Researchers in Denmark say a project to store wind energy in giant synthetic air bags buried under sand dunes has been successful.

A test in Southern Jutland showed 97 percent efficiency in storing wind energy, the Copenhagen Post reported Friday.

Wind powered compressors inflate the bags, and the compressed air is later released to generate power using the same kind of pump and turbine system used for energy storage in lakes, the newspaper said.

Researchers said the most difficult challenge of the storage is making certain that the massive air bags can handle repeated inflation and deflation.

"But the synthetic membrane has proved to be unproblematic," Ole Hededal, a lecturer at the Technical University of Denmark, said. "In our tests the bags only stretched 0.5 percent, and they're made to tolerate tension of up to 14 percent."

For the final phase of testing, a 150-foot by 150-foot air bag will be used, a storage unit that can hold up to 34 kilowatts of wind energy, the Post reported.