A bypass diode is a diode that is connected across a circuit or module and then conducts as soon as the circuit is supplied with a reverse voltage or has negative effects on other circuits.
Inphotovoltaic systems, a series connection of several solar modules is called a string. This series connection has the disadvantage that the weakest link, in the case of the solar module the solar cell with the lowest energy yield, determines the current flow.
This means that individual soiled or shaded solar cells negatively affect the current flow in the entire solar module and thus reduce energy production. To avoid this, there are bypass diodes in parallel to all solar cells, which become active when a solar cell reduces the total current flow. The bypass diodes protect the solar cells from thermal overload.
The current of the other solar cells is then bypassed via the bypass diode connected in parallel without affecting this solar cell. Bypass diodes are also available as module bypass diodes and string bypass diodes.