UEHARA Cycle OTEC

 Experimental OTEC plants in 1970s built by various parties were all based on so-called Rankine Cycle and pure ammonia substance was used as the working fluid for power generation. The theoretical cycle itself was proved by those tests but the commercial use of OTEC technology was not verified due to inferior overall power generation efficiency owing to poor efficiency of heat exchangers of that time.

Saga University, whose business arm we are, had worked out a new system called Uehara Cycle and improved greatly efficiency of heat exchangers by deploying plate type. Thus, the commercial application of OTEC has become quite realistic.

Read more about System Comparison of OTEC Cycles

 Applicable regions of OTEC power generation

OTEC is economically feasible in any area where there is a minimum differential temperatures of 15℃ between warm surface seawater and deep cold seawater.

Fig. 1 depicts vertical distribution of seawater temperature in tropical and sub-tropical regions, Warm surface seawater is somewhere between 25 - 29℃, while deep cold seawater remains stable at 4 - 5℃ temperature. This means there is some 20℃  difference in temperature between the two, which offers the basic needs for OTEC application.

Fig. 2 shows the difference of seawater temperatures at surface and at a depth of 1000m

As you see, OTEC power generation is in principle applicable in the regions of 30 degrees north and south latitude respectively.