Following the construction of an OTEC prototype by DCNS in Indian Ocean Island of La Reunion in May, 2012, three tests have recently been conducted been conducted. DCNS is a naval defense company based in France. The three configurations were tested by DCNS in collaboration with the University of Réunion Island’s Laboratory of Physical and Mathematical Engineering for Energy and the Environment focused on the configuration of the heat exchanger, specifically the evaporator, which has the greatest potential for improvement.
- The first test was with a shell and tube heat exchanger with the seawater flowing through the tubes and the working fluid in the shell. Despite very predictable thermodynamic behavior with this configuration, the thermal output was not comparable with other heat exchangers on a similar scale.
- A second test was done with a shell & tube heat exchanger, this time with the seawater flowing through the shell and the working fluid through the tubes, maximizing evaporation. However, this setup requires a circulation pump for the working fluid in the tubes, consuming a portion of the electricity generated.
- A third test used a plate heat exchanger. The vapor leaving this heat exchanger contains liquid droplets, requiring a downstream separator. While this setup is more complicated, it results in the greatest thermal power output.
The prototype is not yet connected to the sea, instead using hot and cold water supplied by a heat pump at reasonable ocean temperatures. The ultimate goal within the next 20 years is to implement this technology with the design, construction, and operation of a 1000-meter-long pipe that is several meters in diameter.
In parallel with these developments, a 10MW OTEC pilot plant is under way in the Caribbean Island of Martinique. This project will have a nominal installed capacity of 14 MW and a net power of 9.5 MW generated in an ammonia closed loop Rankine cycle with four turbo-generators. The inlet pipe is a 6 meter diameter riser spanning 1.1 kilometers in depth. Unfortunately this project suffers from delays due to the weak returns from the sale of carbon emission permits under the European Commission’s NER300 financing package. The collapsing carbon prices that are now at record lows results in very uncertain funding from the NER300 call.