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Alternative Energy Sources
Alternative energy sources are resources that are constantly replaced and are usually less polluting. They are not the result of the burning of fossil fuels or splitting of atoms. The use of renewable energy is contributing to our energy supply. Some alternative energy sources are: biomass, geothermal, hydroelectric, solar, wind power, fuel cells, ocean thermal energy conversion, tidal energy, and wave energy.
Biomass is renewable energy that is produced from organic matter. Biomass fuels include wood and forest and mill residues, animal waste, grains, agricultural crops, and aquatic plants. These materials are used as fuel to heat water for steam or processed into liquids and gases, which can be burned to do the same thing. With more use of biomass at lower production costs and with better technology, the United States could generate as much as 4.5 times more biopower by 2020. It is estimated that biomass will have the largest increase among renewable energy sources, rising by 80% and reaching 65.7 billion kWh in 2020.
Geothermal energy uses heat from within the earth. Wells are drilled into geothermal reservoirs to bring the hot water or steam to the surface. The steam then drives a turbine-generator to generate electricity in geothermal plants. In some places this heat is used directly to heat homes and greenhouses, or to provide process heat for businesses or industries. The United States leads the world in electricity generation with geothermal power. Most geothermal resources are concentrated in the western part of the United States. With technological improvements much more power could be generated from hydrothermal resources. Scientists have been experimenting by pumping water into the hot dry rock that is 3-6 miles everywhere below the earth's surface for use in geothermal power plants.
Hydroelectric (hydropower) energy employes the force of falling or moving water to drive turbine generators to produce electricity. Hydropower is the largest renewable electricity source in the world, accounting for about 92 percent of all the renewable energy produced across the planet. It accounts for 6 percent of all the electrictiy generated in the United States and 76 percent of all the renewable electricity produced in the United States.
Solar power is generated when special panels of solar cells, or modules, capture sunlight and convert it directly into electricity. The electricity produced by solar panels can be used right away, fed into the power grid for others to use, or stored in a battery so it is also available on cloudy days. Solar thin films are light-absorbing materials that are rolled, sprayed, or painted onto rooftops and other surfaces. Thermal solar power uses mirrors or panels containing tiny tubes filled with water that absorb heat from the sun. On rooftops, they can supply hot water for individual buildings. Concentrated solar power can also be used to create steam that spins turbines at electric power plants. Solar power currently provides less than 1 percent of the electricity generated in the United States; however, solar power could provide up to 15 percent of new U.S. peak electricity capacity that is expected to be needed by 2020.
Wind energy can be used to produce electricity. As wind passes through the blades of a windmill, the blades spin. The shaft that is attached to the blades turns and powers a pump or turns a generator to produce electricity. Electricity is then stored in batteries. The speed of the wind and the size of the blades determine how much energy can be produced. Wind energy is more efficient in windier parts of the country. Most wind power is produced from wind farms—large groups of turbines located in consistently windy locations. Wind, used as a fuel, is free and non-polluting and produces no emissions or chemical wastes. Wind power generates about 2 percent of all electricity used in the United States. This is equal to the amount of electricity used by about 8.7 million households in a year.
Fuel cells are electrochemical devices that produce electricity through a chemical reaction. Fuel cells are rechargeable, contain no moving parts, are clean, and produce no noise. Scientists are exploring ways that they could be used as a power source for nearly exhaust-free automobiles and how they can be used as electricity-generating plants. The high cost of manufacturing fuel cells has prevented the mass use of this valuable energy source.
Ocean sources. Oceans, which cover more than 70% of the Earth, contain both thermal energy from the sun’s heat and mechanical energy from the tides and waves.
Ocean thermal energy conversion (OTEC) converts solar radiation to electric power. OTEC power plants use the difference in temperature between warm surface waters heated by the sun and colder waters found at ocean depths to generate electricity.
The power of tides can be harnessed to produce electricity. Tidal energy works from the power of changing tides but it needs large tidal differences. The tidal process utilizes the natural motion of the tides to fill reservoirs, which are then slowly discharged through electricity-producing turbines.
Wave energy conversion extracts energy from surface waves, from pressure fluctuations below the water surface, or from the full wave. Wave energy uses the interaction of winds with the ocean surface. This technology is still in the exploratory phases in the United States.
Energy Statistics: U.S. Energy Information Administration (www.eia.doe.gov)