From Solar Cells to Solar Modules

A solar array consists of many solar modules, whereas a solar module consists of many solar cells/wafers.  Solar cells can be connected in series or in parallel.  In series, the voltages add up, while in parallel, the currents add up (see diagrams above).  Physically, a series connection involves connecting the bus bars of one solar cell to the back contact of another solar cell.

There is also an additional bypass diode connected to each solar cell as shown in the diagram above (where the 6th cell is shaded).  This is to overcome the situation where one or a few solar cells are shaded and hence produce less power.  This situation will result in less current and voltage from these shaded cells, and hence, the shaded cells will operate in reverse bias from the current driven by the non-shaded cells.  The effect is shown in the diagram below (for the situation shown in the diagram above).  Continuous shading will result in power dissipation through overheating of the shaded cells, which may damage the shaded cells.

Reference:
4.5 From Solar Cells to Solar Modules, Delft University of Technology, https://www.youtube.com/watch?v=VqfcnbyPDCA