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Dossier Océan et Énergie  - Énergie Thermique des Mers

Proposal for a European contribution to the development of the exploitation of the marine resource known as "Ocean Thermal Energy Conversion OTEC" for the production of electricity and fresh water in the Ultra Peripheral Regions of the Union. 

Le Club des Argonautes - Octobre 2006


During last decades, the idea developed that the recourse to renewable and clean energies would be essential to meet the needs of the world for primary energy. This, not only to mitigate possible shortages of fossil and nuclear fuels supplies because of conflicts and embargoes or the rarefaction of resources , but also to reduce as much as possible the serious and durable (if not irreversible) effects that the use of these traditional fuels could cause to our natural environment.

To act and challenge this evolution the ways are many: to save energy, to produce energy while polluting less, to exploit new clean and renewable resources. And to follow this third way the marine resources offer an important production potential.

Exploitation of the marine resources of renewable energy.

Tidal, offshore wind, wave, sea current and ocean thermal energy (OTEC) are the marine phenomena for which conversion processes to primary energy have been already tested at sea at sizes enabling extrapolation to capacity up to several megawatts (MW) and for which production costs are considered acceptable in the more or less long term.

The processes developed for the exploitation of these phenomena are by nature considered non polluting insofar as they introduce into the biosphere neither energy, nor chemical components. They create disturbances of natural flows of energy and matter, increase marine area occupation and add constraints for navigation with other effects, visual and possibly auditive, that could be - a priori - benign for offshore sitings. This assertion remains to be validated as exploitation of these resources will develop in order to specify its impacts and bearable limits.

The OTEC resource is stored in the form of heat in the surface water heated by the sun. Largely distributed in the whole ocean within the intertropical belt where are located some European UPR , it is abundant and stable .Its theoretical energy potential is estimated one hundred times that of the tide and ten times that of the wind - and it is base load - available 24 hours a day, 365 days a years - a very significant advantag.

OTEC principle and industrial development prospects.

When a suitable fluid under liquid form is heated up to its boiling temperature , it transforms into vapor. If one makes this vapor pass through a turbine coupled to an alternator before directing it towards a condenser - where it cools and turns back again to liquid - one has produced a gaseous turbogenerator. OTEC functions according to this process. The "heat" necessary to the vapor formation is taken from the warm water reservoir at the surface of the ocean where the temperature can reach 25 to 28 °C, and the "coldness" necessary to vapor condensation is provided by the water pumped from a few hundred meters of depth, under the thermocline, where temperatures approaches zero degrees centigrade. The OTEC process is complementary to that of our traditional power stations burning fossil or nuclear traditional fuels . Only the operating conditions are different. The small temperature difference available for OTEC makes the process less efficient and requires different equipment with different levels of investment.

 Thanks to the first experimental work achieved  during the 1930s, it was shown that OTEC was viable. Today the United States and Japan have taken over the pioneer ing role to better explore the technical solutions,and their economic s, rendering OTEC exploitation increasingly attractive. They optimized the performances of the equipment : heat exchangers and turbines, and consolidated the degree of confidence for the behaviour "at sea" of the deep water pipes. They also developed the concept of "multi-products ». This concept adapted to OTEC plants of modest sizes of a few tens of MWs allows to develop other usages of the deep cold water: for air conditioning and for production of fresh water and aquaculture products .

Also American and Japanesese scientists studied the extrapolation of OTEC to floating plants of several hundreds of MWs to produce synthetic fuels transportable by tankers to meet the demand of countries located far from OTEC resource zones. 

Also during the operation of their experimental plants, American and Japanese scientists acquired data on the impact of consequent sea motion on the natural environment - in particular that of the deep water, still cold and rich in nutrients - and began to study the limits of the durable exploitation of the resource. 

 OTEC : a marine energy neglected by Europe.

OTEC resource is renewable, stable and abundant. It offers particularly attractive multiform prospects for exploitation. American and Japanese promoters imagined OTEC development in 3 complementary phases of increasing difficulty - the success of the first phase authorizing the engagement of the second, and then the implementation of the third. 

The first phase will aim at the industrialization of small "multi-products" plants meeting the immediate needs for countriesof the "South" having direct access to the resource .It would be carried out in partnership and with the technical and financial support of the international community of industrialized countries.

During the second phase, the experience gained during the exploitation of the plants of first generation will be used to extrapolate technology towards plants whose production capacity meets the requirements of industrialized countries, initially to supply coastal cities in the tropical zone and then, during the third phase, for the production and the transport of synthetic fuels (ammoniac, methanol, hydrogen) anywhere in the world

In parallel with the evolution of the technology and the reduction of costs which will accompany this exemplary OTEC development, the observation over several decades of the operation of power plants of increasing capacities over increasingly long period of time will allow the study of the effects of the plants consequent water motions on the local, regional and global environment, and to develop adapted policies and procedures for water motion management.

After having been the pioneer country for OTEC at the beginning of the past centuries from its invention by d’Arsonval in the 1880s, and after having still been heavily involved between 1982 and 1985 in the of preliminary study of a 5 MW OTEC pilot plant for French Polynesia, France in 1986 gave up its activities in this field for the reason that the cost of OTEC energy was not competitive with that of the energy market on the Territory. Obviously that was an predictable situation for a first pilot plant of still, immature technology. 

One can regret this aborted project and the absence of initiatives to organize at the national or European level the continuation of activities for the development of OTEC. All the European Union funding for the development of renewable energy is allocated to "indigenous" resources. That implicitly excludes OTEC whose resource is in the tropical oceans. This argument of exclusion used by the Commission is doubly unjustified. On the one hand because the resource is available in the EEZ of Ultra Péripheral Regions of the E U and in addition because this restrictive policy is likely to exclude de facto the energy sector of European Industry from a future equipment market that some foreign countries estimate promising and very large. 

Here above are briefly presented the reasons for this demand for a European contribution to the development of the exploitation of the marine resource known as "Ocean Thermal Energy Conversion OTEC" for the production of electricity and fresh water in the Ultra Peripheral Regions of the Union. The content of this contribution remains to be defined.

Le Club des Argonautes - Octobre 2006