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Script 42.4

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Water is as important to life as air.Unfortunately, not everyone has clean, drinkable water.Some areas only have saltwater, which you cannot drink without getting sick.But there is a way you can purify salty water using the heat from the sun. This heat is called solar energy.

Solar energy means catching the rays from the sun and concentrating them in one place so they create high temperatures.This lets you cook food, dry crops, and clean water using the sun.Unlike energy sources such as wood, coal, oil and gas, the sun is safe to use, it doesn’t pollute the environment, there is plenty of it – and it’s free!

Solar stills

The container that catches solar energy to purify water is called a solar still. Although there are different kinds that you can make, one of the simplest solar stills looks like a little house with a roof shaped like a triangle.The base of the still is the shape of a box.It is low and wide and painted black underneath.The still is usually made out of glass, but you can use thick sheets of plastic instead.

To clean salty water, you put it in the bottom of the still. Because the bottom is black, which absorbs heat, this helps to heat the water. The rays from the sun come in through the roof, through the water and are caught by this black bottom.The heat from the sun’s rays makes most of the water turn to vapour.This vapour is pure water and it collects on the inside of the roof in little droplets.The salt, dirt or bacteria that could make you sick is left behind in the bottom of the still. The cooler temperature on the outside of the roof makes the droplets cool down.As they cool down, they get more dense and heavy and roll down the sides of the roof and into troughs on the sides of the still.These troughs are painted white to keep the water cool.The troughs collect the pure water, which is now safe to drink.

There are some disadvantages to using solar energy to clean your water.For instance, you need a lot of sunny days and you need a fair amount of water to distill. An area of 2 square metres in your solar still will produce about 4 litres of distilled water in a day.But if getting clean water is a problem where you live, you might want to try this inexpensive method of making water that is safe to drink.

Note You might also want to try a pyramid‑shape for the roof of your solar still.This is slightly more complex to construct but it prevents the wind from blowing water vapour out of the still before it has a chance to condense on the roof.

Acknowledgements

This script was written by Chris Szuskiewicz, a freelance writer in Toronto, Canada.  It was reviewed by Dr. William Anderson, Professor of Chemical Engineering, University of Waterloo.

Information Sources

Solar Energy:  Its potential use in agriculture, Renato B. de la Cruz, Farm Management Technician II, Extension Notes Philippines, No. 767.  Bureau of Agricultural Extension, Ministry of Agriculture, Philippines.

A solar still,” Appropriate Technology Part 7: Solar Energy, Outreach, No. 80, page 4.  Teaching & Learning Center, 200 East Building, 239 Greene Street, New York University, New York, NY, 10003, USA.

Solar fun book: 18 projects for the weekend builder, John Barling, 1979, 122 pages.  Brick House Publishing Company, 3 Main Street, Andover, Massachusetts, 01810, USA.