INTRODUCTION All life on Earth depends on energy from the sun Solar energy is the source of energy for photosynthesis It provides the warmth necessary for plants and animals animals to survive The heat from the sun causes water on the Earth’s surface to evaporate and form clouds that eventually provide fresh rainwater fusion Solar energy is the result of thermonuclear thermonuclear reactions deep within the sun These reactions produce produce so much energy that they keep the surface temperature of the sun at about 10,300 degrees Fahrenheit 5,700 degrees Celsius Even though solar energy is the largest source of energy received by the Earth its intensity at the Earth’s surface is actually very low due to the large distance between the Earth and the sun and the fact that the Earth’s atmosphere absorbs and scatters scatters some of the radiation Even on a clear day with the sun directly overhead the energy that 4
Solar energy is light heat and other forms of energy given off by the sun Solar energy can be collected and used to heat buildings and to make electricity reaches the Earth’s surface is reduced about 30 percent by the atmosphere When the sun is near the horizon and the sky is overcast the solar energy at ground level can be negligible It also varies from one point to another on the Earth’s surface A number of devices for collecting solar energy and converting it into usable energy 5
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
