Clean energy's impact on global climate

Renewables could slash carbon emissions by two-thirds

DENVER - Exploiting the potential of renewable energy while improving energy efficiency could cut 1.1 billion tons of U.S. carbon emissions annually by 2030 - roughly two-thirds of the 1.63 billion tons the U.S. Energy Information Administration says Americans burned skyward in 2004.

That's the conclusion of several researchers presenting at the Solar 2006 national solar conference this week. All cautioned that their projections hinge on assumptions the future may scoff at.

Many climate scientists view drastic reductions of the greenhouse gas carbon dioxide, growing at about 2 percent per year, as the only way to prevent catastrophic global warming in the coming century. Charles Kutscher, a National Renewable Energy Laboratory solar engineer and chairman of the Solar 2006 conference , asked colleagues and others to contribute original research to the effort.

"It shows that we would be on track to reduce carbon emissions by 60 (percent) to 80 percent by 2030 using today's technology," Kutscher said.

The researchers based their conclusions on technical as well as economic factors, taking into account such details as the vagaries of the U.S. electric grid to the point at which the need to grow food outweighs future fuel-crop production.

Wind power has the greatest potential impact. Assuming federal tax credits persist, U.S. wind power could explode from today's 9,100 megawatts to 360,000 megawatts by 2030, said Michael Milligan, a consultant to NREL.

Xcel Energy says a megawatt can power about 1,000 homes in Colorado; a typical coal-fired power plant is about 500 megawatts.

Such growth would displace 400 million tons of carbon a year, Milligan said.

The widespread use of plug-in hybrid-electric vehicles, which themselves may reduce carbon emissions 50 million tons a year by 2030, could further boost the amount of U.S. wind power, said NREL analyst Peter Lilienthal. Wind, like solar energy , is a whimsical resource for electricity, varying based on the weather and heedless of demand that utilities must instantly quench.

If utilities can tap the batteries of parked cars, as much as 800,000 million megawatts of wind could be possible without upsetting the nation's electrical grid, Lilienthal said.

Rooftop photovoltaic systems would displace another 100 million tons of carbon, said NREL analyst Paul Denholm. Denholm's estimates require technology improvements and manufacturing scale to lower solar-electric costs from today's 23 cents per kilowatt hour to about 6 cents per kilowatt hour.

If that happens, rooftop systems could produce 15 percent of the country's electricity by 2030, or about 600,000 megawatts. Less than one-tenth of 1 percent is generated via solar panels today.

Solar farms consisting of thousands of mirrors and central towers could displace another 40 million tons of carbon, said Mark Mehos, an NREL engineer who specializes in the field of concentrating solar power. That would require capacity climbing from about 400 megawatts today to 30,000 megawatts by 2030, he said.

Power plants that convert crop and forest waste to electricity could cut carbon emissions another 230 million tons, said Ralph Overend, a retired NREL research fellow. Biomass could generate 110,000 megawatts nationally by 2030, he said.

NREL analyst Martin Vorum said geothermal power could offset 100 million tons of carbon each year, in generating 50,000 megawatts by mid-century.

Finally, energy efficiency in homes and businesses could reduce carbon emissions by 200 million tons by 2030, said Patrick Hughes of Oak Ridge National Laboratory. A widespread transition to light-emitting diode-based lighting, which is 10 times more efficient than incandescent bulbs, would bring two-thirds of the energy savings, he said.