The world will not need 60TW of energy in 2050.
In 2004, we used 15TW of energy.
In order to hit 60TW, we would need to quadruple energy use in 46 years. The basic compound interest model tells us that we would need to increase global energy use by 3%/year.
The yearly increase in energy use was 2% a year between 1980 and 2004. This was in an era of rapidly declining energy prices, strong economic growth, and strong population growth.
Between 2004 and 2050, none of that will be true.
Energy prices will be high will likely stay high throughout that entire period. Economic growth will not be as strong as it was in the previous 2 decades. Population growth between 2004 and 2050 will be at a slower rate than it was between 1980 and 2004.
These three factors should
decrease that 2% figure, not increase it.
Even pretending that the next 40+ years will be the same as the 1980-2004 period, global energy demand in 2050 will only be 37TW, not 60TW (15TW growing at a compounded 2%/year for 46 years).
We've just saved 23TW of energy without having to turn off a single light bulb.
Assuming that economic conditions will likely favor energy efficiency rather than waste over the next 40+ years, surely we can assume that energy use growth will be reduced by at least half a percentage point compared to the 1980-2004 period.
Now global energy demand in 2050 is roughly 30TW. We've just cut that 2050 target in
half without turning off a single air conditioning unit.
How about we start off with a more realistic end point for 2050?
Otherwise, the debate about scalability is a waste of time.