Assuming maximum efficiency is not the primary concern (but net positive efficiency is), to what extent could a wind turbine operate in water and vice versa?
How do the different turbine types fare in this respect? I.e., HAWT / VAWT (Savonius, Darrieus, Gorlov) for air turbines, reaction (Francis, Kaplan, Gorlov) / impulse (Turgo, Jonval) turbines (Pelton wheels are probably out) for water turbines?