Tidal energy is the energy obtained from the movements of water caused by the tides. It represents a source of renewable energy since it uses an inexhaustible resource.
The tide, the rhythmic rise and fall of sea level caused by the gravitational action of the moon and the sun, generally has a width (difference between high tide and low tide) of less than one meter, but in some areas, due to the particular configuration of the site, the difference in height can reach high values, interesting for the exploitation and production of energy, which is currently predominantly electrical. In some areas of the planet, for example, there are tides even with 20 m vertical width.
In ancient times, it was tried to exploit the tidal energy by the construction of "tidal mills". The water was collected, during the flow, in a small basin, which was then closed with a bulkhead. At the time of the outflow, the water was transported through a channel to a wheel that moved a millstone.
Types of tidal power installations
Today there are several projects to exploit the tides, which involve different methods of exploiting this source of renewable energy:
- lifting a weight against the force of gravity
- the compression of air in the containers and the handling of appropriate hydraulic turbines as a result of their expansion.
- movement of the paddlewheel
- Filling of tanks and subsequent emptying with passage in hydraulic turbines.
The filling of tanks and subsequent emptying seems to give the best results, in real employment. However, the most important problem for the development of this technology is still the phase change between the maximum available tide range (whose frequency is predictable based on the lunar and solar phases) and the energy demand at peak hours . In fact, in the days of insufficiency in the entrance of water, the production of electricity would cease.
How does tidal energy work?
In a typical tidal power plant, the water flows and flows in a vast basin, passing through a series of tunnels in which, gaining speed. Thanks to the kinetic energy of the water, the hydraulic turbines connected to the generators can be operated.
During low tide, the water in the basin flows into the open sea, again turning the turbine.
When the sea level begins to rise again and the tide is high enough, the sea water flows into the basin and the turbine turns again.
To obtain the production of energy with rising and falling tides, special reversible hydraulic turbines are used, that is, they work in both directions of the flow.
Disadvantages of tidal energy
The main limits of these plants are:
- The high installation cost.
- The difficulty of the placement (indicatively, the appropriate sites must have tide widths greater than 3 meters and topography favorable to the installation)
- Production discontinuity
- Coastal erosion created by power plants that modify tidal flows.
- The tendency to sedimentation within the basin (especially if it is placed at the mouths of rivers)
- The disturbance of the ecosystem, in particular for the fauna.