What is solar pond? What is the principle on which it works? State the merits and limitations of solar pond. | Explain how thermal energy is harnessed from solar pond.

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Q. Explain how thermal energy is harnessed from solar pond. (R.GP.V., June 2016)

Ans. A solar pond is a large area brine pond, which acts as a large scale solar energy collector. It works on the following principle -

All fluids, when heated become lighter and starts to rise. When water is heated by Sun's rays, it become hot and starts to rise from bottom of the pond to its surface and losses its heat to the atmosphere. But, if dissolved salts are present in the bottom layer of the pond, this energy can be entrapped in the ponds in the form of thermal energy.

A solar pond is a mass of shallow water about 1 or 2 metres deep with a large collection area, which acts as a heat trap. It contains dissolved salts like magnesium chloride, sodium chloride or sodium nitrate with concentration varying from 20-30% at the bottom to almost zero at the top. Due to the salt concentration gradient, convection is almost eliminated, and heat can be lost from lower layers by conduction.

A solar pond as shown in fig. 1.7 consists three zones. The top zone or surface convective zone lies from 0.3-0.5 m contains salt concentration less than 5%. In this zone temperature is nearly atmospheric. The salt concentration increases with depth and at a depth of 1.5-2 m it reaches about 20%. This zone is known Return as storage zone, having very high temperature about 70-90°C. In between these two zones, there is an intermediate zone which acts as a transparent insulator, permitting sunlight to reach bottom zone and entrapped thermal energy collected by bottom zone. This thermal energy can be used for thermal electricity generation, process heating, water desalination, referigeration, etc.

Q. What is solar pond? What is the principle on which it works? State the merits and limitations of solar pond. (R.GP.V., June 2012)
Or
What is solar pond? Give an account of merits and demerits of a solar pond. (R.GP.V., Dec. 2012)

Ans. Solar Pond -A solar pond is a large area brine pond, which acts as a large scale solar energy collector. It works on the following principle -

All fluids, when heated become lighter and starts to rise. When water is heated by Sun's rays, it become hot and starts to rise from bottom of the pond to its surface and losses its heat to the atmosphere. But, if dissolved salts are present in the bottom layer of the pond, this energy can be entrapped in the ponds in the form of thermal energy.

A solar pond is a mass of shallow water about 1 or 2 meters deep with a large collection area, which acts as a heat trap. It contains dissolved salts like magnesium chloride, sodium chloride or sodium nitrate with concentration varying from 20-30% at the bottom to almost zero at the top. Due to the salt concentration gradient, convection is almost eliminated, and heat can be lost from lower layers by conduction.

A solar pond as shown in fig. 1.7 consists three zones. The top zone or surface convective zone lies from 0.3-0.5 m contains salt concentration less than 5%. In this zone temperature is nearly atmospheric. The salt concentration increases with depth and at a depth of 1.5-2 m it reaches about 20%. This zone is known Return as storage zone, having very high temperature about 70-90°C. In between these two zones, there is an intermediate zone which acts as a transparent insulator, permitting sunlight to reach bottom zone and entrapped thermal energy collected by bottom zone. This thermal energy can be used for thermal electricity generation, process heating, water desalination, refrigeration, etc.

Merits-

(i) They have a low cost per unit area.

(ii) They can be constructed over a large area, enabling solar radiation to be concentrated on a large scale.

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(iii) They can supply energy even during the monsoon season.

Limitations-

(i) Solar pond power plant has high capital cost.

(ii) They require large areas.