Energy supply is the total amount of usable energy available to people for doing work. We use forms of energy to operate machinery; to heat and cool our homes and offices; to cook; to provide light; and to transport people and goods. Heat energy is the most commonly used form of energy.
Energy may be obtained directly from an energy source, as when people burn wood to produce heat. Energy may also be obtained indirectly. For example, at a power plant, oil is burned to create steam and that steam produced is used to power a generator which is used for electricity.
Energy that is produced by businesses and the government and then sold to the public is called commercial energy. About 85 percent of all commercial energy comes from petroleum, coal, and natural gas. Petroleum, coal, and natural gas are called fossil fuels because they developed from the fossilized remains of prehistoric plants.
The earth contains only a limited supply of fossil fuels. But the amount of fossil fuel burned by people to produce energy has nearly doubled every 20 years since 1900. It is projected that soon, the supply will run out. Scientists and engineers are working to develop other sources of energy. .
Energy use creates serious problems. They include the depletion of fuel reserves and environmental effects.
People have used up sources of energy that accumulated for millions of years. For about 40 million years, large quantities of dead trees and other plants were buried in the earth through natural processes. Time, heat, and pressure slowly changed this buried plant material into coal. Petroleum and natural gas were both formed in much the same way from the remains of ocean plants. Fossil fuels are still being made, but people burn the fuels thousands of times faster than they form.
The rapid growth of energy use endangers the world's supply of energy. Petroleum may become the first fuel to give out. Some scientist expect that it will run out by the mid-2000.
