They must all provide a positive energy balance. That is to say, the energy necessary for their generation must be a great deal less than the energy provided once used.
Biomass energy is the oldest of all, as it has been used since fire was discovered. With the progress in this type of technology the exploitation processes have become more efficient, generating less waste than in previous processes.
Currently biomass can be used to generate electricity, heat, solid fuel, and liquid and gas fuels.