Wind has the problem that it increases the need for loadbalancing if you use it to meet "Grundlast" demand, since it can, and will, go to zero across the board on a regular basis - Up to a certain percentage of total power supply, you can simply use it to let you run your gas turbines (for mittlelast) less, which isnt entirely nuts, economically, but it doesnt really let you stop burning gas, either.
If you want a 100% co2 free grid, wind wont do it, because there is no way to build enough pumped storage for a week of dead wind, which will happen far to often. - nukes will, but you are still going to need either pumped storage enough to turn that graph  entirely flat, or a use for umpteen thousand kilowatt hours of surplus nighttime electricity you wind up with if you just build enough plant to meet peak demand.  - I think everyone recharging their cars while they sleep would just about do it, but that really needs to be checked with math..

Other solutions: Solar actually follows the middlelast curve fairly well, if you stick the plants in the sahara.