In photovoltaic systems we often hear about diodes but sometimes there is confusion as the functions and peculiarities of thediode is bypassed mounted in the junction boxes behind the solar panels with iblocking diodes which should instead be inserted, se serve, on parallel connections of multiple panels. Let's analyze the function of both in detail:
DIODI BYPASS: they are installed in the junction box behind the solar panel and serve to safeguard a panel from possible overheating effects due to the shading of some cells as well as ensuring better productivity of the system. Such diodes areconnected in parallel relative to the panel and when there are shaded cellsthey work as an alternative to the cells themselves, i.e. if the diodes are active the cells are bypassed and vice versa if the cells are supplying the diodes are not active.
Therefore they, when they are activated (in the presence of shadows), they have a double function:
– they allow the bypass of the shaded cells to prevent them from overheating while acting as a load.
– if there are multiple panels in series they prevent the shaded cells from blocking the string entirely.
The bypass diode therefore when activated protects the shaded cells from overheating and at the same time avoids (bypassandole) that a few shaded cells completely block the solar system's production.
USE: the function of bypassing the shaded cells that do not produce is all the more important the longer the string of solar panels, i.e. the increase in the number of panels connected in series; therefore whether 12V or 24V is used in a given applicationa single photovoltaic module the presence of the diode is totally irrelevant: in fact if the diode is activated bypassing the shaded cells, the panel voltage typically drops by half so it is no longer sufficient to charge the battery… so the advantage of bypassing the shaded cells is effectively lost.
BLOCK DIODES OR STRING DIODES they are used to solve any problem due to the parallel connection of strings of photovoltaic panels when one or more of these are less exposed to sunlight than others. In this case there is the possibility that these partially suck the energy from the well exposed strings. These diodes, block sayings, they must be connected in SERIES to the strings, on the output positive of each string. These diodes have the function of “non-return valve” that is, they only allow the string to supply current, preventing any energy input (forced by other strings). With these diodes, if strings with different voltages are placed in parallel, the one with higher voltages is prevented from transferring part of the energy to the string with lower voltage, somehow guaranteeing independence between the strings connected in parallel.
