You don't need to cover half a continent for enough power production using solar, IIRC 0.3% of all the sun power in the Sahara would be enough to power Europe. And you'd probably want to use not PV cells but molten salt or boiling water or something which is heated by mirrors. The effect won't be that big if you cover 1%, I suppose (besides, it's probably not going to be your sole power source so it will be less).

Biggest problems are transportation (but that is possible, but very expensive to implement) and costs.