To add to the previous post, capacitors can also store electricity, although batteries are the best source for storage, while capacitors are well suited for, among other things, providing a quick increase in power when the load suddenly increases. . . You can store enough power to run a large building by using large banks of batteries for ~20 minutes. Usually that is meant as a temporary measure until generators are brought online. The trouble is that you need so many batteries that maintenance and safety become serious problems.. . In summary, the technology we have is limited. Even the newer Lithium-Ion batteries, while they can store quite a bit of power for their size, are prohibitively expensive on a large scale.