Ocean Thermal Energy Conversion (OTEC) utilizes the energy potential created by temperature difference between sun-warmed surface water and colder parts at the bottom to generate electricity.
OTEC uses this natural temperature gradient to drive a turbine, which is connected to a generator. It is desirable that the temperature difference between the warm surface water and the cold deep water be at least 20 degrees C.
This is what Wikipedia has to say about OTEC: “The total energy available is one or two orders of magnitude higher than other ocean energy options such as wave power; but the small magnitude of the temperature difference makes energy extraction comparatively difficult and expensive, due to low thermal efficiency. Earlier OTEC systems had an overall efficiency of only 1 to 3% (the theoretical maximum efficiency lies between 6 and 7%). Current designs under review will operate closer to the theoretical maximum efficiency. The energy carrier, seawater, is free, though it has an access cost associated with the pumping materials and pump energy costs. Although an OTEC plant operates at a low overall efficiency, it can be configured to operate continuously as a Base load power generation system. ”
This is a nascent technology, have no doubt. But the potential is significant because a very large part of sunlight falling on earth is captured by the oceans. (Oceans occupy over 70% of the total earth’s surface, so that shouldn’t be exactly a surprise!)
While I am sure there are estimates for the potential worldwide for OTEC, I would rather disregard it at the moment because this is a very nascent concept and most such estimates would prove to be close to guessworks!
I’d take estimates for India with the same pinch of salt – however, if you are looking for estimates of potential, I understand MNES has estimate that India has a potential of exploiting between 80,000 – 180,000 MW of OTEC based power. Even if it is 80 GW, it’s not a bad amount, assuming these folks indeed have done a good estimate. We have about 160 GW of installed electricity capacity, so that’s 50% of what we have today.
I’ll tell you why I find the OTEC thing quite interesting, even though it is going to be quite a while before we get the first unit of electricity from it. There are concurrent, non-power benefits from OTEC. These are the ones that Wikipedia lists: Air-conditioning, chilled-soil agriculture, aquaculture, desalination, hydrogen production and mineral extraction. I suggest you spend a couple of minutes reading the Wikipedia article.