Dossier Océan et énergie - Énergie Thermique des Mers

Sommaire IOA News Letters

FRENCH POLYINESIA-POTENITAL SITE FOR OTEC/DOWA

The is1and of Tahiti and many other si1ands in the Territory of French Polynesia are known world wide as a place of sun, beautiful people and blue lagoons. In addition, they may someday be a potential OTEC/DOWA site. This was what many participants felt after they visited the French Polynesia last month for the second IOA Planning Meeting Dr. Vincent Coutrot, Director of the South Pacific Institute for Renewable Energy (S.P.I.R.E.)informed the meeting that the Institute is interested in all forms of renewable energy, and OTEC can someday be one of the most promising sources for the increasing energy needs of the Territory and the region.

Mr. Michel Gauthier provided a summary of activities performed at the IFREMER by himself and others leading to the oceano-graphic survey and preliminary design of a 5Mwe OTEC plant for Tahiti Mr. Gauthier said that they started their work in 1976 when IFREMER obtained a small budget to design, deploy and operate a system to draw ocean water from a 600 meter depth through a 10 cm polyethylene pipe at their mariculture research station in Tahiti. Un-fortunately, the pipe failed after a short period of operation Later, in 1978, funds were obtained for conceptual studies of both open-and closed-cycle 1and-based and floating OTEC plants as well as site selection studies in the Ivory Coast, Guadeloupe and French Polynesia. Their studies concluded with the proposal for a 5 MWe land-based OTEC pilot plant in Papeete, Tahiti. A group called ERGOCEAN was organized by the IFREMER and seven working groups were formed. Approximately US$7 million was spent in the early 1980's in the design and laboratory testing studies. The two-year site survey including bathymetry, temperature profiles, waves currents, etc. was performed at a cost of US$3 million. Based on the data collected from the site survey, IFREMER developed the environmental design criteria. Their preliminary design of the 5MWe OTEC plant can be summarized as follows:

	Land-based for easy accessibility;
	5.5MWe net power pilot plant scaleable up to a 50 MWe size commercial plant;
	Double flow axial turbine;
	2.5 meters FRP neutrally buoyant pipe suspended from buoy/ring/anchor systems over the cliff;
	Schedule: 9 months for final design and 33 months for construction and acceptance tests;
	Cost:US$100 million.

Mr. Michel Gauthier indicated that most of their technical effort was dedicated to the design cold water pipe (CWP) they designed would be made of a sandwich construction, synthetic polyester foam between two layers of fiberglass reinforced plastic (FRP) walls. The pipe would be fabricated in 15 m long sections, and assembled into 300 m long units stored in the lagoon. Those longer sections would be mechanically butted as the CWP was pulled and deployed. The main features of the bathymetric profile they obtained for the site under consideration consist of:

	A relatively flat portion, mainly live coral, with slopes between 15¢Xand 25¢X, extending from the barrier reef to a water depth of about 80m;
	A vertical escarpment made of compacted coral, over 100m high;
	A steep slope of about 45¢Xresulting from old basaltic flows covered with some sediments and rubble, between water depths of 200m to 500m;
	The deep water zone, with a slope progressively decreasing from 25¢Xto 10¢Xin the offshore direction, and a fairly smooth bottom made of sand or silt deposits.

Mr. Gauthier then described their proposed anchoring scheme for the CWP in the shallow water section, the proposed configuration of CWP in the deep water section and the techniques to be used for the deployment of CWP.
After Gauthier's report, many participants found the island of Tahiti to be a potential site for the development of OTEC/DOWA and felt that the IOA may well provide the impetus and structure necessary to take this vast potential and turn it into useful fact. Dr. Vincent Coutrot further indicated that French Polynesia welcomes the inputs of IOA and looks forward to a long and mutually beneficial relationship.