When the sun is shining and there is strong wind, renewable energy facilities produce large quantities of electricity, which strains the networks. New technical possiblities are needed to store superfluous energy on a large scale. Energiepark Mainz shows how this can be done. Together with partners from industry, the local utility company is testing the world's largest electrolysis plant. It converts green electricity into hydrogen, which can also be fed into the gas network, where it is available for gas heaters or cogeneration networks. The facility, which has been in commercial test operation since the beginning of 2017, is making an important contribution to the success of the energy turnaround.