A solar pond is a large scale energy collector with integrated heat storage for the thermal application. In the solar pond, the water in the pond is made dense artificially by adding salt to it. This prevents water after getting hot from rising to the top of the pond. The solar energy remains trapped in the pond and temperatures in the range of 85’ Celsius are attained.
The solar pond has three distinct layers. The first top layer or the upper convective layer zone consists of very low salinity water about 50cm thick. The middle layer is the non-convective zone acting as an insulator, is 1.5 m thick. The third convective layer stores heat has saturated solution and is 1.5 m thick. Plastic liners are used to prevent seepage of saline water. The density gradient in the middle layer measures the performance of the solar pond. This density gradient is established by floating layers of water on top of the salt solution. For monitoring the density of solution at different levels, the solution is extracted by vacuum pumps to measure density and temperature. After establishing the gradients, the pond is left for 2-3 months for heating up. Then it can be utilized for various applications like process heat, preheating of boiler fed water, drying, refrigeration, power generation and water desalination. It supplies thermal energy, electrical energy, and potable water.
India is the first country in Asia to have a solar pond in the Kutch district of Gujarat, called the Bhuj Solar Pond Project developed in 1987. It is a joint venture of the Gujarat Dairy Development Corporation, Gandhinagar, the Gujarat Energy Development Agency, Baroda and the Tata Energy Research Institute, New Delhi.