Researchers are seeking ways to store solar and wind power for times when the sun doesn't shine or the wind dies down. Huge batteries, caverns filled with compressed air and water-pumping stations are among the options being considered, but no leading technology has emerged. "We have done a good job in developing the renewable energies," says Eicke Weber, founder of the German Energy Storage Association. "We have not done an equally good job in making sure we have enough storage."

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