Power plants are modules that provide the ships and bases with the energy needed for their operation. There are several types:
Fission and fusion reactors produce a fixed amount of energy. In contrast, solar plants produce an amount of energy that is determined by the distance to the star, which makes them useless for spacecraft that usually move very large distances from the stars.
Fission reactors occupy little space and need a large amount of [radioisotopes]. Fusion reactors occupy a larger volume, but consume huge amounts of water. The fuel is deducted during the construction of the module, so it is not necessary to provide fuel to the rectors later.
Solar plants can be very useful and inexpensive when they are installed on bases close to the star, being able to produce enormous amounts of energy.