Solar Desalination Systems
A Global Water Crisis?
Water is the most essential-to-life compound on our planet. With great generosity, 71% of the earth's surface is water. But only just 2.5 to 3% of all that water is freshwater. The remaining 97.5%, representing the bulk of water on our planet, is saltwater, unusable in that form for any purpose by humans and other animals. Much of that freshwater is underground and not immediately accessible. Only 0.3% of freshwater is in liquid form on the surface covering just 1% of the earth's surface! The rest is underground and not immediately accessible. Of the 0.3% of freshwater available on our planet, just 2% flow through our rivers with 87% contained in lakes and the remaining 11% in swamps.
According to the United Nations,
2.2 billion people lack access to safely managed drinking water services.
Almost 2 billion people depend on health care facilities without basic water services
Over half of the global population or 4.2 billion people lack safely managed sanitation services.
297,000 children under 5 years old die every year from diarrhoeal diseases due to poor sanitation, poor hygiene, or unsafe drinking water.
2 billion people live in countries experiencing high water stress.
90 per cent of natural disasters are weather-related, including floods and droughts.
80% of wastewater flows back into the ecosystem without being treated or reused.
Around two-thirds of the world’s trans-boundary rivers do not have a cooperative management framework.
Agriculture accounts for 70% of global water withdrawal.
It is superfluous to add, in reflection on these stats, that sub-Saharan Africa, the world's poorest and least developed sub-region, that does not yet know how to find innovative solution to its problems, is at always the greatest risk. With increasing population, underdevelopment and rising poverty, freshwater scarcity in Africa is predicted to reach dangerously high levels by 2025!
The Right To Water
In July 2010, the United Nations General Assembly declared that access to enough water (50 to 100 litres per day and not exceeding 3% of household income and accessible within 1kM from the home or within a collection time of at most 30 minutes) for personal and domestic use to be a 'human right'.
It is not difficult to disagree with the United Nations whose work is to make declarations. Yet, nature is not compelled to grant anyone his right to water as such or any other rights. The challenge of water, just like many of mankind's issues may have long ago ceased to be humanitarian or even ecological but technological! To give a view, with already 76 seawater desalination plants, Egypt plans to install 17 solar-powered desalination plants by 2025. South African added its and Africa's first solar-powered desalination plant in 2018 that produces 150,000 litres of drinking water everyday, with four more planned. In 2019, Namibia, Kenya and Uganda all got their own first solar-powered desalination plants.
How Does Solar Desalination Systems Work?
Desalination processes are ways freshwater is extracted from saline ocean water by the removal of mineral components. A high liquid concentration of salt which can be reused or reintroduced into the ocean is the by-product of desalination processes. Desalination works by the well-known processes of distillation and osmosis. Saltwater is boiled either by concentrated solar heat or with heating elements powered by electric parts and made to evaporate into another location where it is cooled or re-condensed into freshwater and the salt and other impurities are left behind.
In another method, the reverse osmosis method, water is forced at high pressure through a semi-permeable membrane and impurities are left behind. These methods are the most effective way of purifying not only seawater but for the treatment of all kinds of impure water.
However, the traditional desalination is energy-intensive. This alone makes it a rather unattractive (or luxury, as there are 21,000 desalination plants in the world) option for water purification processes. To make the process more cost-effective, scientists try to co-locate the power-generating systems. In solar-powered desalination systems, solar panels are used to produce electricity needed to power the plants. They need not incorporate batteries as they can work only during the day with storage provided for treated water. In this way, initial costs are driven down as well as maintenance costs over the of the plants.
A downside to solar desalination plants is the cost of the components, in comparison to, say, digging a well or importing bulk water.
The major downside is what to do with the brine that is collected as the other by-product of the process besides freshwater. Solar energy solutions are often touted as eco-friendly solutions. But solar desalination produces an undesired effect on the ecosystem: the dumping of large volumes of brine into the sea near such facilities, destroys sea life and damages the ecosystem. Conventional desalination plants are not exempt from this problem though they are guilty of a worse effect on the environment. But the promise of better brine management can seal solar desalination's legitimacy as a more viable and eco-friendly option.
The heating effect on saltwater for distillation can be achieved with the help of a 'solar dome'. A field of mirrors holding thousands of mirrors are used to concentrate sun rays at a water container or 'dome' thus producing the heating effect that causes the water to become vapours to be cooled into freshwater. This is not a solar solution per se rather a thermal one as the sun is the direct supplier of heat rather than solar-cell generated and converted electricity.
Portable Desalination Systems
In February 2020, researchers at MIT unveiled a more sophisticated and portable adaptation of the solar dome that can more than 1.5 gallons of fresh drinking water per hour for every square metre of solar collecting area.
Before them, in 2014, a British company founded by William Janssen took upon itself the global water challenge, the by-product of which would be the Desolenator. The portable device measures 120cm by 90cm, and works as both an electricity generating device and as a thermal device. The solar panels convert sunlight to electricity but they also act as 'mirrors' using the heat generated in the process.
Solar desalination systems, in the form of plants or portable devices like the Desolenator, can solve much of the world's water problems in both eco-friendly and cost-effective ways. 73% of the world’s population live in coastal areas, with access to saltwater with well water often heavily saline and in need of extra treatment. Since majority of the world's water still has to be treated before use anyway, in the cases where the problem is not water scarcity but water contamination, these systems as effective.
Like all solar systems, solar desalination systems are high-end solutions that cost more, but only in the short run giving a full return on investment throughout their life cycle.