HOW TO BUILD - AND USE! - A SOLAR STILL

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by D.S. HALACY

©1959 by D.S. Halacy, Jr., and originally published by the Macmillan Company as a chapter of the book, Fun With
The Sun. Reprinted by permission of the author.

Ninety years ago, mine owners in the high country of Chile were faced with the problem of providing drinking water for their workers. The only available supply was unfit to drink, and so a means of purifying the liquid had to be found. Amazingly, the solution was a sun-operated distilling plant in which a large area of glassed-over wooden frames evaporated the contaminated water, recondensed it . . . and thus produced as much as 6,000 gallons of fresh water in a day!

This solar still used no fuel or power except that from the sun's rays and was thus able to provide pure water at a cost unmatched by any other means of distillation. Oddly, the method was forgotten in the intervening years and fueloperated stills were used whenever it was necessary to convert salty—or otherwise undrinkable water—to fresh.

Not until World War II were solar stills used again except by experimenters. Fliers forced down at sea needed a source of supply of drinking water until they could be rescued. Dr. Maria Telkes developed an inexpensive, lightweight plastic still that could be included in even one-man life rafts and that would produce a quart of fresh water a day.

Since that time Dr. Telkes and other scientists have worked with solar stills of various sizes. Our government's Department of the Interior is interested in the idea, and plans have been made for large seacoast installations to purify salt water for drinking and irrigation. In some designs no pumps would re needed because the sea itself would fill the condensing tanks at high tide.

At present it is felt that the cost of such a system would be too high, even considering that cost of operation would be less than that of a fuel-run still. Engineers are hopeful, however, that improved methods and materials will make the plan feasible.

The principle of the solar still is a simple one, and is observed on a grand scale in nature. Clouds are droplets of water evaporated from the surface of the sea or from damp ground and then condensed high in the air. In the process of evaporation, solids such as salt are left behind. Many readers will be familiar with the commercial harvesting of salt in shallow ponds, for this is one of the oldest of man's uses of solar energy.

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