Something so that the long term slow generators aren't so prone to becoming time/bed = power with a single bulk investment?
Namely, some ideas being:
Water Mills: You'd have the surface of it be "overgrown with barnacles". This'll just gradually block it off and make it slower, should take a spectacularly long time to form, and take a quick second to clean out?
Wind Mills: I'm not sure, greasing? Perhaps just attracting lightning somehow would be a nice way to make "maintenance" as it is, though I don't know what else would be fitting.
Can't think of much at the moment for geogenerators, same with coal generators, which may not even need maintenance as it is. Nuclear reactors already have maintenance in spades.
Any other ideas? Do these seem reasonable?