Floating power generator should be added to FA eco buildings.
For example, it could look like this:
T1 Floating Power Generator aka FPgen.
Mass cost: 90m (20% higher than land-based T1 pgen)
E-cost: the same T1 pgen.
Energy production: +20
Why this should be available and a few points to consider:
1) Most importantly, this would make landless water maps playable. In a landless map, you can have unique dynamics for a navy game: f.e. no low tech air units are available early on and hover flak/shields are not available.
2) The concept has already been tested in Total Annihilation. There was a floating pgen (called Tidal Generator) and there was at least one popular map (Brain Coral) where there was no land at all. I see no reason why the same concept couldn't work in FA. (well, nuke subs would probably be an issue since there is no water-based antinuke...)
3) The pgen should be done in a way that it doesn't affect the existing balance: it could produce the same 20 e as t1 pgen does, but cost 20% more or so. This way it would only be useful when land based power is not available.
4) One balance issue to be considered: In some watery land maps, like Finn's Revenge, water pgens are better protected against land units (can't be reached) and thus, the higher cost should be a compensation for this advantage.
5) The water pgen should be floating, not submerged. This way the floating pgen would be visible to a standard t1 air scout the same way t1 land based pgen is. If it was submerged this would make it harder to find and t1 air units could not hit it. It would affect the balance too much if it was submerged.