Read this essay to learn about:- 1. Introduction to Solar Pond 2. Layers of Solar Pond 3. Applications 4. Limitations.
Essay # 1. Introduction to Solar Pond:
Solar ponds are also called solar salt ponds. Natural ponds convert solar radiation into heat, but the heat is quickly lost through convection in the pond and evaporation from its surface.
A solar pond is designed to reduce convective and evaporative heat losses by reversing the temperature gradient with the help of no uniform vertical concentration of salts. A greater salt concentration at the bottom than at top causes bottom water to have greater density and remains at the bottom and is also hotter. The solar energy is absorbed in deep layers and is usefully trapped.
The solar ponds are useful in two ways:
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i. The conversion of solar energy to useful work as a result of the temperature difference between bottom and top layers of the pond.
ii. The use of pond as a thermal storage medium.
A solar pond is a combination of solar collector and storage medium.
A schematic of an artificial solar pond and conversion system is shown in Fig. 8.14.
Essay # 2. Layers of Solar Pond:
The pond is divided into three layers:
a. Top Layer:
Low density convective layer.
b. Central Layer:
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Non-convective layer and contains the required salinity and density gradient with salinity greatest at the bottom.
c. Bottom Layer:
High density-salinity convective storage layer.
The bottom warm water is used as the heat source and top cool water as the heat sink. The hot bottom water is pumped through an evaporator and back to the bottom. An organic fluid is evaporated and drives a turbo generator. The turbine exhaust is condensed and the condensate is fed back to evaporator. The cooling water for condenser is taken from the top cool layer of the pond.
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A leak-proof pond is constructed. 330 kg of salt per square meter of pond area is added. The bottom layer can achieve a temperature of 93°C. The salinity gradient is maintained in the pond by injecting salt to the bottom layer and flushing the top layer with fresh water periodically .The efficiency is very low but these plants have large potential for tapping solar energy.
Essay # 3. Applications of Solar Pond:
The main applications of solar ponds are:
i. Power generation,
ii. Space heating and cooling,
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iii. Crop drying,
iv. Desalination, and
v. Process heat.
Essay # 4. Limitations of Solar Pond:
The main limitations are:
i. Need for large land area.
ii. Sunny climate.
iii. Availability of water.
iv. Availability of salt (brackish water).
A solar pond power plant of 5 MW capacities is in operation in Dead sea, Israel.