Energy & Resources
Renewable energy's Achilles' heel
Lisa M. Pinsker

Renewables profiles

Not all renewable energy is environmentally friendly, according to new research from Cornell University. If fully developed, renewable energy would occupy large tracts of U.S. lands, while replacing only about half the U.S. consumption of oil, natural gas and coal.

“The greatest surprise and disappointment was that we could not produce 100 percent of U.S. energy needs using renewable energy technologies and still have agriculture and forests,” says David Pimentel, an ecologist at Cornell University.

In work published in the December BioScience, Pimentel and his graduate students analyzed 10 alternative energy sources. “We defined maximum implementation as to where there was a suitable geographic location to establish a particular renewable energy technology,” Pimentel says. At that maximum level, renewable energy sources could take up 17 percent of U.S. lands.

Of the 10, they deemed two — geothermal systems and the biofuels ethanol, methanol and vegetable oils — not truly sustainable. “Ethanol production requires more than 30 percent more fossil energy to produce a gallon of ethanol than the energy yield in a gallon of ethanol,” Pimentel explains. Also, the ethanol technology causes serious environmental problems, including air, water, biological and soil pollution, he adds.

Pimentel suggests that the most environmentally sound alternative energy is wind power because each turbine occupies only a small footprint. Wind power produces 6.6 billion kilowatt-hours of electricity each year in the United States. Using all economically feasible land sites, the article says, wind power could contribute as much as 675 billion kilowatt-hours of electricity, with offshore wind-power sites providing an additional 102 billion kilowatt-hours. In the end, wind power could provide 23 percent of U.S. electrical energy needs. The downside? Wind power does create some visual and noise pollution as well as electromagnetic interference with telecommunication transmissions.

“Wind energy technology is improving and with further analysis of some key environmental issues, such as visual impacts and migratory bird issues, we could see active deployment of the technology on a large scale,” says John Krummel, a senior research analyst at the Argonne National Labs, funded by the U.S. Department of Energy.

In the end, Krummel says, the primary drivers in large-scale renewable energy development will be cost and the ability to integrate renewable energy into the current energy network. For the wind power example, large-scale wind energy development shows potential if the wind resource is located near the grid, he explains.

Despite the environmental concerns uncovered, Pimentel still believes renewable energy sources have a role to play in U.S. energy production and consumption. With the United States currently importing more than 60 percent of its oil, Pimentel doubts the the United States can become oil independent in the future.

Regardless of the current and future state of U.S. oil consumption, Krummel says that renewable energy should be part of the U.S. energy landscape. Pimentel’s work, he says, “shows the Achilles’ heel of renewable energy: large land areas are needed for full deployment.” But the best possible strategy for the United States, he stresses, is to continue an active research and development program on a diversified mix of energy technologies. “That way we will have the opportunity to move to new sources when market prices dictate the need for new sources."
Renewables Profiles


Hydroelectric systems

Makes electricity from water-storage reservoirs and dammed rivers.
Key finding: Although it has one of the lowest energy costs at about 2 cents per kilowatt hour, hydroelectric takes up 26 million hectares of land and would occupy 17 million hectares more with full development.

Type: Biomass
Grows, harvests and burns woody material for cooking, heating and conversion to electricity.
Key finding: While less harmful than burning coal, biomass burning is more harmful than burning natural gas.

Type: Wind power
Generating electricity from high-efficiency wind turbines.
Key finding: Because each turbine’s “footprint” occupies only 2 percent of the surrounding land, farmers can grow and harvest some crops beneath the spinning blades of the turbines.

Type: Solar thermal conversion systems
Converts solar radiation into heat and electricity; includes solar ponds that store heat in a bottom layer of brine and parabolic troughs that concentrate reflected sunlight onto central, liquid-filled tubes.
Key finding: While electricity from solar ponds costs about 15 cents per kilowatt hour, parabolic troughs and steam-driven turbines can generate electricity for as little as half that price. Barring leaks, the solar troughs are environmentally benign.

Type: Photovoltaic systems
Produces electricity from sunlight and silicon
Key finding: “The durability of photovoltaic cells must be lengthened and production costs reduced several times to make their use economically feasible,” according to the report. Also, manufacturing some photovoltaic cells requires toxic materials.

Type: Hydrogen
Key finding: Commercially produced hydrogen today is more than twice the cost of an energy-equivalent amount of gasoline in the United States. A hydrogen fuel-cell car would cost $100,000; prices should decline with mass production.

Type: Passive heating and cooling of buildings
Includes hot-water heating, “superwindows” (with high insulating values) and “smart windows,” which respond to changing conditions.
Key finding: Every year the poorly insulated doors and windows in the United States lose the energy equivalent of all the oil pumped in Alaska.

Type: Biogas
Generates electricity from burnable methane produced by microbes that eat animal dung.
Key finding: Biogas production is thriving in India, where a system to handle dung from a 50-cow family farm costs less than $1,000 to build and produces biogas at an electricity price equivalent of 6 cents per kilowatt-hour.


Type: Biofuels, such as ethanol, methanol and vegetable oil
Key finding: Although biofuels burn cleaner than gasoline and diesel fuels, their production consumes more energy than the biofuels yield.

Type: Geothermal energy
Key finding: Commercially exploited hot springs, geysers and dry hot rock tend to decline over 40 to 100 years, the report says, based on numbers from 1997 and 2000. Additionally, drilling opportunities are limited, and geothermal energy creates air pollution and brings up sludge residues from deep in Earth.

Information on winners and losers in alternative energy technologies was taken from the December BioScience article, “Renewable Energy: Current and Potential Issues.”

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