Physics of Solar Ponds

Abstract

Solar pond is essentially a solar radiation based heat collection and storage device with a built—in semitransparent insulation. This insulation is in the form of a nonconvective zone for salt gradient ponds, a honeycomb in case of honeycomb ponds and a Gel in the case of Gel ponds. Shallow ponds and roof ponds usually have opaque insulation covers, which, can be removed during Sunup hours. The significance of solar ponds as an option is that they are cheaper than conventional collectors, their construction primarily requires civil engineering expertise and easily available low energy input materials and they will use well proven technologies e.g. algal control as in swimming pools, brine pumping from chemical plants, heat exchangers as used in heat recovery systems etc. Also, they are the only solar thermal systems, which provide energy storage at the point of collection. By suitable design, the period of energy storage dould be extended from usual weekly basis to monthly or seasonal, if required. Honeycomb and Gel ponds are still in their infancy in terms of development and application where as salt gradient ponds have been used for quite some time for low grade heat needed for space heating, agriculture drying, chemical plants process water and for power generation till 5 mW scale [1,2]. Most salt gradient ponds are unsaturated ponds and till now have used Sodium Chloride [3,4] and Bittern from the sea [5]. Work on saturated ponds and marginally stable ponds [6,7] is yet to mature to yield applications. Recently, Hull has proposed ponds using Fertiliser salts [8] so as to reduce the possibility of any adverse environmental risks in case of liner rupture or construction and failures to simplify