Because one of the Environmental Left's other pipe dreams are set to be implemented in the same time period, namely eliminating natural gas as a heating and cooking fuel, you really need 10 times that amount of storage capacity.
If you had a week of minimal wind during a really cold winter period after everyone is on resistance heat that energy storage reserve could easily be exhausted.
Hey, but what is a few thousand dead citizens as long as we save the planet from getting warmer?
We can always get more third world welfare recipients to vote for us.
It's a start toward their published goal of eliminating 8 Billion of us to reach a "sustainable" world population of 500 million.