Subject:- Renewable Energy Sources

Topic:- Geothermal Energy

Difficulty:- Medium

• The temperature gradient across the depth of sea can be used generate electrical power. It is called ocean temperature energy conversion (OTEC).

• Out of the total solar radiations incident on sea water, lakes, rivers etc. only 14% of the heat is absorbed. It is equivalent to 100 W/m2 approx.

• According to Lamberts law of absorption, the absorption of solar energy by water by each layer of equal thickness absorbs the same fraction of light that goes through it.

• According to this law,

I (h) = I0 . e-μh

Where,

I0 = Intensity of radiation of surface

When h = 0.

I (h) = Intensity of radiation at a depth of h meters from surface.

μ = Absorption coefficient

h = Depth of water surface from top

• Value μ is approximately 0.05 per m for clear water, 0.5 for very salty water and 0.275 for turbid water.

• The most of solar heat absorption takes place at the surface just below the water and most of the absorption ( about 95% ) takes place within 6m depth.

• While the deep water in ocean remains cool because no convection currents are set since warm water is lighter compared to heavier cold water.

• The temperature of sea water at its surface is on an average of 250C in tropical regions and the temperature of water at a depth of 1000m is about 50C.

• Therefore this temperature difference between the warm surface water and the colder deep water can be utilized to run a heat engine coupled to a generator to produce electrical power.

• The plants using temperature differential of sea water are called Ocean thermal energy conversion plants.

• This plant can operate indefinitely and their best location is in the tropical belt of 200 N and 200 S latitude.