The Sun is the star of our galaxy and its rays provide us with all the energy we will ever need. Even so, because of the distance between Earth and the Sun, coupled with the effects of clouds and our atmosphere, very little of the energy that began the journey reaches us.
By the time sunlight arrives on the earth’s surface, it is composed of 49 percent visible light, 45 percent infrared radiation, plus lesser amounts of ultraviolet and other types of radiation. Most people who are unaware of the science, assume that we harness the light element of sunlight, but that is not so. It is the radiation that can be converted into electrical energy or – which is the easier route – into heat (thermal energy).
The science of solar power is in a very early stage. If only we had better technology, we could use sunlight for all of the planet’s energy requirements. The advantages of this are easy to see: it is a never-ending supply (for the next million or more years, at least) and is totally pollution-free, unlike the rapidly disappearing supply of fossil fuels we currently rely on.
Solar energy is relatively cheap. It’s free at source and the costs of harnessing it – although high at the moment – are coming down all the time. Most people just do not realize how vast the potential is. Every single day, 200,000 (that’s two hundred thousand) times the electricity we generate on earth in a day, arrives in the shape of solar power.
Solar panels are called “collectors” in the trade, and their job is to collect solar energy and to convert it into thermal energy, or heat. There are two overall types of solar collectors, known as concentrating collectors and the more common flat-plate collectors. Because of the low concentration of sunlight reaching the earth’s surface, both need large areas of panelling in order to collect the radiation needed. A single person would need something like forty square meters, even in a sunny location such as California, Arizona, Sri Lanka, Italy or Greece.
Simple flat-plate collectors are made up of a blackened metal plate, covered with sheets of glass. The sunlight falls on the panel and the heat is trapped. Tubes at the rear of the device hold what are known as “carrying fluids” – usually water treated with antifreeze -and that will take the heat to an insulated boiler or other collection and storage device.
“Solar furnaces” are used when a much higher temperature is needed. Also known as “concentrators”, they collect sunlight over a much larger area and focus it using mirrors and lenses. The temperatures can get as high as 3,600 degrees fahrenheit (2,000 centigrade) and normally they’ll make steam to be used in engines for electrical generation.
We will probably be more used to seeing the third type of solar device, which are called photovoltaic – or solar – cells. The cells work when light hits a junction of a semiconductor and a metal, generating a small electric voltage of roughly two watts. These are what you find on solar-powered calculators, radios and wristwatches. If you need to generate thousands of kilowatts of electricity, you have to connect hundreds and hundreds of cells together to make what is known as a solar electric plant. Because the energy efficiency of current photovoltaic cells is less than 20%, the scientists are hard at work, hoping to increase this efficiency to make solar cells viable as viable generating units.