There a 4 big applications for photovoltaic solar cells:

1) In space

Satellites and space explorers need an energy source for many years. Photovoltaic solar cells are ideal for space application. They don't need maintainance (this is also not possible in space), and there is sufficient sun (there are no clouds in space of course). The solar radiation is converted by the solar cells into electricity, which is stored in batteries in the satellite.

For some satellites, for example the one that is heading towards Pluto, it is not possible to use photovoltaic solar energy, because the sun is only a little dot when the space explorer reaches Pluto. In that case, a "battery" that works on the radioactive plutonium is used. Of course, when something goes wrong with the lauch of the satellite, the use of radioactive materials is dangerous. So, when possible, photovoltaic solar energy is used for most satellites.

Satellites use very efficient, very complex and very expensive solar cells. These special solar modules are too expensive for earthly use. But for a satellite, it may cost some money. Every kilogramme that has te be send into space, costs a lot of money, so to save mass, the most efficient solar celles are necessary.

2) At isolated places

3) In apparatus with a low consumtion

4) In regions with a dense electricity network