Yeah unless the wind stops blowing then waddya gonna do then huh? HUH?
When the wind stops you use a natural gas power plant. Duh. DUH!
The point is to reduce the amounts of fossil fuels used to generate electricity. If you still need it sometimes, who cares. You have still reduced the amount of fossil fuels used.
Batteries are becoming cheaper and more reliable. In the end, we will likely store large amounts of power in battery banks when the wind blows and the sun shines. This will further reduce our reliance on fossil fuels. Maybe we still need fossil fuels in the future, but our consumption of them will be reduced by 80%. It won't be the end of the world. Except if your entire fortune is based in the fossil fuel business.
Sorry I was making an attempt at being ironic but, being American, I can't do irony very well.
At any rate I wasn't serious...