

they might have done it this way because hydro, nuclear (or any steam turbine based) or gas (or any gas turbine based) generation is rotating generation, which helps to stabilize grid in a way that solar or (some of) wind power doesn’t. on top of that, many of solar installations won’t output energy without mains (grid-followers). getting rid of that would be a is a complex problem that would require infrastructure buildout and policy changes
you can just put a flywheel on synchronous machine and it also works, especially where you have infra left over after coal plant shutdown or something similar