The availability and cost of energy are determining factors in the economic health and growth of societies. It absorbs its energy from the sun through photosynthesis and stores it as sugars and fiber. For thousands of years biomass was the main source of energy for humans, as people burned wood to heat homes and cook food. Many forms of biomass, including corn, wheat or yard wastes can also be turned into ethanol - an alcohol fuel that burns cleaner than gasoline. In the future, biomass energy crops may become a staple for American farmers, as many have shown great interest in the technology.
Geothermal energy comes from the heat within the earth, and is used to make electricity.
People have used geothermal energy for thousands of years. Hot springs have often been used for bathing, and some believe these springs have healing powers. Geothermal heat pumps are used to heat and cool homes and public buildings because the power source can reduce conventional heating costs up to 70 percent and cooling costs up to 40 percent. Some scientists think that someday we will be able to capture the energy in volcanoes, the ultimate geothermal resource. Coal supplies nearly 25 percent of the nation's energy needs, mostly to produce electricity, but also to make steel, iron and bricks.