Application Notes

During construction of solar modules, single cells are switched in series to so called “strings” to achieve higher system voltages.

If one or more cells are shaded (e.g. by branches of trees, antennas, etc.), the affected solar cells are no more acting like a current source, but as power consumers. Non-shaded cells are delivering further current through them, generating high power losses. “Hot spots” may occur and even cell breakdowns.

To overcome this problem, bypass diodes are switched parallel to every single or some combined cells, bypassing current flow across the darkened strings.

Like every semiconductor device, also bypass diodes have got a certain leakage current, which in normal mode of operation reduces the current supplied by the cells and therefore decreases efficiency of the solar module. Therefore leakage current especially at higher temperatures (full sun irradiation!) should be as low as possible. Compared to that, partly shading of modules is only an extreme operation mode which should be completely avoided or at least occurs only during short time periods. For this mode of operation, low forward losses are desirable.

Finally, the bypass diode has to be rugged against overvoltage spikes. Such spikes may occur during assembly of the system, if
e. g. current conducting cables are interrupted, or during operation, caused by lightning etc.

You will find more information in our Application Note Solar Bypass Diodes - you can download the PDF down below.