At the fuel production from biomass resource, much energy input (Ef) from outside is necessary for the producing process. In addition, a part of biomass becomes biomass waste (Ew) (Fig. 1.2.3). For a energy production system, [Ez-Ef-Ew] should be higher than zero at least. Ez: the gained bio-fuel energy.

[Biomass Eo] —— (production process) —— [Bio-fuel Ez]

[Fossil, electric Ef]—J 1——[Biomass waste Ew]

Fig. 1.2.3. Biomass energy balance for the income and expense.

Total energy yield in this system is shown as Ez/[Eo + Ef], if the value is lower than 0.5, the biomass is merely auxiliary fuel. But even small part of biomass can contributes to new energy system if energy balance ratio (products/invested fossil fuel) is over than 1, in the case of coal-biomass mixed combustion generation. When biomass waste can substitute a fossil fuel in the system, the Ef is so decreased that the energy balance ratio is much improved. The typical success example is found at cane sugar industry which uses bagasse as an alternative fossil fuel. Biomass production system with inferior energy balance ratio often loses its casrbon-neutral sustainability. In agriculture, production of grain and potatoes, the energy balance ratio is about 1.5~5 (neglected man-power calculation), while lower than 0.5 in almost vegetables that is on loss-making railroad line. In this point, forestry is more excellent than agricultural crops because of a little cultivation energy.

(a) Man-power investment. Inceasing of man-power is often able to cut down a fossil and/or electric energy consumption, causing an improvement of apparent energy balance ratio. However, man-power and fossil energy has a trade-off relation. Energy unit for man-power is estimated by 0.073 toe/yr/man (biological standard)~1 toe/yr/man (total life consuming). Labor intensive production often gives a faked saving energy system.

(b) Cycling of N, P,K. N (nitrogen), P (phosfer), and K (kalium) are main components of fertilizer. They so often disappears by exploitative production that a recycling system is necessary to hold N, P and K in soil. At a woody thermal power station, it is necessary to return the ash for sustaining P and K. Component N cannot stay in the ash, so another N-supply route is indispensable to restore the system. Exceptionally, traditional forestry need not any fertilizer because there is sufficient nitrate-N from rain. But future energy forestry will demand N-fertilizer because the N-balance will collapse.

(c) Conservation of biodiversity. Biodiversity is often fragile by enhancing a biomass production according to the uniformity, the large scale farm, and the intensive process. For example, mixed cropping like agroforestry, is hopeful to have a sustainable soil conservation.

Further information

Sano, H.in “Biomass Handbook”, Japan Institute of Energy Ed., Ohm-sha, 2002, pp.311-323. (in Japanese)

UN Energy “Sustainable Bioenergy: A Framework for Decision Maker”, 2007.