An energy-efficient vacuum-based solar-powered desalination system developed by US researchers could help meet the growing need for fresh water in many parts of the world.
Existing desalination systems such as solar evaporation stills, used for converting sea to drinking water in areas like the Middle East, are heavy energy users. This makes them impractical in many poor countries facing water shortages.
Engineers at the University of Florida have developed a method using a gravity-induced vacuum and solar energy instead of electricity or fossil fuels to desalinate water. Tests show that 90 per cent of the solar energy piped into the evaporator is used in desalination, whereas standard solar stills have an efficiency of around 50 per cent.
The system, developed by mechanical engineering professor Yogi Goswami, director of the university’s Solar Energy and Energy Conversion Laboratory, uses the principle of barometric pressure to create a vacuum in a vertical tube. The Earth’s atmospheric pressure can only support water within a column up to a height of around 9m. If a tube taller than this is filled with water, the liquid drops back, creating a vacuum.
In a vacuum the rate of evaporation is much faster than normal, meaning less energy is needed. ‘The system mimics the Earth’s water cycle by using the sun to evaporate sea water and produce fresh water,’ said Goswami. ‘But using a vacuum allows us to improve on nature.’
In Goswami’s system the area of the pipe where the vacuum occurs is surrounded by an evaporator that circulates water heated in a solar collector. The heat forces the sea water to evaporate and the resulting steam then enters a condenser where the fresh water collects and drips down a pipe into a collection tank.
Goswami said the system is simple and inexpensive enough to be built in remote locations where conventionally powered technologies would be either too expensive or impractical.
The group is now refining its calculations to determine how large a plant would be needed, depending on local water consumption and the sunlight available.