Seawater energy
tidal energy is the energy obtained by taking advantage of the tides: by using an alternator the system can be used to generate electricity, thus transforming tidal energy into electrical energy, a safer and more usable form of energy. It is a type of renewable energy, since the primary energy source is not exhausted by its exploitation, and it is clean since in the energy transformation no gaseous, liquid or solid polluting by-products are produced. However, the relationship between the amount of energy that can be obtained with current means and the economic and environmental cost of installing the devices for its process have prevented a notable implementation of this type of energy.
Other ways of extracting energy from the sea are: waves (wave energy), from the difference in temperature between the surface and the deep waters of the ocean, the oceanic thermal gradient; salinity, ocean currents or offshore wind energy.
In Spain, the Government of Cantabria and the Institute for Energy Diversification and Saving (IDAE) want to create an R&D center on the Santoña coast. The plant could meet the annual domestic consumption of about 2,500 homes.
Methods for generating electrical energy
Tidal Stream Generator
Tidal stream generators tidal stream generators (or TSGs) make use of the kinetic energy of moving water to power turbines, similar to wind (moving air) used by wind turbines. This method is gaining market due to lower costs.
Tidal barrages
Tidal barrages make use of the potential energy that exists in the height difference (or head loss) between high and low tides. Dams are essentially levees across the width of an estuary, and suffer from high civil infrastructure costs, a global shortage of viable sites, and environmental issues.
Dynamic tidal energy
Dynamic tidal energy is a theoretical generation technology that exploits the interaction between kinetic and potential energies in tidal currents. Very long dams (30 to 50 km in length) are proposed to be built from the shorelines outward; in the sea or ocean, without enclosing an area. Tidal phase differences are introduced by the dam, leading to a significant water level differential (at least 2.3 metres) in shallow coastal marine waters with tidal currents oscillating parallel to the shoreline, such as the UK, China and South Korea
Rance tidal power plant (France)
In the Rance River estuary, EDF installed a tidal power plant. It has been in operation since 1966 and produces electricity to cover the needs of 225,000 inhabitants, equivalent to a city like Rennes (9% of Brittany's needs). The plant itself is 390 m long and 33 m wide. It is made up of 24 "bulb" with generators of 10 MW each, through which a total flow of 6,600 m³ per second passes. It has a 22 km² reservoir that houses 184,000,000 m³ of water regulated by six gates 10 m high by 15 m wide.
The tidal power plant is a reversible hydroelectric plant, which takes advantage of both high and low tide, since its turbines work in both directions, during the filling and emptying phases of the reservoir. The turbines also allow water to be pumped: at low tide, the plant works "backwards" and pumps seawater to further raise the reservoir's water level. Pumping makes it possible to increase production because the height of the water falls increases and the period of time between high tide and low tide decreases.
The 750 m long dam closes off the river estuary and includes a lock that allows the passage of some 20,000 ships a year. A highway with an average traffic of 30,000 vehicles a day (up to 60,000 in summer) takes advantage of its route to link the towns of Saint-Malo and Dinard.
The cost per kWh was similar to or cheaper than that of a conventional power plant, without the cost of greenhouse gas emissions into the atmosphere, the consumption of fossil fuels, or the risks of nuclear power plants (13 meters tidal difference).
The environmental impact was quite serious, such as siltation of the river, changes in salinity in the estuary in its vicinity, and changes in the ecosystem before and after the installations.
Other projects are exactly the same, such as that of a much larger plant planned in France in the area of Mont Saint-Michel, or that of the Bay of Fundy, in Canada, where there are up to 15 meters of tidal difference, or that of the Severn River estuary, in the United Kingdom, between Wales and England, has not been carried out due to the risk of a strong environmental impact.
Operation
The operation of a tidal power plant is simple. If it is reversible, when the tide rises the water is turbined inside the reservoir and vice versa when the tide falls.
Today, electricity is transported by cables on artificial islands, on which there are more turbines.
Other renewable energies
- Energy olamotriz
- Wind energy
- Solar energy
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