- Rectifiers and Diodes
Photovoltaic (PV) modules are composed of many individual solar cells that are arranged in such a way as to achieve desired voltage and current output. The system needs to be protected against reverse current flow in order to avoid dissipating the harvested energy as heat. To simplify the wiring of the cells, bypass diodes must be placed in proximity to the panel in the “junction box” that is typically made of plastic and mounted on the rear side of the panel, and thus exposed to rather high temperatures with limited heat dissipation capabilities. Schottky diodes are well suited and widely adopted for this application because of low conduction losses. The preferred package is axial, but new designs are going to SMD parts. Crystalline PV Modules use the junction box to connect the PV solar cells as strings to the inverter system. The bypass diodes are integrated into the junction box parallel to the strings in order to optimize the generated power of the PV module, even when part of the module is not working due to shadow effects, and to protect the non-working cells against overheating and hot spots. Newer trends involve separating the junction box and the bypass diodes and integrating the diodes into the PV module. Thin Film PV Modules require so-called ""blocking diodes"" between the PV module connectors that should withstand the maximum ""system voltage"" of the PV equipment, which can reach 1000 V. For improved efficiency, some designs use Schottky bypass diodes not only for the strings as in the crystalline concept, but also use several bypass diodes integrated into the module for a group of PV solar cells. Concentrator PV Modules are built with high concentrating lenses that project solar light onto a small solar cell that is mounted on a ceramic substrate. The application requires high-current Schottky bypass diodes and sometimes require ""bare dies"" for direct mounting on the ceramic substrate.
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