Performance research and comparison of integrated passive solar-concentrated stills buried in soil: With/without heat recovery

Abstract

Although interfacial evaporation based on new materials and configurations has recently attracted great interest, there is still considerable potential for breakthroughs in low-cost, sustainable conventional solar stills. Conventional solar stills have always suffered from low evaporation temperatures, condensation droplets interference to the solar light transmission, and the inconvenience of heat recovery design. This paper addresses these shortcomings by designing an integrated passive solar-concentrated still with an embedded light concentration form, a suitable light transmission and evaporation–condensation structure, and a well-matched heat recovery configuration. The proposed solar still helps achieve better energy transfer and conversion and increase the yield and efficiency. This paper analyses and discusses the solar radiation transmission characteristics inside the proposed solar stills and conducts an experimental study of the solar-thermal-water conversion performance. The results show a maximum solar radiation transmission efficiency of 73.5%, identifying the key factors governing the solar radiation transmission efficiency. The discussion has pointed in the direction where the overall performance of the device can be further improved by refining the surface optical properties. The outdoor experiments show that the total water yield of the solar still with heat recovery could reach 3.67 kg/m2 per unit solar concentrator aperture area. The water production and practical evaporation efficiencies are about 37% and 57.8%, respectively, showing the superior performance of the solar-concentrated device with such an integrated structure. The experimental result comparison indicates that the solar still shows a 16.8% yield increment with the assistance of the heat recovery unit, illustrating the effectiveness of heat recovery configurations at sidewalls. This paper provides meaningful future directions for the development of passive solar stills.