Germany needs 1.6 TWh of electricty per day. If you know the caloric value of methane for example, you will be able to calculate the amount of methane you need to synthesize to just store the electricity of one day which will be roughly 3.2 million gas trucks (45.000 liters each).

There is a reason why the UK is building or planning new nuclear power plants in Hinkley Point, Sizewell and Bredwell.