Pitiful Fuel Generator

This generates Energy, but only accepts Wood items as fuel.

Also check out the Petrified Fuel Generator which can accept all solid fuels and produces more Energy per tick depending on the fuel.

Petrified Fuel Generator

This generator will accept solid fuels and generate Energy. Each fuel lasts ~36 seconds, but the output depends on the fuel's burn time.

Bioreactor

This machine accepts certain bio-degradable items and turns them into Biofuel to be used in the Biofuel Generator. This machine will accept all vanilla Sapplings, all Seeds, all Dyes, Carrots, Potatoes, Netherwart, Both types of Vanilla Mushrooms and Industrial Dye. You can increase Efficiency by having more types of items producing Biofuel at once. Higher Efficienty will produce more Biofuel. This machine requires a bit of power to work but a Pitiful Generator powered by Wood is enough to supply the required energy.

Biofuel Generator

This machine accepts Biofuel and turns it into a decent amount of energy.