The earth has always indirectly depended on the sun for energy. Its rays provide the heat that human, animal, and plant life need to survive. With the discovery of fire, wood became the first source of controllable energy, and even today one-third of the world’s population depends on firewood as its principal source of fuel.
Bathed in the sun’s rays for millions of years, the remains of plants and animals were chemically changed into the fossil fuels-coal, oil, and natural gas.
The sun continuously evaporates some of the earth’s waters, which return as rain to feed streams and rivers, Water mills powered early industry, and modern hydroelectric plants are an import ant source of power.
Finally, the unequal amounts of solar heat falling on different parts of the earth’s surface generate winds, which move sailing ships and power windmills.
Compared with other ways of producing energy, solar energy has many advantages. Clearly, enough solar energy reaches the earth to make it a significant resource. The total solar energy striking the United States in one year is equal to one million times the energy output of an average electric power plant. Solar energy is inexhaustible, available everywhere, requires no fuel, does not damage the environment, and cannot be rationed by other nations. However, solar energy does have some disadvantages. It is spread diffusely over the earth. Although solar energy is in a sense free, it must be collected to make it practical to use. It is also intermittent and therefore requires some means of storing energy when there is no sun.
The challenge to all designers is the inexpensive capture and efficient use of the sun’s renewable resource. This is the only way to gain widespread use of the solar energy.
In Connecticut, a conventional home with its longest axis facing south receives as much as 14 percent of its energy for space heating from the sun. Add sufficient insulation and double-glazed windows along the southern exposure and the figure rises to 25 percent. With heat storage, the contribution of solar to the energy needs of the home is 50 percent! Yet, only 10 percent of the 169 towns and cities in Connecticut have used their zoning regulations to encourage solar techniques. An attached solar greenhouse may be a partial solution to increased use of the sun’s energy for existing houses in Connecticut.