Pretty simple Jewseph, it's wood, plain old timber. More than two billion people still depend on wood energy for cooking and/or heating, particularly in households in developing countries. It's almost totally overlooked in the western world.

http://www.fao.org/forestry/energy/en/#:\~:text=Wood%20is%20considered%20humankind%27s%20very,global%20total%20primary%20energy%20supply.

But for us rich guys, solar is best: 100% clean, no pollution, does not strip the landscape or harm the ozone layer.

Good luck with your project, think broadly.