Tribewanted: Vorovoro

We had a great forum the other day on the topic of desalination. Of course we don’t have one of those expensive reverse osmosis units that fire seawater under very high pressure through a semi permeable membrane, such as are found on ocean going yachts. You might remember that TW has a desalination plant installed in Vorovoro, but that it hasn’t been working as well as it should. This design is supposed to heat up seawater in a copper tube using sunlight focused onto the pipe by a parabolic dish, and then condense the vapor in a coiled tube in a bucket of cool water. The main problem is that in Fiji it is difficult to find a highly reflective material that can be shaped into a parabolic dish. So, as a group, we tossed around some alternative ideas about how we could improve it, and came up with a few ideas, that are doable in Fiji.

IDEA No. 1.
We build a solar still which is a sort of black shallow tray covered by a transparent roof. When the sun shines, it evaporates the fresh water, separating it from the salt. The water vapor then condenses on the undersurface of the transparent roof, then drips down that and collects in a gutter. This is ok but can only yield about 4 gallons per day for an 8’x4’ still.

IDEA No. 2.
We heat sea water in a copper pipe in a fire thus creating steam which then passes through a water jacket, and condenses. This is potentially faster, but requires combustion with resulting addition of greenhouse gases into the atmosphere.

IDEA No. 3. CHUCK’S IDEA
We heat salty water in a long coiled black plastic pipe laid on the beach soaking up the sun. When this turns to steam, we cool it in a water jacket.

Probably the best idea would be a hybrid system such as…
a. Pass water though a black pipe in the sun to preheat it then…
b. Add extra heat to this water using a copper pipe in a fire then…
c. Spill this hot water into a black tray to evaporate and condense this on a clear plastic roof, cooled by salty water that is flowing down the roof into a gutter then going into the black pipe etc.

Most info on the net says that if you have any alternative supply for water you should invest in that as stills are too costly when compared with how much water they can produce.

But what do you think?