The power system of a satellite is of pivotal importance for the functioning of all the subsystems. A satellite that has to survive for a long time in the space has to; essentially, produce its own power for its sustenance. This is done by generating electricity from the sunlight falling on photo-voltaic cells or solar panels and storing it in batteries to account for power even when the sun is eclipsed or is far away.
The solar cells serve as the primary source of power when the sun is shining. The solar panels mounted on the body of the satellite absorb the power that comes from the sunlight. The shape of the satellite maximizes the power absorbed by them. This energy is supplied for the functioning of the satellite. The rest of the energy is stored in the batteries. The power in the batteries is used when the satellite gets eclipsed by the earth, thus being unable to receive energy from the sun. It is also used when the satellite consumes more power than that is supplied by the solar cells.