Methods of electricity storage are considered essential in grids that have large proportions of wind capacity. This is because, surprisingly, winds have been known to quieten down a bit from time to time.
Some people take this fact too far. For example, there is the “Northern European Winter High Pressure” lobby, who continue to insist, in a number of forums, that low aerial flow entirely compromises wind energy expansion, just because there are several days in December or January that might be a little flat.