Freiburg, Germany - Clean water with free energy is the goal of German scientists who are using the sun's rays to power small water treatment plants for developing countries. The system is designed for arid areas of Africa and Asia where a lack of electricity makes it impossible to use large industrial plants for the desalination of seawater, like those in the Middle East.
"The regions have a very poor infrastructure. Quite often there is no electricity grid, so conventional desalination plants are out of the question," says Joachim Koschikowski.
The engineer and his team at the Fraunhofer Institute for Solar Energy Systems (ISE) have developed small decentralized units with their own solar power supplies that can transform salt water or brackish water into pure drinking water.
"Our plants work on the principle of membrane distillation," says Koschikowski, comparing the technology to that used in breathable, waterproof fabrics, where the membrane prevents rainwater from penetrating through to the skin, while allowing water vapour to pass through to the outside.
"In our plant, the salty water is heated up and guided along a micro-porous, water-repellent membrane. Cold drinking water flows along the other side of the membrane," he says.
The steam pressure gradient resulting from the temperature difference causes part of the salt water to evaporate and pass through the membrane.
"The salt is left behind, and the water vapour condenses as it cools on the other side. It leaves us with clean, germ-free water," says Koschikowski.
The German researchers have so far built two different systems, both with their own energy supply.
"Our compact system for about 120 litres of fresh water per day consists of six square metres of thermal solar collectors, a small photovoltaic module to power a pump, and the desalination module itself," says Koschikowski.
In the dual-circuit system, on the other hand, several desalination modules are connected in parallel, enabling several cubic metres of water to be treated every day.
One cubic metre of drinking water, the equivalent of 1,000 litres, will cost about 10 euros (14.50 dollars).
"When you think how much the inhabitants currently have to pay for the same amount of bottled water or soft drinks, the plant will pay off very quickly," says Koschikowski.
His institute has been successfully operating pilot projects on the Spanish island of Gran Canaria and in Jordan.
The researchers are planning to market the plants through a spin-off company known as SolarSpring from the middle of 2008.
