Upgrading PV Standards for better performance

 To retain market trust in the IEC standards, maintenance of the pertinent standards needs to assure compliance with state-of-the-art knowledge and best practices
The commercial success of photovoltaic (PV) is largely based on the long-term reliability of the PV modules. Current PV modules tend to carry a performance warranty of 25 years. These modules are typically qualified to IEC 61215 or IEC 61646 (design qualification and type approval for terrestrial crystalline Si or thin-film technologies) and IEC 61730 (PV module safety qualification).
These qualification tests have shown adequately identify design, material, and process flaws that could lead to premature field failures. Consequently, PV module customers have come to appreciate the criticality of the tests in IEC standards 61215, 61646 and 61730. Since the last revisions of the standards the knowledge of PV failure modes has increased dramatically. To retain market trust in the IEC standards, maintenance of the pertinent standards needs to assure compliance with state-of-the-art knowledge and best practices. The performance related IEC 61215 and 61646 standards will be combined to allow better recognition of technology specifics. Due to the new materials, components and processes it is also necessary to dramatically update the safety standard IEC 61730. This is in particular important because cells, front and back-sheets are getting thinner and it must be ensured that the module will operate safely in the intended time of use. Since those issues are not new to electronic devices the new edition of IEC 61730 will and must follow the guidance of horizontal IEC standards and incorporates concepts like overvoltage category, pollution degree and material groups. Over the past three years Working Group 2 (WG2) of the technical committee for Solar PV Energy Systems (TC82) within the International Electrotechnical Commission (IEC) invested a considerable effort to align IEC 61730 with horizontal IEC standards and to update and merge the terrestrial PV module design qualification and type approval standards into a single IEC 61215 series. Especially the merger of IEC 61215 and IEC 61646 is important throughout the value chain. It is now clear that a PV module needs safety qualification by IEC 61730 and type approval by IEC 61215 with equivalent pass or fail criteria. In the former structure this was not the case. On one hand there were crystalline and on the other side thin-film modules. Most of the applied tests were developed during the block-diagram testing in the 80’s with having mainly crystalline silicon in mind. In the 90’s there was a growing interest in thin film technologies, mainly amorphous silicon. Based on that IEC 61646 standard focused mostly on amorphous silicon, clearly visible in the requirements for light-soaking.
Due to IEC standard development and maintenance cycles typically the equipment requirements in both standards were not identical. Still testing for type approval for a PV module that is indented to operate in the same environment those differences caused a lot of confusion. This problem is nicely overcome with the new IEC 61215 standard series since all technologies refer to the same tests and test definitions. The most prominent and most discussed issue here is the UV-preconditioning test (MQT 10). MQT here refers to Module Quality Test and is a unique identifier for each test.
To be able to refer for each technology to the same tests and requirements a new standard structure was developed as it is shown in Figure 1. Requirements from IEC 61215 and IEC 61646 were merged into Part 1 while all testing (formally clause 10) was moved into Part 2. Part 1 states all requirements like pass/fail criteria and defines the test flow. Unequal certification conditions due to specific properties of a technology are thereby eliminated. Technology specifics as for example measurement uncertainties and reproducibility during performance test (MQT 06.1) are addressed in the sub-standards of Part 1. Here especially the stabilisation, formally light-soaking procedure, is important. While e.g. crystalline Si (c-Si) only needs a few hours of light to get into a stable state a-Si might take several hundreds of hours. The test duration and test limits e.g. maximum device temperature is therefore stated in the subpart of IEC 61215-1, in this particular example for c-Si in Part 61215-1-1 and for a-Si in Part 61215-1-3. In addition to use light for stabilisation a new procedure is given for validation of an alternative stabilisation procedure e.g. by using temperature and an applied current in the dark (dark-current soak).
The new structure greatly enhances transparency enabling customers and investors as well as other stakeholders up and downstream the value chain to assess the standards applied to certain components of the PV system – in this case the PV module. By the merger the perception that thin film technologies are inferior to crystalline technologies is eliminated. Product research and selection is based on one PV module qualification standard: IEC 61215.
The new structure allows for easy updates based on new data as well as the possibility to swiftly add standards related to new technologies, such as OPV or Perovskite-based solar cells and modules.
Since release of Edition 1 of IEC 61730 series the PV industry has experienced rapid growth and undergone a large number of changes. As a result, during the past years the project team invested a considerable effort in updating the governing PV module safety standards to respond to PV industry needs as well as reflect technological changes and advances. In particular, with the revision of IEC 61730 a need to reflect the current understanding of low voltage DC (up to 1,500 V DC) components and materials used in the construction of PV modules arouse. This includes permitting new materials and new designs (e.g. cemented joints) while at the same time complying with international horizontal standards that need to be met in order to comply with governing national electric codes.
The principle structure of IEC 61730 is unchanged. Part 1 of IEC 61730 addresses the minimum requirements for module design while Part 2 deals with the required tests protocols and test sequences. New tests have been added to Part 2 of Edition 2 as the material requirements necessitate the confirmation of their properties during PV module operation. In addition the following objectives were set:Align the PV safety standard and its requirements with horizontal IEC standardsFull implementation of 1,500 V system voltage requirementsUpdates related to technology and material advances such as cemented joints.
To reflect and fulfil the objectives for the new standard series of IEC 61730 numerous key definitions and a detailed understanding of electro technical horizontal standards are needed. IEC defines a horizontal standard as follows:“Standard on fundamental principles, concepts, terminology or technical characteristics, relevant to a number of technical committees and of crucial importance to ensure the coherence of the corpus of standardisation documents.”
Horizontal standards are assigned by the Standardisation Management Board (SMB) with the purpose of ensuring the coherence of the corpus of standardisation documents, avoiding duplication of work and contradictory requirements, and are part of IEC Guide 108 “Guidelines for ensuring the coherency of IEC publications – Application of horizontal standards”.The most important and fundamental concepts from the horizontal standards that have to be applied to PV safety standards are the following:Concept of insulation coordinationOvervoltage categoryConcept of classes (IEC 61140)Concept of pollution degree (IEC 60664-1 Clause 4.6)Concept of material group (IEC 60664-1 clause 4.8).
How those requirements impact PV modules is summarised in Table 1 where a comparison to edition 1 of IEC 61730 is given.
Besides the implementation of horizontal standards in the PV safety standard the requirements for 1,500 V system voltage and cemented joints were requested. The system voltage highly impacts the required Clearances distance (cl) and Creepage distances (cr).  The requirements for such spacing are derived from IEC 60664 and while designing a PV module the pollution degree and material properties (material group) must be considered. Based on the installation location different overvoltage categories might apply (based on IEC 61140) but PV modules are defaulted to overvoltage category III. The combination of pollution degree, material group, overvoltage category and the manufacturer’s set system voltage clearance and creepage distances can extracted from Table 3 and 4 in IEC 61730-1. To lower the requirements for spacing the new concept of Cemented joints is introduced. This concept allows smaller spacing but requires much better and tighter production control, tolerances and material quality and homogeneity.
Due to the modifications in Part 1 also Part 2 that deals with testing requirements had gone through some revisions. The following list gives a brief summary of the changes made to Part 2 mainly including new tests:MST 05 Durability of markings: Checks for readability of the markings on the PV module before and after stress tests.
MST 06 Sharp edge test: All accessible modules surfaces should be smooth and pose no risk for injury; verified via test.  MST 13 Continuity test of equipotential bonding: Test renamed to better reflect its purpose.MST 23 Fire test: new reference, also see Appendix of IEC 61730-2 Ed. 2.
MST 24 Ignitability test: This new test determines the ignitability of PV modules by direct small flame impingement under zero impressed irradiance using vertically oriented test specimens and is based on ISO 11925-2. This is important for all polymeric materials used in a PV laminate.
MST 33 Screw connections test: Any screw connection in the module should remain secure. Tests described in MST 33 look for proper material design, installation and tightness of screws.
MST 35 Peel test: The purpose of this test is to provide confidence regarding the durability of the adhesion between different layers of the PV module stack.
MST 36 Lap shear strength test: The purpose of this test is to provide confidence regarding the durability of the adhesion between rigid-to-rigid bonded assemblies (e.g. glass/glass modules) for cemented joints of the PV module stack.
MST 37 Materials creep test: Validates that the materials used in the module will not show creep or lose adhesion when operated at the highest temperatures that modules normally experience in the field. In particular the test determines possible creep between the following interfaces: Frontsheet to backsheetFrontsheet or backsheet to directly attached mounting system (e.g. back rail)Junction box to backsheet respectively frontsheet.
The implementation of new tests is the result of changes in module manufacturing as well as requirements from horizontal standards implemented in Part 1 of IEC 61730 Edition 2. Consequently the test flow has been updated.  The latest revision includes all comments from national committees (NCs) that were received based on the drafts distributed to all NCs in spring 2014 and winter 2014/2015. The documents are currently in CDV stage.
Both standards, IEC 61215 series and IEC 61730 have undergone major revisions and have approved CDVs. The main documents (Part 1 and Part 2) for IEC 61215 as well as for crystalline silicon PV modules (Part 1-1) are submitted as FDIS (Final Draft International Standard) to IEC central office. For thin film technologies (Parts 1-2, 1-3 and 1-4) the documents are distributed as CDVs (final Committee draft for voting). Publication date for IEC 61215 is expected to be in the beginning of 2016. IEC 61730 Part 1 and Part 2 are expected to be send to IEC central office as FDIS in Q4 2015. Publication date is therefore expected to be middle of 2016.
Authored by__Dr. Bengt JaeckelPrincipal Engineer (PE) – Renewable EnergyUL International Germany GmbH

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Upgrading PV Standards for better performance

 To retain market trust in the IEC standards, maintenance of the pertinent standards needs to assure compliance with state-of-the-art knowledge and best practices
The commercial success of photovoltaic (PV) is largely based on the long-term reliability of the PV modules. Current PV modules tend to carry a performance warranty of 25 years. These modules are typically qualified to IEC 61215 or IEC 61646 (design qualification and type approval for terrestrial crystalline Si or thin-film technologies) and IEC 61730 (PV module safety qualification).
These qualification tests have shown adequately identify design, material, and process flaws that could lead to premature field failures. Consequently, PV module customers have come to appreciate the criticality of the tests in IEC standards 61215, 61646 and 61730. Since the last revisions of the standards the knowledge of PV failure modes has increased dramatically. To retain market trust in the IEC standards, maintenance of the pertinent standards needs to assure compliance with state-of-the-art knowledge and best practices. The performance related IEC 61215 and 61646 standards will be combined to allow better recognition of technology specifics. Due to the new materials, components and processes it is also necessary to dramatically update the safety standard IEC 61730. This is in particular important because cells, front and back-sheets are getting thinner and it must be ensured that the module will operate safely in the intended time of use. Since those issues are not new to electronic devices the new edition of IEC 61730 will and must follow the guidance of horizontal IEC standards and incorporates concepts like overvoltage category, pollution degree and material groups. Over the past three years Working Group 2 (WG2) of the technical committee for Solar PV Energy Systems (TC82) within the International Electrotechnical Commission (IEC) invested a considerable effort to align IEC 61730 with horizontal IEC standards and to update and merge the terrestrial PV module design qualification and type approval standards into a single IEC 61215 series. Especially the merger of IEC 61215 and IEC 61646 is important throughout the value chain. It is now clear that a PV module needs safety qualification by IEC 61730 and type approval by IEC 61215 with equivalent pass or fail criteria. In the former structure this was not the case. On one hand there were crystalline and on the other side thin-film modules. Most of the applied tests were developed during the block-diagram testing in the 80’s with having mainly crystalline silicon in mind. In the 90’s there was a growing interest in thin film technologies, mainly amorphous silicon. Based on that IEC 61646 standard focused mostly on amorphous silicon, clearly visible in the requirements for light-soaking.
Due to IEC standard development and maintenance cycles typically the equipment requirements in both standards were not identical. Still testing for type approval for a PV module that is indented to operate in the same environment those differences caused a lot of confusion. This problem is nicely overcome with the new IEC 61215 standard series since all technologies refer to the same tests and test definitions. The most prominent and most discussed issue here is the UV-preconditioning test (MQT 10). MQT here refers to Module Quality Test and is a unique identifier for each test.
To be able to refer for each technology to the same tests and requirements a new standard structure was developed as it is shown in Figure 1. Requirements from IEC 61215 and IEC 61646 were merged into Part 1 while all testing (formally clause 10) was moved into Part 2. Part 1 states all requirements like pass/fail criteria and defines the test flow. Unequal certification conditions due to specific properties of a technology are thereby eliminated. Technology specifics as for example measurement uncertainties and reproducibility during performance test (MQT 06.1) are addressed in the sub-standards of Part 1. Here especially the stabilisation, formally light-soaking procedure, is important. While e.g. crystalline Si (c-Si) only needs a few hours of light to get into a stable state a-Si might take several hundreds of hours. The test duration and test limits e.g. maximum device temperature is therefore stated in the subpart of IEC 61215-1, in this particular example for c-Si in Part 61215-1-1 and for a-Si in Part 61215-1-3. In addition to use light for stabilisation a new procedure is given for validation of an alternative stabilisation procedure e.g. by using temperature and an applied current in the dark (dark-current soak).
The new structure greatly enhances transparency enabling customers and investors as well as other stakeholders up and downstream the value chain to assess the standards applied to certain components of the PV system – in this case the PV module. By the merger the perception that thin film technologies are inferior to crystalline technologies is eliminated. Product research and selection is based on one PV module qualification standard: IEC 61215.
The new structure allows for easy updates based on new data as well as the possibility to swiftly add standards related to new technologies, such as OPV or Perovskite-based solar cells and modules.
Since release of Edition 1 of IEC 61730 series the PV industry has experienced rapid growth and undergone a large number of changes. As a result, during the past years the project team invested a considerable effort in updating the governing PV module safety standards to respond to PV industry needs as well as reflect technological changes and advances. In particular, with the revision of IEC 61730 a need to reflect the current understanding of low voltage DC (up to 1,500 V DC) components and materials used in the construction of PV modules arouse. This includes permitting new materials and new designs (e.g. cemented joints) while at the same time complying with international horizontal standards that need to be met in order to comply with governing national electric codes.
The principle structure of IEC 61730 is unchanged. Part 1 of IEC 61730 addresses the minimum requirements for module design while Part 2 deals with the required tests protocols and test sequences. New tests have been added to Part 2 of Edition 2 as the material requirements necessitate the confirmation of their properties during PV module operation. In addition the following objectives were set:Align the PV safety standard and its requirements with horizontal IEC standardsFull implementation of 1,500 V system voltage requirementsUpdates related to technology and material advances such as cemented joints.
To reflect and fulfil the objectives for the new standard series of IEC 61730 numerous key definitions and a detailed understanding of electro technical horizontal standards are needed. IEC defines a horizontal standard as follows:“Standard on fundamental principles, concepts, terminology or technical characteristics, relevant to a number of technical committees and of crucial importance to ensure the coherence of the corpus of standardisation documents.”
Horizontal standards are assigned by the Standardisation Management Board (SMB) with the purpose of ensuring the coherence of the corpus of standardisation documents, avoiding duplication of work and contradictory requirements, and are part of IEC Guide 108 “Guidelines for ensuring the coherency of IEC publications – Application of horizontal standards”.The most important and fundamental concepts from the horizontal standards that have to be applied to PV safety standards are the following:Concept of insulation coordinationOvervoltage categoryConcept of classes (IEC 61140)Concept of pollution degree (IEC 60664-1 Clause 4.6)Concept of material group (IEC 60664-1 clause 4.8).
How those requirements impact PV modules is summarised in Table 1 where a comparison to edition 1 of IEC 61730 is given.
Besides the implementation of horizontal standards in the PV safety standard the requirements for 1,500 V system voltage and cemented joints were requested. The system voltage highly impacts the required Clearances distance (cl) and Creepage distances (cr).  The requirements for such spacing are derived from IEC 60664 and while designing a PV module the pollution degree and material properties (material group) must be considered. Based on the installation location different overvoltage categories might apply (based on IEC 61140) but PV modules are defaulted to overvoltage category III. The combination of pollution degree, material group, overvoltage category and the manufacturer’s set system voltage clearance and creepage distances can extracted from Table 3 and 4 in IEC 61730-1. To lower the requirements for spacing the new concept of Cemented joints is introduced. This concept allows smaller spacing but requires much better and tighter production control, tolerances and material quality and homogeneity.
Due to the modifications in Part 1 also Part 2 that deals with testing requirements had gone through some revisions. The following list gives a brief summary of the changes made to Part 2 mainly including new tests:MST 05 Durability of markings: Checks for readability of the markings on the PV module before and after stress tests.
MST 06 Sharp edge test: All accessible modules surfaces should be smooth and pose no risk for injury; verified via test.  MST 13 Continuity test of equipotential bonding: Test renamed to better reflect its purpose.MST 23 Fire test: new reference, also see Appendix of IEC 61730-2 Ed. 2.
MST 24 Ignitability test: This new test determines the ignitability of PV modules by direct small flame impingement under zero impressed irradiance using vertically oriented test specimens and is based on ISO 11925-2. This is important for all polymeric materials used in a PV laminate.
MST 33 Screw connections test: Any screw connection in the module should remain secure. Tests described in MST 33 look for proper material design, installation and tightness of screws.
MST 35 Peel test: The purpose of this test is to provide confidence regarding the durability of the adhesion between different layers of the PV module stack.
MST 36 Lap shear strength test: The purpose of this test is to provide confidence regarding the durability of the adhesion between rigid-to-rigid bonded assemblies (e.g. glass/glass modules) for cemented joints of the PV module stack.
MST 37 Materials creep test: Validates that the materials used in the module will not show creep or lose adhesion when operated at the highest temperatures that modules normally experience in the field. In particular the test determines possible creep between the following interfaces: Frontsheet to backsheetFrontsheet or backsheet to directly attached mounting system (e.g. back rail)Junction box to backsheet respectively frontsheet.
The implementation of new tests is the result of changes in module manufacturing as well as requirements from horizontal standards implemented in Part 1 of IEC 61730 Edition 2. Consequently the test flow has been updated.  The latest revision includes all comments from national committees (NCs) that were received based on the drafts distributed to all NCs in spring 2014 and winter 2014/2015. The documents are currently in CDV stage.
Both standards, IEC 61215 series and IEC 61730 have undergone major revisions and have approved CDVs. The main documents (Part 1 and Part 2) for IEC 61215 as well as for crystalline silicon PV modules (Part 1-1) are submitted as FDIS (Final Draft International Standard) to IEC central office. For thin film technologies (Parts 1-2, 1-3 and 1-4) the documents are distributed as CDVs (final Committee draft for voting). Publication date for IEC 61215 is expected to be in the beginning of 2016. IEC 61730 Part 1 and Part 2 are expected to be send to IEC central office as FDIS in Q4 2015. Publication date is therefore expected to be middle of 2016.
Authored by__Dr. Bengt JaeckelPrincipal Engineer (PE) – Renewable EnergyUL International Germany GmbH

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