New energy: climate change and sustainability shape a new era

SHINING PROMISE

If there's any ray of hope here, it could be the one that travels 186,000 miles per second – sunlight. Even though silicon solar cells still supply less than half a percent of the world's electricity – 40 years after their invention – some people now see the growth curve bending upward.

"2008 was a historic year," points out Daniel Kammen, an energy physicist at the University of California at Berkeley, and visiting scientist at the World Bank in Washington, D.C. "That was the first year that global production of high-purity silicon for the solar industry was greater than for the computer [chip] industry."

Today's rate of solar-cell manufacturing allows the added energy production of only the equivalent of about 10 nuclear power plants each year. To put that in perspective: The US would need to build one nuclear plant per week for almost 10 years to replace the power it gets from fossil fuels.

But the global solar photovoltaic industry is growing on average 50 percent per year – driven by innovations and policies in some countries that encourage their use. And another type of solar – sunlight concentrating – which uses mirrors to focus sunlight, heat gases, and turn an engine to generate electricity, is also blossoming.

Several weeks ago, the first large, sunlight-focusing solar plant received approval for construction on federal land – a 709-megawatt installation planned by Tessera Solar for 10 square miles of desert in California's Imperial Valley. The project still faces hurdles. Existing transmission lines can only transport half the electricity that it will generate. In fact, many of the US's 170,000 miles of high-tension lines will need to be rerouted to connect solar and wind plants to the grid – a $150 billion expense, says Smil.

If you're a homeowner wanting to put solar on your roof, the upfront cost of installing those solar cells presents another challenge. Averaging the installation costs over years and adding the financial incentives offered in some areas, the cost of home-generated solar electricity starts at 15 to 20 cents per kilowatt-hour – double the US average of 9 cents for grid electricity from fossil fuels.

Even so, industry observers expect that solar power produced in power plants and on rooftops will together generate 10 to 20 percent of American electricity by 2030. "We can accelerate that or slow it down," says Mr. Kammen; it will depend on government policies. "Reaching for the Sun" explains how group buying can drive down solar costs.)

Solar does suffer one major drawback – and this also affects wind power, which still produces twice as much electricity worldwide as solar and is steadily growing. Each source relies on a natural condition – the presence of sun or wind, respectively – to generate electricity. Ways must be found to store that energy – say, by pumping water uphill or pressurizing air in caverns – so it can be used at other times to produce electricity.

Until that happens, solar will be relegated to providing power during daytime, when electricity usage is highest. Another source will have to provide base-load electricity, which is consumed day and night – and this almost certainly means fossil fuels.

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