Barbara GoodsSolar water distillation is a handy means to process water and economically reduce the use of contaminated water. Solar power experts explain how it uses the energy from the sun to separate clean water from dissolved salts and other contaminants.
Water is one of the essential substances for the survival of all living things. But several parts of the world still struggle to supply safe water for domestic and industrial uses.
Solar distillation follows the process of evaporation through the absorption of heat. It has been in use for several decades. But though the usage dropped recently with technological advancement globally.
This article covers the principles of solar distillation, the types, advantages, disadvantages, and more.
What Is Solar Distillation?
Solar distillation is a process that uses solar energy to evaporate freshwater from a large water body such as a sea or lake. The process is more profitable for small remote areas or arid regions in solving issues of limited access to fresh water.
Also, using solar power cuts down electricity costs for processing clean water from the salty water. Usually, solar distillation works best in places with high solar radiation, which is the energy from the sun to the Earth.
Advantages
- Solar stills provide better and cheaper options for getting clean water, especially in remote locations.
- There are no moving parts in the distillation units.
- The construction and maintenance of the systems are pretty low.
- Solar distillation system requires no electricity costs to function.
- It is helpful in climate change goals.
- The system is highly beneficial at the household level and offers excellent opportunities for scaling up large production.
Disadvantages
- Solar stills or distillers do not heat the collected water to its boiling point. So, they do not eliminate harmful chemical substances or kill bacteria.
- The distillation rate in the solar stills is very slow with conventional solar energy.
- The productivity of the distillation units will not satisfy greater demands for drinking water.
- It may be hard to obtain all the materials for the design of the distillers in some places.
- Larger roof surface covers for the distillers could attract and trap bugs and others insects.
Operations of Solar Distillation
Solar water distillation operates based on two major principles; evaporation and condensation. The two principles lead to the separation of fresh water from salty or brackish water. Hence, the resulting freshwater is useful for domestic consumption such as drinking, cooking, washing, etc.
Solar water distillation runs with high energy efficiency. Unlike desalination, a process is a low-cost approach to getting clean water for drinking. It is carried out in a solar distiller or still containing all the distillation equipment.
Evaporation Process
During the process, water evaporates from the body of water, leaving salts, minerals, and other impurities below. The distiller equipment comprises a transparent glass cover serving as a roof over a body of water. The area is flat, having good access to sunlight exposure for faster evaporation.
Usually, water can evaporate due to the temperature difference between the water body and the atmosphere. However, the heat from sunlight increases the evaporation rate of the water.
The absorbed solar energy is insufficient to raise the water temperature from 0oC to 100oC and cause boil and vaporization. But the latent heat released when the water vapor condenses to water droplets returns the body of water to cause further evaporation.
Condensation Process
This process ensures the collection of water molecules as the vapor loses its heat. Usually, the transparent cover is the condenser surface where the water vapors condense and are collected through funneled poles. The surface is tilted to a contact angle at the water collection point.
Some distillers take up more space, like six square meters, to allow the production of enough pure water within the region. In some cases, there could be multiple solar distillation systems on large-scale productions.
Types of Solar Water Distillers
The solar distillation systems consist of solar stills that ensure the distillation process of water through evaporation and condensation.
There are two main types of solar distillers.
Active Solar Distillers
In an active solar water distiller, the entire heating of the saline water does not depend only on the energy from solar radiation. There are added efforts to increase the efficiency of the distiller.
Usually, the saline water is preheated by another thermal energy source to speed up the evaporation rate during an active solar distillation. Thermal conductivity can be set up in the system by introducing discharged hot water or waste heat from different industries.
Generally, solar distillers are designed to be airtight. This checks against efficiency drops during distillation and contaminants from the air.
Passive Solar Distillers
Passive solar stills depend solely on the energy from the sun. Hence, the efficiency of such a solar distillation system is usually low. However, these solar stills can have a larger surface area with more exposure to sunlight. This helps for faster water evaporation by increasing the ambient temperature.
Some factors can influence the performance and productivity of a solar still, such as the still design and climatic and operating parameters. The parameters include water depth, water temperature, top cover temperature, thickness and inclination, collector area, and wind velocity.
Here are some passive solar water distillers.
Single-effect Solar Still
This is the simplest and commonest type of still. The distiller is designed with just a single interface for transferring the heat for distillation and collecting the condensate.
Multiple-effect Solar Still
In multiple-effect still, the design must ensure tight seals to avoid unnecessary heat loss. This is because the condensation heat of a previous effect is used in heating the polluted water in the next effect.
Wick Solar Still
This still type uses cloth-like materials that allow capillary action to maintain the right water movement throughout the still production. Usually, solar radiation still passes through the wick surface and provides the energy for heating the water. The flow is maintained by capillary action through the wick for greater efficiency.
Multi-wick Solar Still
A multi-wick still will exponentially increase the production of distilled water by enhancing the surface range of the still. Its capacity is equivalent to that of multiple wick stills.
Basin-type Solar Still
Basin-type stills are also common, with less complexity in their design. They have a material that resembles a basin which is the component for housing the salty water.
Diffusion Solar Still
A diffusion still operates like an advanced combination of the wick and multi-effect stills. Diffusion stills have parallel partitions closely spaced and in contact with wicks soaked in the water.
Heat flow with the still is through diffusion among the wicks. This type of solar still is highly productive for sustaining rural areas.
Solar Desalination
Solar desalination is a process used to obtain drinking water from salt water through the use of solar energy. It copies the Earth’s natural water cycle, which entails how nature makes rain. The desalination process comes in two basic methods; direct and indirect.
The direct method uses desalination plants as basic solar stills. The saltwater in the still will receive direct exposure to the sun, which heats and converts the solution to water vapor. On hitting the top roof, the vapor will condense and flows to the collection containers. Generally, the direct method produces a low quantity of water and is unsuitable for commercial purposes. This is because it lacks higher temperatures to increase the rate of water vaporization and produce more desalinated water.
The indirect method is more suitable for producing larger scales of purified water. It combines two technological approaches for increased efficiency. These include solar energy collection, such as photovoltaic panels for more heat to generate high temperatures in the plants. Also, there’s the proven desalination process, such as reverse osmosis desalination, multiple effect evaporation (MEE), or multistage flash (MSF) distillation.
Conclusion
Solar distillation has become one of the outstanding processes for meeting the demand for good water. The process depends majorly on the heat from the sun to trigger distill water suitable for drinking.
In line with the World Health Organization (WHO) specifications, it is essential to maintain water safety plans (WSP) for water supply from solar desalination.
