Thanks to an innovative airlift and water ducting system, the TU Delft team came up with a design that may finally mean a kick-off in Ocean Thermal Energy Conversion (OTEC). The research of Berend Jan Kleute (MSc Offshore Engineering), George Dodoros (MSc Management of Technology), Jody Verpoort (MSc System Engineering, Policy Analysis and Management) and Yosef Safi Harb (MSc Aircraft Design) shows that OTEC is more attractive than the two main competing sustainable energy sources (wind and solar) for Curacao, one of the Islands of the Netherlands Antilles. Further on you can read which inovations may let their dOmeTEC design overcome the challenges of high technical riscs, substantial capital investments and significant environmental impact which have until now withheld commercial applications of OTEC.

Intro

Ocean Thermal Energy Conversion (OTEC) is a method for generating electricity using the thermal potential (temperature difference) from the upper and lower sea waters. The thermal potential drives a Rankine Cycle, which produces electricity (think of an inverted refrigerator process). Interesting areas for OTEC applications are in the equatorial zone, where the thermal potential is highest.

History

OTEC is an advanced technology having a long history of developments. Since 1800 there have been several attempts to develop and refine the OTEC system. So far, these attempts were purely experimental and consisted of demo plants, which were too small to be scaled to commercial size systems. Besides that, most systems were not successful due to economical and technological difficulties, like shortly mentioned in the first section.

Current situation

The situation is changed now. Renewable energy is in the spotlights, offering opportunities for the OTEC technology. Developments such as the rise of the fossil fuel prices and an increasing knowledge in the offshore industry, result in the OTEC system to be economically more attractive and technologically more feasible.
Although, the commercial interest in the OTEC system rises, several remaining difficulties and challenges keep the industry from investing. In general these are:

• The environmental impact (biofouling, large seawater flows);
• Required capital investment (5-11 million $ per MW);
• Technical risks (deployment, environmental loading, size, efficiency).

To proceed beyond the experimental phase and towards commercialization, innovative solutions for these problems are required.

Technological challenges

The main challenges can be specified for the key components of the OTEC system:

Innovation!

Innovation is the key to tackle the problems. Focusing on the key components, various concepts were analyzed in detail and optimized using simulation programs. A extensive selection resulted in the final concept, with the following innovation incorporated:

Dome: The Dome is a strong & lightweight structure providing a cheap solution for protecting the heat engine against environmental influences.

Airlift system: The design is equipped with an airlift to drive the cold water flow of 22m3/s. An air fraction equal to 0,2 is injected inside the pipe at 5 meter below sea level, so the column weight of water inside pipe is decreased and a sufficient flow is maintained. With a power consumption of only 0,5MW, the innovative application of the airlift within OTEC provides the best performance, compared to alternatives like the centrifugal pump.

Water ducting: The seawater flows are arranged in such a way that the influence on the environment is minimized. This is done by enabling the warm water to flow in over the whole circumference of the warm water reservoir. Furthermore, the discharge of both the cold and warm water is arranged via two 3m diameter pipe, which injects the mixture back to 200m depth. At this depth the temperature is around 15 degrees Celsius, which is equal to the mixture temperature.

Each of these innovations contribute significantly to an improvement in the OTEC system performance. Thereby, the CAPEX is significantly reduced. This innovative design proves OTEC to be a technical and economical feasible solution!

The solution!

The dOmeTEC design is the solution for an innovative and low cost 10MW OTEC Power Plant for Curacao. Integrating the innovations as mentioned above will optimize the operating performance, resulting in a relative high system efficiency of 3,4% and with a gross power of 11,16 MW. Thereby, the significant reduction of the OTEC capital investment result in a CAPEX of 77 Million USD with a break-even time of 5 year, showing OTEC to be an economical viable and technical feasible solution.

The dOmeTEC design can provide a sustainable energy supply for Curacao and is the opportunity to kick-off in developing the first commercial OTEC power plant!

For further information contact the OTEC design team at otecdesign@gmail.com. The pictures and advice for the winning team came from delta-life.