Solar pond technologies: a review and future directions

Abstract

Solar ponds, specifically salinity gradient solar ponds, present a number of advantages compared with other solar thermal technologies. They are relatively simple in concept, use abundant natural resources, and can provide heat upon demand since they include innate storage. They utilize established chemical, civil, materials, mechanical and industrial engineering practices, adapted for practical use in harnessing renewable energy. Solar pond technology has been significantly advanced during the last 15 years with three international forums focusing on their science and development. This chapter reviews the advances that have occurred, especially during the past 20 years. Pond hydrodynamics are increasingly well understood, at least for ponds using common salt, and operational stability has been maintained in field-operated ponds over annual cycles. Demonstrations of a broad range of new technologies, systems and components have provided valuable operational test results and a firm basis for predicting the performance of larger-scale commercial installations. A variety of useful applications have been tested and their feasibility demonstrated, including 234industrial process heating, electric power generation, mariculture, biogas production, desalination, and chemical (in particular salt) production. Key research projects at the Royal Melbourne Institute of Technology (RMIT) University in Australia and the University of Texas at El Paso, USA, that have contributed to these advances are described. Solar pond developments in other institutions and countries are reviewed. Priority areas identified as requiring more research and development to realize more economically viable systems include heat engines for electrical power generation from solar ponds, in particular trilateral and Kalina cycle engines; lining techniques; the use of alternative salts to sodium chloride; salt recycling systems; solar pond–multistage and/or multiple-effect flash desalting systems; and integration of solar ponds into salinity mitigation and arable land reclamation projects, mariculture and biotechnology applications.