ENERGY USE EFFICIENCY IN BIOMASS PRODUCTION SYSTEMS - Economics of Sustainable Energy in Agriculture - page 78

In Table 6.4, the efficiency of the use of both solar and fossil
energy is given. For systems at the same location, it can be concluded that
higher yields imply higher solar energy use efficiency. In the system,
energy yield (GJ of biomass) is 1.3% of the incoming solar radiation; in the
system, only 0.15%. This does not hold for systems at different
locations: both low-input systems have the same yields, while the solar
energy use efficiency in the system is higher than in the system.
These differences are caused by the different climatic conditions. The
system is the most efficient system for converting solar energy into
biomass (in other words, Portugal is the ideal place for growing biomass).
4.3 Energy use in agriculture
Studies on energy use in agriculture were conducted to evaluate the
possibilities of reducing energy use in agriculture in general. Energy use
can be reduced by more efficient use of this resource. Based on the fact
that energy use efficiency in low-input systems is higher, the conclusion
can be drawn that a shift to low-input agriculture will lead to an energy use
reduction in agriculture (since more food is produced per unit of energy).
The choice of a low-input agricultural system, however, will mean that at a
higher level of scale, the effect will be reversed, as the following
calculation based on data obtained in this chapter shows.
Assume that yields in high and low-input systems differ by a factor
of 5 (the average of the Dutch and the Portuguese systems). A change to a
low-input agriculture would imply a five-fold increase in the acreage
required for food production. For a high-input system, the inputs required
will be in the order of magnitude of 50 GJ/ha; for a low-input system,
about 5 GJ/ha. When this energy is obtained from biomass (net yield 200
GJ/ha), one hectare of biomass is enough to grow the energy required for 4
ha high-input agriculture. Overall, 5 hectares are required for the
production of a certain amount of food.
The low-input system requires 4*5 hectares for the agricultural
production and these 20 hectares require (20*5 GJ/ha) 100 GJ for
cultivation, which implies 0.5 ha for energy. The low-input system requires
20.5 ha for the production of the same amount of food. (This value is even
higher when energy is grown under low-input conditions.) When these
(15.5) extra hectares are used for the production of biomass, 15.5*200 GJ
of fossil energy can be saved by using high-input agricultural systems.
The results of these simple calculations are in accordance with the
data given by Uhlin (1998; 1999) concerning energy use in the entire
Swedish agricultural system. This implies that in order to study energy use
in agricultural production systems, other indicators than fossil energy use