Biomass is a renewable source of energy that refers to different biological materials derived from living, or recently living organisms. The most common biomass sources include wood, waste and alcohol fuels.
Biomass is a renewable source of energy because plants can be re-grown time and time again on the same piece of land.
Wood is today the most widely used source of biomass. In United States, for instance, close to 90% of biomass comes from using wood as the fuel.
There are three types of processes used to convert biomass into a useful form of energy: thermal conversion of biomass, chemical conversion of biomass, and biochemical conversion of biomass.
Biomass is renewable energy source but this doesn't necessarily mean that biomass is totally environmentally friendly source of energy. The question whether we should use more biomass or not has stirred lot of controversies in the last few years. The opponents say that going for more biomass could account for even bigger greenhouse gas emissions (from burning wood), even bigger than those coming from coal fired power plants.
The proponents on the other hand say that the concept of sustainable biomass could be relatively easy achieved with very strict regulation of what materials are harvested and how are they burned.
The concept of biomass being carbon neutral means that biomass takes carbon out of the atmosphere while the plant is growing, and returns it as it is burned. This should, at least in theory, maintain a closed carbon cycle with no net increase in atmospheric carbon dioxide (CO2) levels.
Biomass currently produces around 1.5 % of total U.S. electricity supply. The worldwide biomass capacity was 58 GW in 2011.