Bypass diodes, also known as free-wheeling diodes, are wired within the PV module and provide an alternate current when a cell or panel becomes shaded or faulty.
Why do solar panels use bypass diodes?
This use of bypass diodes in solar panels allows a series (called a string) of connected cells or panels to continue supplying power at a reduced voltage rather than no power at all. Bypass diodes are connected in reverse bias between a solar cells (or panel) positive and negative output terminals and has no effect on its output.
How do bypass diodes work?
Bypass diodes are connected in reverse bias between a solar cells (or panel) positive and negative output terminals and has no effect on its output. Ideally there would be one bypass diode for each solar cell, but this can be rather expensive so generally one diode is used per small group of series cells.
When is a bypass diode blocked?
The bypass diode is blocked when all cells are illuminated, and conducts when one or several cells are shadowed. Figure 5. Bypass diodes are rarely mounted directly on the solar panel. They are soldered in a so called junction box that is placed at the rear of solar panel.
The bypass diode can possibly be damaged when the output voltage of the solar cell block is greater than the breakdown voltage from power dissipation. The equation for power dissipation is Pd = VBR x IBR, where VBR = breakdown voltage, and IBR = current at breakdown status. 3. Reverse Leakage Current
It is defined by the cell manufacturer and is the minimum value of the manufacturing distribution. Figure 7. Considering poly-silicon solar cells with a breakdown voltage Vc of 12 V and a bypass diode forward voltage VF of 0.5 V, the maximum number nmax of solar cells bridged by the bypass diode is 24.
In regular operation the diode is reverse biased with a small amount of leakage current (Fig. 2 - quadrant 3). In the solar cell bypass function, the breakdown voltage of the diode is always higher than the total output voltage in VOC of the solar cell in the string which is paralleled with the bypass diode.