8 biillion * 1400 watts = 11.2 terawatts

current global average electricity production = approximately 3.6 terawatts

But then again these systems do not use 1400 watts all the time. We would probably have much more then 11.2 terawatts demand if all humans turn on all their electrical consumers at the same time.

So demand quadruples if they are always on, and doubles if they are on 1/3 of the time. Either way, too much.