As previously answered on this site, the brain uses 20W of power. However, how much of this power consumption is for information processing and how much of it is for maintenance of biological conditions for information processing, such as temperature regulation?
According to "Tightly coupled brain activity and cerebral ATP metabolic rate" which is summarised in the Scientific American article "Why Does the Brain Need So Much Power?", conscious computation accounts for 50% of the brain's power consumption. From the Scientific American article:
Chen and his colleagues used MRS specifically to track the rate of adenosine triphosphate (ATP) production, the primary source of cellular energy, in rat brains. MRS employs a magnetic resonance imaging (MRI) machine programmed to pick up particular elements in the body—in this case, the three phosphorus atoms in each ATP molecule...
The team noted that when the lab rats were knocked out, they produced 50 percent fewer ATP molecules than when they were mildly anesthetized.The ATP produced when the brain is inactive, says Chen, seems to go mostly toward cell maintenance, whereas the additional ATP found in the more alert animals fueled other brain functions. He speculates that only a third of the ATP produced in fully awake brains is used for housekeeping functions, leaving the rest for other activities.