Solar pond

Solar pond is an artificial pond which is constructed in such a way that temperature rise at lower regions are facilitated by preventing convection. Dissolving salt in the water is the best method to prevent convection which also maintains a good concentration gradient. Such ponds are known as salt gradient solar pond. Some other commonly constructed solar ponds are gel solar pond and equilibrium solar pond. The experiment with solar pond was first initiated by Tabor in Israel about 50 years ago. India’s largest solar pond is situated at Bhuj, Gujarat. A thick durable plastic liner is laid at the bottom of the pond to facilitate long term storage. Low density polyethylene, high density polyethylene, woven polyester yarn and hypalon reinforced with nylon mesh are used for this. Commonly used salts are magnesium chloride, sodium chloride and sodium nitrate. Concentration should be 30% at the bottom and zero at the top to obtain a good concentration gradient in the pond. During extraction of energy, hot water is removed continuously from the bottom. Solar pond is normally characterized by three zones- surface convective zone (SCZ), non-convective zone (NCZ) and lower convective zone (LCZ).