Evaporation suppression and solar energy collection in a salt-gradient solar pond Jeffrey A. Ruskowitz a , Francisco Sua ´rez b , Scott W. Tyler c , Amy E. Childress d,⇑ a Department of Civil and Environmental Engineering, University of Nevada, Reno. 1664 N. Virginia St. MS 258, Reno, NV 89557, USA b Department of Hydraulic and Environmental Engineering, Pontificia Universidad Cato ´ lica de Chile, Av. Vicun ˜a Mackenna, 4860 Santiago, Chile c Department of Geological Sciences and Engineering, University of Nevada, Reno. 1664 N. Virginia St. MS 172, Reno, NV 89557, USA d Astani Department of Civil and Environmental Engineering, University of Southern California, 3260 South Vermont Ave., KAP 210, Los Angeles, CA 90089-2531, USA Received 6 June 2013; received in revised form 15 October 2013; accepted 28 October 2013 Available online 26 November 2013 Communicated by: Associate Editor Aliakbar Akbarzadeh Abstract Evaporation represents a significant challenge to the successful operation of solar ponds. In this work, the suppression of evaporative losses from a salt-gradient solar pond was investigated in the laboratory. Two floating element designs (floating discs and floating hemi- spheres) and a continuous cover were tested; all three covers/elements were non-opaque, which is unique from previous studies of evap- oration suppression in ponds or pools where increasing temperature and heat content are not desired. It was found that floating discs were the most effective element; full (88%) coverage of the solar pond with the floating discs decreases the evaporation rate from 4.8 to 2.5 mm/day (47% decrease), increases the highest achieved temperature from 34 °C to 43 °C (26% increase), and increases heat content from 179 to 220 MJ (22% increase). As a result of reduced evaporative losses at the surface, the amount of heat lost to the atmosphere is also reduced, which results in lower conductive losses from the NCZ and the LCZ and hence, increased temperatures in the NCZ and LCZ. The magnitude of evaporation reduction observed in this work is important as it may enable solar pond operation in locations with limited water supply for replenishment. The increase in heat content allows more heat to be withdrawn from the pond for use in external applications, which significantly improves the thermal efficiencies of solar ponds. Ó 2013 Elsevier Ltd. All rights reserved. Keywords: Salt-gradient solar pond; Solar energy; Evaporation suppression; Transparent pond covers; Distributed temperature sensing 1. Introduction 1.1. Energy collection and storage For most bodies of water (e.g., lakes and ponds), as solar radiation penetrates into the lake or pond, warmed water rises to the surface due to its decreased density. Once the warmed water reaches the surface, heat is easily lost to the atmosphere through evaporation and long-wave radia- tion. In salt-gradient solar ponds (SGSPs), which are spe- cifically designed to store heat, this circulation of water is suppressed via salinity stratification. The heat is then stored in the bottom of the solar pond for use in renewable energy applications. Long-term heat collection and heat extraction applications include heat for buildings, power production, process heating, and agricultural crop drying (Rabl and Nielsen, 1975; Hull et al., 1989; El-Sebaii et al., 2011). Solar ponds have also been utilised as an energy source for freshwater production by membrane distillation (Solis, 1999; Walton et al., 2004; Sua ´rez, 2010; El-Sebaii et al., 2011). 0038-092X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.solener.2013.10.035 ⇑ Corresponding author. Tel.: +1 213 740 0606. E-mail addresses: ruskowitz@gmail.com (J.A. Ruskowitz), fsuarez@ ing.puc.cl (F. Sua ´rez), styler@unr.edu (S.W. Tyler), amyec@usc.edu (A.E. Childress). www.elsevier.com/locate/solener Available online at www.sciencedirect.com ScienceDirect Solar Energy 99 (2014) 36–46