Energy comes from two types of resources, renewable and nonrenewable. A renewable energy resource, according to the U.S. Energy Information Administration, or EIA, is one that can naturally replenish its supply in a short period of time. In contrast, a nonrenewable energy resource cannot replenish its supply quickly. Nonrenewable resources are limited supplies that will eventually run out or become unavailable because of cost or impracticality.
Types
Most renewable energy comes from five main types of sources--biomass, water, geothermal, wind and solar. Most people are more familiar with water, wind and solar sources of energy than with biomass and geothermal sources. Biomass energy comes from plants and materials derived from plants, such as wood, food crops and residues from forestry and agriculture. Even the fumes from landfills can produce biomass energy. Geothermal energy uses heat from deep inside the earth. The heat is recovered as hot water or steam to produce energy. Both types of energy, renewable and nonrenewable, are converted into secondary energy sources, such as electricity.
Considerations
Energy from four of the main renewable sources--solar, wind, water and biomass--comes from the sun, either directly or indirectly, according to the National Renewable Energy Laboratory. Solar energy comes directly from sunlight and provides heating and lighting for homes and other buildings. Other direct uses of solar energy include hot water heating, generating electricity and solar cooling.
Heat from the sun forces the winds, generating energy captured by wind turbines. The sun's heat and the winds cause water evaporation. The vapors convert to rain and snow, which falls into rivers and streams, creating energy from water that is generated using hydropower. Finally, the sunlight contributes to plant growth, which leads to the production of biomass energy. Biomass is the organic matter that makes up plants. Examples of energy produced from biomass include electricity, fuels and chemicals.
Significance
The EIA reports that, as of 2008, nonrenewable energy sources account for about 93 percent of the energy used in the United States. Predictions indicate that the use of renewable resources will continue to increase over the next three decades, but the United States will continue to rely on nonrenewable resources for most of its energy needs.
History
The United States has not always had to rely so heavily on nonrenewable sources of energy. According to the EIA, wood supplied almost 90 percent of the energy needs of the United States at one time. However, that was more than 150 years ago, before natural gas, coal and petroleum became so readily available. As those resources were developed, the United States relied less on wood for its energy and eventually became heavily dependent on fossil fuels as energy resources. Because of the rising costs of oil and natural gas, the United States is looking to return to renewable resources for its energy needs.
Effects
Nonrenewable energy sources such as fossil fuels harm the environment because they directly produce greenhouse gases. Four of the five main renewable energy sources--geothermal, hydropower, solar and wind--do not directly emit such gases.
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