Solar & Wind Technology Vol. 1, No. 3, pp. 161-165, 1985 0741--983X/85 $3.00+0.00 Printed in Great Britain. Pergamon Press Ltd. STUDIES ON VARIOUS DESIGNS OF SOLAR DISTILLATION SYSTEMS G. N. TIWARI and H. P. GARG Centre of Energy Studies, Indian Institute of Technology, Hauz Khas, New Delhi--110016, India (Received 8 February 1984; accepted 15 June 1984) Al~'aet--In this paper, the pcfformano." of Various designs of solar stills has been presented. The ~cct of design and operational parameters on the performance of singlebasin solar stills has been discussed in d©tail. On the basis of experiments as well as theoretical observations, it is concluded that the multiwick solar still is the most economic and ¢tticicnt among existing solar stills. INTRODUCTION Solar distillation has been practised since the early nineteenth century. The great French chemist Lavoisier (1982) used a concentrator of solar energy for the distillation of the contents of a flask [1]. Use was made of solar distillation for supplying fresh water to a nitrate mining community in 1872 near Las Salinas in Northern Chile [2], with the help of a conventional single basin solar still. Since other methods of distillation were of popular interest, solar distillation did not grow much till World War I, when several types of device e.g. roof type, V- covered, wick type, inclined tray, tubular and air inflated stills were developed. Malik et al have presented a historical review of the work done on solar distillation [3]. Several attempts have been made to improve the efficiency of the solar distillation process. Forced circu- lation of air inside the still was one of the means suggested to enhance the performance. Use of the latent heat ofvaporisation in either multi effect systems or for preheating the brine to increase the output of stills has also been suggested. Though large scale basin type solar stills were installed in different parts of the world, yet it was realised that the basin type stills could not compete economically with other methods of desalination for producing fresh water. But a phenomenal increase in the cost of energy and other energy intensive modes of getting fresh water have triggered renewed interest in solar distillation. In addition to numerous testing of various designs of solar stills, extensive investigations have been undertaken to study different aspects of basin type solar stills (also called greenhouse type or roof type). Graphical [4] as well as digital [5, 6] simulation methods have been formulated to study the transient performance of a still. Theoretical models to predict the performance of the solar still have been developed by various authors, viz. Malik and Tran [7], Garg and Mann [8], and Hirschmann and Roeflcr [10]. Baum et al. [11] have presented periodic solutions for the still performance Frick [12] has shown the convenience of his mathematical model for the still using the diagrams of Sankey and thermic circuits and has illustrated the model considering only a sine heat flow. Recently periodic as well transient analysis of various solar stills, viz. single basin, double basin and multi wick have been presented by Nayak et al. [ 13], Sodha et al. [ 14-16] and Tiwari and Malik [ 17]. Several other types of still have also been proposed and studies have been made on the performance. EFFICIENCY OF THE STILL If Q~Jm- 2 day- 1) denotes the solar flux incident on the still and Q, (J m- 2 day- 1), the amount of energy utilized in vaporising the water, the daily output of the distilled water Me (kg m -2 day- 1) is given by Me Qe L where L is the latent heat of vaporisation of water. The efficiency 07) of the still is given by = Q--~ x 100%. Qt PERFORMANCE OF SINGLE AND DOUBLE BASIN SOLAR STILLS Schematic and the energy flow diagram of a single basin solar still is shown in Fig. I. There are three major 161