TYPES OF BIOMASS
The global biomass resource is the vegetation on Earth’s surface. This is equivalent to around 220 billion dry tonnes, or 4500 EJ (4500 x 1018 J), of energy according to the World Energy Council. Between one- and two-thirds of this (the proportion depends on the means used to estimate the amount of carbon fixed annually) are regenerated each year by photosynthesis. At the beginning of the 21st century, as already noted, biomass equivalent to 50 EJ was being used each year to provide energy, mostly from wood fuel for heating and cook- ing. Estimates suggest that between 200 EJ and 500 EJ could eventually be utilized for power generation. With primary energy demand expected to reach between 600 EJ and 1000 EJ by 2050, biomass sources could, in principle at least, provide a significant proportion of total demand.
From the perspective of power generation biomass can be divided into two categories: biomass wastes and energy crops. Biomass wastes are the most readily available forms of biomass but their quantities are limited. Energy crops, grown on dedicated plantations, are more expensive than wastes but they are capable of being produced in much larger quantities as and where required. Location is important because biomass has a lower energy content than coal and cannot be transported cost effectively over great distances. It is normally considered to be uneconomical to transport it more than around 100 km, although some biomass is traded over much greater distances today, confounding conventional economics. If energy plantations are established close to a biomass power plant, transportation costs can be minimized.