The world needs a new source of energy, an unspillable source.

less commonly known alternative energy sources?

iwhat are some not-so-well known alternative energy sources. google it and you don’t find much. when i google alternative energy i usually get:
hyrdoelectric energy
photovoltaic energy
wind energy
geothermal energy
ethanol
biodiesel
biomass
tidal energy
hydrogen fuil cells
passive solar

besides that i know of:
microbial fuel cells
artificial photosynthesis
syngas
biogas

what else is there?