You can, it's called OTEC: https://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion https://en.wikipedia.org/wiki/Ocean_thermal_energy_conversio... Just

You can, it's called OTEC: https://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion https://en.wikipedia.org/wiki/Ocean_thermal_energy_conversio... Just like this scheme, it's not very economically efficient. Carnot efficiency is proportional to the temperature ratio between the hot end and the cold end in degrees Kelvin. If both temperatures are in the 200's, then efficiency will be low. OTEC does provide lots of potable water though, so that's one advantage.