Solar energy storage by salinity gradient solar pond: Pilot plant construction and gradient control

An experimental solar pond pilot plant was constructed in Solvay-Martorell, facilities, Catalonia (NE part of the Iberian Peninsula) to capture and store solar energy. The body of the pond is a cylindrical reinforced concrete tank, 3 m height, 8 m diameter and total area of 50 m2. Salinity and thermal gradient were properly established by using the salinity distribution methodology. The gradient in the pond was maintained by feeding salt (NaCl) through a cylindrical salt charger to the bottom at a height of 80 cm from the pond floor. Continuous surface washing using tap water supply maintained the salinity of the top convective layer at a low level and compensate loses by evaporation. An acidification method by addition of HCl at different heights was used to control the clarity of the pond. The salinity gradient was fully established on 30 September 2009 and has been maintained until the date. After winter time (February 2010), the pond warms up and the temperature increased continuously until it reached its maximum (55 °C) in August 2010. The salinity gradient observed great stability after one year of continuous control and maintenance and under different weather conditions.