Fuel energy is associated with the release of humongous amounts of greenhouse gasses known for causing global warming. To combat adverse climate change, environmentalists are pushing for the substitution of fuel energy with renewable energy like solar. In recent years, the use of solar energy in water treatment has gathered momentum, especially in off-grid locations.
The proliferation in the use of solar-powered desalination systems is primarily driven by the high solar potential of arid and semi-arid regions. Additionally, there are presently effective and highly efficient solar technologies as well as saline water desalination systems. Solar-powered desalination is equally effective as fuel-powered desalination and it is more environmentally sound.
As of 2016, over 300 million people depended on desalinated water and it is safe to conclude that this figure has risen considerably as more regions have been hit by freshwater scarcity. Our today’s article dwells on solar-powered desalination, the distinct equipment in use, and its feasibility in off-grid applications.
What is a Portable Solar Water Desalination System?
A portable solar water desalination system is a mobile water purification unit that converts saline water into fresh water using solar energy directly or indirectly. In the last few years, the use of solar desalination has proliferated immensely in off-grid locations as the demand for freshwater soars even higher. Modern solar desalination units are divided into two;
- Direct solar desalination equipment.
- Indirect solar desalination equipment.
• Direct Solar Desalination Equipment.
Direct solar desalination equipment eradicates dissolved salts from saline water using direct solar energy. Solar energy is harvested and used to power the desalination process in a centralized location. Solar stills are the most prominent devices used in direct solar desalination.
Essentially, direct solar energy is used to heat the salty water, subsequently provoking evaporation, which alienates the dissolved salts from the water. The vaporized water is consequently condensed to generate fresh, liquid water. Another renowned desalination technology reliant on direct solar energy is humidification dehumidification (HDH).
• Indirect Solar Desalination Equipment.
Indirect solar desalination systems collect and utilize solar energy using separate solar collection systems and desalination systems. The solar collection system can be located in a region far from where the desalination system is located. A comprehensive solar collection system consists of a solar collector, a photovoltaic panel, an exchanger, and storage batteries. The most prominent indirect solar desalination units include;
- Solar-powered reverse osmosis systems.
- Multi-effect distillation (MED) systems.
- Multi-stage flash distillation (MSF) systems.
- Vapor compression units.
Solar-Powered Desalination Technologies.
In the recent past, saltwater desalination has become a widely used and dependable alternative way of generating fresh water. Desalination is an illustrious process that alienates dissolved salts from saline water to make it potable. Thanks to impeccable innovations, we presently have over 5 desalination technologies helping off-grid communities survive the ravaging freshwater undersupply.
• Solar-Powered Reverse Osmosis.
Solar-powered reverse osmosis utilizes solar energy indirectly and it is one of the most effective and renowned saltwater desalination technologies. In reverse osmosis, solar energy is essentially used to power up integrated high-pressure pumps. It is a pressure-driven process that alienates dissolved salts from water using partially porous membranes.
In reverse osmosis, the osmotic flow is reversed meaning that water flows from the stream with a higher concentration to the stream with a lower concentration. The desalinated water collected as the end product is referred to as reverse osmosis permeate, while the solution containing the expunged salts is referred to as brine. Reverse osmosis has a salt removal rate of 99.7% and is extremely proficient at extracting other objectionable pollutants. Here is a visual representation of a solar-powered reverse osmosis system.
• Solar-Powered Distillation.
Solar-powered distillation is a simple yet effective and efficient saline water desalination technology. It is also referred to as evaporative desalination and it separates dissolved salts from water in a manner likened to the typical rain formation process.
Evaporative desalination uses a solar-powered heating medium to boil saline water to the point of evaporation. The vaporized water is consequently driven into the condenser, where it is chilled to produce fresh liquid water. Solar-powered distillation can be achieved using either of the following technologies.
Multi-Effect Distillation (MED).
In multi-effect desalination, the evaporation of water is undertaken in cells with equilibrium temperatures ranging from 40 ° C to 68 ° C. The latent heat of vapor condensation is used to heat the subsequent cell thereby minimizing the use of solar energy.
Advantages of Multi-Effect Distillation.
- High-quality desalinated water with salts of 50 ppm or lower.
- The chances of scaling are pretty low.
- Pretreatment is hardly necessitated.
- Operates on low temperatures.
- It is cost-efficient, especially when integrated with vapor compression. Presently, the cost of desalinating saltwater using a multi-effect distillation (MED) unit is approximately $0.7/m3.
Multi-stage flash (MSF) distillation.
In multi-stage flash distillation, saline water is heated up to a temperature of 120 ° C in the brine heater before being transferred into a second chamber (stage) with lower ambient pressure. The resulting vapor is subsequently chilled in a range of tubes running through the vessel.
Advantages of MSF distillation.
- It is highly dependable.
- The probability of scaling is quite low.
- It does not necessitate complex pretreatment systems.
- High-grade fresh water with salt concentrations of <50ppm.
- Relatively low production costs at <$1/m3.
Why It Is Worth Having a Portable Solar Water Desalination Equipment.
It is reported that in the early 1950s, each person was entitled to 4000m3 of fresh water per year. That figure has shrunk immensely and it is presently estimated that every person is entitled to only 1000m3 of fresh water annually.
However, with feasible water purification technologies such as desalination, mankind has the upper hand in fighting water scarcity. Here are some of the rewards one can bag by utilizing a portable solar water desalination unit.
• It Helps Conserve the Environment.
Solar-powered water makers are essentially powered by clean energy drawn from the sun. They do not utilize fossil fuels, which when burned produce carbon dioxide. CO2 is a greenhouse gas primarily responsible for global warming and adverse climate change.
On the contrary, solar desalination machines help reduce carbon emissions consequently averting global warming. Additionally, they provide a sustainable alternative source of fresh water, thereby mitigating the overexploitation of accessible freshwater reserves.
• You Get an Uninterrupted Supply of High-Quality Potable Water.
Without fresh water, human life is untenable. Solar water cleaning systems guarantee a continuous supply of high-grade potable water for households in off-grid regions. A portable solar-powered reverse osmosis system eliminates 99.7% of dissolved salts as well as undesirable microbes, organic chemicals, minerals, and heavy metals.
The quality of freshwater generated is constantly high and has a maximum salt concentration of 1,000 ppm. This water is fit for human consumption as it meets the stringent threshold set by the WHO organization.
• You Can Easily Transport the Equipment.
Portable desalination systems are compactly designed, light in weight, and easy to transport. You can easily and cheaply move around the system or even share it with neighbors, friends, or relatives. In addition, the mobility of portable solar water desalination equipment makes them ideal for emergency response services.
• Comparatively Low Production Costs.
Long gone are the days when desalination was viewed as an impractical solution to water scarcity due to high production costs. Modifications brought about by technological breakthroughs have tremendously shrunk the operational and maintenance costs of desalination equipment.
At present, desalinating seawater using a solar-powered RO water maker costs approximately $0.5/m3. Desalinating a similar amount of saline water using a multi-stage flash distillation device costs approximately $1/m3. The production costs, when using a multi-effect distillation unit presently average $0.7/m3.
• A Protracted Lifespan.
Typically, solar desalination devices are long-lasting systems with nonchalant maintenance demands. For instance, a portable solar-powered RO desalination system has an average lifespan of 15 years. However, if the system is rightfully utilized and serviced frequently, its lifespan can be extended to 20 years.
Challenges Associated With Portable Solar Desalination Equipment.
Portable solar desalination machines are generally high-yielding investments with multiple gains. However, they are not perfect. There are two problems linked to saltwater desalination that mildly affect the reputation of solar desalination systems.
• Production of Brine as a By-Product.
Saltwater desalination machines generally produce two streams of water; the permeate stream and the brine stream. The brine stream consists of expunged salts and it is extremely concentrated and dangerous. If re-injected into the ocean or other waterbodies, brine possess a significant threat to marine life. However, the brine can be disposed of appropriately or treated sufficiently for reuse.
• Considerably High Energy Demand.
The power consumption rate of desalination systems has fallen greatly in recent years. However, there is no denying that desalination is still a power-intensive process. Multi-effect distillation and multi-stage flash distillation consume more power than reverse osmosis. However, with solar energy, this is not necessarily a major concern given that solar energy is freely harvested from the sun.
With the levels of global warming at an alarming level, the need for people to ditch fossil fuels for renewable energy sources has never been greater. Desalination, which is generally a power-intensive technology is slowly adopting the use of solar energy and the resulting rewards are pretty impressive.
Solar-powered desalination not only help solve the dire water scarcity crisis, but it also helps reduce carbon emissions. In the near future, it is projected that solar desalination will grow more popular as more breakthroughs in technologies are made. Contact NEWater for any information on solar desalination systems or order placement.