You've misremembered/misunderstood this, I think. You can certainly use self-generated electricity directly, pretty much everywhere. In many places you will need some sort of permit/inspection if you're self-generating and connected to the grid, though, because if done incorrectly that's potentially dangerous (in particular, in a power cut either you need to self-isolate or switch off your self-generation, because otherwise lines will unexpectedly have current.)