Transient performance of a stepped solar still with built-in latent heat thermal energy storage

The transient performance of a stepped solar still with built-in latent heat thermal energy storage was studied. The still was designed for heating and humidification of agriculture greenhouses (GH) in remote areas. The solar still consists of five stepped basins with an inclined glass cover and is insulated on the bottom. The basin was placed on a slab filled with a layer of paraffin wax (phase change material, PCM) that acts as a latent heat thermal energy storage system (LHTESS). Air from GH enters the still from the bottom, flows between the basins and glass cover where it is heated and humidified, and then flows back into the GH. The still performance parameters investigated were analyzed, and the results compared with the case of a still without the LHTESS. The results showed that the still with LHTESS has an efficiency of 57%, and the total daily yield is about 4.6 L/m(2). The still temperature as well as outlet air temperature and GH heat load are more uniform compared to the sinusoidal trends for the still without LHTESS. It was found that the relative humidity of circulating air increased along the still and always leaves at saturation conditions. The results indicated that decreasing the air flow rate has an insignificant influence on the still yield, while the GH heat load experiences a decrease. For a selected design and operational parameters, the still was able to provide heat for the GH for 24 h/d. This finding is important since heat could be provided to the GH at night and when it is most needed.