1、Designation: E 2481 06Standard 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 (e) 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 peri
3、odic “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 theencap
4、sulation, 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 t
5、hat 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 This standard does not purp
6、ort 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:2E 7
7、72 Terminology Relating to Solar Energy ConversionE 927 Specification for Solar Simulation for PhotovoltaicTestingE 1036 Test Methods for Electrical Performance of Non-concentrator Terrestrial Photovoltaic Modules and ArraysUsing Reference CellsE 1328 Terminology Relating to Photovoltaic Solar Energ
8、yConversionE 1799 Practice for Visual Inspections of PhotovoltaicModulesE 1802 Test Methods for Wet Insulation Integrity Testing ofPhotovoltaic Modules3. Terminology3.1 Definitionsdefinitions of terms used in this testmethod may be found in Terminology E 772 and TerminologyE 1328.3.2 Definitions of
9、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 photovoltai
10、c 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 modul
11、e 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 orcombusti
12、on 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
13、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 cells, one of which, cell Y, is partiallyshadowed. The amount of electrical power dissipated in Y isequal to the product of th
14、e module current and the reversevoltage developed across Y. 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 a1This test method is under the jurisdiction of ASTM Committee E44 on Solar,Geot
15、hermal and Other Alternative Energy and is the direct responsibility ofSubcommittee E44.09 on Photovoltaic Electric Power Conversion.Current edition approved March 1, 2006. Published March 2006.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at s
16、erviceastm.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.maximum when the module is short-circuited. This is
17、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 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
18、bias, thereby limiting the power dissipation in thereduced-output cell.NOTE 2If the module 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 gr
19、eater than one, the hot spot test should bepreformed with that number of modules in series. 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 ha
20、ve either high shunt resistance wherethe reverse performance is voltage-limited or have 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 shadowi
21、ng conditions occur whenthe whole cell (or a large fraction) is shadowed.4.6.1.2 Often 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 gr
22、eat deal of scatter inperformance of this type of cell. Cells with the lowest shuntresistance 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 Shun
23、t Resistance Cells:4.6.2.1 The worst case shadowing conditions occur when asmall fraction 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
24、.4.6.2.3 Because the heating is uniform over the whole areaof the cell, it can take a long time for 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
25、 cells that can beprotected by each diode.FIG. 1 Hot Spot EffectFIG. 2 Bypass Diode EffectE24810624.7 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
26、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 the currentflow through the shadowed cell can be monitored directly.However, many PV modules do not have removable diodes oraccessible electric ci
27、rcuits. 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 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 cur
28、rent at the point where thediode turns on was taken when the cell with the lowest shuntresistance 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 para
29、llel strings, each stringmust be tested separately.4.10 This test method may be specified 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 minimumacceptan
30、ce criteria for physical or electrical degradation.5. Apparatus5.1 In addition to the 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 simu
31、lator as defined in SpecificationE 927.5.1.2 Set of opaque covers for test cell shadowing. 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
32、.1.4 Appropriate meter(s) to measure module voltage andcurrent.6. Procedure6.1 Measure 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 m
33、odule to an irradiance of 800 to1000 W/m2using either:6.4.1 Apulsed simulator where the module temperature willbe close to room temperature (25 6 5 C),6.4.2 A steady-state simulator where the module tempera-ture must be stabilized within 65 C before beginning themeasurements, or6.4.3 Natural sunligh
34、t where the module temperature mustbe stabilized within 65 C before beginning the measure-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 Completel
35、y shadow each cell in turn, measure theresultant 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).6.7 For each of the selected cells
36、 determine the worst caseshadowing condition by taking a set of I-V curves with each ofthe test cells shadowed at different levels as shown in Fig. 4.The worst case shadowing condition occurs when the “kink” inFIG. 3 Module I-V Characteristics with Different Cells Totally ShadowedE2481063the I-V cur
37、ve of the shadowed module coincides with IMP1.(line “c” in the figure)6.8 Select one of the three lowest shunt resistance cellsselected in 6.6. Shadow that cell to the worst case condition asdetermined in 6.7. Short-circuit the module.6.9 Expose the module to the illumination source. Irradi-ance mus
38、t 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 total exposure time of 1hour.6.11 Repeat 6.8-6.10 for the other two low shunt resistancecells selected in 6.6.6.12 Shadow the highest
39、 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 between 800 and 1200 Wm-2. Record the value ofshort circuit current ISC, irradiance, ambient temperature andmodule temperature.6.14
40、Measure the irradiance every 5 min until the totalradiant exposure reaches 180 MJm-2. (This is equivalent to 50h at 1000 wm-2.)6.14.1 If using a steady-sate solar simulator, remove themodule from the illumination source for a minimum of 1 hafter every5hofexposure.6.15 Measure the electrical performa
41、nce (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 E 18027. Report7.1 The report shall include the following items as aminimum:7.1.1 Module manufacturer and complete test specimenid
42、entification,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 exposure,7.1.5 Ambient conditions during the test,7.1.6 Measured values of module current and temperature,7.1.7 A description
43、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 accessibility of live parts,7.1.8 Identification of areas of the module where problemswere found, and7.1.9 Any deviations fr
44、om 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 evaluating the precision and bias of these testmethods. However, the precision and bias of the electricalmeasurements, when perfor
45、med 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 spotFIG. 4 Module I-V Characteristics with the Test Cell Shadowed at Different LevelsE2481064ASTM International takes no position r
46、especting 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.Thi
47、s 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 withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM Inte
48、rnational 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
49、below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).E2481065
