Actually about 20 W — if you ignore the 80 W used by the rest of the body (which seems debatable). And clearly far more than this was required to 'train' the human brain to the level of intelligence we have today.[1] But this still probably doesn't take away from your point. The human brain seems to be many orders of magnitude more efficient than our most advanced AI technology.
Though the more I think about this, the more I wonder how they really would compare if you made a strictly apples-to-apples comparison.
