What is the energy consumption of the brain, and is there a difference in consumption when waking and sleeping?
I assume that you mean energy consumption.
Talking in round numbers the daily energy requirement of a sedentary human is 2,500 kcal. It's usually said that the brain uses 20% of this energy.
What does this mean in terms of power consumption?
500 kcal = 500 x 1000 x 4.2 J - 24 h = 24 x 60 x 60 s - 1 W = 1 J/s therefore brain power = / = approximately 24 W
Most of the energy consumed by the brain is used in maintaining membrane potentials so energy is used continuously. I would think that there will be very little difference between waking and sleeping.