FRANKFURT—Germany needs to focus on cost-effective renewable energy sources and start drilling for shale gas to avoid sapping its wealth while cutting carbon emissions, said energy expert Daniel Yergin.

Europe's largest economy is pursuing one of the world's most ambitious climate-protection strategies, aiming by midcentury to nearly eliminate greenhouse gas emissions. To achieve this it plans to drop all nuclear and most fossil-fueled power generation in favor of alternatives like wind and solar power.

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