1、Designation: E 2481 08Standard Test Method forHot Spot Protection Testing of Photovoltaic Modules1This standard is issued under the fixed designation E 2481; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision
2、. 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 perio
3、dic “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 theencaps
4、ulation, 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 th
5、at 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 unit
6、s 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 pract
7、ices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 772 Terminology Relating to Solar Energy ConversionE 927 Specification for Solar Simulation for PhotovoltaicTestingE 1036 Test Methods for Electrical Performance of Non-concentra
8、tor Terrestrial Photovoltaic Modules and ArraysUsing Reference CellsE 1328 Terminology Relating to Photovoltaic Solar EnergyConversionE 1799 Practice for Visual Inspections of PhotovoltaicModulesE 1802 Test Methods for Wet Insulation Integrity Testing ofPhotovoltaic Modules3. Terminology3.1 Definiti
9、onsdefinitions of terms used in this testmethod may be found in Terminology E 772 and TerminologyE 1328.3.2 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 d
10、issipate 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 m
11、odule(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
12、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
13、such acondition 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 spot damagefrom occurring.4.4 Fig. 1 illustrates the hot-spot effect in a module of aseries string of cel
14、ls, 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 reverse1This test method is under the jurisdiction of ASTM Committee E44 on Solar,Geothermal and Other Alternative Energy Sources and is the direct resp
15、onsibility ofSubcommittee E44.09 on Photovoltaic Electric Power Conversion.Current edition approved Nov. 1, 2008. Published December 2008. Originallyapproved in 2006. Last previous edition approved in 2006 as E 2481-06.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact A
16、STM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.voltage developed across Y.
17、 For any irradiance 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
18、-V characteristic 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 mo
19、dule does not 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 se
20、ries. For convenience, 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 hav
21、e low shuntresistance 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
22、 low shunt resistance 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 shuntres
23、istance have 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 fract
24、ion of the cell 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
25、long time for the cell to heat to thepoint of causing damage.FIG. 1 Hot Spot EffectFIG. 2 Bypass Diode EffectE24810824.6.2.4 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
26、 each diode.4.7 The major technical issue is how to identify the highestand 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
27、 IR camera toobserve hot spots. If the module circuit is accessible 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 module
28、s.4.8 The selected approach is based on taking a set of I-Vcurves for 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 shun
29、tresistance was shadowed. The curve with the lowest leakagecurrent at 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 specif
30、ied as part of a series ofqualification tests including performance measurements anddemonstration 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
31、apparatus required for the electricalperformance (I-V) measurements of Test Methods E 1036, thefollowing apparatus is required:5.1.1 Illumination Sourcenatural sunlight or Class C (orbetter) steady-state solar simulator as defined in SpecificationE 927.5.1.2 Set of opaque covers for test cell shadow
32、ing. The areaof the covers shall 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
33、 the electrical performance (I-V characteristics)of the module according to Test Methods E 1036.6.2 Perform visual inspection per Practice E 1799.6.3 Perform insulation test per Test Methods E 1802.6.4 Expose the module to an irradiance of 800 to 1000Wm-2using either:6.4.1 Apulsed simulator where th
34、e module temperature willbe close to 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, or6.4.3 Natural sunlight where the module temperature mustbe stabilized within 65C before beginning the measure
35、ments.6.5 After thermal stabilization is attained, determine themaximum power current IMP1according to Test MethodsE 1036. It is not necessary to correct the value to standard testconditions (STC).6.6 Completely cover each cell in turn, measure the result-ant I-V curve and prepare a set of curves li
36、ke Fig. 3.6.6.1 Select the three cells with the lowest shunt resistance(highest leakage current).FIG. 3 Module I-V Characteristics with Different Cells Totally ShadowedE24810836.6.2 Select the cell with the highest shunt resistance(lowest leakage current).NOTE 3It is important to ensure that individ
37、ual 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 ofth
38、e 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
39、 worst 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
40、total 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 be
41、tween 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 simulat
42、or, 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 E 1036.6.16 Perform visual inspection per Practice E 17996.17 Perform insulation test per Test Methods
43、E 18027. 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 s
44、pot exposure,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 resu
45、lt in accessibility of live parts,7.1.8 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 these test methods do notproduce numeric results that would be subject to ASTMrequirements for
46、evaluating the precision and bias of these testmethods. However, the precision and bias of the electricalmeasurements, when performed in accordance with Test Meth-ods E 1036, are subject to the provisions of that document.9. Keywords9.1 solar; energy; photovoltaics; modules; electrical testing;hot s
47、potFIG. 4 Module I-V Characteristics with the Test Cell Shadowed at Different LevelsE2481084ASTM 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 determinatio
48、n 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, either reapproved or withdra
49、wn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Indivi
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