There is an already pretty old (2013) study from Fraunhofer, which shows how 100% renewable energy in electric power and heating is possible in the medium term future (2050). Their ideas for storage are battery storage (52Gwh), pumped storage (60Gwh) and methane storage (86Twh) on the electric side.

See [1] for a very short English description and [2] for the German original.

[1] https://deepresource.wordpress.com/2017/09/16/blueprint-100-... [2] https://www.ise.fraunhofer.de/de/veroeffentlichungen/studien...