Electricity from the solar (photovoltaic) panel is used in the process of electrolysis to split water into hydrogen and oxygen gases. 

The hydrogen is used as fuel in the fuel cell.  The process that takes place in the fuel cell is the opposite of electrolysis: the hydrogen gas is combined with oxygen to make water and to produce electricity.

In this demonstration, the electricity produced by the fuel cell is used to operate a fan.  The fuel cell has a typical efficiency of about 50%.

This apparatus uses Proton Exchange Membrane (PEM) technology.  A PEM is a proton-conducting polymer membrane that is covered with a layer of catalyst material on both sides.  The two layers form the cell's cathode and anode. One PEM is used to separate the hydrogen and oxygen from the water, while the second PEM is used to recombine the hydrogen gas with oxygen gas to form water.