Re: DO you have any ideas on how to purify water using solar energy?

Hi Jeremy,

Thanks for the question. There are lots of resources on the world wide web on solar cooking and I found a few specifically for solar powered water purification. Here are some of them:

Web pages on solar cooking:(1)(2)

Web page on all kinds of solar devices, including ovens:(1)

Web pages of companies selling solar powered water purifiers:(1)(2)

A large scale approach to setting up ecology-based wastewater treatment:(1)

I recently answered a question on cooking using solar power only. You can find that reply on the Mad Scientist Network. This problem is similar. There are several ways to tackle it. The simplest, easiest, and most useful for small applications would be to build a solar powered still. This would eliminate the need for photovoltaics and electronic components. The principles of building a solar powered still would be the same as for the solar powered oven that I described, but you would heat water instead of "a sausage". A still is a device that separates liquids based on differences in their boiling points. A mixture of liquids is heated, and gas that is evolved as they boil or evaporate is channeled up out of the original container and into a condenser. Here, the gas is cooled (or at least removed from the heat) and allowed to recondense into a liquid. The condenser is designed so that as the liquid recondenses, it drips down into a new chamber. The liquid with the lowest boiling point will distill over first, and can be separated from the rest. Then the original mixture can be further distilled. The distilled product can also be redistilled to further purify it. After two or three rounds of distillation, the product will reach a maximum purity. Depending on the properties of the mixture, this may or may not be 100%. For example, ethanol can only be purified to about 95% from water in this way, and vice-versa. To get it any more pure, more difficult chemical separation techniques are necessary. Distillation will remove all solid contaminants from water and most others contaminants, including microorganisms. There are some organic solvents which will not be removed, but they aren't usually present at high levels unless the water is really contaminated. They can be gotten rid of by allowing the distilled water to trickle through a charcoal filter. However, this would be veering slightly from our goal of making a "purely" solar powered water purifier.

Stills have been around for a long time. They were made infamous in the U.S. by being used by "moonshiners" during prohibition. These people used them to manufacture whiskey illegally when making and selling alcoholic drinks was outlawed for a brief time earlier this century. Their designs are in principle very simple, but there are many elaborations. Any still design should in principle work for this. The only difference will be that this one will use sunlight as the heat source.

Here is a site with plans for building a solar powered still. The design is one for a larger still, but could be scaled down.

I used dogpile to find all of the above links except the last one. I am sure it would have found it too if I had phrased my search a little more specifically.

Good luck and thanks for the question.

Sincerely,

J. Todd Holland

Biophysics Graduate Student

Hollandtodd@hotmail.com