Keys to ensure the quality and safety of modules

Manufacturing process 

Years ago, photovoltaic modules were not manufactured to such exacting norms and standards as they are today. Often, the manufacturing process ended with placement of the frame, and the manufacturer dispensed with the junction box, cables and connectors, which were added later. 

However, during exposure to the elements over the years, it was evident that modules suffered from a multitude of defects, such as hotspots, delamination, corrosion and other defects, which broke the modules. They even caused fires, since elements added later could not guarantee the module's watertightness; water, air and particles entered the modules and caused irreparable damage. Over the past 30 years, manufacturers have been learning from defects that arose over long years of exposure to climatic agents, and have optimized their materials and methods; today, the photovoltaic module is the end product of a sophisticated production and assembly process. 

Fabrication and assembly 

Starting from the central array of photovoltaic cells, welded together, 2 layers of EVA, the back sheet and the front glass are added, providing rigidity to the module with the aluminum frame. During the process, any impurities are removed, air and moisture are extracted and the assembly is sealed with silicone. 

The junction box, cables and connectors are then added to the back. To ensure the module is watertight, the connection between the junction box and the module is sealed with silicone. It is a delicate operation that must be welded with great precision. The quality of this process is crucial, as all the current from the module will be conducted through the junction boxes. Minor defects can have fatal consequences. In the field, poor weld quality is often one of the most frequent causes of failure and damage. A complete PV module leaving the factory must be prepared to withstand 25 years and more without problems and all types of climatic impacts, in addition to direct solar radiation, to generate electricity. 

IEC Standards 

Apart from the manufacturing process, which is individual to each manufacturer, international standards are intended to ensure the quality and safety of PV modules. IEC standards are of particular importance for use in Europe. For the Americas, and specifically Mexico, UL standards are emphasized, although IEC standards are also important. Both entities attempt to harmonize standards, and it is common for a UL standard to have its IEC equivalent, as we can see in the standards we will discuss, IEC 61215 and IEC 61730. 

The International Electrotechnical Commission (IEC), an independent, multinational body, has developed many norms and standards. The most important of these for PV modules are IEC 61215, on design qualification of photovoltaic modules, and IEC 61730, on operational safety. In addition, IEC will soon publish an updated standard unique to junction boxes, IEC 62790, which defines the tests that must be passed without failure, underscoring the importance of this component. 

Each module that does not meet these standards constitutes a potential risk to the PV plant, so many legislators require that PV modules installed in their national territories meet these standards. For testing, the manufacturer sends manufacturing samples, chosen at random, to an independent laboratory. This laboratory performs the tests, defined in IEC standards, to check the quality of the photovoltaic module or component, and its ability to operate without failure for such a long time. In the case of modules, after exposure to a test, the actual power is measured to verify that the test will not damage the modules.

Safety tests

During the tests, modules are pelted with snowballs, exposed to extreme heat and cold, or covered with flames, as shown in the picture below.

Another example is the MST 17 test, which tests the tightness of the modules against leakage currents, which are very dangerous for plant safety, as they can cause electric shocks and endanger the lives of professionals, especially during maintenance.

As shown in the picture, the entire PV module, including junction box, cables and connectors, is immersed in water, a voltage is applied and any deviations are measured. Only watertight modules pass these tests.

Conclusion 

If the PV module is to serve for a long time without causing problems, its integrity must be guaranteed from the outset. This requires the manufacturer to produce photovoltaic modules that are watertight sets of cells, EVA, backsheet, frame, junction box and other elements. This is the only way the module can be operated safely and at maximum performance throughout its service life. Any noncompliance with these requirements jeopardizes the plant profitability and people's health, and must be strictly avoided.