Due to the “arbitrary” nature of renewable energy sources, they’re only available at certain times and in particular quantities. That is, they can’t be considered a continuous, on demand power source. Power generation systems based on renewables usually use an electronic power converter as an interface between the power source system (solar, wind, tidal…).
Generally, when these units are designed, the interface systems are created to connect to an already existing “master” network. Renewable systems inject power upon the reference voltage and frequency of a “master” network but, if a breakdown causes this network to fail, these systems stop operating, they’re not capable of managing the network as masters, and their power availability doesn’t allow this either.
When the renewable power generation system is located in an isolated or weak electrical network, the use of generator sets becomes vital in order to guarantee a stable and reliable power supply. That is because the generator set is capable of generating a “master” electrical network, defining the network’s voltage and current.