While Siemens Gamesa's and Henrik Stiesdal’s thermal storage systems could make wind and solar power dispatchable, there will never be enough sun and wind during the cold European winter to meet all the demand for energy. If most electricity is to come from renewable sources in the future, a more long-term storage solution will be required.

One potential solution being put forward is “green” hydrogen — using excess wind and solar power in the summer months to split water molecules into hydrogen and oxygen using electrolysers and then converting the hydrogen back into electricity in the winter months using fuel cells or by burning it in power plants.