So we would need this 9% as backup energy and a rated backup power of 26% of the wind turbine capacity.
This could be produced from gas turbines, which cost roughly 250 €/kW. (In the last years the market for gas turbines has grown considerably and therefore, the prices almost doubled to 500 €/kW in 2001.)
The investment in the backup system is about 7% of the investment in the wind turbines.

If we now consider producing the equivalent of the demand from wind Energy.
For the demand EU & Norway we need to install 660 GW to within all regions.