Dossier Océan et énergie - Énergie Thermique des Mers

Sommaire IOA News Letters



Scientific Rational

The ocean is far and away the world's main solar heat reservoir. Heat transfer between
the ocean and the atmosphere powers global weather. Heat transfer within the ocean produces the ocean current systems. Conspicuous ocean energy resources-wave, tides, ocean wind and currents-can make an important contribution locally or regionally or regionally to energy needs. Winds and waves are, how-ever, stochastic resources. Tides and tidal currents are periodic resources (more correctly complex harmonic). They all inherently have significant spatial and temporal variations. This means that the potential of these resources is 1imited. Collectively, conspicuous ocean energy and other clean alternative energy types (geothermal, hydropower, solar, ponds, land wind, photovo1taics, and direct solar),could perhaps, at best, supply 10¢M of the world's energy needs. In addition, the variability of resource means that they cannot intrinsically supply base1oad (continuous) electrical power, requiring energy storage facilities.

The inconspicuous Ocean Thermal Energy resource dwarfs present and future human energy demand by several orders of magnitude. Since it results from direct absorption and transfer of solar energy, variations in its magnitude and distributions are very small. Estimates of future energy needs for a world population of 10 billion people amounts to less than 1/10 of 1¢M

Environmental and Practical Rationale

Burning fossil fuels releases ancient solar energy that is stored as carbon bond energy. The burning releases carbon dioxide to the atmosphere, increasing the absorption of reflected energy and its re-emission as infrared radiation the so called enhanced 'green-house effect'. This effect has very serious climatic and sea level rise implications. Carbon based fuels also emit su1phur oxides, nitrogen oxides, and particu1ates to the atmosphere. Such emissions are heavily polluting to life, as are the effects of fuel spillage. (It is worth remembering that the nu-clear fission energy alternative carries severe toxic waste disposal risk and sccident risk, as well as hugely expensive technology).

Comparing projected future energy demand with estimates of fossil fuel reserves, we see that readily accessible reserves of oil and natural gas will be gone in a few decades; coal reserves will be gone in few centuries. Fossil fuel costs will rise to reflect this in-escapable fact.

For these reasons, the gradual move towards a global scale renewable energy alternative not only seems attractive, it seems unavoidable.

Overview of the Prospects

New OTEC demonstrators and model plants will likely emerge in Polynesia and Tropical Pacific Asia first. Once the pilot projects have been proven, the medium term marketplace will include all regions of the world with high fuel costs and access to suitable ocean thermal gradients. The long term market could be global, since very large scale off-shore (EEZ or High Seas) OTEC plants, coupled with the plausible option of OTEC based Synthetic Fuel Production (another important R&D area), makes global energy distribution theoretically possible. Tropical EEZ countries could build their own OTEC plants or lease the resource prorata ($/kWh). Rich nations could operate High Seas OTEC plants to supply their own needs and/or sell to others.

Synthetic Fuel Production

Floating OTEC plants close to is1ands could be connected to shore with transmission cables. For open ocean OTEC a system of fuel transportation is required . This could be achieved by using OTEC energy to synthesize fuel cells: hydrogen electro1ysed
from water; hydrogen combined with nitrogen removed from the air to make ammonia; or methano1 from carbon and hydrogen. Fuel cells would be distributed by plant ships. Notably, West Germany is investing in hydrogen fuel technology research. Fuel cells will become a vital energy source for future remote ocean working. Hydrogen-powered cars and aero-planes have already been tested successfully (note:2/3 of detrimental CO2 emissions come from road vehicles).

The move away from carbon based energy and toward hydrogen based energy is very desirable.

Deep Ocean Water Applications (DOWA)

The use of nutrient-rich deep ocean water (DOW) effluent is being investigated in parallel R&D with OTEC. The prospects for enhancing local ocean bio-productivity (mariculture) with DOW are good. Mariculture, together with fresh water production (a by-product of Open Cycle OTEC), land irrigation, and coolant production (for air conditioning ), improves the economic viability of OTEC. Indeed, for small is1and communities, OTEC is made more appropriate by its support of commercial mariculture and fresh water production.

Attention has recently been focused on the shortage of fresh water in new key areas. California has an acute water shortage problem which may well be a symptom of global warming and continue to increase. With its strong economy and inclination towards environmental problem solving, Ca1ifornia would be a prime market for OTEC energy and fresh water. It is also relatively close (1800 miles) to the Eastern C1ipperton Fracture Zone of the Pacific Ocean, which has a 20¢J temperature differential.

International OTEC Association

OTEC Group recognizes the formation of IOA as a very significant development in collective work. IOA provides an important forum for collaboration. The UK plants to become more heavily involved in IOA.

Economic Viability

The economic viability of any renewable resource is very site specific. It depends on three main factors: the price of oil (base price and local price ), interest rates (local and those of investors), and fundamentally, on the quality of the renewable energy resource. Secondary to this are benefits that are mainly environmental, and for OTEC, useful commercial by-products.

It is anticipated that environmental costs will in due time be passed on to fossil fuel costs in the form of financial penalties or taxes. The resultant rise in fossil fuel prices will improve the economic viability of renewable energies and stimulate a new definition of energy production with more money being made available for R&D into renewable. It is also possible that increased public concern about environmental problems will make clean energy a preferred choice; this would be reflected in political decisions.

OTEC Group Strategies

There are two perceived ways for UK industry, research establishments, and research institutes to collaborate and penetrate the OTEC Technology research market:

Target component technology areas- there are many component technologies involved with OTEC; for many of these UK has significant relevant experience and expertise. Use current information and knowledge to improve awareness of scope for work and seek to involve new parties. Form links with international R&D work approach is the best initial strategy.
Pioneer (probably collaboratively) offshore OTEC plant development-larger scale commitment to compete in the R&D of offshore OTEC plants. This undertaking could involve international partnerships to cover higher costs but would draw heavily on UK maritime technology skills and component technology skils. The aim here would be to develop a demonstration model of a floating structure and cold water pipe to handle realistic flow rates. (Tim Downs, the Marine Technology Directorate Ltd. U. K. )