What are some of the renewable energy sources used today?
What will be an ideal response?
Answer: Renewable energy includes a diverse range of technologies, from traditional wood-burning, to hydroelectricity that has been used for more than a century, to technologies such as solar and wind-generated electricity, ethanol and biodiesel, photovoltaics, tidal energy, and geothermal power production that are emerging today or are still in development.
Wood fuel is a substantial source of energy for cooking and heating, mainly in poor countries. Hydroelectricity is the most important renewable source for commercial power, producing about 6 percent of global commercial energy. All the other renewable technologies together are responsible for less than 2 percent of global energy production. Many forms of plant matter can be converted to biofuels, liquid or gaseous fuels that can be burned, for example, in modern automobiles. But, it takes a significant amount of land to produce the feedstock for biofuels, taking much land that could have been used for food. Also, the amount of fuel energy that is produced from manufacturing ethanol from corn or biodiesel from soybeans is small after one accounts for the amount of fuel consumed for tractor fuel, fertilizer, and other energy inputs to biofuel production.
Canada, China, Brazil, and the United States are the largest producers of hydroelectric power in the world. Most of the best sites for hydroelectric generation are already in use in the United States and Europe, but in many areas, there is considerable undeveloped potential. Opposition to construction of big dams and reservoirs is strong among people who fear the environmental damage they cause, such as loss of farmland or animal habitat.
At present, solar energy is used in two principal ways: thermal energy and photovoltaic electricity production. Solar thermal energy is heat collected directly from sunshine in collectors on the roofs of buildings. The heat absorbed by these collectors is then carried in water or other liquids to the places where it is needed. Photovoltaic electric production is a direct conversion of solar energy to electricity in photovoltaic cells. Photovoltaic power is competitive in price with conventional electricity in much of the world, and offers considerable potential as economies of scale bring prices down. However, it suffers from the problem that solar energy is not reliable: it varies with season and with weather.
Geothermal energy use in the United States is mainly in the form of electricity production at a handful of sites, led by California's Geysers plant. (In addition, several new uses for geothermal energy are being utilized, including shafts drilled deep into the subsoil beneath new construction in urban areas.) Wind generation of electricity is one of the fastest-growing renewable energy technologies today, although it still amounts to less than 2 percent of total U.S. electricity production. Environmentalists are divided on wind energy: some favor wind generation because it is renewable and pollution-free, while others oppose it—where it involves especially large windmills and turbines—on the grounds of visual impacts and its hazards to birds.
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You may wish to list the major problems, as you see them, in decreasing order of importance. Justify your answer with an explanation. What will be an ideal response?
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A. 2?4 B. 5?22 C. 30?44 D. 62?75 E. 83?95
Which of the following statements is true of electromagnetic radiation?
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Suppose we could take the Atlantic Ocean north of the equator and divide it into two compartments along a north-south line (for example, if sea level were much lower and the Mid-Atlantic Ridge was mergent along its length)
What would happen to the North Atlantic Gyre? a) The gyre would grind to a halt because its north and south currents are blocked. b) The Mid-Atlantic Ridge barrier would turn equatorial currents north and northern boundary currents south, resulting in two gyres, one on each side. c) The ridge would cause surface water to sink as it piles up against the barrier and has nowhere else to go. d) The ridge would have almost no effect, and the currents would just go over or around it. e) The ridge would cause deep water upwelling as the currents strike the barrier.