ASTM E2481-12(2023)

Standard Test Method for Hot Spot Protection Testing of Photovoltaic Modules

SIGNIFICANCE AND USE
4.1 The design of a photovoltaic module or system intended to provide safe conversion of the sun's radiant energy into useful electricity must take into consideration the possibility of partial shadowing of the module(s) during operation. This test method describes a procedure for verifying that the design and construction of the module provides adequate protection against the potential harmful effects of hot spots during normal installation and use.  
4.2 This test method describes a procedure for determining the ability of the module to provide protection from internal defects which 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 current (ISC) of a shadowed or faulty cell or group of cells. When such a condition occurs, the affected cell or group of cells is forced into reverse bias and must dissipate power, which can cause overheating.
Note 1: The correct use of bypass diodes can prevent hot spot damage from occurring.  
4.4 Fig. 1 illustrates the hot spot effect in a module of a series string of cells, one of which, cell Y, is partially shadowed. The amount of electrical power dissipated in Y is equal to the product of the module current and the reverse voltage developed across Y. For any irradiance level, when the reverse voltage across Y is equal to the voltage generated by the remaining (s-1) cells in the module, power dissipation is at a maximum when the module is short-circuited. This is shown in Fig. 1 by the shaded rectangle constructed at the intersection of the reverse I-V characteristic of Y with the image of the forward I-V characteristic of the (s-1) cells.
FIG. 1 Hot Spot Effect  
4.5 Bypass diodes, if present, as shown in Fig. 2, begin conducting when a series-connected string in a module is in reverse bias, thereby limiting the power dissipation in the reduced-output cell.  
FIG. 2 Bypass Diode Effect  
Note 2: If the ...
SCOPE
1.1 This test method provides a procedure to determine the ability of a photovoltaic (PV) module to endure the long-term effects of periodic “hot spot” heating associated with common fault conditions such as severely cracked or mismatched cells, single-point open circuit failures (for example, interconnect failures), partial (or nonuniform) shadowing, or soiling. Such effects typically include solder melting or deterioration of the encapsulation, but in severe cases could progress to combustion of the PV module and 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 large resistance in the circuit, or by having a low resistance area (shunt) such that there is a high current flow in a localized region. This test 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 beyond the scope of this test method.  
1.4 The values stated 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 responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Jul-2023
• ICS: 27.160 - Solar energy engineering
• Technical Committee: E44 - Solar, Geothermal and Other Alternative Energy Sources
• Drafting Committee: E44.09 - Photovoltaic Electric Power Conversion

Relations

• Refers: ASTM E1036-15(2019) - Standard Test Methods for Electrical Performance of Nonconcentrator Terrestrial Photovoltaic Modules and Arrays Using Reference Cells
• Effective Date: 01-Apr-2019
• Refers: ASTM E927-19 - Standard Classification for Solar Simulators for Electrical Performance Testing of Photovoltaic Devices
• Effective Date: 01-Feb-2019
• Refers: ASTM E927-10(2015) - Standard Specification for Solar Simulation for Photovoltaic Testing
• Effective Date: 01-Nov-2015
• Refers: ASTM E1036-15 - Standard Test Methods for Electrical Performance of Nonconcentrator Terrestrial Photovoltaic Modules and Arrays Using Reference Cells
• Effective Date: 01-Feb-2015
• Refers: ASTM E772-13 - Standard Terminology of Solar Energy Conversion
• Effective Date: 01-Sep-2013
• Refers: ASTM E1799-12 - Standard Practice for Visual Inspections of Photovoltaic Modules
• Effective Date: 01-Dec-2012
• Refers: ASTM E1036-12 - Standard Test Methods for Electrical Performance of Nonconcentrator Terrestrial Photovoltaic Modules and Arrays Using Reference Cells
• Effective Date: 01-Dec-2012
• Refers: ASTM E1802-12 - Standard Test Methods for Wet Insulation Integrity Testing of Photovoltaic Modules
• Effective Date: 01-Dec-2012
• Refers: ASTM E772-11 - Standard Terminology of Solar Energy Conversion
• Effective Date: 01-Sep-2011
• Refers: ASTM E927-10 - Standard Specification for Solar Simulation for Terrestrial Photovoltaic Testing
• Effective Date: 01-Jun-2010
• Refers: ASTM E1036-08 - Standard Test Methods for Electrical Performance of Nonconcentrator Terrestrial Photovoltaic Modules and Arrays Using Reference Cells
• Effective Date: 01-Nov-2008
• Refers: ASTM E1799-08 - Standard Practice for Visual Inspections of Photovoltaic Modules
• Effective Date: 01-Apr-2008
• Refers: ASTM E1036-02(2007) - Standard Test Methods for Electrical Performance of Nonconcentrator Terrestrial Photovoltaic Modules and Arrays Using Reference Cells
• Effective Date: 01-Nov-2007
• Refers: ASTM E1802-07 - Standard Test Methods for Wet Insulation Integrity Testing of Photovoltaic Modules
• Effective Date: 01-Mar-2007
• Refers: ASTM E927-05 - Standard Specification for Solar Simulation for Terrestrial Photovoltaic Testing
• Effective Date: 01-Apr-2005

Overview

ASTM E2481-12(2023): Standard Test Method for Hot Spot Protection Testing of Photovoltaic Modules provides a rigorous procedure to determine a photovoltaic (PV) module’s ability to withstand long-term effects from “hot spot” heating. Hot spots can arise due to partial shadowing, cracked or mismatched cells, open circuit failures, or soiling, leading to potential module degradation or safety hazards like insulation loss or combustion. This ASTM International standard supports manufacturers, inspectors, and installers in evaluating the robustness of PV modules and ensuring they meet essential safety benchmarks for reliable solar energy conversion.

Key Topics

• Hot Spot Formation and Risk: Hot spots can occur when parts of a module are shaded or have internal defects, forcing affected cells into reverse bias and dissipating excess power as heat. This may result in solder melting, encapsulation failure, or even module combustion.
• Types of Cell Defects:
  • Low Shunt Resistance Cells: These have a high likelihood of localized heating leading to quick hot spot failure.
  • High Shunt Resistance Cells: These tend to heat more uniformly and slowly, making failure less immediate but still possible.
• Role of Bypass Diodes: Proper use of bypass diodes helps prevent hot spot formation by limiting power dissipation in shadowed or faulty cells.
• Testing Approach:
  • Identification of cells most prone to hot spot effects (lowest and highest shunt resistance).
  • Measurement of current-voltage (I-V) characteristics under controlled shading and irradiance.
  • Visual and insulation integrity inspections before and after hot spot exposure.
• Test Conditions:
  • Exposure to specified irradiance with either natural sunlight or a solar simulator.
  • Temperature and electrical monitoring to observe performance changes.
• Reporting and Documentation:
  • Comprehensive data collection, including physical observations, electrical measurements, and identification of any damage or deviations from testing procedures.

Applications

• Quality Assurance for PV Manufacturers: Confirms that photovoltaic modules are designed to minimize risks associated with hot spot heating, ensuring product durability and long-term performance.
• Regulatory and Certification Testing: Provides a standardized method essential for module certification, compliance checks, and meeting safety regulations in the solar power industry.
• Installation and System Design: Informs best practices in PV system installation, especially regarding shading analysis and the strategic use of bypass diodes to protect against localized heating.
• Field Assessment and Maintenance: Assists in identifying and mitigating risks in existing modules subject to faults or partial shading, supporting ongoing maintenance strategies for solar arrays.

Related Standards

Several ASTM standards complement E2481-12(2023) by providing additional testing and classification methods for PV modules:

• ASTM E772: Terminology of Solar Energy Conversion
• ASTM E927: Classification for Solar Simulators for Electrical Performance Testing of Photovoltaic Devices
• ASTM E1036: Test Methods for Electrical Performance of Nonconcentrator Terrestrial Photovoltaic Modules and Arrays Using Reference Cells
• ASTM E1799: Practice for Visual Inspections of Photovoltaic Modules
• ASTM E1802: Test Methods for Wet Insulation Integrity Testing of Photovoltaic Modules

Summary

ASTM E2481-12(2023) is a critical standard for assessing hot spot protection in photovoltaic modules, enhancing PV system safety, reliability, and performance. By specifying robust test methods and linking to related standards, it underpins quality control, regulatory compliance, and best practices in the solar energy sector. This contributes to building trust in PV technology and supporting the growth of sustainable solar power solutions.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E2481 − 12 (Reapproved 2023) An American National Standard
Standard Test Method for
Hot Spot Protection Testing of Photovoltaic Modules
This standard is issued under the fixed designation E2481; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method provides a procedure to determine the
E772 Terminology of Solar Energy Conversion
ability of a photovoltaic (PV) module to endure the long-term
E927 Classification for Solar Simulators for Electrical Per-
effects of periodic “hot spot” heating associated with common
formance Testing of Photovoltaic Devices
fault conditions such as severely cracked or mismatched cells,
E1036 Test Methods for Electrical Performance of Noncon-
single-point open circuit failures (for example, interconnect
centrator Terrestrial Photovoltaic Modules and Arrays
failures), partial (or nonuniform) shadowing, or soiling. Such
Using Reference Cells
effects typically include solder melting or deterioration of the
E1799 Practice for Visual Inspections of Photovoltaic Mod-
encapsulation, but in severe cases could progress to combus-
ules
tion of the PV module and surrounding materials.
E1802 Test Methods for Wet Insulation Integrity Testing of
Photovoltaic Modules
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
3. Terminology
large resistance in the circuit, or by having a low resistance
3.1 Definitions—Definitions of terms used in this test
area (shunt) such that there is a high current flow in a localized
method may be found in Terminology E772.
region. This test method selects cells of both types to be
3.2 Definitions of Terms Specific to This Standard:
stressed.
3.2.1 hot spot—a condition that occurs, usually as a result of
1.3 This test method does not establish pass or fail levels.
shadowing, when a solar cell or group of cells is forced into
The determination of acceptable or unacceptable results is
reverse bias and must dissipate power, which can result in
beyond the scope of this test method.
abnormally high cell temperatures.
1.4 The values stated in SI units are to be regarded as
4. Significance and Use
standard. No other units of measurement are included in this
4.1 The design of a photovoltaic module or system intended
standard.
to provide safe conversion of the sun’s radiant energy into
1.5 This standard does not purport to address all of the
useful electricity must take into consideration the possibility of
safety concerns, if any, associated with its use. It is the
partial shadowing of the module(s) during operation. This test
responsibility of the user of this standard to establish appro- method describes a procedure for verifying that the design and
priate safety, health, and environmental practices and deter- construction of the module provides adequate protection
against the potential harmful effects of hot spots during normal
mine the applicability of regulatory limitations prior to use.
installation and use.
1.6 This international standard was developed in accor-
dance with internationally recognized principles on standard-
4.2 This test method describes a procedure for determining
ization established in the Decision on Principles for the
the ability of the module to provide protection from internal
Development of International Standards, Guides and Recom- defects which could cause loss of electrical insulation or
mendations issued by the World Trade Organization Technical combustion hazards.
Barriers to Trade (TBT) Committee.
4.3 Hot spot heating occurs in a module when its operating
current exceeds the reduced short-circuit current (I ) of a
SC
shadowed or faulty cell or group of cells. When such a
This test method is under the jurisdiction of ASTM Committee E44 on Solar,
Geothermal and Other Alternative Energy Sources and is the direct responsibility of
Subcommittee E44.09 on Photovoltaic Electric Power Conversion. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Aug. 1, 2023. Published August 2023. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 2006. Last previous edition approved in 2018 as E2481 – 12 (2018). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/E2481-12R23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2481 − 12 (2023)
condition occurs, the affected cell or group of cells is forced resistance have a high likelihood of operating at excessively
into reverse bias and must dissipate power, which can cause high temperatures when reverse biased.
overheating. 4.6.1.3 Because the heating is localized, hot spot failures of
low shunt resistance cells occur quickly.
NOTE 1—The correct use of bypass diodes can prevent hot spot damage
4.6.2 High Shunt Resistance Cells:
from occurring.
4.6.2.1 The worst-case shadowing conditions occur when a
4.4 Fig. 1 illustrates the hot spot effect in a module of a
small fraction of the cell is shadowed.
series string of cells, one of which, cell Y, is partially
4.6.2.2 High shunt resistance cells limit the reverse current
shadowed. The amount of electrical power dissipated in Y is
flow of the circuit and therefore heat up. The cell with the
equal to the product of the module current and the reverse
highest shunt resistance will have the highest power dissipa-
voltage developed across Y. For any irradiance level, when the
tion.
reverse voltage across Y is equal to the voltage generated by the
4.6.2.3 Because the heating is uniform over the whole area
remaining (s-1) cells in the module, power dissipation is at a
of the cell, it can take a long time for the cell to heat to the
maximum when the module is short-circuited. This is shown in
point of causing damage.
Fig. 1 by the shaded rectangle constructed at the intersection of
4.6.2.4 High shunt resistance cells define the need for
the reverse I-V characteristic of Y with the image of the
bypass diodes in the module’s circuit, and their performance
forward I-V characteristic of the (s-1) cells.
characteristics determine the number of cells that can be
4.5 Bypass diodes, if present, as shown in Fig. 2, begin
protected by each diode.
conducting when a series-connected string in a module is in
4.7 The major technical issue is how to identify the highest
reverse bias, thereby limiting the power dissipation in the
and lowest shunt resistance cells and then how to determine the
reduced-output cell.
worst-case shadowing for those cells. If the bypass diodes are
NOTE 2—If the module does not contain bypass diodes, check the
removable, cells with localized shunts can be identified by
manufacturer’s instructions to see if a maximum number of series modules
reverse biasing the cell string and using an IR camera to
is recommended before installing bypass diodes. If the maximum number
observe hot spots. If the module circuit is accessible the current
of modules recommended is greater than one, the hot spot test should be
flow through the shadowed cell can be monitored directly.
performed with that number of modules in series. For convenience, a
constant current power supply may be substituted for the additional However, many PV modules do not have removable diodes or
modules to maintain the specified current.
accessible electric circuits. Therefore a non-intrusive method is
needed that can be utilized on those modules.
4.6 The reverse characteristics of solar cells can vary
considerably. Cells can have either high shunt resistance where
4.8 The selected approach is based on taking a set of I-V
the reverse p
...