1、Designation: E2481 08 E2481 12Standard 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 r
2、evision. 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 the ability of a photovoltaic (PV) module to endure the long-term effects
3、of periodic “hot spot” heating associated with common fault conditions such as severely cracked or mismatched cells, single-pointopen circuit failures (for example, interconnect failures), partial (or non-uniform) shadowing or soiling. Such effects typicallyinclude solder melting or deterioration of
4、 the encapsulation, but in severe cases could progress to combustion of the PV moduleand surrounding materials.1.2 There are two ways that cells can cause a hot spot problem; either by having a high resistance so that there is a largeresistance in the circuit, or by having a low resistance area (shu
5、nt) such that there is a high-current flow in a localized region. Thistest method selects cells of both types to be stressed.1.3 This test method does not establish pass or fail levels. The determination of acceptable or unacceptable results is beyondthe scope of this test method.1.4 The values stat
6、ed in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety a
7、nd health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E772 Terminology of Solar Energy ConversionE927 Specification for Solar Simulation for Photovoltaic TestingE1036 Test Methods for Electrical Performance of Nonconcentr
8、ator Terrestrial Photovoltaic Modules and Arrays UsingReference CellsE1328 Terminology Relating to Photovoltaic Solar Energy Conversion (Withdrawn 2012)3E1799 Practice for Visual Inspections of Photovoltaic ModulesE1802 Test Methods for Wet Insulation Integrity Testing of Photovoltaic Modules3. Term
9、inology3.1 Definitionsdefinitions of terms used in this test method may be found in Terminology E772 and Terminology E1328.3.2 Definitions of Terms Specific to This Standard:3.2.1 hot spota condition that occurs, usually as a result of shadowing, when a solar cell or group of cells is forced into re
10、versebias and must dissipate power, which can result in abnormally high cell temperatures.4. Significance and Use4.1 The design of a photovoltaic module or system intended to provide safe conversion of the suns radiant energy into usefulelectricity must take into consideration the possibility of par
11、tial shadowing of the module(s) during operation. This test methoddescribes a procedure for verifying that the design and construction of the module provides adequate protection against thepotential harmful effects of hot spots during normal installation and use.1 This test method is under the juris
12、diction 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 Nov. 1, 2008Dec. 1, 2012. Published December 2008December 2012. Originally approved in 200
13、6. Last previous edition approved in 20062008as E2481-06.-08. DOI: 10.1520/E2481-08.10.1520/E2481-12.2 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards
14、 Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, A
15、STM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14.2 T
16、his test method describes a procedure for determining the ability of the module to provide protection from internal defectswhich could cause loss of electrical insulation or combustion hazards.4.3 Hot-spot heating occurs in a module when its operating current exceeds the reduced short-circuit curren
17、t (Isc) of a shadowedor faulty cell or group of cells. When such a condition occurs, the affected cell or group of cells is forced into reverse bias andmust dissipate power, which can cause overheating.NOTE 1The correct use of bypass diodes can prevent hot spot damage from occurring.4.4 Fig. 1 illus
18、trates the hot-spot effect in a module of a series string of cells, one of which, cell Y, is partially shadowed. Theamount of electrical power dissipated in Y is equal to the product of the module current and the reverse voltage developed acrossY. For any irradiance level, when the reverse voltage a
19、cross Y is equal to the voltage generated by the remaining (s-1) cells in themodule, power dissipation is at a maximum when the module is short-circuited. This is shown in Fig. 1 by the shaded rectangleconstructed at the intersection of the reverse I-V characteristic of Y with the image of the forwa
20、rd I-V characteristic of the (s-1)cells.4.5 By-pass diodes, if present, as shown in Fig. 2, begin conducting when a series-connected string in a module is in reversebias, thereby limiting the power dissipation in the reduced-output cell.NOTE 2If the module does not contain bypass diodes, check the m
21、anufacturers instructions to see if a maximum number of series modules isrecommended before installing bypass diodes. If the maximum number of modules recommended is greater than one, the hot spot test should bepreformed with that number of modules in series. For convenience, a constant current powe
22、r supply may be substituted for the additional modules tomaintain the specified current.4.6 The reverse characteristics of solar cells can vary considerably. Cells can have either high shunt resistance where the reverseperformance is voltage-limited or have low shunt resistance where the reverse per
23、formance is current-limited. Each of these typesof cells can suffer hot spot problems, but in different ways.4.6.1 Low-Shunt Resistance Cells:4.6.1.1 The worst case shadowing conditions occur when the whole cell (or a large fraction) is shadowed.4.6.1.2 Often low shunt resistance cells are this way
24、because of localized shunts. In this case hot spot heating occurs becausea large amount of current flows in a small area. Because this is a localized phenomenon, there is a great deal of scatter inperformance of this type of cell. Cells with the lowest shunt resistance have a high likelihood of oper
25、ating at excessively hightemperatures when reverse biased.4.6.1.3 Because the heating is localized, hot spot failures of low shunt resistance cells occur quickly.4.6.2 High Shunt Resistance Cells:4.6.2.1 The worst case shadowing conditions occur when a small fraction of the cell is shadowed.4.6.2.2
26、High shunt resistance cells limit the reverse current flow of the circuit and therefore heat up. The cell with the highestshunt resistance will have the highest power dissipation.4.6.2.3 Because the heating is uniform over the whole area of the cell, it can take a long time for the cell to heat to t
27、he pointof causing damage.4.6.2.4 High shunt resistance cells define the need for bypass diodes in the modules circuit, and their performancecharacteristics determine the number of cells that can be protected by each diode.4.7 The major technical issue is how to identify the highest and lowest shunt
28、 resistance cells and then how to determine theworst case shadowing for those cells. If the bypass diodes are removable, cells with localized shunts can be identified by reversebiasing the cell string and using an IR camera to observe hot spots. If the module circuit is accessible the current flow t
29、hrough theFIG. 1 Hot Spot EffectE2481 122shadowed cell can be monitored directly. However, many PV modules do not have removable diodes or accessible electric circuits.Therefore a non-intrusive method is needed that can be utilized on those modules.4.8 The selected approach is based on taking a set
30、of I-V curves for a module with each cell shadowed in turn. Fig. 3 showsthe resultant set of I-V curves for a sample module. The curve with the highest leakage current at the point where the diode turnson was taken when the cell with the lowest shunt resistance was shadowed. The curve with the lowes
31、t leakage current at the pointwhere the diode turns on was taken when the cell with the highest shunt resistance was shadowed.4.9 If the module to be tested has parallel strings, each string must be tested separately.4.10 This test method may be specified as part of a series of qualification tests i
32、ncluding performance measurements anddemonstration of functional requirements. It is the responsibility of the user of this test method to specify the minimum acceptancecriteria for physical or electrical degradation.5. Apparatus5.1 In addition to the apparatus required for the electrical performanc
33、e (I-V) measurements of Test Methods E1036, thefollowing apparatus is required:5.1.1 Illumination Sourcenatural sunlight or Class C (or better) steady-state solar simulator as defined in Specification E927.FIG. 2 Bypass Diode EffectFIG. 3 Module I-V Characteristics with Different Cells Totally Shado
34、wedE2481 1235.1.2 Set of opaque covers for test cell shadowing. The area of the covers shall be based on the area of the cells in the modulebeing tested, in 5 % increments.5.1.3 Appropriate temperature detectors to measure ambient temperature and module surface temperature.5.1.4 Appropriate meter(s)
35、 to measure module voltage and current.6. Procedure6.1 Measure the electrical performance (I-V 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
36、800 to 1000 Wm-2 using either:6.4.1 A pulsed simulator where the module temperature will be close to room temperature (25 6 5C),6.4.2 A steady-state simulator where the module temperature must be stabilized within 65C before beginning themeasurements, or6.4.3 Natural sunlight where the module temper
37、ature must be stabilized within 65C before beginning the measurements.6.5 After thermal stabilization is attained, determine the maximum power current IMP1 according to Test Methods E1036. It isnot necessary to correct the value to standard test conditions (STC).6.6 Completely cover each cell in tur
38、n, measure the resultant 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 individual cells ar
39、e completely covered during the I-V curve characterization procedure. Leaving even 1% ofa cell uncovered may cause the wrong cell to be selected for the stress testing.6.7 For each of the selected cells determine the worst case covering condition by taking a set of I-V curves with each of thetest ce
40、lls covered at different levels as shown in Fig. 4. The worst case covering condition occurs when the “kink” in the I-V curveof the shadowed covered module coincides with IMP1. (line “c” in Fig. 4)6.8 Select one of the three lowest shunt resistance cells selected in 6.6. Cover that cell to the worst
41、 case condition as determinedin 6.7. Short-circuit the module.6.9 Expose the module to the illumination source. Irradiance must be between 800 and 1200 Wm-2. Record the value of shortcircuit current ISC, irradiance, ambient temperature and module temperature.6.10 Maintain this condition for a total
42、exposure time of 1 h.6.11 Repeat 6.8-6.10 for the other two low shunt resistance cells selected in 6.6.FIG. 4 Module I-V Characteristics with the Test Cell Shadowed at Different LevelsE2481 1246.12 Cover the highest shunt resistance cell to the worst case condition as determined in 6.7. Short-circui
43、t the module.6.13 Expose the module to the illumination source. Irradiance must be between 800 and 1200 Wm-2. Record the value of shortcircuit current ISC, irradiance, ambient temperature and module temperature.6.14 Measure the irradiance every 5 min until the total radiant exposure reaches 180 MJm-
44、2. (This is equivalent to50 h at 1000 Wm-2.)6.14.1 If using a steady-sate solar simulator, remove the module from the illumination source for a minimum of 1 h after every5 h of exposure.6.15 Measure the electrical performance (I-V characteristics) of the module according to Test Methods E1036.6.16 P
45、erform visual inspection per Practice E17996.17 Perform insulation test per Test Methods E18027. Report7.1 The report shall include the following items as a minimum:7.1.1 Module manufacturer and complete test specimen identification,7.1.2 Description of module construction,7.1.3 Description of elect
46、rical measurement equipment,7.1.4 Module I-V measurement results before and after the hot 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 of any apparent changes as a result of the testing. For example, indications of
47、 shorting, arcing, excessiveheating, damage to module materials, or other failures which result in accessibility of live parts,7.1.8 Identification of areas of the module where problems were found, and7.1.9 Any deviations from the test procedure.8. Precision and Bias8.1 The procedures described by t
48、hese test methods do not produce numeric results that would be subject to ASTM requirementsfor evaluating the precision and bias of these test methods. However, the precision and bias of the electrical measurements, whenperformed in accordance with Test Methods E1036, are subject to the provisions o
49、f that 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 revi
