OTEC (Ocean Thermal Energy Conversion) exploits the temperature difference between warm surface water and cold deep water. Warm water boils a low-boiling-point working fluid (e.g. ammonia) in a closed Rankine cycle; the vapor spins a turbine-generator, then cold deep water condenses it back to liquid to repeat the cycle.
eta_Carnot = 1 - T_cold / T_warm (Kelvin, theoretical max)
eta_actual = 0.35 x eta_Carnot (real cycle losses)
P_net = eta_actual x flow x deltaT x 40 - load x 3
- Warm surface water — higher intake temperature increases the theoretical Carnot efficiency ceiling.
- Cold deep water — colder deep intake widens ΔT, the main driver of usable power.
- Working-fluid flow rate — how fast ammonia circulates through evaporator, turbine and condenser; spins the turbine faster.
- Turbine load — electrical load applied to the generator; too much load stalls the turbine, too little wastes potential power.
Real-world: tropical OTEC plants (Hawaii, Japan) exploit typical ~20°C gradients between surface and 1000 m depth to generate steady baseload renewable electricity, unlike intermittent solar or wind.