SOLAR POWER have been developed These include concentrating collectors flat-plate collectors and photovoltaic cells Concentrating collectors use the sun’s heat to make electricity A concentrating collector has mirrors mirrors that focus large amounts of solar energy into a small area A flat-plate collector is a large plate of black metal covered with a sheet of glass It is usually placed on the roof of a building The plate absorbs sunlight and uses it to heat air or water that flows through pipes behind it The air or water then goes through the building’s heating or plumbing system Photovoltaic cells also called solar cells use the sun’s light rather than its heat When the sun shines on a solar cell the cell turns the light energy into electricity A single solar cell makes only a little electricity However groups of solar cells can provide provide electricity for whole buildings Because the intensity of the sun’s radiation at the surface of the Earth is so low collectors designed to capture solar energy must be large in area Even in sunny parts of the world’s temperate regions for instance a collector must have a surface area of about 430 square feet 40 square meters to gather enough energy to serve the energy needs of one person Nevertheless the total amount of solar energy incident on Earth is vastly in excess of the world’s 6
INTRODUCTION Many calculators use solar cells The solar cells in the calculator in this photo are the black strip in the top left corner above the buttons current and anticipated energy requirements If suitably harnessed this highly diffused source has the potential to satisfy all future energy needs In the twenty-first century solar energy is expected to become increasingly attractive as an energy source because of its inexhaustible supply and its nonpolluting nonpolluting character in stark contrast to the finite fossil fuels coal petroleum and natural gas 7
Chapter One THE SUN Although the sun is a rather ordinary star it is very important to the inhabitants of Earth It is the source of virtually all Earth’s energy It provides the heat and light that make life on Earth possible Yet Earth receives only about half a billionth of the energy that leaves the sun The sun is a huge ball of hot gases Like other stars it produces enormous enormous amounts of energy by converting hydrogen to helium deep within its interior The sun looks like a burning sphere It is too hot however for an Earth-type chemical reaction such as burning to occur there Besides if burning produced its energy it would have run out of fuel long ago Instead thermonuclear reactions are the source of solar energy The vast amount of matter in the sun 8
THE SUN The sun is a yellow dwarf star a kind that is common in the Milky Way Galaxy Its diameter is about 864,950 miles 1,392,000 kilometers which is about 109 times the diameter of Earth can provide the fuel for billions of years of atomic reactions Astronomers believe that the sun is nearly halfway through its lifetime of 10 billion years STRUCTURE AND ENERGY PRODUCTION The sun can be divided into several different layers layers Energy is produced in the dense hot central 9
