecificationE927.5.1.2 Set of opaque covers for test cell shadowing. The areaof the covers shall
34、 be based on the area of the cells in themodule being tested, in 5 % increments.5.1.3 Appropriate temperature detectors to measure ambienttemperature and module surface temperature.5.1.4 Appropriate meter(s) to measure module voltage andcurrent.6. Procedure6.1 Measure the electrical performance (I-V
35、 characteristics)of the module according to Test Methods E1036.6.2 Perform visual inspection per Practice E1799.6.3 Perform insulation test per Test Methods E1802.6.4 Expose the module to an irradiance of 800 to 1000Wm-2using either:6.4.1 Apulsed simulator where the module temperature willbe close t
36、o room temperature (25 6 5C),6.4.2 A steady-state simulator where the module tempera-ture must be stabilized within 65C before beginning themeasurements, orFIG. 2 Bypass Diode EffectFIG. 3 Module I-V Characteristics with Different Cells Totally ShadowedE2481 12 (2018)36.4.3 Natural sunlight where th
37、e module temperature mustbe stabilized within 65C before beginning the measurements.6.5 After thermal stabilization is attained, determine themaximum power current IMP1according to Test MethodsE1036. It is not necessary to correct the value to standard testconditions (STC).6.6 Completely cover each
38、cell in turn, measure the resul-tant I-V curve and prepare a set of curves like Fig. 3.6.6.1 Select the three cells with the lowest shunt resistance(highest leakage current).6.6.2 Select the cell with the highest shunt resistance(lowest leakage current).NOTE 3It is important to ensure that individua
39、l cells are completelycovered during the I-V curve characterization procedure. Leaving even1% of a cell uncovered may cause the wrong cell to be selected for thestress testing.6.7 For each of the selected cells determine the worst casecovering condition by taking a set of I-V curves with each ofthe
40、test cells covered at different levels as shown in Fig. 4. Theworst case covering condition occurs when the “kink” in theI-V curve of the shadowed covered module coincides withIMP1. (line “c” in Fig. 4)6.8 Select one of the three lowest shunt resistance cellsselected in 6.6. Cover that cell to the w
41、orst case condition asdetermined in 6.7. Short-circuit the module.6.9 Expose the module to the illumination source. Irradi-ance must be between 800 and 1200 Wm-2. Record the value ofshort circuit current ISC, irradiance, ambient temperature andmodule temperature.6.10 Maintain this condition for a to
42、tal exposure time of 1 h.6.11 Repeat 6.8 6.10 for the other two low shunt resistancecells selected in 6.6.6.12 Cover the highest shunt resistance cell to the worstcase condition as determined in 6.7. Short-circuit the module.6.13 Expose the module to the illumination source. Irradi-ance must be betw
43、een 800 and 1200 Wm-2. Record the value ofshort circuit current ISC, irradiance, ambient temperature andmodule temperature.6.14 Measure the irradiance every 5 min until the totalradiant exposure reaches 180 MJm-2. (This is equivalent to50 h at 1000 Wm-2.)6.14.1 If using a steady-sate solar simulator
44、, remove themodule from the illumination source for a minimum of 1 hafter every5hofexposure.6.15 Measure the electrical performance (I-V characteris-tics) of the module according to Test Methods E1036.6.16 Perform visual inspection per Practice E17996.17 Perform insulation test per Test Methods E180
45、27. Report7.1 The report shall include the following items as aminimum:7.1.1 Module manufacturer and complete test specimenidentification,7.1.2 Description of module construction,7.1.3 Description of electrical measurement equipment,7.1.4 Module I-V measurement results before and after thehot spot e
46、xposure,7.1.5 Ambient conditions during the test,7.1.6 Measured values of module current and temperature,7.1.7 A description of any apparent changes as a result ofthe testing. For example, indications of shorting, arcing,excessive heating, damage to module materials, or otherfailures which result in
47、 accessibility of live parts,FIG. 4 Module I-V Characteristics with the Test Cell Shadowed at Different LevelsE2481 12 (2018)47.1.8 Identification of areas of the module where problemswere found, and7.1.9 Any deviations from the test procedure.8. Precision and Bias8.1 The procedures described by the
48、se test methods do notproduce numeric results that would be subject to ASTMrequirements for evaluating the precision and bias of these testmethods. However, the precision and bias of the electricalmeasurements, when performed in accordance with Test Meth-ods E1036, are subject to the provisions of t
49、hat document.9. Keywords9.1 solar; energy; photovoltaics; modules; electrical testing;hot spotASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised,
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