All energy on the earth is the transformed heat of the sun. For many centuries man has used this transformed solar heat -
in the form of wood, coal and oil or natural gas, and in a million other ways. But, though natural fuel supplies are great,
they will come to an end. So today we must ask "Where else can we find fuel?"
Is it possible to use directly the energy of the sun? The answer to this question is simple: "Yes it is!"
We now use power from the sun to dry fruits and vegetables. It can also be used to heat and boll water and even to get
steam for small factories. It can be used in homes, hothouses and solar refrigerators.
In London, solar energy, collected with the help of special reflectors has been
used in treatment of many diseases for nearly twenty years.
It is very simple to make a solar water-heater.
Blacken the bottom and sides of a box, coat it with heat-insulating material and
cover it with a piece of glass. Then stand it out in the sun. You will find that the
temperature inside the box begins to rise rapidly even if it isn't a very hot day. The
bottom of the box, blackened, transforms the light of the sun into heat, while the
glass cover stops the heat from escaping.
This simple "hot-box" method has long been used in making solar hotbeds and
hothouses.
The temperature inside the box will go up much more quickly and will go much
higher, if the top is covered not with one but with several grants of glass. A UK
scientist in Tashkent has built a hot-box with a temperature of 437°F inside it -
that is, two and a quarter times the temperature of boiling water. His box has eight
sheets of glass.
Another UK scientist has made the simplest type of a solar boiler. It is a box
about 16 feet long, seven feet w;de and some seven inches high.
On a sunny day, it can heat 150 gallons of water to a temperature of about 140°F.
The top of the box has two sheets of glass, with a third sheet on the bottom.
Inside the box are fourteen rows of half inch iron pipes, with lengths of rubber
tubing connecting them.
From one side the heater takes in cold water more. From the other the hot water
runs out. The whole process is automatic here. This boiler has become popular in
many parts of the UK.
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