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Alternative Energy Sources

Geothermal energyAlternative 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 the splitting of atoms. Alternative energy sources include biomass, geothermal, hydroelectric, solar, wind power, fuel cells, ocean thermal energy conversion, tidal energy, and wave energy.

Biomass is organic matter (such as wood, agricultural crops or wastes, and municipal wastes) that is collected to create energy in the form of electricity, heat, steam, and fuels. Biomass can be burned in an incinerator to heat water to make steam, which turns a turbine to make electricity. It can also be converted into a liquid or gas, which can be burned to do the same thing. Biomass includes energy crops like wood, grains, kelp, and beets grown primarily for use as a fuel. Another type of biomass is methane gas, a by-product of decay in landfills. As garbage rots in the ground, it gives off gases that can be collected and burned to produce heat. These gases can also be burned to heat water into steam, which can be used to turn a turbine and generate electricity.

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 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, with most geothermal resources concentrated in the western part of the country. 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 employs the force of falling or moving water to drive turbine generators to produce electricity. Traditional hydropower involves dams built on rivers to trap water and release it through a turbine to generate electricity. Most traditional hydropower facilities are found in hilly or mountainous areas. New hydropower uses energy from the natural movement of water to produce electricity without changing the water flow. For example, the constant flow of water in a river can spin the blades of underwater turbines to produce electricity.

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.

Wind energy is one of the world's fastest-growing sources of renewable energy. 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. Small wind turbines can be used for individual homes, businesses, and boats. They can be used to pump water, or the electricity can be stored in large batteries for use at another time. Wind, used as a fuel, is free and non-polluting and produces no emissions or chemical wastes.

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. 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 extracts energy from surface waves, from pressure fluctuations below the water surface, or from the full wave, and uses the interaction of winds with the ocean surface. This technology is still in the exploratory phases in the United States.