Ocean thermal energy conversion can produce net electricity, but the small temperature difference forces enormous seawater flows, large pipes and expensive offshore infrastructure that have kept OTEC from becoming a commercial-scale option.
A 100 MW net OTEC reference design requires about 705 m³/s of seawater — roughly an Olympic pool every 3.5 seconds — creating major civil-engineering demands.
Thermodynamic limits (≈6.7% theoretical efficiency between 25°C and 5°C) and real-cycle losses mean massive thermal throughput per useful MWh.
OTEC may suit steep tropical islands with deep water close to shore where electricity is expensive and seawater cooling or desalination add value, but it must compete with local alternatives.
Ocean thermal energy conversion (OTEC) relies on a straightforward idea: use the temperature difference between warm surface water and cold deep water to run a heat engine. Tropical seas can have surface temperatures near 25°C while water around 1 km depth is roughly 4–5°C. The concept has produced net electricity in past demonstrations, including projects in Hawaii and Japan, but it has not scaled to utility deployment.
The thermodynamics explain part of the problem. A heat engine operating between 25°C and 5°C has a theoretical maximum efficiency of about 6.7%. Real OTEC cycles, after accounting for heat exchangers, turbines, pumps and internal loads, land in the low single digits. Low efficiency is not fatal when the heat source is free, but it changes the engineering problem: every useful megawatt requires processing a very large amount of thermal energy.
A detailed 100 MW net reference design makes the scale concrete. It needs roughly 235 m³/s of cold deep water and about 470 m³/s of warm surface water, for a total flow of 705 m³/s. That volume equals an Olympic-size pool every 3.5 seconds and more than 24,000 such pools per day. All that water must enter through intakes, pass through large pipes and heat exchangers with manageable pressure losses, and then be safely discharged back to the ocean.
Floating platforms change the geometry but not the scale of the challenge. Shortening the horizontal run to deep water can reduce pipe length, but then a kilometer-scale intake must hang beneath a platform exposed to currents, storms, corrosion and stationkeeping loads. Heat exchangers and turbines still must move several gigawatts of thermal energy to yield roughly 100 MW of electricity, so the machinery and structural systems are substantial.
The immediate gap for OTEC is not another proof that the physics work. It is a multi-megawatt demonstration in a prime location that publishes net output after pumping loads, installed cost, maintenance data and availability, and that leads to follow-on projects. Until engineers can show repeatable, cost-competitive installations that handle the seawater-flow problem at scale, OTEC will remain a technically valid but commercially limited option.
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