Solar power systems installed in the areas defined by the dark disks could provide more than the world's current total primary energy demand (assuming a conversion efficiency of 8%, which is quite low considering we can achieve around 20% efficiency now I think). That is, all energy currently consumed, including heat, electricity, fossil fuels, etc., would be produced in the form of electricity by solar cells. Now we'd obviously need a lot of solar panels to achieve this, but still, this area has a lot of potential.