Numerical and experimental analysis of a salt gradient solar pond performance with or without reﬂective covered surface Nalan C ¸ . Bezir a , Orhan Do ¨ nmez b , Reﬁk Kayali b, * , Nuri O ¨ zek a a Department of Physics, Faculty of Art and Science, Su ¨ leyman Demirel University, 32260 Isparta, Turkey b Department of Physics, Faculty of Art and Science, Nig ˘ de University, 51200 Nig ˘ de, Turkey Received 21 September 2007; received in revised form 21 February 2008; accepted 21 February 2008 Available online 3 April 2008 Abstract An experimental salt gradient solar pond having a surface area of 3.5  3.5 m 2 and depth of 2 m has been built. Two covers, which are collapsible, have been used for reducing the thermal energy loses from the surface of the solar pond dur- ing the night and increasing the thermal eﬃciency of the pond solar energy harvesting during daytime. These covers having reﬂective properties can be rotated between 0° and 180° by an electric motor and they can be ﬁxed at any angle automat- ically. A mathematical formulation which calculates the amount of the solar energy harvested by the covers has been devel- oped and it is adapted into a mathematical model capable of giving the temporal temperature variation at any point inside or outside the pond at any time. From these calculations, hourly air and daily soil temperature values calculated from ana- lytical functions are used. These analytic functions are derived by using the average hourly and daily temperature values for air and soil data obtained from the local meteorological station in Isparta region. The computational modeling has been carried out for the determination of the performance of insulated and uninsulated solar ponds having diﬀerent sizes with or without covers and reﬂectors. Reﬂectors increase the performance of the solar ponds by about 25%. Finally, this model has been employed for the prediction of temperature variations of an experimental salt gradient solar pond. Numer- ical results are in good agreement with the experiments. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Solar pond; Analytical function; Daily and hourly temperatures; Performance; Reﬂector 1. Introduction A salt-gradient solar pond (SGSP) which consists of three distinct zones: an upper convecting zone (UCZ), a non-convecting zone (NCZ), and a lower convecting zone (LCZ), is an inexpensive solar energy collection and storage system for low-temperature heat-sources. The concept of the solar pond appears very simple: 0306-2619/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2008.02.015 * Corresponding author. Tel.: +90 388 2252152. E-mail address: reﬁkkayali@nigde.edu.tr (R. Kayali). Available online at www.sciencedirect.com Applied Energy 85 (2008) 1102–1112 www.elsevier.com/locate/apenergy APPLIED ENERGY