Where do defects show up in solar modules? Which cells contribute to producing energy? Are there parts of the cell that function in a restricted way, or not at all? Manufacturers and developers have faced such questions since the birth of this innovative technology. For the first time, they have the technical means to answer them. Thanks to electroluminescence imaging of solar cells and solar panels, it is now possible to provide more certainty about the quality of individual cells. Director of the Research Department at PCO, Dr. Gerhard Holst, explains how highly-sensitive cameras reveal production errors in photovoltaic modules.
The more photovoltaics are used, the more important it becomes for the manufacturing of solar panels to be efficient and error-free. Producing solar panels is a complex process with numerous sources of defects; micro-cracks, damage in the coating of the surface and faulty edge isolation are some of the most common defects.
Micro-cracks can develop during the “burning”, i.e., the strengthening of the printed electrodes in the oven. They can become a big hindrance for generating energy and, in extreme cases result in the total malfunctioning of the solar panel. A second possible explanation for the solar cell’s limited efficiency is manufacturing errors in the panel’s anti-reflex coating. This coating ensures that as little sunlight as possible is reflected on its surface during the operation of the solar panel. Light is only turned into electricity if the light actually hits the cell. A third common source of defect is edge isolation. Although the individual cells within a panel lie close together, they should not touch each other. If they do, as a consequence of faulty isolation, this can lead to a short circuit.
Researchers and developers still have little knowledge about how to recognise possible defects on a solar cell or a solar panel before the errors become visible. Until recently, the technical possibilities to visualise manufacturing errors in solar cells did not exist. Today, there are special optical systems, for example the scientific cameras made by PCO, that can visualize such defects. The key difference is a highly sensitive image sensor which allows these cameras to capture and photograph near infra-red light.
