Long-Term Experimental Analysis of Solar Still Performance for Water Desalination in Poland

Solar Energy to Water Desalination: Long-Term Experimental Studies of Solar Still in Poland

Abstract: Water scarcity is an increasing global concern that also impacts Poland. One solution to this issue is seawater desalination, particularly using solar stills (SSs). SSs provide a sustainable and low-cost method for desalination, but their efficiency largely depends on local solar conditions. This study presents long-term experimental data on the performance of a single-basin, single-slope SS in Krakow, Poland, from May to September 2022. The results indicate that the SS effectively removed over 98% of total dissolved solids, achieving productivity rates between 1084 and 5014 mL/(m²·day), with water temperatures reaching as high as 80.4 °C. These findings underscore the viability of solar-powered desalination in Poland and offer valuable insights for future optimizations.

1. Introduction

Water is essential for daily life and is utilized across various industries. Globally, approximately 4.0·10² m³ of freshwater is consumed each year, with 70% allocated to agriculture, 20% to industry, and 10% to domestic use. Although total global water resources far exceed the amount withdrawn, nearly 97% consists of saline water, which cannot be used directly in industry or agriculture. Thus, water desalination emerges as a crucial solution to meet the growing water demand.

Several methods for water desalination exist, including multi-stage flash, multi-effect distillation, reverse osmosis, electrodialysis, and nanofiltration. Most of these techniques require electricity or thermal energy, primarily derived from fossil fuels, which contribute to CO2 emissions. Consequently, there is an increasing demand for alternative desalination technologies, especially solar-powered options.

Solar desalination can be categorized into direct and indirect methods. Indirect methods integrate solar collectors or photovoltaics with traditional desalination technologies. In contrast, direct solar-powered desalination methods, such as humidification–dehumidification and solar stills, directly utilize solar energy to heat and evaporate water.

Solar stills mimic the natural hydrologic cycle: solar radiation is absorbed, converted to heat, and transferred to saline water, causing evaporation and condensation within a glass cover. SSs have multiple advantages, including low capital and maintenance costs, straightforward design, and operation solely on solar energy. However, their most significant drawback is low productivity, which is influenced by various factors, including meteorological conditions.

Most existing literature on solar stills focuses on short-term studies, often disregarding seasonal variations. Long-term experimental or theoretical studies are limited, though some research has been conducted by various authors.

This paper presents long-term experimental results for a solar still in Krakow, Poland, focusing on the impact of feed water salinity on removal efficiency and productivity. It aims to provide a comprehensive database for future research and methodology development related to solar still performance.

2. Materials and Methods

2.1. Experimental Setup

The experimental setup consists of a solar still, a feed water tank, a distillate tank, a supporting structure, measuring devices, and a data acquisition system. For experiments involving phase-change material (PCM), pockets filled with PCM were placed on the absorber of the solar still.

The solar still is constructed from stainless steel with an absorber measuring 1.0 × 0.5 m², painted black to enhance absorptance. The glass cover is inclined at 30° to optimize annual productivity. The water level in the still is maintained by the feeding tank.

2.2. Experimental Procedure

Experiments were conducted at the AGH University of Krakow from May to September 2022. Initial tests examined the impact of feed water salinity on productivity and distilled water quality, using three salinity levels (0, 20, and 40 g/kg). Following these initial trials, further experiments assessed the productivity of the solar still under various weather conditions and with different PCM masses.

3. Results and Discussion

3.1. Effect of Water Salinity on Removal Efficiency

The productivity of the solar still and the electrical conductivity of the distilled water were measured against feed water salinity. The results indicated a removal efficiency of over 98%, confirming the effectiveness of the solar still in desalinating water.

3.2. Productivity of Solar Still

The productivity rates across 23 experiments varied depending on meteorological and operational conditions, ranging from 1084 to 5014 mL/m²/day. Solar irradiance was shown to be the most significant factor influencing productivity.

3.3. Comparison to Literature

The findings were consistent with previous studies on single-slope solar stills. However, many earlier studies lacked comprehensive meteorological data, which is crucial for comparing different systems.

4. Conclusions

The research confirms that solar stills represent a feasible method for water desalination, achieving over 98% removal efficiency of total dissolved solids. The distilled water exhibited low electrical conductivity, suggesting potential applications in areas requiring high water quality. Despite the promising results obtained during the study, further research is necessary to evaluate the solar still’s performance throughout the year and to explore additional methods for enhancing its efficiency.

This study highlights the importance of meteorological parameters in evaluating solar still performance and suggests future work should focus on developing methodologies that facilitate comparisons of results across varying conditions.