By now, you've heard it in a thousand political speeches—the shopping-list-style recitation of newfangled-sounding alternative energy sources and technologies. Clean coal! Solar and wind! Switch grass!
Yet few people take the trouble to examine the energy technology field as a whole, comparing a cross-section of future sources across the same set of objective criteria, especially price. The following is reason's attempt to rectify this gap, giving consumer and policymaker alike a quick guide to alternative energy.
Supercritical pulverized coal
Pulverizing coal is the predominant method for generating electricity in the U.S. and around the world. In a pulverization plant, coal, after being ground to the texture of flour, is blown into a furnace to burn. This converts circulating water into steam, which turns the blades of a turbine to produce electricity. "Supercritical" units heat up to 1,000 degrees Fahrenheit and make steam at 3,600 pounds per square inch.
Technology invented: The first coal-fired electric plant was Thomas Edison's Pearl Street Station in lower Manhattan, which began operations in 1882. Pulverized coal plants began coming online in the 1920s.
Federal research dollars since 1976: $27.4 billion ($5 billion on pollution control) for all coal technologies (all monetary figures are in 2009 dollars)
Carbon emitted: 0.86 metric ton per megawatt-hour
Cost per plant without carbon capture: $2.8 billion
Estimated cost with carbon capture in 2025: $3.9 billion to $4.7 billion
Production cost of a kilowatt-hour without carbon capture: 6.5 cents
Estimated production cost of a kilowatt-hour with carbon capture in 2025: 8.5 cents to 10 cents
Waste: The U.S. burns about 1.1 billion tons of coal annually, producing 125 million tons of solid waste, consisting of fly ash (fine particles), bottom ash (sand-like particles), slag (glass-like crud), and flue sludge. A 1,000-megawatt plant typically will emit 2,500 tons each of sulfur dioxide and nitrogen oxide, plus around 700 tons of particulates. Eighty percent of coal-produced slag is used for sandblasting or as grit on roofing shingles; 40 percent of bottom ash is used as gravel substitute; 44 percent of fly ash is used as a Portland cement substitute, and flue gas scrubber residues are converted into synthetic gypsum wallboard. Other waste includes rock removed from surface and underground mines and water drained from mines.
Advantage: Domestic supplies are abundant, at over 275 billion tons.
Disadvantage: Produces excess waste and greenhouse gas.
Representative example: The $1.8 billion plant in Longview, West Virginia, will produce a maximum 700 megawatts by 2011.
Integrated gasification combined cycle (IGCC) plants mix coal with steam and oxygen to produce a synthetic gas. The gas is burned much like natural gas to fire a turbine and produce electricity. Waste heat from the gas turbine is then used to produce steam to run a steam turbine. This "combined cycle" of gas and steam power is more efficient than conventional coal-fired plants.
Technology invented: Coal gasification was invented by a Scottish engineer in 1792 and first licensed in the U.S. to what became the Baltimore Gas Company in 1813. As natural gas production became possible, coal gasification fell out of favor. New IGCC plants started operation in the U.S. in the 1990s.
Federal research dollars since 1976: See entry for supercritical pulverized coal.
Carbon emitted: 0.83 metric ton per megawatt-hour
Cost per plant without carbon capture: $3.4 billion
Estimated cost per plant with carbon capture in 2025: $3.7 billion to $4.6 billion
Production cost of a kilowatt-hour without carbon capture: 7.2 cents
Estimated production cost of a kilowatt-hour with carbon capture in 2025: 7.9 cents to 9.3 cents
Waste: This process produces the same solid wastes as other coal-fired plants but makes it easier to remove sulfur, particulates, and mercury from coal gas before combustion.
Advantage: Uses abundant coal and is more energy efficient than pulverization; makes it easier to capture carbon dioxide emissions.
Disadvantage: Capital costs are higher than those of pulverized coal plants.
Representative example: The $2.2 billion plant in Kemper County, Mississippi, will produce a maximum 582 megawatts by 2013.
Combustion turbine combined cycle
In a combined-cycle gas turbine power plant, the hot gases produced by burning natural gas drive a turbine. Heat recovered from the gas turbine is then used to produce steam, which powers a steam turbine generator and produces additional electric power.
Technology invented: The first gas turbine combined-cycle generation system was built by General Electric for the Oklahoma Gas and Electric Company at its Belle Isle Station in 1949.
Federal research dollars since 1976: $6.5 billion Carbon emitted: 0.38 metric ton per megawatt-hour
Cost per plant: $920 million. The Electric Power Research Institute doesn't estimate the cost or price with carbon capture, possibly because carbon emissions are comparatively low.
Production cost of a kilowatt-hour: 7.5 cents to 8.9 cents
Estimated production cost of a kilowatt-hour in 2025: 6.8 cents to 8.1 cents
Waste: Natural gas produces no ash and contains practically no sulfur or metals, so emissions of these substances are virtually zero.
Advantage: The U.S. consumes 23 trillion cubic feet of natural gas per year. Proven reserves are 277 trillion cubic feet, and the total domestic resource is estimated at around 1,500 trillion cubic feet.
Disadvantage: The byproducts of concern from these plants are nitrogen oxides and carbon dioxide, although the emissions are much lower than those of coal-fired plants.
Representative example: The $405 million plant in Brookings, North Dakota, will produce a maximum 300 megawatts by 2012.
In a nuclear plant, uranium and other fissile materials are used to produce nuclear chain reactions as a way to heat water into steam, which then drives power generation turbines.
Technology invented: The Shippingport atomic power station in Pennsylvania began operating in 1958 as the first commercial nuclear power plant. It was jointly operated by the Department of Energy and the Duquesne Light Company until it was decommissioned and dismantled, a process that lasted from 1982 to 1989.
Federal research dollars since 1976: $27.4 billion
Carbon emitted: none
Cost per plant: $4 billion
Production cost of a kilowatt-hour: 7.5 cents
Estimated production cost of a kilowatt-hour in 2025: 6.6 cents
Waste: A typical nuclear power plant generates 22 tons of highly radioactive used nuclear fuel per year. The industry as a whole generates about 2,200 tons of used fuel annually. During the last four decades, the nation's nuclear plants have produced about 64,000 tons of used nuclear fuel. That amount of waste would cover a football field about seven yards deep. Currently, the used fuel assemblies are stored in steel and concrete containers at each plant site. These wastes could be dramatically reduced if they were used to fuel fast-breeder reactors and/or thorium reactors.
Advantage: Nuclear power plants emit no greenhouse gases. Recoverable uranium reserves might last 1,000 years. If the world adopts fast-breeder nuclear technologies, the reserves are essentially limitless.
Disadvantage: Lots of political opposition, plus concerns that fuel can be diverted to make nuclear bombs.
Representative example: No nuclear power plants have been built in the United States since 1996.
Wind turbines are driven by the wind to generate electricity. The 1.8-megawatt Vestas V90 turbine, for example, has three 148-foot blades on a 262-foot tower, totaling 410 feet in height. The blades sweep a vertical airspace of more than an acre and a half.
Technology invented: In 1888 Charles Brush built the first large windmill to generate electricity in Cleveland, Ohio. Some 17,000 utility-scale wind generators were built in California between 1981 and 1988.
Federal research dollars since 1976: $1.7 billion
Carbon emitted: none
Cost per facility: $5.6 billion
Production cost of a kilowatt-hour: 9.3 cents
Estimated production cost per kilowatt-hour in 2025: 7.3 cents
Waste: none once in operation
Advantage: Wind turbines do not emit greenhouse gases and need no fuel.
Disadvantage: Wind turbines depend on an intermittent source of energy and occupy a lot of space. The best wind resources generally are far from big cities, requiring the construction of thousands of miles of additional high-voltage wires. Some wind turbines kill birds and bats.
Representative example: The $1 billion wind farm in Washington, Iowa, will produce a maximum 500 megawatts by 2013.
Agricultural residues, industrial and urban wood wastes, forestry residues, and dedicated energy crops such as hybrid poplar and willow trees can be used to drive turbines and produce electricity. The biomass can be burned directly to heat water into steam or be converted into a synthetic gas before being burned.
Technology invented: The first small biomass plants, using sawdust, began generating electricity in California in 1982. Biomass plants today burn wastes such as turkey manure.
Federal research dollars since 1976: $3 billion
Carbon emitted: 0.10 metric ton per megawatt-hour
Cost per plant: $3.5 billion
Production cost of a kilowatt-hour: 7.5 cents to 8.8 cents
Estimated production cost of a kilowatt-hour in 2025: 7.5 cents
Waste: Biomass plants produce mineral ash, which can be used as a fertilizer, along with some fine particulates, nitrogen oxides, and carbon dioxide.
Advantage: Biomass plants use renewable fuels and burn wastes, which eliminates the need to store them in landfills.
Disadvantage: Increased use of biomass would require more land for energy crops, e.g., hybrid poplars, willows, and switch grass, perhaps displacing food crops and wild lands.
Representative example: The $400–500 million biomass plant in Appling County, Georgia, will produce a maximum 100 megawatts by 2014.
Solar thermal plants use mirrors to concentrate sunlight into a small area to produce heat, which is used to make steam for driving power generators. Some solar thermal plants consist of acres of parabolic mirrors focusing sunlight on tubes containing liquids, which then heat water into steam. Another configuration involves gigantic dish mirrors concentrating sunlight onto a Stirling engine, which drives a piston that turns a power generator.
Technology invented: In 1981 the Solar One thermal power plant was built in Daggett, California, as a joint project of the U.S. Department of Energy, Southern California Edison, the Los Angeles Department of Water and Power, and the California Energy Commission.
Federal research dollars since 1976: $2.5 billion
Carbon emitted: none
Cost per facility: $12.5 billion
Production cost of a kilowatt-hour: 17.9 cents
Estimated production cost of a kilowatt-hour in 2025: 17.9 cents
Waste: None, except for waste water from cleaning mirrors.
Advantage: Solar thermal plants produce no air pollution, create little or no noise, and require no fuel.
Disadvantage: Like wind turbines, solar thermal plants rely on an intermittent energy source and take up a lot of space. The U.S. Bureau of Land Management has received applications for more than 130 projects in the desert Southwest that could occupy more than 1 million acres (more than 1,500 square miles).
Representative example: In March 2009, NV Energy announced plans to build a $1 billion solar thermal plant in Southern Nevada that will be able to produce 250 megawatts at its maximum capacity.
Silicon solar photovoltaic
Photovoltaic solar cells are thin disks of highly purified silicon crystals that convert sunlight directly into electricity. Technology invented: Daryl Chapin, Calvin Fuller, and Gerald Pearson developed the silicon photovoltaic cell at Bell Labs in 1954.
Federal research dollars since 1976: $3.6 billion
Carbon emitted: none
Cost per facility: $18 billion to $20 billion
Production cost of a kilowatt-hour: 33.5 cents to 39.4 cents
Estimated production cost of a kilowatt-hour in 2025: The Electric Power Research Institute has no current estimate, although technological improvements should lower costs, perhaps considerably.
Waste: In a 2008 life-cycle analysis of various photovoltaic technologies, researchers at the Brookhaven National Laboratory found that "the differences in the emissions between different photovoltaic technologies are very small in comparison to the emissions from conventional energy technologies that photovoltaics could displace."
Advantage: Silicon photovoltaic solar cells produce no air pollution, create little or no noise, and require no fuel.
Disadvantage: Solar cells supply energy intermittently and occupy a lot of land.
Representative example: In February 2009, Pacific Gas & Electric announced plans to build solar cell arrays at various locations on land it already owns, at a cost of $1.4 billion. When completed, they will all together produce 250 megawatts at their maximum capacity.
Thin-film solar photovoltaic
Like silicon crystal photovoltaic cells, this technology produces electricity directly from sunlight. Thin-film photovoltaics weigh less and cost less than crystalline silicon-based technologies. Some companies use combinations of copper, indium, gallium, and selenium to make their solar cells while others produce cadmium and telluride cells.
Technology invented: The Institute of Energy Conversion at the University of Delaware began research on thin-film photovoltaic cells in 1972.
Federal research dollars since 1976: $3.6 billion
Carbon emitted: none
Cost per facility: $10 billion to $12 billion
Production cost of a kilowatt-hour: 24.6 cents to 31.5 cents
Estimated production cost of a kilowatt-hour in 2025: No estimate is available, but technological improvements should lower costs, perhaps considerably.
Waste: Concerns have been raised about handling the heavy metals, such as cadmium, that are used to manufacture thin-film solar cells. In a 2008 life-cycle analysis, researchers at the Brookhaven National Laboratory estimated that toxic cadmium emissions from thin-film photovoltaic cells are 90 to 300 times lower than those from coal power plants.
Advantage: Thin-film solar photovoltaic cells produce no air pollution, create little or no noise, and require no fuel.
Disadvantage: Solar cell arrays supply energy intermittently and occupy a lot of space.
Representative example: In July 2008, Southern California Edison announced a $1 billion project in which solar thin-film arrays would be installed on 150 commercial rooftops, producing 250 megawatts at their maximum capacity.