here is a scheme, similar to one I and many other people had independently thought up, to generate electricity from the temperature difference between the water deep in the ocean and that of its surface water:
This isn't a new idea and many people had independently thought up similar schemes in the past.
I think this could have great potential but it should also come with a small note of caution:
if it is ever done all over the oceans world wide on too much on a large scale, it would have the effect of reducing the average temperature difference between the deep water and surface water as well us reducing the rate of heat loss through surface water to the atmosphere due to lowering of surface temperature and those two effects combined would indirectly cause a net thermal expansion of the water of the oceans that would cause a sea level rise sufficient to cause problems.
Thus, although I think this source of power should be explored and probably even exploited, it should be exploited only sparingly and with limits placed to its applied scale. Perhaps it should be set up so it is only turned on to produce power whenever we are currently struggling to get enough power from other renewables (and not cause any heat exchange while it is turned off ) and thus reduce the need for expensive off-the-grid energy storage?