Wind energy 297fermentation in the absence of oxygen (anaerobic digestion) of these
wastes produces biogas, which is mostly methane and which can be used
as a fuel to produce energy. There is room for an increasing contribution
from these sources. If the potential for power generation from agricultural
and industrial waste was taken into account, the savings in emissions
arising from domestic waste already mentioned could be approximately
doubled.
Turning now to the use of crops as a fuel, the potential is large.
Many different crops can be employed as biomass for energy production.
In Brazil, for instance, since the 1970s large plantations of sugar cane
have produced alcohol for use as a fuel mainly in transport, generating,
incidentally, much less local pollution than petrol or diesel fuel from
fossil sources. A lot of potential has been recognised for the sugar cane
industry to produce both sugar and energy together with other byproducts
as well (see box above). Biomass from wood plantationson agricultural
land no longer needed for food crops features as an important future
source in Sweden’s energy plans^40 ; the most efficient use of the biomass
is first to turn it into biogas and then burn it in a gas turbine to produce
electricity. For the UK, trials indicate that the most promising option is
willow and poplar grown in coppices.^41
Because of the low efficiency of conversion of solar energy to
biomass, the amount of land required for significant energy production
by this means is large – and it is important that land is not taken over
that is required for food production. However, there is in principle no
shortage of land for this purpose. Plenty of suitable crops are available
which could be grown on land only marginally useful for agriculture. In
many developing countries biomass plantations can provide suitable fuel
for local electricity generation more competitively than other means of
generation.
The growth of the use of biomass for energy in industrialised coun-
tries (Table 11.6) is substantial but is limited by the cost differential that
exists between energy from biomass and that generated from fossil fuels
(Table 11.6). This problem is addressedlater in the chapter.
Wind energy
Energy from the wind is not new. Two hundred years ago windmills were
a common feature of the European landscape; for example, in 1800 there
were over 10 000 working windmills in Britain. During the past few years
they have again become familiar on the skyline especially in countries
in western Europe (for instance, Denmark, Great Britain and Spain) and
in western North America. Slim, tall, sleek objects silhouetted against
the sky, they do not have the rustic elegance of the old windmills, but
they are much more efficient. A typical wind energy generator will have