Type: 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.
Grows, harvests and burns woody material for cooking, heating and conversion
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 turbines
footprint occupies only 2 percent of the surrounding land,
farmers can grow and harvest some crops beneath the spinning blades of
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
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
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.
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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