Techniques used to improve the performance of the stepped solar still—A review

Solar still is widely used in solar desalination processes. But the productivity of the solar still is very low. To enhance the productivity of the single basin solar still many research works is being carried out up till now. The various factors affecting the productivity of solar still are solar intensity, wind velocity, ambient temperature, water–glass temperature difference, free surface area of water, absorber plate area, temperature of inlet water, glass angle and depth of water. The solar intensity, wind velocity, ambient temperature cannot be controlled, as they are metrological parameters. Whereas, the remaining parameters can be varied to enhance the productivity of the solar stills. Depth of water in the solar still inversely affects the productivity of the solar still. Maintaining minimum depth in the solar still is very difficult. For maintaining minimum depth, wicks, plastic water purifier and stepped solar still were used. Investigations indicated that a reduction of the brine depth in the still improves the productivity, mainly due to the higher basin temperature. So that stepped solar stills can increase the distillate productivity about conventional solar stills, many reports studied the performance of stepped solar still. In this review, we are attempting to study the present status of different designs of stepped solar stills.