solar power vs water power

solar power

noun
  • The conversion of energy from sunlight into electricity, either directly using photovoltaics, indirectly using concentrated solar power, or a combination of the two. 

water power

noun
  • Mechanical or electrical energy derived from running or falling water; originally obtained from a waterwheel immersed in a stream; modern hydroelectric power is obtained from turbines fed from reservoirs. 

  • Used other than figuratively or idiomatically: see water, power. 

  • A site capable of generating power or the right to use a site to generate power. 

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