The more I think about it, the more I am beginning to see the reasoning behind your suggestion.
No matter how weak "free" energy is, players can always just build bigger and bigger generator arrays. If there were no solar or wind, players would flock to water instead. It allows the creation of "fire-and-forget" power systems that just feed you infinite energy.
That being said, I don't like the idea of banning them outright. It would practically remove the core of this mod. Perhaps if the renewable energy generators had some sort of ongoing cost or risk instead?
example maintenance cost: Generators containing inverters that wear out every 5 million eu (approx 69.4hrs of continuous operation for a solar panel).
example risk cost: Outdoor generators getting damaged by thunderstorms. Doesn't happen often, but requires some time spent repairing them when it does.
This would leave renewable energy as far far more efficient than standard generators, but they would still require some ongoing time investment to keep it functional.