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Lo-Tech Windmills + Hi-Tech Filters = Desalination
Alex Steffen, 20 Mar 08

Water shortages are a major looming crisis. We've covered lots of good resources for understanding the water crisis and looked at some new innovative tools for tackling it, by, for example, converting sea water into drinking water.

Now, researchers at the Delft University of Technology have come up with an interesting idea -- combining windmills with reverse osmosis filters to produce comparatively rugged and low-cost desalination systems:

Desalination is an energy intensive process and Reverse Osmosis (RO) desalination is by far the most energy efficient technology to desalinate water. Reverse Osmosis is a pressure difference separation technique. It uses the natural osmosis process that occurs through a semi-permable membrane with two solutions that have different concentrations of salts in it. At equal pressure and temperature the water will flow through the membrane from less concentrated solution to one with larger concentration, and will delute it, till the concentrations are equal. When a certain pressure applied that is larger then a certain osmotic pressure the flow goes the other way, flowing from a more concentrated side to a more deluted solutions. That process is called Reverse Osmosis.

There are a few experimental RO installations throughout the world that are driven by electricity produced by wind turbines. In these systems the wind energy first transformed to electricity, then stored, and transferred to mechanical energy back to drive the high pressure pumps that pressurize the feed water for the RO-installations. Throughout these transformations energy losses occur. To minimize the energy losses a direct connection between the windmill and the high pressure pump is developed. The RO installation is operated intermittently due to the variable character of the wind and product water is stored, which is much less expensive then the electricity storage facilities. The desalination installation is operated fully mechanically and hydraulically.

This particular combination may or may not prove itself in the field, but it's a great example of what ought to become more and more possible, which is a form of hybrid appropriate technology, combining easily maintained simple tools (like windmills) with select advanced parts (like RO filters) to produce something inexpensive, rugged and useful.

This is the kind of thing I could see innovators like William Kamkwamba (who, you may remember, built his own power-generating windmill in Malawi at age 19) taking and running with.

(Thanks Futurismic!)

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Even better perhaps, is the "CETO" combined wave power/desalination unit being trialled in Australia. This unit uses bouys as a high pressure wave power pump to pump water through hydraulic generators and/or an RO filter. The advantage of having no electrical parts at sea is a key improvement to wave power where saltwater corrosion is a significant cost.

Posted by: rs-d on 24 Mar 08

Apologies, link for the above is

Posted by: rs-d on 24 Mar 08

I've long wondered if gravity can produce enough pressure to operate a reverse osmosis filter. A windmill pump and water tower? A ram pump in a tidal channel? electricity may not even be necessary.

Posted by: Paul Barthle on 9 Apr 08



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