Renewable Energy Sources

Renewable energy is energy produced from sources that are continuosly replenished by nature. The widespread and abundant renewable energy sources fall into four categories. The medium conducting energy of each of these four categories correspond to one of the four states of matter, and even, if only metaphorically, to one of the four or five ancient elements.

energy type	example	state of matter	ancient element
geothermal	ground-source heat pump	solid	earth
water wave or current	wave buoy	liquid	water
wind	wind turbine	gas	air
sunlight	rooftop solar panel	plasma	fire