A ReNEWable Day
Oil, coal, and natural gas, also called fossil fuels, were formed from the remains of prehistoric plants fed by sunlight, plus the animals that ate those plants. That means fossil fuel is solar power stored underground from sunlight that shone long ago. These kinds of energy took millions of years to form, and it will take another few million years to make more. So when we rely on fossil fuels to heat our houses and run our cars, we are counting on types of energy that will one day run out. Once fossil fuels are all taken out of the ground, there won’t be any more for millions of years. The Sun, however, shines every day, so its energy
won’t run out. Even on cloudy days when the Sun doesn’t “come out,” our home star is up there wrapping Earth in its powerful blanket of energy. That’s why solar energy is called renewable — it sustains itself constantly, which means it will give us life and won’t run out for at least another 5 billion years. Every single hour, enough of the Sun’s energy reaches Earth to supply all humankind’s energy needs for an entire year. Even though the Sun has so much positive poten-
tial, we use solar energy for only a tiny amount of our energy supply. Just 7 percent of our energy comes from all renewable sources put together, including solar, wind, hydroelectric, tidal, geothermal, and biomass power. But only 1 percent of this 7 percent comes from solar power! That means less than 1/10 of 1 percent of our total energy supply comes from the Sun. That’s a tiny amount! The Sun doesn’t care where it falls or on whom its rays
shine. The Sun reaches all places — high and low; wet and dry; tropical, temperate, and covered with snow and ice. Despite this abundance of sunshine, there are about two billion people in the world who still don’t have elec- tricity. It would cost less to power these households with solar energy than it would to create new power plants and power lines. There is a lot of potential for solar power. How can you help?
Capture the Sun
Like a wild bronco, the Sun’s energy is all over the place. But we can tame that energy and put it to work. There are several ways to do this.
Passive Solar
Simply catching the rays of the Sun is called passive solar. Passive solar is used in three ways: (1) to heat a house or other space; (2) to heat water; and (3) to bring light into dark spaces.
Passive Solar Heat. To heat spaces or water with passive solar, all you need is a sunny window or something dark to absorb solar heat. The darker the color, the more of the Sun’s energy it absorbs. Spaces can be solar-heated by building them with large, south-facing insulated windows for catching and holding the heat. If the walls and floors are a dark color where the sun strikes, they will absorb solar heat during the day and radiate that same heat into
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the house at night. Some people keep large, often dark- colored containers of water in the sunlight. Once water heats up, it radiates that heat for a long time. Many solar water heaters consist of dark tubes that are
enclosed in a glass-covered flat box, or panel, and exposed to the Sun. Fluid that runs through tubes is used to heat water. In some systems, the water is heated directly by the sun. These solar collectors can be placed on a roof or on a raised platform in a sunny place on the ground. There are a lot of solar water heaters already being used in North America, including those that are designed for heating pools.
Passive Solar Light. Some houses have interior rooms with no windows or dark rooms with small windows. Many times, with good planning, small daylight shafts, such as the Solatube, can be made to catch and direct light from a brightly lit part of a roof or wall down into the dark room. These shafts are either painted white or lined with a shiny metal surface to reflect the light down.
Sun-tricity
With the right kid of equipment, it’s possible to use sun- light to generate electricity.
Photovoltaic, which means “electricity from light,” comes from the Greek word for light (phot-) and the name of the Italian inventor, Alessandro Volta, who created the first battery. Picture tiny electrons moving around the nucleus of
an atom. When the Sun’s energy strikes a photovoltaic solar panel, which is usually made from an element called silicon, the electrons become energized. They escape their atomic bonds and can only move from bottom to top through the photovoltaic (PV) cell’s two thin layers of silicon. (The lower section, which has too few electrons, is called the positive ‘p-type’ layer, and the upper is the negative ‘n-type’ layer.) Opposing charges on the top and bottom cause electrons to flow through the circuit of wires attached to the PV cell to form a current. The electrons moving along the wire from the PV cell
form direct current, or DC. This current can be used to power things that run on electricity, or it can be stored in batteries for use later on. If someone wants to feed this power into a household electrical system, it is usually run through an inverter, which changes the DC current to alternating current or AC — which is what our household appliances are designed for. Less than 1/2 of 1 percent of all the electricity that is
generated in the world is made using photovoltaic panels. Isn’t it high time that we put more of the Sun’s colossal power to work?
Michael J. Caduto is an environmental educator, ecolo- gist and the co-author of the landmark Keepers of the Earth® series. Apart from Catch the Wind, his recent other book is Riparia’s River (Tilbury House). Learn more about his programs at
www.p-e-a-c-e.net.
GREEN TEACHER 93
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