1 Photovoltaic connectors and power station benefits
Usually, photovoltaic modules, inverters and combiner boxes are the main focus of daily maintenance of photovoltaic power plants, while the failure risk of some small components is easily overlooked, and photovoltaic connectors are the most representative cases.
The photovoltaic connector accounts for less than 0.5% of the initial investment cost of the system, but it is a key component of the photovoltaic system, which ensures that the power generated by the system can be stably transmitted from the components to the inverter and the user. Without a reliable electrical connection or connector failure, the power generation capacity of the power station is affected, and the owner cannot receive a stable subsidy, which will also lead to a decrease in the profitability and return of the power station. According to the actual operation and maintenance data of 746 power stations, the EU Hor izon 2020 "SolarBankability" project team gave a list of TOP20 technical failures in power station operation and maintenance. "Broken and burned PV connectors" is No. 2 on the list of failures.
The profitability of a power plant is closely related to the selection of high-quality components. It is not wise for homeowners to save money on PV connectors. Because, not focusing on quality usually means subsequent high losses and risks that could have been avoided. The low contact resistance and long-term reliability of photovoltaic connectors can ensure the efficient and safe operation of the power station. The continuous increase of contact resistance will lead to a significant increase in the safety risks of photovoltaic projects and reduce the operating efficiency of power plants.
2 Analysis of the Failure Causes of Photovoltaic Connectors
The following three reasons for the failure of photovoltaic connectors - poor quality, mutual insertion of photovoltaic connectors and irregular installation are analyzed.
2.1 Poor quality
From the appearance and texture of the photovoltaic connector, you can roughly understand the shape design of the product and the selection of insulating materials. However, the core indicator for evaluating the quality of photovoltaic connectors is the contact resistance after the male and female connectors are inserted into each other. A high-quality connector must have very low contact resistance and be able to maintain this low contact resistance state for a long time. According to the latest international standard IEC 62852 for photovoltaic connectors, the contact resistance after male and female mating is tested by TC200+DH1000, the increment cannot be greater than 5 mΩ or the final resistance value is less than 150% of the initial value. And this is only the minimum requirement, the contact resistance value of the connector of different manufacturers depends on the technical level of the manufacturer.
2.2 Interconnection of photovoltaic connectors
During the construction of photovoltaic power plants, the phenomenon of inter-plugging of photovoltaic connectors of different brands is common. In some power plants, components, inverters and combiner boxes use connectors from different manufacturers. EPC companies also sometimes purchase photovoltaic connectors separately, which may involve inter-plug issues. The reason for inter-plugging is that customers do not understand the risks of inter-plugging, and the other reason is that some manufacturers make claims such as "MC4 compatible" or "MC4 intermateable". What needs to be explained here is that everyone calls the connector "MC4", but in fact MC4 is a connector product launched by Stäubli in 2002. become an industry standard or norm. In this way, the so-called compatibility or mutual matching concept will appear in the market.
Both UL and IEC clearly stipulate that photovoltaic connectors from different manufacturers are not allowed to be inserted into each other. At the same time, laboratory and field data do not support inter-plugging. Reasons for not recommending inter-plug include: differences in technology and product materials, differences in production processes and quality standards, inconsistent tolerances, and different raw materials. In addition, it should be pointed out that the mutual insertion of photovoltaic connectors will lead to the invalidation of IEC 62852 product certification, resulting in technical and legal risks. If a fire is caused by the mutual insertion of photovoltaic connectors, and then the court case, the cost will be very expensive, and it will be time-consuming and labor-intensive.
After the photovoltaic connectors are inserted into each other, although the connection is completed on the surface, the hidden danger of mutual insertion already exists. The mutual insertion of photovoltaic connectors will lead to problems such as temperature rise, contact resistance change and IP protection level cannot be guaranteed. In severe cases, fire will occur, which will affect the power generation efficiency and safety of the power station.
2.3 Irregular installation
Irregular installation is another risk that affects the overall functionality and profitability of PV power plants. The irregular installation here usually refers to irregular crimping, especially the crimping of photovoltaic cables and the metal core of photovoltaic connectors. On-site workers sometimes directly use inferior or even general-purpose tools for crimping, which is difficult to ensure the quality of crimping, which is easy to cause poor crimping, such as bending of the copper wire of the cable at the joint, part of the copper wire not being crimped in or mistakenly pressing the cable insulation layer. .
Improper installation and poor crimping can result in the following: non-compliant standards, unstable contact resistance, and seal failure. Therefore, Stäubli recommends using professional crimping tools and following the manufacturer's installation instructions to ensure a safe and regulated installation.