This use of bypass diodes 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.
solar panel with bypass diode
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.
A “solar panel” is constructed using individual solar cells, and solar cells are made from layers of silicon semiconductor materials. One layer of silicon is treated with a substance to create an excess of electrons. This becomes the negative or N-type layer. The other layer is treated to create a deficiency of electrons, and becomes the positive or P-type layer similar to transistors and diodes.
When assembled together with conductors, this silicon arrangement becomes a light-sensitive PN-junction semiconductor. In fact photovoltaic solar cells or PV’s as they are more commonly called, are no more than big, flat photo sensitive diodes.
Photovoltaic solar cells convert the photon light around the PN-junction directly into electricity without any moving or mechanical parts. PV cells produce energy from sunlight, not from heat. In fact, they are most efficient when they are cold!.. Ripple Electrical
When exposed to sunlight (or other intense light source), the voltage produced by a single solar cell is about 0.58 volts DC, with the current flow (amps) being proportional to the light energy (photons). In most photovoltaic cells, the voltage is nearly constant, and the current is proportional to the size of the cell and the intensity of the light.
photovoltaic equivalent circuit
The equivalent circuit of a PV, shown on the left, is that of a battery with a series internal resistance, RINTERNAL, similar to any other conventional battery. However, due to variations in internal resistance, the cell voltage and therefore available current will vary between photovoltaic cells of equivalent size and structure, connected to the same load, and under the same light source so this must be accounted for in the solar panel assemblies you buy.
The silicon wafer of the photovoltaic solar cell that faces the sunlight consist of the electrical contacts and is coated with an anti-reflective coating that helps absorb the sunlight more efficiently. Electrical contacts provide the connection between the semiconductor material and the external electrical load, such as a light bulb or battery.
When sunlight shines on a photovoltaic cell, photons of light strike the surface of the semiconductor material and liberate electrons from their atomic bonds. During manufacture certain doping chemicals are added to the semiconductors composition to help to establish a path for the freed electrons. These paths creates a flow of electrons forming an electrical current which starts to flow over the surface of the photovoltaic solar cell.