[AlexanderHowl]

7.5 billion people at $31,000 per capita at TL8 requires a lot less energy than 30 billion people at $47,000 per capita at TL9. TL9 energy consumption would likely be much higher per $1 than TL8 energy consumption, probably a minimum of 4x as much energy per $, so you are probably talking about a minimum of 24x as much energy consumption (assuming you were distributed throughout the Solar System rather than concentrated on Earth). In addition, 7.5 billion people at $31,000 per capita at TL8 would consume 5x as much energy as our current civilization, meaning that the final difference for a distributed society would be 120x as much energy consumption (~2.16 PW).

If you are concentrated though, you have to spend energy to bring resources from off the Earth to the Earth, as it would likely be more efficient than mining the Earth when consumption needs to be 4x to 100x greater (depending on the resource). Interplanetary travel is energy expensive, so the total energy used by human civilization increases greatly. Energy consumption rapidly reach K1 levels, >10 PW, as more and more resources are transported from places further and further from the Earth. In addition, you also need to worry about cooling, ventilation, etc., as the waste heat alone starts cooking the Earth, which increases energy consumption even more. Eventually, the Earth ends up looking like a WH40K Hive World.