Electrical power

Electrical power is so convenient that $350 billion worth of it was sold by utility companies in the United States alone in 2008. However, a need for greater efficiency and environmental care will probably slow growth in sales, and it is possible that in the future power distribution methods and the mix of power sources will change radically.

Background

People have always feared the power of lightning. Ancient peoples undoubtedly knew of static electricity (as in making sparks by walking across wool rugs). Some archaeologists believe that certain ancient Mesopotamian and Egyptian pots might have been batteries, perhaps for creating metal plating on jewelry or weapons. However, nothing lasting was developed until electricity had a scientific basis. Benjamin Franklin’s famous experiment—flying a kite in the thunderstorm—proved that lightning is essentially the same phenomenon as static electricity. Besides leading to lightning rods to protect from lightning, the discovery encouraged other researchers to seek the power of lightning.

Development of Electrical Power

In 1800, Alessandro Volta demonstrated that two different metals, connected by a wire and placed in an acid solution, could generate electricity—just as millions of lead-acid car batteries have done in the twentieth century. In 1801, Sir Humphry Davy demonstrated an arc lamp, which got some use. In 1832, both Michael Faraday and Joseph Henry demonstrated generators, although these were only laboratory-scale machines.

Batteries were still the major power source in 1837, when the first electrical appliance arrived: the telegraph. This device revolutionized communications. A telegraph operator could instantly send a coded message through a wire by using a “key” to connect and disconnect electrical power. Hundreds or thousands of kilometers away, the message was received when the bursts of transmitted electricity moved a tiny electromagnet in a pattern that could be decoded by the operator at that end.

Then Thomas Edison, the towering figure in electrical power, invented the incandescent lightbulb in 1870 (the same year that Joseph Wilson Swan also developed one in England). When Edison tried to sell lights, there were few buyers because batteries were too expensive. In a desperate race with creditors, Edison’s company built improved industrial-sized generators, strung wires, and discovered vital refinements, including fuses and switches. Edison invented the electric utility, which allowed thousands of electrical inventions to follow.

Edison’s direct current, however, could not be increased in voltage to go more than a few kilometers. Nikola Tesla’s invention of the alternating current (AC) motor allowed electricity to increase in voltage to press through resistance in the wires and then decrease in voltage at the using site. AC electrical grids began to serve customers tens, hundreds, then thousands of kilometers away. Mass production and improvements in technology allowed the price per kilowatt of electricity to drop from dollars to mere cents.

Power from Coal

Anything with chemical energy, motion, or a difference in temperature has the potential to generate electrical power. Combustion of fossil fuels has been the greatest energy source, and coal is the most heavily used fossil fuel. Its abundance (particularly in the United States and China) makes it cheap, and some estimate that coal could provide most of the world’s total energy by itself for more than a century.

Most coal-fired generators boil water to steam, which flows through turbine blades similar to those of jet engines. Such plants cause complaints because they also release soot and sulfur dioxide (from sulfur impurities in the coal) through their smokestacks. Also, they only transform one-third of the coal energy into electricity, the balance being lost as “waste heat.”

For older plants in rich countries, low-sulfur coal is burned or various scrubbing technologies are used to clean the exhaust gas. Filters or electrostatic plates may be used to catch exhaust dust. Calcium carbonate (CaCO₃) dust in the combustion chamber turns the sulfur dioxide into sodium sulfate, which can be caught as dust. Coal can also be cleaned of sulfur and metals before being burned. However, poorer countries that cannot afford to implement such technologies often simply must suffer with dirty, unhealthful air.

More advanced coal-fired plants avoid generating pollutants that must be cleaned from the exhaust gases. Combined-cycle plants heat a water-coal mixture, so hydrogen and oxygen in the water (H₂O) generate hydrogen sulfide (H₂S, which can be easily stripped out), methane (CH₄), and carbon monoxide (CO). Burning the latter two gases shoots hot gases through a turbine. Gases leaving the turbine “topping cycle” make steam in a boiler, just as in the old plants. Combining the two cycles yields efficiencies greater than 50 percent.

Another advanced method, fluidized-bed combustion, uses a hot bed of sand with coal, air, and calcium carbonate flowing up through the sand. Slag at the top contains calcium sulfate, so air cleaning is easier. Fluidized-bed systems often increase efficiency with a liquid-metal topping cycle. Molten metals, such as sodium or potassium, can stand hotter temperatures than steam, so one of these metals is circulated through pipes in the fluidized bed and out to a turbine. Waste heat from that topping cycle then powers a steam boiler.

Coal-fired plants can be clean and efficient, but the required equipment generally involves large, expensive plants, with the equipment cost being a major part of the electricity cost. Hence, coal-fired plants must run nearly continuously to pay for themselves. As such, they are “base-load” plants.

Power from Oil, Hydroenergy, and Fuel Cells

Plants burning oil or natural gas (CH₄) use the same gas and steam turbines as coal-fired plants. They can be built much more cheaply because the fuel can be easily cleaned of sulfur, they have more concentrated energy, and pumping fluids is easier than moving solids. However, these fuels are more expensive. Thus, oil- and gas-fired electricity is more expensive than coal-fired, and it is cheaper for the owners not to run them all the time. Consequently, oil- and gas-fired plants are often “peaking plants,” switched on when electrical demand is highest and off when demand drops.

Hydroelectric power (hydroenergy) is the modern version of ancient waterwheels. Water from a dammed river flows down through a turbine. Hydroenergy is cheap and is available on a few minutes’ notice. The limitation is that most good sites in the developed countries already have dams. Likewise, tidal power, as in the Bay of Fundy and the Rance River delta, has limited sites.

Fuel cells are also more efficient and less polluting. They operate as batteries do, except that fossil fuels become carbon dioxide and water at the electrodes. Fuel cells yield efficiencies as high as 70 percent; if the catalysts can be made cheaply enough, fuel cells may eventually dominate the market. Some researchers have even suggested the development of sugar-powered fuel cells, based on the principle that all life is powered by biological sugar fuel cells.

Power from Nuclear Reactors

Nuclear fission (splitting atoms) is another way to get heat to spin turbines. Heavy metals (uranium and heavier elements) are less stable than other elements. Certain isotopes (versions of an element with more or less neutrons) are radioactive because they naturally fission into lighter elements, emitting heat and radiation in the process. When a critical mass of fissionable material is brought together, neutrons released from radioactive decay trigger fissions of enough other atoms to cause a self-sustaining nuclear chain reaction.

A secret Allied World War II project culminated in two fission bombs being dropped on Japan in 1945, ending the war. It was predicted that this awesome technology would supplant other energy sources and produce “electricity too cheap to meter.” Breeder reactors were designed both to produce power and to bombard slightly radioactive material to transmute it into fuel.

Fission energy has not achieved prices lower than coal-fired electricity, and there are long-term costs of protecting spent (but still radioactive) fuel from accidental release or diversion into bombs. The most important immediate cost factor is that a power plant, as opposed to a bomb, must operate for years without killing people or damaging the equipment. This protection involves great expense, because a fission reactor produces intense radiation. Personnel must be shielded by massive amounts of lead and concrete, and much of the structure of a reactor can be weakened by neutron embrittlement during years of operation. Worse, an out-of-control fission reactor can overheat, explode (although not as powerfully as a bomb), and release highly poisonous radioactive materials. Consequently, fission reactors must have complex redundant safety features and containment domes to protect against radioactive leaks. Breeder reactors, with their massive neutron fluxes, are the most likely reactors to have serious accidents.

High-temperature gas reactors could operate at higher temperatures, could have greater safety margins, and could have continuously replaced spherical fuel elements. However, the 1986 Chernobyl reactor disaster (in what was then the Soviet Union) and the earlier accident at Three Mile Island, Pennsylvania, in 1979, have caused the public to have a negative view of fission, so research into gas reactors has not received sufficient funding.

Nuclear fusion (combining lighter atoms into heavier ones) is being researched, but it is an unlikely competitor. In the Sun, four hydrogen atoms are fused into one helium atom. A reactor on Earth making a similar reaction could not achieve the pressure of the Sun, so it would have to compensate with higher temperature (held in by a magnetic field) and heavier isotopes of hydrogen (deuterium and tritium). Advantages to fusion would be that hydrogen isotope fuels are essentially inexhaustible and that a fusion reactor with mechanical problems would simply stop rather than going out of control. The problems would be that fusion, with its heavier hydrogen isotopes, generates neutron fluxes comparable to those of a fission breeder, which would soon damage the complex magnetic containment system. Worse, fusion reactor heat flux per unit volume is less than that of fission reactors, so costs per kilowatt would be high.

Power from Wind, Photovoltaic Cells, and Geothermal Sources

Wind power was reborn in the energy crisis of the 1970’s. Tax incentives given during the energy crisis allowed “wind farms” in high-wind areas to approach profitability. Eventually, these machines evolved into more cost-effective systems. Then gears were developed to accommodate a range of wind speeds. Today, wind systems produce power at prices comparable to coal-fired plants, and wind systems can operate profitably in areas with less than maximum wind. However,wind power is variable. An electrical grid cannot count on receiving more than 20 percent of its power from wind lest a calm day cause a power failure.

Photovoltaic (solar) cells are large transistors that produce electricity when struck by sunlight. Prices of photovoltaic power dropped from hundreds of times that of grid power in the 1960’s to three times that of coal-fired power in the mid-1990’s. Further price drops from lower production cost, higher cell efficiencies, and the integration of cells into building construction could allow photovoltaics to produce many times the electricity presently used. (Production peaks during afternoon peak demand, but production stops after dark.) Even if prices do not decline, photovoltaics are competitive for small and distant sites (such as roadside phones and railroad signals) because they do not require large installations and they have no moving parts.

Geothermal energy taps hot steam underground to run turbines. Advanced systems can use hot water, and future systems may pump fluids (such as water or helium) into areas of hot rock so the fluids can carry heat back up to a power plant. If drilling costs could be reduced sufficiently, geothermal energy could grow into a major source of electricity.

Ocean Energies, Efficiency, and Cogeneration

If the foregoing systems do not provide enough power, more exotic methods may conceivably be used in the future. Ocean waves and currents could supply a major fraction of energy used. The difference between hot tropical ocean waters and the near-freezing deep water has powered experimental power plants, and this ocean thermal energy conversion (OTEC) could theoretically supply many times the world’s electrical use. However, many practical problems remain to be solved.

Finally, increased efficiency of electrical use would have the same effect as more generators, perhaps as much as 75 percent more, and at costs cheaper than building new power plants. There are hundreds of ways to increase the efficiency of electrical use, including more efficient electric motors, compact fluorescent lights, greater use of light-emitting diodes (LEDs), more insulation, smart windows, and solid state displays instead of picture tubes in televisions and computer monitors. (The last item alone could retire the equivalent of several nuclear power plants.)

A similar increase in efficiency comes from cogeneration, the use of “waste heat” from power plants for other uses, such as district heating or chemical processing. Because most power plants are far less than 50 percent efficient, full cogeneration would effectively double energy from electric utilities. Many industrial plants are adding cogeneration to existing heating operations. Ultimately, fuel cells might be made small enough to combine water heating and space heating with electrical generation, making houses tiny power plants.

Issues for Electric Utilities

The electric power industry is one of the largest in the world, generating power and maintaining cables linking generators and power uses. Such networks entail technology and management issues affecting trillions of dollars. First, the power sources must be chosen.

Second, storing electricity is expensive, so generated power must be used when generated. Consequently, generating capacity must be enough to cover the highest use “peaks” in early afternoon (notably air-conditioning), morning, and early evening. Generators are not fully used at other times. Consequently, utilities increasingly charge extra for peak times, charge less for off-peak hours, and offer bonuses for appliances that switch off on command.

Likewise, some areas have seasonal variations in supply and demand. Pacific Northwest power dams have maximum water flow during spring and summer, when the Southwest has the greatest air-conditioning load. In the winter, water flow is low, but the Southwest has less demand then. High voltage lines allow the two regions to exchange power. A world grid has been suggested for much greater savings.

Batteries for vehicles and portable appliances are a growing part of electricity use. Dry cells cost the equivalent of dollars per kilowatt hour. Liquid-cell batteries, such as the lead-sulfuric acid batteries for cars, are cheaper, but they are still expensive and heavy. Furthermore, as much as one-third of energy is lost. Increasing battery performance and lowering costs are key to practical electric-driven cars. Such cars would decrease pollution (one big plant cleans emissions better than thousands of car engines), and energy efficiency would increase (gasoline engines have low efficiency). They would vastly increase power plant construction, and nightly charging would help balance the day peak.

Finally, electrical utilities are large enough to be a major factor in possible greenhouse warming caused by increased carbon dioxide in the atmosphere. If greenhouse warming continues at its present rate, there will be a greater push toward efficiency and away from fossil fuels.

Bibliography

Bodanis, David. Electric Universe: How Electricity Switched on the Modern World. London: Little, Brown, 2005.

Breeze, Paul. Power Generation Technologies. Burlington, Mass.: Elsevier/Newnes, 2005.

Casazza, J. A., and Frank Delea. Understanding Electric Power Systems. New York: Wiley, 2003.

Flavin, Christopher, and Nicholas Lenssen. Powering the Future: Blueprint for a Sustainable Electricity Industry. Washington, D.C.: Worldwatch Institute, 1994.

Gabriel, Mark A. Visions for a Sustainable Energy Future. Lilburn, Ga.: Fairmont Press, 2008.

Grigsby, Leonard Lee, ed. Electric Power Generation, Transmission, and Distribution. Boca Raton, Fla.: CRC Press, 2007.

Grubb, Michael, Tooraj Jamasb, and Michael G. Pollitt. Delivering a Low-Carbon Electricity System: Technologies, Economics, and Policy. New York: Cambridge University Press, 2008.

Kutz, Myer, ed. Environmentally Conscious Alternative Energy Production. Hoboken, N.J.: John Wiley, 2007.

Shively, Bob, and John Ferrare. Understanding Today’s Electricity Business. San Francisco: Enerdynamics, 2007.

Warkentin-Glenn, Denise. Electric Power Industry in Nontechnical Language. 2d ed. Tulsa, Okla.: PennWell Books, 2006.

U.S. Environmental Protection Agency. Electric Power. http://www.energy.gov/energysources/electricpower.htm