Return To Index

Environmental Issues
Going Green

By Alan J Hartley

Solar Furnaces



The principal that Solar Furnaces operate on goes back to the times of the ancient Greeks when they realised that they could warm water in a bottle by leaving it in the sun. As a schoolboy, some 40 odd years ago, I used to have fun playing with a magnifying glass in the sunshine. Properly focused, a small hand held magnifying lens was more than capable of burning bits of green grass or setting fire to a piece of paper. Nowadays the more adventurous can go to alarming lengths with a special, but common lens, readily removed from old style, scrap TV’s. Apparently, if the lens is focused, it will easily melt metal!

Modern science has applied these principals, but taken them up a scale, to make large experimental, Solar furnaces capable of reaching temperatures of 3,000°C.

The world’s largest solar furnace is in the Pyrenees Mountains on the French/Spanish border. Built in 1970, it uses more than 10,000 mirrors to reflect light onto a single large concave mirror which then focuses the suns energy into a small area. Such a high temperature can be reached that high temperature experiments can be conducted on metals, or it can simply be used to drive a steam turbine.

The site in the Pyrenees was chosen, because it gets up to 300 sunny days a year. This reliance on sunny weather is a problem to using solar furnaces as a   source for producing massive amounts of renewable energy on Earth, but the solar furnace principle is being used to make inexpensive solar cookers and solar-powered barbecues that can be of use in many countries.

A simple solar cooker that consists of the most basic materials and nothing much else typically reaches a temperature of 150 °C. Whilst this is not as hot as a normal cooker it does mean that food can safely be left in the cooker all day without burning. Most foods will cook quite happily at lower temperatures than normally recommended if left heating longer. These low cost “Green Fuel” cookers are being promoted in some of the poorer parts of the world for the cooking of simple meals as the users do not need a regular supply of firewood  that can be difficult to obtain. Panel solar cookers are very inexpensive solar cookers that use shiny panels to direct sunlight on to a cooking pot that is enclosed in a clear plastic bag to increase efficiency. A further refining of the concept resulted in “Parabolic” cookers that can reach high temperatures and cook quickly, by actually focusing the Suns rays. In China hundreds of thousand are regularly used, but they do require frequent adjustment to keep them at optimum focusing and constant supervision for safe operation.



Gardening Tips
By Mrs FM


Unusual & Old
Fashioned Fruit


Herbs & Other
Edible Plants.


Books By
Alan J Hartley