Major Types of Renewable Energy Sources

Biomass. Biomass includes wood, agricultural crops and residues, municipal refuse, wood and paper products, manufacturing process waste, and human and livestock manure. It can be used to heat homes and buildings, produce electricity, and as a source of vehicle fuel. Wood and paper manufacturers and sugar mills use biomass residues for process heat and electricity production. There are power plants that burn wood, agricultural residues, and household trash to produce electricity. Biogas (composed of methane, carbon dioxide, and other gases) produced by decomposing biomass in anaerobic conditions is captured from landfills, municipal sewage treatment plants, and livestock waste management operations. This gas can be used for heat or to generate electricity.

Ethanol is used as a transportation fuel in the United States, Brazil, and a few other countries. Nearly all the fuel ethanol in the United States is made from corn, although it can also be produced from other sources, including wastepaper. There is a small but growing consumption of “biodiesel” made from grain oils and animal fats.

Geothermal systems. Geothermal energy (heat from the earth) created deep beneath the earth’s surface is tapped to produce electricity in twenty-two countries, some of which include the United States, Iceland, Italy, Kenya, and the Philippines. Geothermal hot springs can also heat buildings, greenhouses, fish farms, and bathing pools.

Hydropower. Hydropower, produced from flowing water passing through hydroelectric turbines , is the leading renewable energy source, contributing to approximately 9 percent of the electricity generated in the United States. Most hydropower is produced at large dams, although there are many small systems operating around the world, such as the small hydropower plant in Namche Bazar, Nepal, which provides power for the tourist and market town near Mt. Everest. The production of hydroelectricity from year to year varies with precipitation.

Ocean energy. The world’s oceans are a vast and practically untapped source of energy. There are a few operating wave and tidal power plants around the world, and several experimental ocean thermal energy conversion (OTEC) plants have also been built. A small wave power plant in Norway captures water from waves in a dam and lets the water out through a turbine. A 240-megawatt tidal power facility on the Rance River in France produces electricity as tidal flows move back and forth through turbines located at the mouth of the river. In Hawaii, a small OTEC plan was built which uses the temperature of warm surface water to evaporate cold seawater in a vacuum to produce steam that turns a turbine and generator.

Solar energy systems. The simplest uses of solar energy are for drying crops, and heating buildings and water. Solar-heated homes and solar water heaters can be found in nearly every country around the world. Crops can be simply laid in the sun to dry, or more sophisticated collectors can be used to heat air to dry food stored on drying racks. Solar water heaters use collectors

to heat water that is stored in a tank for later use. Homes can be heated by using a masonry floor to absorb sunshine coming through windows, or by using solar collectors to heat a large tank of water than can be distributed for heating at night.

Concentrated sunlight can be used to produce high-temperature heat and electricity. Nine concentrating solar parabolic trough power plants, with a combined generation capacity of 354 megawatts, are located in the Mojave Desert in California. (A megawatt is 1 million watts, or 1,000 kilowatts.) The U.S. Department of Energy built and tested a ten-megawatt solar thermal central receiver power plant near Barstow, California, which operated successfully for about seven years. Another type of concentrating solar thermal power system is a parabolic dish. Systems with a capacity of up to twenty-five kilowatts have been developed.

Photovoltaic (PV) systems are based on solar electric cells, which convert sunlight directly to electricity. They can be used to power hand calculators or in large systems on buildings. Many PV systems are installed in remote areas where power lines are expensive or unfeasible, although the number of systems connected to electricity transmission systems is increasing, and range in size from 1 to several kilowatts on houses, to systems over one hundred kilowatts on large buildings. PV systems are very suitable for use in developing countries where people have no electricity from electric power lines.

Wind energy systems. Water-pumping and grain-milling windmills have evolved into electric power turbines. There are now tens of thousands of wind turbines operating around the world. They range in size from tiny turbines on the back of sailboats to very large units that can produce as much as

Energy Source (Quads*) (%Total) (Bill. kWh**) (%Total) *A quad is quadrillion British Thermal Units (BTUs), and is the equivalent of about 180 million barrels of crude oil. **Bill. kWh = a billion kilowatt-hours; One kilowatt-hour (kWh) is the equivalent of running a 100-watt lightbulb for 10 hours. Note: values are rounded. SOURCE: Energy Information Administration, U.S. Department of Energy. Total 96 85 3,641 Coal/Coal Coke 22 23 1,891 52 Petroleum 38 39 116 3 Natural Gas 22 23 546 15 Nuclear 8 8 674 19 Renewables (Total) 7.2 7.5 419 12 Hydro 3.5 3.6 339 9.4 Biomass/Biofuels 3.2 3.3 58 1.6 Geothermal 0.4 0.4 17 0.46 Solar 0.07 0.07 0.85 0.02 Wind 0.05 0.05 4.5 0.12

2 to 3 megawatts of electricity, with 100-foot (30-meter) blades. They can be installed on land and in shallow water in coastal areas.

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