Tidal Power Plants (Single Basin System)
The tidal range of 5 m and above available in particular locations can be utilized to operate a hydraulic turbine. The mechanical power of the turbine can be used to run a generator to produce electrical power.
In case of power generation by tides, the water during high tides is first trapped in an artificial basin and then it is allowed to escape during the period of low tides. The water while escaping is utilised to run a hydraulic turbine coupled to a generator.
The first tidal power plant was commissioned by General De Gaulle at La France in 1966.
The three main components of a tidal power plant are :
- The power house
- The dam (barrage) to form basin
- Sluice ways from the basin to the sea and vice versa.
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| Figure A |
The function of the dam is to form a barrier between the sea and the basin.
The sluice ways are used either to fill the basin during high tide or empty the basin during the low tide.
A tidal power plant based on single basin system is shown in Figure A. Here the power house is situated at the mouth of basin. The hydraulic turbine in the power house only operates during the discharge of water from the basin during ebb tide. During the high tide the basin is again filled. The main disadvantage is that the system's operation is intermittent in nature.
However, we also have double cycle system in which the power generation is affected during the ebb as well as in flood tides as shown in Figure B.
The direction of flow through the turbine during the ebb and flood tides alternates and generation of power is accomplished, both during the emptying and filling cycle of basin.
Though the double cycle system has only short duration interruptions in turbine generator operation, but the continuous power generation is still not possible. Further, the power generation coincides occasionally with the peak power demands. This problem is overcome in double-basin system described below.
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| Figure B |
- Tidal Power Plant-Double Basin System :
This system has two basins at different levels and a dam is provided in between these basins as shown in Figure C. Inlet and outlet sluice gates are provided in the dam.
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| Figure C |
The upper basin is filled with water during high tide and lower basin is emptied during the low tide. Therefore, a permanent head is created between the upper and lower basins.
When sufficient head is developed, the turbines of the power plant are started. The water flows down from upper basin to the turbine which discharges into the lower basin. Thus the electrical power is generated.
When the water level in upper basin is maximum during high tide the inlet sluice is closed and the level of water in lower basin keeps on rising due to discharge of water by the turbine. When the level of water in lower basin equals during the ebb tide, the outlet sluice is opened and it is closed when the water level reaches to its minimum level, equal to the level of water in upper basin. Again the inlet sluice is opened and the cycle is repeated.
The advantage of this system is that the power can be generated continuously during discharge and filling of basins. However, in this method also the power generated may not coincide with peak load demand. This problem can be overcome by pumping water by other means from lower basin to upper basin during peak power demands.