Let us estimate that there are 50 million computers in the US.

A computer and its monitor each consume about 100 watts.  Let us estimate that each US computer system is turned on 50% of the time.  Therefore, one-half of the 200 turned-on watts is the around-the-clock average power consumption, namely 100 watts.

Then the average electrical power used for running the 50 million computers is 5 billion watts, the full power output of five very large power stations.

By comparison, during the period 1985 to 1997, the US electrical power demand grew about 90 billion watts.