I saw a demo by the Sea Scouts of how to make fresh water with a beer
can and plastic bag. He placed a can (top cut off) full of sea water
in large clear bag and closed the bag. Put in the sun it made maybe a
half pint of water a day, not too impressive.
What if you used more than one can?
OK, so I got interested in solar stills and googled em, nothing
impressive.
It seems that all of em I see have a defect in that the sunlight must
pass through the water that has condensed on the plastic greatly
reducing the efficiency. My specialty happens to be really weirdly
shaped reflective optics so this whole thing seemed interesting to me.
So, why not use aluminized reflective mylar in a shape of a compound
parabolic concentrator to concentrate light onto the water. This
special optical shape is much more efficient than a parabola for
concentrating diffuse light like sunlight. In this case, the light
would be concentrated onto heat transfer rods immersed into a
container of seawater. Evaporation increases with temp so the evap
rate would be very high. Fresh water would condense on a membrane
BELOW the reflective one and maybe you could have a cloth soaked in
cooler seawater adjacent to it to facilitate condensation. This cloth
would wick seawater into the container as the seawater evaporates.
This device would be hung from a shroud or pole with another line at
the bottom to roughly aim it toward the sun. As the sun moved the
bottom line would be repositioned but this is not critical as this
type of concentrating optic has no focus.
I have not yet calculated the production capacity as I think that
uncertainties in fabrication would exceed the actual capacity.
Eventually, I will order the mylar and try this.