Hydrogen has since the late eighties been put forward as the solution, since hydrogen can be produced using solar and wind power; but never really caught on due to hydrogen's low energy density and high cost of vessels for the storage.
With the decision by the Danish parliament in March 2012, that Denmark in 2050 must be free of fossil energy, and thus natural gas, solutions must be found fairly quickly to the storage problem.
The solution is to replace natural gas with biogas, and increase its energy density by using hydrogen produced by wind power. In this way the already existing distribution infra-structure and storage facilities, large enough to cover the country's gas consumption for several months will be utilized.
This homepage describes the technology that can store wind energy in the natural gas network, as well as backgrounds for the need to do it.
The figure shows at system level, the link between wind energy, electrolysis, biogas production and production of hydrocarbons, primarily for the transport sector and for electricity in windless periods.(view image to see actual size)