Application and Development in Solar Stills: A Review

Abstract

One-third of the Earth is covered by the sea water, yet there is a constant lack of water in many places. 97% of the water is present in the sea as saltwater, only 3% water is potable, out of which only 1% clean water reaches to the people. Therefore, a device is needed that can convert saltwater into clean water. Solar still is a sustainable device, through which dirty and salt water can be converted into clear water. Due to the very low productivity of conventional solar still; it is not popular in the market. Increasing the productivity of conventional solar still is a major challenge for researchers. Researchers are continuously working on the performance of solar still to increase its productivity. In present paper studies the modifications and designs made by researchers in solar still over the last 10 years. In which PCM, nanoparticles, reflectors, collectors, external condenser, wick material and differential angle based solar still have been studies and applications of distilled water produce by solar still have been also covered.

Introduction

Water is essential for life, yet only 3% of Earth's water is freshwater, with just 1% accessible for human use. The rest is saline and unsuitable for drinking. As global populations grow, the demand for potable water increases, highlighting the need for efficient desalination methods. Solar stills (SS) offer a sustainable solution, using solar energy to convert saline water into freshwater.

Types of Solar Stills

• Passive Solar Stills (PSS): Operate naturally without external energy sources.

• Active Solar Stills (ASS): Utilize external energy sources, such as pumps or fans, to enhance performance.

Both can be further categorized into single-slope and double-slope designs, based on the structure of the condensing cover.omicsonline.org+1mdpi.com+1

Enhancements to Improve Productivity

Researchers have developed various modifications to increase the efficiency and output of solar stills:

• Reflectors: Placing external and internal mirrors increases solar radiation inside the still, enhancing evaporation rates.

• Collectors: Integrating solar collectors, like evacuated tube or flat plate collectors, preheats water before it enters the still, reducing energy requirements for evaporation.

• External Condensers: Adding separate condenser chambers increases the condensation area, improving overall productivity.

• Ultrasonic Vibrators/Foggers: Ultrasonic devices break water molecules into smaller droplets, increasing evaporation rates.

• Wick Materials: Materials like jute cloth or sponges increase the surface area of water, enhancing evaporation.

• Tilt Angles: Adjusting the tilt angle of the still optimizes solar radiation absorption, improving efficiency.

• Parabolic Trough Collectors: Using curved reflectors focuses solar energy onto the still, increasing water temperature and evaporation rates.

• Charcoal Cylinders: Charcoal's high absorption capacity retains heat, allowing for continued evaporation even after sunset.

• Stepped Basins: Multiple layers of water reduce the volume per layer, allowing for quicker heating and evaporation.

• Nanoparticles: Adding materials like CuO or SiO? to the water increases thermal conductivity, enhancing evaporation rates.

• Phase Change Materials (PCMs): Substances that absorb and release heat during phase transitions help maintain consistent temperatures, improving night-time productivity.

Performance Improvements

Studies have shown significant enhancements in solar still productivity through these modifications:

• Reflectors: Increase productivity by up to 50%.

• Collectors: Enhance efficiency by 20–30%.

• External Condensers: Boost productivity by 40–50%.

• Ultrasonic Devices: Improve evaporation rates by 15–25%.

• Wick Materials: Increase yield by 20–30%.onlinelibrary.wiley.com

• Tilt Angles: Optimize efficiency by adjusting to seasonal solar angles.scijournals.onlinelibrary.wiley.com

• Parabolic Troughs: Enhance productivity by focusing solar energy.onlinelibrary.wiley.com

• Charcoal: Maintain evaporation rates post-sunset.

• Stepped Basins: Accelerate heating and evaporation.

• Nanoparticles: Increase thermal conductivity, boosting evaporation.

• PCMs: Maintain consistent temperatures, improving night-time productivity.

Conclusion

The productivity of solar still depends on the solar radiation. The higher the amounts of solar radiation received by the setup, itincreases the productivity. Hence, solar collectors, wick materials, stepped basins, and parabolic trough collectors have been used by the authors to increase the surface area for receive the large amount of solar radiation. Heat storage materials are used to store solar radiation such as PCM, charcoal cylinders, etc. The higher the amount of solar radiation reaches to the basin, the increase the evaporation rate of the basin water, so, the mirrors and reflectors have been used by the authors. Increasing the evaporation rate alone does not increase productivity, for this, the condensation rate also has to be increased. That is, the faster the evaporation, the faster the latent heat will release, then the condensation rate will increase, Hence the external condenser has been used by the authors.

References

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Copyright

Copyright © 2025 Shashank Saxena, Avinash Bajpayee. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.