Solar Ponds. The low cost and low tech approach

Salinity Gradient Solar Pond With dwindling sources of fossil fuels, scientists all over the world are looking for alternate forms of energy that can be used by the common man. And one of the most feasible and best forms of alternate energy is solar energy that is available for free to everyone.

One of the best ways of harnessing solar energy is through solar ponds.
A solar pond is basically a pool of water that collects and also stores solar energy. The peculiarity of the solar pond is that it has layers of salt solutions of differing concentration and thus, different densities to a certain depth. Once this depth is reached, you find water with uniform, high salt concentration.

The solar pond is a relatively low tech and low cost approach for harvesting solar energy which is done very easily. To make a solar pond, you have to first fill a pond with three layers of water where the top layer has a low salt content in it. Next comes the intermediate insulating layer that has a salt gradient that has a density gradient. It is this density gradient that helps in preventing heat exchange with the natural convection of water.

The bottom layer of the solar pond has a high salt content that reaches temperatures reaching 90 degrees Celsius. It is because of these different salt contents in the different layers of water that the different layers have different densities. With the different densities in the water, the development of convection currents is prevented, which would have transferred heat to the surface of the pond, and then to the air above.

Without these convection currents, heat is trapped in the salty bottom layer of the solar pond, which is used for heating of buildings, industrial processes, generation of electricity and other purposes. In addition to the above uses, solar ponds can also be used in water desalination and for storage of thermal energy. Of date, there are two solar ponds functioning; one in Bhuj, Gujarat, India and the other in the University of Texas El Paso.

There are many advantages to using a solar pond to meet the energy requirements of a place. The greatest advantage lies in the fact that it has a low cost per unit area of collection and also an inherent capacity for storage purposes. In addition to this, it is possible to easily construct solar ponds over large areas with which it is possible for the diffusion of solar resources to get concentrated on a grand scale.

Not only is a solar pond a great source of generation of electricity, it produces many environmental advantages when compared to the use of other fossil fuels for producing electricity. With a solar pond, the greatest advantage to the environment is that heat energy is provided without the burning of any fuel, which reduces pollution.

Another advantage is that because there is no use of conventional energy resources for creating electricity in solar ponds, conventional energy resources are conserved. And the third advantage of solar ponds to the environment is that it is coupled with desalting units that are used for purifying contaminated or minerally impaired water while the pond itself is the receptacle for waste products.

Photo: Salinity Gradient Solar Pond. University of Texas. Photo by Herb Hein, May 1996

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