A decade ago, Germany launched a renewable-­energy plan on an unprecedented scale. Its parliament, the Bundestag, enacted a law obligating the nation's electric utilities to purchase green power at sky-high rates--as much as 60 cents per kilowatt-hour for solar--under fixed contracts lasting up to 20 years. (German market prices for electricity, largely produced by coal and nuclear plants, were about 12 cents per kilowatt-hour.) The idea behind this "feed-in tariff" was that anyone would be able to build a renewable-power plant--or install rooftop solar panels--and be guaranteed predictable profits by feeding energy into the grid, where utilities would buy it at premium prices. The higher costs would be passed on as monthly surcharges to ratepayers, spread out among all homes and businesses in a country of about 80 million people. Fossil and nuclear fuels amount to "global pyromania," said Hermann Scheer, the German politician who championed the policy. "Renewable energy is the fire extinguisher."

Now, as the United States and other nations look toward creating their own policies for dealing with climate change, the effectiveness of the German experiment is a subject of debate. From one perspective, the Renewable Energy Sources Act of 2000 has exceeded its aims. Germany's first target was to get at least 10 percent of its electric power from renewable sources by 2010. The German grid now gets more than 16 percent of its electricity from these sources, and the government has raised its target for 2020 from 20 percent to 30 percent. The country avoided pumping about 74 million metric tons of carbon dioxide into the atmosphere in 2009. The German environment ministry also touts a side benefit: nearly 300,000 new jobs in clean power. As a result, the feed-in tariff has the support not only of the left-leaning politicians who originally backed it but also of most of the skeptics in the right-leaning parties that fought against it, says Claudia Kemfert, who heads the energy department at the German Institute for Economic Research in Berlin. "The skepticism is over," she says. "We're celebrating the success."