Bathtub Thoughts

Technically, there's only two sources of energy in the universe: nuclear energy and the expansion of the cosmos.

Like, solar is fusion, ofc, the light coming from the sun. So is wind and water and bioenergy (indirectly). Geothermal is fission (heat comes from radioactive decay inside Earth).

But then there's another source of energy that nobody ever talks about: tidal power It works by converting the rise and fall of water with the tides into electrical energy. This energy ultimately comes from the moon orbiting around Earth, more precisely, its mechanical energy: The fact that the moon is distant from Earth is only because the universe expanded after the big bang. Had it not done this, the moon and earth would be located at the same location, and there would be no "orbiting" to extract energy out of :P

I wrote more about the subject of extracting (useful) energy out of cosmic expansion in this post here