Because the sources of non-solids and pure water begin to be more and more limited, the world is looking for other alternatives that will help to cope with this problem. As a result we find one of the options, desalination. This consists of a reverse osmosis program which is responsible for separating salt from seawater with the aim of creating fresh water for people and agriculture.

WHAT IS SOLAR DESALINATION?

   Solar desalination is based on the desalination of water, with solar energy as its main tool. This type of renewable energy exceeds the operating costs of energy that are generally quite high, as well as the greenhouse emissions that conventional reverse osmosis can cause. Reverse osmosis is usually more popular, known and profitable. However, solar desalination has a bigger boom every time.

   There are two basic methods that are used to carry out this type of desalination. Sunlight is able to provide heat for all those evaporation desalination processes, or it can also be for some indirect methods.

Solar desalination methods

  • Direct: This is the direct method, based its operation on a solar collector which is combined with a distillation mechanism. This is a process that takes place in a fairly simple cycle. Here we find solar stills that are described in survival guides; these are provided in marine survival kits as well as being used in some small desalination and distillation plants.

   This type of solar desalination emulation is proportional to the area of ​​the solar surface and the angle of incidence this means that it has an average value of between 3–4 liters per square meter. According to this information, it is deductible that this method is favorable to plants that have a capacity of less than 200 m3 / d

  • Indirect: This in turn applies two separate systems; the first is based on a solar collection matrix, which is mainly composed of photovoltaic and fluid-based thermal collectors, and the other one is a conventional desalination plant that is separated.

   An important aspect of this type of desalination is that it depends on the efficiency of the plant and normally the cost per unit produced is usually reduced by an increase in scale. Many plant arrangements have been analyzed; they have been experienced and sometimes installed. Here you can find multi-effect humidification, instant multi-stage distillation, multi-effect distillation, dehumidification and freeze-effect distillation, however it is not limited to just this and may include others.

Objectives of the solar desalination

  • Among the main objectives of solar desalination we have to focus on innovations that can improve your process and efficiency, while addressing challenges such as scaling and corrosion.
  • Explore what is related to solar energy collection and storage technology while it is low cost, as this can reduce the leveling cost of heat and incorporate important features such as dispatchability and portability.
  • Some projects seek to create integrated solar-thermal desalination systems that can improve system efficiency and also reduce the leveling cost of water.
  • Another objective is to develop analysis tools that are necessary to improve the process itself.

Environmental impact of desalination

   Due to the shortage of fresh water and its high demand in recent decades, methods such as these become the first option and inevitable. However, this is a very intensive process in terms of energy consumption and not only that, but it also has a negative impact on the environment.

   By applying this, there is a concentrated brine discharge, which hinders the life of marine ecosystems. This discharge of waste that comes from desalination processes such as solar has become an important challenge that increasingly takes center stage.

   Probably the most important factor is the high energy consumption.

   Most desalination processes are driven by the energy that is obtained by fossil fuel. When this dependence is present and when the increase in seawater desalination is noticed, the remarkable emissions of gases that pollute the environment are the result.

   However, it is well known that the solar energy desalination process is promising ecologically speaking, as it is considered less harmful because it relieves the environmental impact of water desalination, in addition to a sustainable source of drinking water. All this because it focuses its energy source on the sun and not on the dependence on fossil fuel.

Marine life and solar desalination

   The large amount of concentrated brine discharge in salt water desalination plants is an unpleasant and also harmful waste.

   These discharges are harmful to marine life and are therefore severely affected. Brine by itself is not only composed of salt, but also brings with it chemical products such as antifouling agents before and after treatment. Unfortunately, brine removal has become a problem that defies all desalination technologies. The brine that is discharged as a result of the membrane-based desalination is much more concentrated than the brine discharged from thermal distillation plants. But, the brine that comes from desalination such as solar leaves at a relatively high temperature if compared to membrane-based distillation.

   This type of thing directly influences marine life, so strongly that only a little of organisms, whether plants or marine animals can withstand the high temperature near the exit of thermal distillation plants. The extraction of water is also not ignored, when a large amount of seawater is extracted from the sea, many marine organisms and algae can be absorbed by the intake, this happens to cause disturbance in the ecosystem.

Problems with thermal systems

   There are two design problems that are inherent in regards to solar thermal desalination. In the first hand is the efficiency of the system which is governed by heat transfer rates and also high during evaporation and during condensation. Surfaces must be adequately designed with regard to the contradictory objectives of economy and reliability.

   On the other hand, the heat of condensation is very valuable and important since large amounts of solar energy are needed so that water evaporation is possible and saturated hot air can be generated and charged with steam. 

   The obstacle or challenge in the field today is to achieve the optimum temperature difference between the steam generated by solar energy and also the condenser cooled by seawater, among other things is the maximum reuse of energy of condensation and try to minimize the investment of assets.

SUMMARY

   Drinking water is increasingly considered a much scarcer resource, especially in arid and remote regions. Although conventional desalination technologies are an excellent alternative to meet the demand for water, it is already known that they are processes that produce collateral damage by requiring a lot of electrical energy, so they become good use on a large scale but not for small-scale demands

   For this and more, solar desalination is expected to mark a change in what is known about this group of methods, to alleviate water scarcity and at the same time not produce as many side effects.