hydro vs power source

hydro

noun
  • electrical power supply; specifically, electrical power provided by a utility (as a publicly-owned one); payment or bills for this. 

  • hydroelectric power 

adj
  • hydroelectric 

  • hydroponic 

power source

noun
  • A source of power such as a generator or mains outlet. 

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