In a large photovoltaic solar panel array, each solar photovoltaic module is connected in series and in parallel. A group of solar cells or solar panels connected in series is called a “string”. The combination of series and parallel connection may cause some problems in the solar panel. A potential problem arises from the open circuit of one of the series groups. The current from the parallel series will be lower than the current from the rest of the solar modules. This is electrically the same as the case where a shaded solar cell is connected in series with several good solar cells, and the power of the whole solar cell will be lost.
If the bypass diode rating cannot handle the current of the entire parallel solar panel array, the combination of parallel connection and mismatch effect may also cause problems. For example, in the parallel series of the series solar panels, the bypass diodes of the series mode solar charging panels become parallel. The mismatch of the series solar PV modules will cause the current to flow in the bypass diode, heating the diode. However, heating the bypass diode will reduce the effective resistance. Most of the current will now flow through a slightly warmer set of bypass diodes. These bypass diodes then become hotter, further reducing their resistance and increasing the current. Eventually, almost all of the current flows through a set of bypass diodes. If the rating of diodes cannot handle the current from the parallel combination of solar panels, they will burn out, causing damage to photovoltaic solar panels.
In addition to using bypass diodes to prevent mismatch losses, an additional diode, called a blocking diode, can be used to minimize mismatch losses. Blocking diode is usually used to prevent the solar panel from loading the battery at night and prevent the current from flowing through the photovoltaic array. For parallel components, each string to be connected in parallel shall have its own blocking diode. This not only reduces the current carrying capacity required to block the diode, but also prevents the current from flowing from a parallel string to a lower current string, thus helping to minimize the mismatch loss generated in the parallel array.
If you want to know more about solar panels (single crystal, polycrystalline, Sunpower) and solar folding packs, please contact Shenzhen Huanqi Solar.