Bio Energy is generated from Biomass like animal waste or plant waste. Biomass are fermented in a chamber and the gas is generated by the action of microorganisms. This gas is collected and used as fuel. Even there is a concept called energy farming where specific crop is grown whose basic purpose is to feed such fermentation chamber to generate energy.
Over and above gas generation the biomass with good starch content can also be converted to alcohol like Ethanol or Methanol. These alcohols are also very convenient for use as fuel. One of the major user of Alcohol fuel in the road transport is Brazil. In many countries alcohol is blended with the petrol/diesel to varying degree.