Abstract
Solar cells represent one of the most important sources of clean energy in modern societies. Solar cell manufacturing is a delicate process that often introduces defects that reduce cell efficiency or compromise durability. Current inspection systems detect and discard faulty cells, wasting a significant percentage of resources. We introduce Cell Doctor, a new inspection system that uses state of the art techniques to locate and classify defects in solar cells and performs a diagnostic and treatment process to isolate or eliminate the defects. Cell Doctor uses a fully automatic process that can be included in a manufacturing line. Incoming solar cells are first moved with a robotic arm to an Electroluminescence diagnostic station, where they are imaged and analysed with a set of Gabor filters, a Principal Component Analysis technique, a Random Forest classifier and different image processing techniques to detect possible defects in the surface of the cell. After the diagnosis, a laser station performs an isolation or cutting process depending on the detected defects. In a final stage, the solar cells are characterised in terms of their I–V Curve and I–V Parameters, in a Solar Simulator station. We validated and tested Cell Doctor with a labelled dataset of images of monocrystalline silicon cells, obtaining an accuracy and recall above 90% for Cracks, Area Defects and Finger interruptions; and precision values of 77% for Finger Interruptions and above 90% for Cracks and Area Defects. Which allows Cell Doctor to diagnose and repair solar cells in an industrial environment in a fully automatic way.
Highlights
Solar power is the fastest-growing source of new energy according to the International Energy Agency
These results show that a significant part of the pixels detected as Finger Interruptions or Cracks, are False Positives
Cell Doctor cannot be directly compared with recent works, since they not provide pixel metrics, usually reduce the problem to binary classification, use different types of solar cells and in most cases provide only partial results, being Accuracy and Precision the most common metrics
Summary
Solar power is the fastest-growing source of new energy according to the International Energy Agency. PV employs solar panels composed of solar cells made of semiconducting materials to convert light into electricity. The main component of conventional solar cells is crystalline. Monocrystalline silicon (mono-Si) cells present an octagonal shape cut from cylindrical ingots and an uniform look that indicates high-purity. Polycrystalline or multicrystalline silicon (multi-Si) cells have a square shape and present a “frost” texture caused by different crystals molten and solidified together. Making polycrystalline silicon is simpler and costs less, but multi-Si cells are less efficient than mono-Si cells. Busbars act as conductors for the current produced from the incoming photons that are connected by perpendicular thinner strips called fingers that collect the current and deliver it to the busbars
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