Tidal energy, also known as ocean thermal energy (OTE), is arenewable energy source that harnesses the temperature difference between the surface and deep waters of the oceans. The principle of TME is based on the use of the heat contained in seawater to generate electricity through a thermodynamic cycle, generally a closed cycle.
The ETM concept was imagined by Georges Claude, a French engineer, and popularized by Jules Verne in his novel “L’île mystérieuse”. Since then, several projects have been launched, notably in Tahiti, where a pilot plant was built in 1982, and on Reunion Island, where a Sea Water Air Conditioning (SWAC) project uses cold water from the depths to air-condition buildings.Although this technology is still in its infancy, it has considerable potential for the production of clean, sustainable electricity in coastal regions around the world.
How tidal energy works
TME is a form of thermal energy derived from the seas and oceans. The temperature difference between the warmer surface waters and the colder deep waters creates a thermal gradient. This gradient is used to power an ETM plant, producing electricity. TME plants are installations that use the temperature difference to generate electricity from the thermal energy contained in seawater.
The operation of an ETM plant is based on a closed cycle, where hot surface water is pumped and used to vaporize a heat transfer fluid, usually a low-boiling gas. The steam produced drives a turbine that generates electricity. The fluid is then cooled using cold water pumped from below, returning it to a liquid state to start the cycle again.
Advantages and disadvantages of tidal energy
Advantages
- Renewable energy : Tidal energy is a renewable, low-carbon energy source, as it relies on the temperature difference between surface and deep waters, which is constant throughout the year.
- Continuous energy production: Unlike intermittent energy sources such as solar and wind power, tidal-thermal energy can be produced 24/7, enabling stable, reliable power generation.
- Significant energy potential: The oceans represent an immense source of energy, and tidal energy could make a significant contribution to meeting global energy demand if harnessed effectively.
- Environmentally-friendly air-conditioning: Tidal energy can be used to air-condition buildings using cold water from the depths, reducing the energy consumption and greenhouse gas emissions associated with traditional air-conditioning.
Disadvantages
- High costs: Construction and maintenance of tidal-thermal power plants can be costly, particularly for pilot projects and first installations. Costs may fall as technologies improve and production scales increase.
- Limited geographical deployment: Tidal energy can only be harnessed in regions where the temperature difference between surface and deep waters is sufficiently large, generally in tropical and equatorial zones.
- Impact on marine life: The installation and operation of tidal-thermal power plants could disrupt marine life, particularly as a result of water circulation and the noise generated by the equipment.
- Need for research and development: Tidal energy is still in its infancy, and there is a need to invest in research and development to improve technologies and reduce associated costs.
Tidal energy installation projects
Numerous tidal energy tests, installations and projects have been carried out around the world, testifying to the growing interest in this renewable energy source. Here’s an overview of some of the highlights:
- NEMO project (France): Naval Group and Naval Energies are working on the NEMO (New Energy for Martinique and Overseas) project to develop an ETM power plant in Martinique. This project aims to establish a pilot plant to demonstrate the technical and economic feasibility of tidal-thermal energy in French overseas territories.
- OTEC in Hawaii (USA): The Natural Energy Laboratory of Hawaii Authority (NELHA) has built a pilot OTEC (Ocean Thermal Energy Conversion) plant on the island of Hawaii. Makai Ocean Engineering has also developed a research and development facility to study OTEC technologies and seawater air conditioning (SWAC) systems.
- Tahiti pilot plant (French Polynesia): In 1982, an ETM pilot plant was built in Tahiti by the French company DCNS (formerly DCN). Although the project was not pursued on a large scale, it demonstrated the technical feasibility of tidal-thermal energy in tropical regions.
- OTEC project in La Réunion (France): La Réunion, a French island in the Indian Ocean, has set up a seawater air-conditioning (SWAC) project that uses cold deep-sea water to air-condition buildings. The project is based on the principles of tidal-thermal energy to reduce energy consumption and greenhouse gas emissions.
- Cuba’s OTEC project: An ETM project is currently under development in Cuba, with support from the European Union. This project aims to build a pilot plant to study the feasibility of tidal-thermal energy in the Caribbean and contribute to the diversification of the country’s energy sources.
- Kiribati project (Oceania): The Pacific archipelago of Kiribati has launched a project to harness tidal energy to meet its energy needs. The project is supported by the World Bank and the International Energy Agency.