Energy from biomass — Some basic physical and related considerations

Abstract

The production of vegetable matter (biomass) by photosynthesis is determined by species and by meteorological factors (especially, but not exclusively, solar radiation). Annual net primary production of land-based biomass corresponds to only about 1/1000 of the intercepted irradiation at ground level, but even so, is 10 times the world's estimated energy needs. The exploitation of this energy potential at any one place is critically influenced by the economic, political and social factors, amongst which are the competition from agriculture (especially food crops), forestry, industrial and urban (including leisure) needs for land and resources. Social factors (e.g. population and population density) also constitute prime influences. Strategies for utilisation range from the cultivation of special energy crops (readily conceivable on the American/ Australasian continents); to the more efficient manipulation of current land-use patterns (including “opportunity” cropping); to the more effective exploitation of biologi cal wastes (e.g. methane from sewage), probably the only immediately practical possibility in any densely populated and highly industrialised country.

The spatial pattern of solar irradiation at ground level is complex. In the summer, total daily irradiation in continental high latitudes can exceed that in maritime temperate regions; and this combined with species differences and the almost infinite variety of shape and orientation of plant parts, result in a photosynthetic production of biomass which does not conform completely to a zonal pattern, but in broad terms annual dry matter production varies from a few kg/ha in Arctic Tundra to tens of tonnes in temperate latitudes rising to nearly 100 t/ha for perennial tropical crops. If a species could be developed to grow throughout the year at the current seasonal rate, a yield of 150 t/yr, ha) seems possible.