Experimental and analytical study of water production of solar still

Abstract

Rapid population growth and industrialization have increased the demand on potable water dramatically, and there are many rural areas and communities around the world which suffer from the shortage of potable water. However, many of these communities inhabit desert areas where the weather is hot and solar energy is plentiful. Therefore, the present study suggests basin-type solar stills for desalination, which uses solar energy to evaporate the saline water. The use of solar stills in large scale commercial systems is limited by the low production rate of desalinated water. Therefore, the present study focuses on the effects of different parameters on the thermal performance and productivity of a single basin double slope solar still. It is well known that the performance of a solar still can vary from one country to another due to the effect of meteorological conditions. The experiments of the present study were conducted in Kuwait. A double slope solar still was designed and fabricated, and the data were collected over a long period of time to achieve high accuracy. The effects of several parameters on the performance of the examined solar still were investigated. These parameters include the following: (1) type of energy storing materials, (2) basin water depth, (3) the cooling of the solar still cover plate. The experimental data were verified using a theoretical model. The investigated energy storage materials included steel metal pieces in different shapes, gravel in two different sizes and encapsulated paraffin wax as a phase change material. This study has concluded that the basin water depth has a significant effect on the daily water production and the water production rate. This rate increases as the water depth in the basin decreases. A correlation was developed to express the relation between the daily water production and the basin water depth. The study has also found that the performance of the solar still with the energy storing materials depends on the material density and specific heat capacity. A new dimensionless factor called “energy storing material factor (β)” was introduced. It was found that the performance of the energy storing materials is proportional to the values of β. For β < 1, the energy storing materials can improve the water productivity. Among the studied energy storing materials, the phase change material has achieved the highest total water production per square meter (about 53% improvements). This present study contributes to improving the design of passive basin-type solar stills which can be used for water production in many rural and desert areas which do not have access to electricity. The study also discusses some ideas to enhance the water productivity of passive solar stills, which is still a big limitation to the widespread use of solar stills.