ABSTRACT
According to a general definition biomass may be considered as animal and plant resources and the wastes deriving from their treatment, which could be used, directly or after a pretreatment as a source of energy. It is therefore a resource directly or indirectly resulting from the photosynthesis process, represented by the following equation (Klass, 1998):
Living plant + CO2 + H2O + Sunlight Chlorophyll−→ (CHmOn) + O2 − 480 kJ/mol For every mole of CO2 absorbed 1 mole of oxygen is released. Zhu et al. (2008) have shown that
the maximum conversion efficiency of solar energy to biomass is 4.6% for C3 photosynthesis at 30◦C and today’s 380 ppm atmospheric concentration of CO2, while C4 plants have an efficiency of about 6%. Losses are distributed thus: loss by reflectance of photo-synthetically active light (4.9% for example); loss in rapid relaxation of higher excited states of chlorophyll (6.6% for example); loss between the reaction center and carbohydrate synthesis (24.6% for C3 plants and 28.7% for C4 plants, for example); loss due to photorespiration (around 6.1% for C3 plants and 0% for C4 plants); loss due to respiration (1.9% for C3 plants and 2.5% for C4 plants). Figure 5.1 shows the minimum energy losses calculated for 1000 kJ of incident solar radiation.
