Getting energy from the middle of the oceans provides one more opportunity to address the problem of sea level rise. Convert liquid ocean volume to gas by electrolysis and transport the energy/water currency – Hydrogen – to shore. Or as others prefer produce NH3 or CH3OH as the energy carrier.
Engineers look at EROI, while disregarding the $28 trillion in potential damage to coast infrastructure the insurance company Allianz has identified and strorms like Hurricane Sandy presage.
OTEC mitigates this problem five ways:
- converting heat to work to lessen thermal expansion.
- desalination with the open cycle.
- electrolysis to convert liquid volume to gas.
- moving surface heat to the depths where the coefficient of expansion is half that of the tropical surface, and
- sapping the tropical energy of storms that move the heat to the poles that is melting the icecaps and the permafrost.
Conventional OTEC structure are massive and costly as a consequence of the need for massive movements of water. For a 50MW plant this is about 400m3/sec. Using a heat pipe design however – moving heat by phase changes of a working fluid you can produce 50MW with the movement of only 8m3/sec of ammonia in a closed system that avoids environmental damage. This reduces the size of the piping one order of magnitude with a commensurate reduction in cost.
By using a counter-current heat transfer system diagramed in this link, as does a typical heat pipe, you also limit the amount of heat transferred from the surface to the depths and thus you maximize the amount of energy you can produce. With such an approach, 25TW would be a lower limit because with an ideal heat pipe the amount of heat taken in at the evaporator end equals the amount lost through condensing end. With conventional OTEC you move 20TWh to the depths to produce 1TWe. With the heat pipe and counter-current you extract 2TWh from the surface, produce 1TWe and dumpt 1TWh to the depths.
OTEC will have a meaningful impact on global warming because first it is carbon free and combined with 25 plus TWh conversion you get a reduction of about 40 ppm of CO2 every century once you stop adding CO2 to the environment. In 300 years you would be back to pre-industrial concentrations and in the meantime you would be extracting the excess heat from the oceans that is doing all the damage.
Current projections are global warming is locked in for 1000 years after CO2 emissions are completely stopped and that the seas will rise an additional 320% this century due thermal expansion.
The problem is accumulating heat in the oceans.
It is hard to see how you address climate change by avoiding the problem.
There is no question the use of energy on land adds to the problem but I don't think you are going to prevent the energy deprived from seaking to thwart their deprivation.
You can fill there need, say 30TW, with nuclear or fission and add an additional 60TW of waste heat to the ocean or take that 30TW out of the ocean in the first place.
To my simple mind the answer is fairly obvious. It is ocean energy reduced on investment.