Single & Double Basin Tidal Power Plant Working Principle

Hi friends, in this article I am discussing about the tidal power plant working principle.
 
Tides in the sea are produced due to the gravitational attraction of moon and sun upon the rotating earth. Rise and fall of tides occur twice a day.
 
The highest level of tidal water is called high tide or flood tide whereas the lowest level of tidal water is called low tide or ebb tide. The level difference between high and low tides is called tidal range.
 
The tidal range is time, season and location dependent. The maximum tidal range takes place at the time of new and full moon known as spring tides. Availability of 5 m tidal range or above in particular location can be used to operate a hydraulic turbine.
 

Tidal Power Plant Working Principle

 
In a tidal energy power plants, the water during high tides is first collected in an artificial basin and it is released during the period of low tides. The water while escaping is used to spin a hydraulic turbine connected to a generator. The three main components of a tidal energy power plant are:
 

  • powerhouse,
  • dam to form the basin,
  • sluiceways from the basin to sea and vice versa.

 
The function of the dam is to create an obstacle between sea and the basin. The sluiceways are used to either fill the basin during high tide or empty the basin during the low tide.
 

Single Basin Tidal Power Plant Working

 
In single basin tidal power plant, the powerhouse is located at the mouth of the basin. The hydraulic turbine in powerhouse only operates during the discharge of water from the basin during low tide. The basin is filled again during the high tide. Intermittent operation is the main disadvantage of this system.

tidal power plant working principle

However, in a double cycle system, power generation is possible during the low as well as high tide. The direction of flow during the low and high tide alternates and generation of power takes place during the both the emptying and filling cycle of the basin.

single basin tidal power plant working

Double Basin Tidal Power Plant Working

 
In double basin tidal power plant, two basins at different levels are made and a dam is provided in between them. Inlet and outlet sluice gates are made in the dam. The water level in upper basin is maintained above the level of water in the lower basin.

double basin tidal power plant working

The upper basin is filled with water during high tide and the lower basin is evacuated during the low tide. Therefore, a permanent head is produced between upper and lower basins.
 
When a sufficient head is created, the turbines of the power plant are started. The water flows from upper basin to turbine which discharges into the lower basin and 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 the water in lower basin keeps on rising due to the discharge of water by the turbine.
 
When the level of water in lower basin equals during the low tide, the outlet sluice is opened and it is closed when the water level reaches to its minimum level. In this system, the power can be produced continuously during emptying and filling of basins.
 

Power Output of Tidal System

 
The power of a tidal turbine can be expressed as:
 
P = ρQgH watts
 
Where, P = power of turbine in watts,
Q = quantity of water flow in m3/s
g = acceleration due to gravity = 9.81 m/s2
H = water head in meters,
ρ = density of sea water = 1025 kg/m3
 
The water head H is generally taken as that from the water surface behind the turbine to the center of the turbine runner. H varies from maximum at the beginning of generation to zero at the end of generation. Though the variation of H during generation is nonlinear, we assume the variation to be linear.
 
As H varies from maximum to zero, the power output also varies from maximum (equal to rated output) to zero. It is seen that ρQgH is the total potential energy of water. Evidently, the generator output is equal to P multiplied by efficiencies of the turbine and the generator.
 

Advantages Disadvantages of Tidal Power Plant

 
Advantages:
 

  • It is pollution free.
  • Energy is freely available.
  • Power is ensured around the year.
  • It is unaffected by the unpredictability of monsoon.

 
Disadvantages:
 

  • The capital cost of the plant is high and needs long construction time.
  • The interest and depreciation component of the generation cost is very high.
  • The construction of tidal barrage calls for advanced technology due to very complex problems associated with it.
  • The regions which are most promising for tidal energy generation tend to be the ones which are difficult from the point of view of barrage construction. So every location is not suitable for installing such a system.
  • Tidal power output is not constant throughout the day (unless pumping is used). The output is the form of pulses (2 pulses everyday and each pulse lasting about 4 to 6 hours). The extent to which the tidal pulses can be absorbed by the power system depends on the static and dynamic characteristics of the system.
  • Sedimentation of basins is a problem.
  • Sea water is very corrosive.
  • Marine life is affected.

 
Thanks for reading about tidal power plant working principle.
 

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