Vinay offers us some great leads on ocean thermal energy conversion (OTEC). OTEC uses the temperature differences between deep cold water and warm shallow water to create power. It's still more theory than practice, but the possibilities are pretty wild - including the use of "large, grazing plantships to produce hydrogen, ammonia, and methanol" or desalinization plants that'd combine energy production, clean water generation and fishfarming. Worth keeping an eye on....
(Thanks, Vinay!)









