for National Geographic News
Residential energy use in the United States will increase 25 percent by the year 2025, according to U.S. Department of Energy (DOE) forecasts. A small but increasing share of that extra power will trickle in from renewable sources like wind, sunlight, water, and heat in the ground.
Last year alternative energy sources provided 6 percent of the nation's energy supply, according to the DOE.
"The future belongs to renewable energy," said Brad Colllins, the executive director of the American Solar Energy Society, a Boulder, Colorado-based nonprofit. Scientists and industry experts may disagree over how long the world's supply of oil and natural gas will last, but it will end, Collins said.
While renewable energy is generally more expensive than conventionally produced supplies, alternative power helps to reduce pollution and to conserve fossil fuels.
"People sometimes get caught up in cost-effectiveness," said Paul Torcellini, a senior engineer at the DOE's National Renewable Energy Laboratory (NREL) in Golden, Colorado. "But it can be a question of values and what we spend our money on."
Below, a look at some recent developments in renewable-energy technology:
Photovoltaic, or solar-electric, systems capture light energy from the sun's rays and convert it into electricity. Today these solar units power everything from small homes to large office buildings.
Technological improvements have made solar-electric modules more cost-effective. In the 1980s the average price of energy captured with photovoltaics was 95 U.S. cents per kilowatt-hour. Today that price has dropped to around 20 cents per kilowatt-hour, according to Collins, of the American Solar Energy Society.
The cheaper rate is still more expensive than the average national price of electricity, which in 2003 was a little over 8 cents per kilowatt-hour, according to the U.S. Department of Energy's Annual Energy Review.
Other recent advances include "thin film" photovoltaic technology, a high-tech coating that converts any surface covered with the film into a solar-electric power source.
Boats and RVs that use the film are now on the market.
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