Development and application of a thermal model for the improved stepped solar still with a built-in passive condenser

Recently, the author proposed, fabricated, and experimentally tested an improved stepped solar still (ISS) with a built-in passive condenser, which exhibited significantly better performance than the standard version. Therefore, this paper presents a detailed transient thermal (theoretical) model for the ISS. The model is based on mass and energy balance equations for various components of the solar still, including the absorber, saline water, glass cover, insulation layer, backplate, condenser plate, and humid air in both the evaporator and condenser chambers. The model was programmed and solved using the MATLAB software. In contrast to previous studies that confined their model validation to a single day and specific conditions, this investigation rigorously validated the developed model using a comprehensive range of experimental data collected under diverse operational and meteorological conditions. Results show that, for all the conditions considered, there is very good agreement between the theoretical and experimental observations. The model has a maximum relative error of 3.7% in the estimation of daily freshwater yields, and it has a root-mean-square error (RMSE) of 4.7, 2.9, and 2.7 0C in the estimation of glass cover, absorber, and brine water temperatures, respectively. Finally, the model is used to predict and theoretically investigate the impact of meteorological design and operating parameters on the performance of the ISS. The analysis showed that a 20% increase/decrease in solar intensity would cause a corresponding increase/decrease in daily production by approximately the same amount.