I address this in my comment though. CO2 is fungible, it does not matter what is producing CO2, all that matters is the net CO2 produced. If it takes 5000 units of solar power to produce 100 units of fuel for airplanes, it is completely stupid to do that when just not making the airplane fuel lets you take 5000 units of coal power production offline with no additional steps.

Saying it another way: If you use the 5000 units of solar or wind power to make jet fuel, that is 5000 units of solar or wind power you can't use to shut down 5000 units of coal power.

Let me break it down for you:

  Use solar to make jet fuel:
  5000 units of net CO2 from coal plant to make electricity.
  0 units of net CO2 from synthetic jet fuel.

  Use solar to make electricity:
  0 units of net CO2 from coal plant that isn't necessary because solar instead.
  +100 units of net CO2 from regular jet fuel.