Solar Power Desalination
Fresh Water For The World's Poorest

January. 9, 2008

Lack of water causes great distress among the
population in large parts of Africa and Asia. Small decentralized water
treatment plants with an autonomous power supply can help solve the problem:
They transform salty seawater or brackish water into pure drinking water.

Large industrial plants for the desalination of seawater deliver 50 million
cubic meters of fresh water every day – particularly in the coastal cities of
the Middle East. However, the technology is complex and consumes large amounts
of energy. It is not suitable for the arid and semiarid regions of Africa and
India, though these are the very places where it is becoming increasingly
difficult to supply drinking water, particularly in rural areas.

“The regions have a very poor infrastructure. Quite often there is no
electricity grid, so conventional desalination plants are out of the question,”
states Joachim Koschikowski of the Fraunhofer Institute for Solar Energy Systems
ISE in Freiburg. In various EU-funded projects over the past few years, he and
his team have developed small, decentralized water desalination plants that
produce fresh drinking water with their own independent solar power supply.

“Our plants work on the principle of membrane distillation,” explains
Koschikowski. This can best be explained by the principle of a Gore-Tex jacket,
in which the membrane prevents rainwater from penetrating through to the skin.
At the same time, water vapor formed inside the jacket by perspiration is passed
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. 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 vapor condenses as
it cools on the other side. It leaves us with clean, germ-free water,” says

The researchers have so far built two different systems, both with their own
energy supply. “Our compact system for about 120 liters of fresh water per day
consists of six square meters of thermal solar collectors, a small photovoltaic
module to power a pump, and the desalination module itself,” explains
Koschikowski. In the dual-circuit system, on the other hand, several
desalination modules are connected in parallel, enabling several cubic meters of
water to be treated every day.

One cubic meter of drinking water – 1000 liters – will cost about 10 euros.
“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,”
claims Koschikowski. The test plants in Gran Canaria and in Jordan have been
operating successfully for some time. The researchers are therefore planning to
market the plants through a spin-off known as “SolarSpring” from the middle of
this year.

Adapted from materials provided by Fraunhofer-Gesellschaft.


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