Performance study on a photovoltaic thermal (PV/T) stepped solar still with it a bottom channel

This study presents a novel type of stepped PV/T solar still in which a bottom channel is designed under the base of the still, aiming to enhance heat transfer. In order to assess the performance of the desalination system, a theoretical model is established, and validated by the existing experimental data, thus can be used for energy and exergy analysis. The effects of bottom channel structure on thermal performance (temperatures of components, heat transfer coefficients, thermal efficiency), exergy performance (total exergy loss of each component, exergy efficiency) and freshwater productivity are investigated. The comparative results show that, when the depth of bottom channel H is 0.01 m, the average heat transfer rate from absorber plate to saline water is improved by 44%, thereby the average temperature of saline water is raised by 16.4% and the daily freshwater productivity is improved by 51.7%. Moreover, the average thermal efficiency and exergy efficiency are increased by 17% and 3% respectively. However, the freshwater productivity could be decreased due to the increase of H. Compared with H = 0.01 m, the daily fresh water production is decreased by 17% when H = 0.03 m. The results of the exergy analysis indicate that the optimum depth of bottom channel is around 0.01 m.