On the Black Forest's western slopes – in the land of cuckoo clocks and Brothers Grimm – there is a city that calls itself "green."
Rich silver deposits first lured settlers to Germany's Freiburg im Breisgau back in the 12th century, but today this quaint city is anything but medieval. Freiburg is a prototype for a clean-energy future that Germany is aggressively pursuing.

Nations across the globe are looking increasingly to wind, water, and the sun to power their economies in the decades to come. But Germany stands apart as a global leader in the industrialized world's push to limit fossil-fuel consumption. Forging a stable path to a post-carbon economy would be a watershed moment in human history – not to mention a tremendous economic boon for whoever finds the way. But it will not be easy to shift off the coal, oil, and natural gas that have powered global economic development for centuries.

In Freiburg – where silicon has overtaken silver as the city's focus – the energy transition is getting a trial run.

Solar panels line the train station's glassy facade, from which visitors alight into a bustling shopping district. Photovoltaic panels top the pitched roofs of churches, schools, and houses in sleepy residential quarters and help power the local soccer stadium and city hall. Students from all over the world study renewable-energy engineering at the University of Freiburg, established under the Habsburgs more than 500 years ago. After they graduate, they might get a job up the street at the Fraunhofer Institute for Solar Energy Systems, Europe's largest solar research facility.

Over the decades, Freiburg expanded its own clean-energy and efficiency infrastructure and worked with regional utilities that trade largely in wind, solar, and hydro power.

By 2011, when Japan's Fukushima Daiichi nuclear plant rekindled anti-nuclear sentiments and prompted the immediate shutdown of Germany's oldest nuclear plants, Freiburg had already cut its carbon dioxide emissions by nearly 20 percent from 1992 levels. And it aims to cut 20 percent more by 2030. But even as it has built an economy and identity around efficiency and renewable energy, Freiburg gets only about 5.5 percent of its electricity from locally generated, renewable sources. The rest is a mix of renewable and nonrenewable energy from regional utilities. Plans are under way to install additional wind energy capacity locally and enact more efficiency measures, with the goal of using 100 percent renewable energy by 2050.

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