| Saudi Arabia's
newest purification plant will use state-of-the-art solar technology.
By Prachi Patel
Saudi Arabia meets much of its drinking water
needs by removing salt and other minerals from seawater. Now the country
plans to use one of its most abundant resources to counter its fresh-water
shortage: sunshine. Saudi Arabia's national research agency, King Abdulaziz
City for Science and Technology (KACST), is building what will be the world's
largest solar-powered desalination plant in the city of Al-Khafji.
The new plant's concentrated PV and reverse-osmosis systems will use advanced materials developed by IBM for making computer chips.
In a concentrated PV system, lenses or mirrors focus sunlight on ultra-efficient solar cells that convert the light into electricity. The idea is to cut costs by using fewer semiconductor solar cell materials. But multiplying the sun's power by hundreds of times creates a lot of heat. "If you don't cool [the device], you end up overheating the circuits and killing them," says Sharon Nunes, vice president of IBM Big Green Innovations. IBM's solution is to use a highly conducting liquid metal--an indium gallium alloy--on the underside of silicon computer chips to ferry heat away. Using this liquid metal, the researchers have been able to concentrate 2,300 times the sun's power onto a one-square-centimeter solar device. That is three times higher than what's possible with current concentrator systems, says Nunes.
For desalination, IBM has worked with researchers at the University of Texas at Austin to develop a robust membrane that makes reverse osmosis more energy-efficient. Desalination is done today with polyamide membranes that get clogged with oil and organisms in seawater. The chlorine used to pretreat seawater also breaks down the membranes over time.
The new polymer membrane contains hexafluoro alcohols, a material IBM uses to pattern copper circuits on computer chips. At high pH, the fluorine groups become charged and protect the membrane from chlorine and clogging. As a result, water flows through it 25 to 50 percent faster than through currently used reverse-osmosis membranes, according to IBM.
The new membrane removes 99.5 percent of the salt in seawater. This is comparable with conventional polyamide membranes, says Menachem Elimelech, chair of chemical engineering at Yale University. "You need to achieve this high rejection, otherwise you can't get good water quality by one pass, you have to desalinate again."
The Al-Khafji desalination plant is the first of three steps in a solar-energy program launched by KACST to reduce desalination costs. The second step will be a 300,000-cubic-meter facility, and the third phase will involve several more solar-power desalination plants at various locations.