If I had to guess, it uses wood gasifier technology to run an ICE engine. I am speculating, but gasification is faster than fermentation.
Edit: sorry I was wrong. It's a steam engine.
From Wikipedia:
"The robot was powered by a steam engine built by the Cyclone Power Technologies company called the Cyclone Waste Heat Engine, which produced power through external combustion of biomass (i.e. combustion outside of the engine), an example of a Rankine cycle engine. The engine would power the vehicle's movement as well as being used to recharge the batteries that run the sensors, arms and ancillary devices."
"Cyclone and RTI swear this robot is strictly a vegetarian.
The only problem with that is how many times I’ve watched a vegan/vegetarian order a meat-dipped meat pizza slice with extra cheese after six hours of drinking."
Yeah having no idea of the premise or game before playing it made uncovering the mystery through the plot a great experience. I didn't even know the enemies were gonna be robots. Great story
Edit: sorry I was wrong. It's a steam engine.
From Wikipedia: "The robot was powered by a steam engine built by the Cyclone Power Technologies company called the Cyclone Waste Heat Engine, which produced power through external combustion of biomass (i.e. combustion outside of the engine), an example of a Rankine cycle engine. The engine would power the vehicle's movement as well as being used to recharge the batteries that run the sensors, arms and ancillary devices."