Chapter Summary

Energy is the capacity to do work. Power is the rate of doing work. Today nearly 80 percent of all commercial energy is generated by fossil fuels, with about 35 percent coming from petroleum. Coal produces 23 percent, and natural gas (methane) accounts for 21 percent of our commercial supply. Petroleum and natural gas were not used in large quantities until the beginning of the twentieth century, but supplies are already running low. Coal supplies will last several more centuries at present rates of usage, but it appears that the fossil fuel age will have been a rather short episode in the total history of humans. Nuclear power provides about 7 percent of commercial energy worldwide.

The environmental damage caused by mining, shipping, processing, and using fossil fuels may necessitate cutting back on our use of these energy sources. Coal is an especially dirty and dangerous fuel, at least as we currently obtain and use it. Coal combustion is a major source of acid precipitation, which is suspected of being a significant cause of environmental damage in many areas. We now recognize that carbon dioxide buildup in the atmosphere has the potential to trap heat and raise the earth’s temperature to catastrophic levels.

The greatest worry about nuclear power is the danger that accidents or terrorist attacks could release hazardous radioactive materials into the environment. Several accidents, most notably the “meltdown” at the Chernobyl plant in the Soviet Ukraine in 1986, have convinced many people that this technology is too risky to pursue. Other major worries about nuclear power include where to put the waste products of the nuclear fuel cycle and how to ensure that the wastes will remain safely contained for the thousands of years required for “decay” of the radioisotopes to nonhazardous levels. Yucca Mountain, Nevada, has been chosen for a high-level waste repository, but many experts believe that burying these toxic residues in nonretrievable storage is a mistake.

Several sustainable energy sources could reduce or eliminate our dependence on fossil fuels and nuclear energy. Some of these sources have been used for centuries but have been neglected since fossil fuels came into widespread use. Passive solar heat, fuelwood, windmills, and waterwheels, for instance, once supplied a major part of the external energy for human activities. With increased concern about the dangers and costs associated with conventional commercial energy, these ancient energy sources are being reexamined as part of a more sustainable future for humankind.

Exciting new technologies have been invented to use renewable energy sources. Active solar air and water heating, for instance, require less material and function more quickly than passive solar collection. Parabolic mirrors collect solar energy to produce temperatures high enough to be used as process heat in manufacturing. Wind is now the cheapest form of new energy in many places. It has potential to supply one-third or more of our energy requirements.

Fuel cells use catalysts and semipermeable electrolytes to extract energy from fuels such as hydrogen or methanol at high efficiency and with very low emissions. Ocean thermal electric conversion, tidal and wave power stations, and geothermal steam sources can produce useful amounts of energy in some localities. One of the most promising technologies is direct electricity generation by photovoltaic cells. Since solar energy is available everywhere, photovoltaic collectors could provide clean, inexpensive, nonpolluting, renewable energy, independent of central power grids or fuel supply systems.

Biomass also may have some modern applications. In addition to direct combustion, biomass can be converted into methane or ethanol, which are clean-burning, easily storable, and transportable fuels. These alternative uses of biomass also allow nutrients to be returned to the soil and help reduce our reliance on expensive, energy-consuming artificial fertilizers.