The fundamental limit to energy expenditure is not the heating and boiling of water (as others have pointed out, that energy can all be captured). Rather, the l

The fundamental limit to energy expenditure is not the heating and boiling of water (as others have pointed out, that energy can all be captured). Rather, the limit is set by the requirement for the entropy of the universe to not decrease when we reduce the local entropy in the salt-water system. According to GPT4, the numbers come out to 760 J/L for seawater with a salt concentration of 35 g/L. That would mean a limit of around 2 L/s*m2 for full intensity sunlight.