The sun has provided the earth with light and heat for billions of years. Without it, our existence on earth would be impossible. We have been using the sun' s heat since time immemorial. In summer, it heats our buildings directly, while in winter we make use of solar energy stored in the form of wood, coal, oil and gas, to provide heat for our buildings and domestic hot water. To protect fuel reserves, the heating industry has committed itself to finding more responsible ways of handling these precious resources, which have accumulated naturally over millions of years. One rational way of achieving this aim is to make direct use of solar energy by means of collectors.