The bulk of renewable energy production varies in a way that typically does not correspond to time dependent energy consumption. This can lead to an energy surplus or a shortage of the energy supply from renewable energies. To smoothen these supply variations, and enable large scale surplus renewable energy storage, an enormous energy storage capacity is required. Gas as energy carrier, and hence Energy, can be stored in such large amounts in subsurface reservoirs like in depleted gas fields. Especially hydrogen gas is an efficient energy carrier and can be produced from surplus renewable energy.