In the past it was only possible to generate electricity with a diesel generator in regions without grid access or where connection to the grid is very expensive, which is both noisy and causes environmental pollution.
Now you can generate energy yourself with a stand-alone system.
If you already have a generator and install a PV system it is like having access to the grid. When the weather is overcast or the battery power is exhausted, the system simply switches over to the generator.
These days, even without grid access, you can have electrical power.