Photo (light) + voltaic (produces voltage) = photovoltaic (PV) system
Solar cells are interconnected in a matrix to form a module. One solar cell produces electricity at a voltage of approximately 0.5 volt at room temperature, so 36 cells connected together in a module produce enough voltage to charge a 12-volt battery. However, the solar cell heats up while exposed to the sun, reducing the operating voltage to about 14-15 volts. A 12-volt battery needs about 14 volts to charge it, so the 36-cell module is the standard used in charging 12-volt batteries. The cells are connected and placed between a tough glass front and a back surface within a frame and sealed, as shown in the illustration.