Researchers in Denmark have succeeded in storing wind energy in giant synthetic bags, reports the Danish trade newspaper Ingeniøren.

The research project, based in Southern Jutland, has been filling massive air bags buried under sand dunes using wind-powered compressors.

The compressed air is then released to generate power using a pump and turbine system similar to those used for storage in lakes, according to the newspaper’s account.

An initial test, carried out in a 5-metre by 5-metre engine room, rated the efficiency of the storage method at 97%. A later, larger-scale test recorded a figure of 99.5%.

Researchers said the toughest challenge is making sure the massive air bags can cope with repeated inflation and deflation.

“‘But the synthetic membrane has proved to be unproblematic,” Ole Hededal, a lecturer at the Technical University of Denmark, told the paper.

“In our tests the bags only stretched 0.5%, and they’re made to tolerate tension of up to 14%.”

The final phase of testing will use a 50-metre by 15-metre air bag, intended to hold up to 34 kW of wind energy.