Renewable Sources of Energy : Tidal Energy

By Apoorbo Roy|Updated : July 5th, 2021

INTRODUCTION

(i) Oceans cover about 71 per cent of the earth's surface. They receive, store and dissipate energy through various physical processes.

(ii) As per the present technological status, recoverable energy in oceans exists mainly in the form of waves, tides and temperature differences (between surface and deep layers).

(iii) Tides and waves produce mechanical energy whereas temperature difference produces thermal energy.

(iv) Main disadvantages common to all of them are:

(a) low energy density and

(b) In general the potential occurs remote from the consumption centre. Because of the diversity in physical processes.

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INTRODUCTION

(i) Oceans cover about 71 per cent of the earth's surface. They receive, store and dissipate energy through various physical processes.

(ii) As per the present technological status, recoverable energy in oceans exists mainly in the form of waves, tides and temperature differences (between surface and deep layers).

(iii) Tides and waves produce mechanical energy whereas temperature difference produces thermal energy.

(iv) Main disadvantages common to all of them are:

(a) low energy density and

(b) In general the potential occurs remote from the consumption centre. Because of the diversity in physical processes.

TIDAL ENERGY

(i) Tidal energy exploits the natural rise and fall of coastal tidal waters caused principally by the interaction of the gravitational fields of the Sun and the Moon.

So we have Lunar Tides (due to moon gravity and earth rotation) and Solar Tides ( due to Sun gravity and earth rotation).

(ii) The ocean level difference caused due to tides contains large amount of potential energy. The highest level of tidal water is known as flood tide or high tide. The lowest level is known as low tide or ebb.

Range = Difference between the high tide and low tide

(iii) The tidal range varies greatly with location. Only sites with large tidal ranges (about 5 m or more) are considered suitable for power generation.

LIMITATIONS OF TIDAL ENERGY

Main limitations of the tidal energy are:

(i) Economic recovery of energy from tides is feasible only at those sites where energy is concentrated in the form of tidal range of about 5 m or more and geography provide favorable site for economic construction of a tidal plant, thus it is site specific.

(ii) Due to mismatch of lunar driven period of 12 hrs 25 min and human (solar) period of 24 hrs, the optimum tidal power generation is not in phase with demand.

(iii) Changing tidal range in two weeks period produces changing power.

(iv) The turbines are required to operate at variable heads,

(v) Requirement of large water volume flow at low head necessitates parallel operation of many turbines.

(vi) Tidal plant disrupts marine life at the location and can cause potential harm to Ecology.

(vii) It requires very large capital cost at most potential installations.

(viii) The location of sites may be distant from the demand centers.

TIDAL ENERGY TECHNOLOGY

Main components of a tidal plant , as shown in figure are:

(i) Dam, barrage or dyke: a barrier constructed to hold water.

(ii) Sluice ways: rapid controlled gates, used to fill basin during high tides or emptying it during low tides.

(iii) A special ,bulb type power turbine-generator set: steel shell containing an alternator and special Kaplan turbine with variable pitch blades.

Power generation from tides

OCEAN TIDAL ENERGY CONVERSION SCHEMES

Main tidal energy conversion schemes are:

(a) Single basin: single effect,

(b) Single basin: double effect,

(d) Two basin: paired basin and

(e) Tidal flow (or tidal current) schemes.

ENVIRONMENTAL IMPACTS

Tidal energy is a renewable source of energy, which does not result in emission of gases responsible of global warming or acid rain associated with the use of fossil fuels.

Changing tidal flows by damming a bay or estuary could, however, result in negative impacts on aquatic and shoreline ecosystem, as well as navigation and recreation. The barrage destroys homes to many birds, fish and other animals.

Studies undertaken so far indicate that the impact at each site is different and depends greatly upon local geography. Very little is understood about how altering the tides can affect incredibly complex aquatic and shoreline ecosystems.

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