Looking At the Solar Still


A photo of Allan DouglasIn the mid-1880s, mine owners in the high country of Chile were faced with the problem of providing drinking water for their workers. The only water available was unfit to drink so a means of purifying that liquid had to be found. The solution was a sun-operated distilling apparatus in which an array of glass-covered wooden frames evaporated the contaminated water and condensed it. This array produced as much as 6,000 gallons of fresh water each day.

Oddly enough, this method of producing fresh water was forgotten for a while and fuel operated stills were used whenever it was necessary to convert salty or polluted water to fresh.

During World War II, to help aviators forced down at sea who needed a source of drinking water until they were rescued, Dr. Maria Telkes developed an inexpensive, lightweight plastic still that could be included in even one-man life rafts and would produce a quart of fresh water a day.

Solar stills operate on the same principles that produce rainfall. The sun heats water to the point that it evaporates. In this process, only pure water rises as vapor, contaminants are left below. The water vapor cools and condenses. In nature, this condensed water vapor forms clouds that then drop their water back to earth as rain. In a solar still, the water vapor condenses on a glass or plastic cover. The cover is sloped and the condensed water runs down to be collected. There are no moving parts in a solar still, and only the sun's energy is required for operation.

Today, interest in solar water stills is increasing due to the need by hikers/campers, survivalists, homesteaders, and poverty and disaster relief efforts to provide potable water where none is available.

I am not a survivalist or off-grid homesteader (not yet anyway), but I am concerned by the prospect of an extended power outage. Our only pure water source is a well. That well is 400 feet deep. At that depth, no hand pump will draw water up to where we can use it. A generator powerful enough to provide enough 240-volt juice to power the submerged 1 hp pump motor is expensive. Too expensive to justify purchase on the chance that the national grid will be taken down by terrorists – or something like that.

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