Certain forms of energy are called “renewable” because these fuel sources are constantly replenished and will not run out. Renewable energy—like the sun and wind—is readily available through-out the United States. Renewable energy technologies take this energy and con-vert it into usable forms of energy—most often electricity, but also heat, chemicals, or mechanical power. These technologies are often described as “clean” or “green” because they produce little or no pollutants.
Most renewable energy comes directly or indirectly from the sun. The sun’s rays transmit solar energy that can heat and light homes, heat water, cook food, generate electricity, and power industrial processes. Heat from the sun causes air temperature differences that, along with the Earth’s rotation, cause the wind to blow. The wind powers generators that produce electricity or mechanical energy. Sunlight is vital to growing plants and trees, also called biomass. Using biomass to generate electricity, fuel vehicles, and yield chemicals is called bioenergy.
Hydropower uses the power in flowing water to operate turbines that generate electricity. The hydrologic cycle, in which water is evaporated into the atmosphere and then falls back to Earth as rain or snow, is powered by the sun. But not all renewable resources come directly from the sun. Geothermal energy uses the heat deep inside the Earth to produce electric power.
Mankind has used renewable energy for thousands of years. Sunlight gives light and warmth, wind powers sailboats, bio-mass from trees makes fires, water turns turbines, and geothermal hot springs are used for practical and spiritual purposes.
Today we cook food, fuel cars, and heat homes primarily by burning fossil fuels that were created over millions of years. Using coal, oil, and natural gas is a convenient way to meet our energy needs, but these fuels are in limited supply. They are being used far more rapidly than they were created, and they will eventually run out. In addition, a significant portion of the country’s nuclear capacity will likely be retired by 2020. At the same time that our nuclear capacity drops and fossil fuel supplies decline, our need for electricity will grow. U.S. electric generation capacity needs are projected to increase by 33% during the next 20 years (Energy Information Administration). Renewable energy can help fill this gap.
Even if we had an unlimited supply of fossil fuels, renewable energy is attractive because it is better for the environment. Burning fossil fuels sends greenhouse gases into the atmosphere. These gases trap the sun’s heat in the atmosphere, contributing to global warm-ing. Climate scientists generally agree that the Earth’s average temperature has risen in the past century. If this trend continues, sea levels will rise, and scientists predict that floods, heat waves, droughts, and other extreme weather conditions could occur more often.
Other pollutants are released into the air, soil, and water when fossil fuels are burned. These pollutants take a dramatic toll on the environment. Air pollution contributes to lung diseases like asthma. Acid rain from sulfur dioxide and nitro-gen oxides harms plants and fish. And nitrogen oxide contributes to smog.
Energy independence is another reason to use renewable energy. The United States imports more than 50% of its oil, up from 34% in 1973. Foreign oil imports can be disrupted by political upheavals, trade disputes, and embargoes. Replacing some of our petroleum with biofuels made from organic matter could save money and strengthen our energy security.