power off vs shut down

power off

verb
  • To turn off, to cut the power to. 

shut down

verb
  • To turn off or stop. 

  • To pass (another vehicle), especially quickly. 

  • To close, terminate, or end. 

  • To emotionally withdraw into oneself as a defense mechanism; to block out external stressors. 

How often have the words power off and shut down occurred in a corpus of books? (source: Google Ngram Viewer )