From SHEILA BATCHELOR
Tim Brown of the National Society for Clean Air and Environmental Protection
expressed the view that biodiesel production does not make sense in energy
terms because the ‘energy output’ from its use is of the same order of magnitude
as the energy input for production (Letters, 23 July). He also stated that
proponents of biodiesel ‘justify’ production of the fuel by factoring in
the by-products of the process, rapemeal and glycerol.
Firstly, I would like to make the point that inclusion of by-products
in an energy and economic assessment of biodiesel is not an artificial means
of ‘justifying’ production. Rather, an assessment which did not account
for the by-products would be unrealistic as both rapeseed and glycerol have
a realisable value which is exploited by existing biodiesel manufacturers.
Studies have shown that even where no by-products are considered, there
is a net energy gain resulting from biodiesel production under all but the
most catastrophic conditions. Inclusion of the by-products meal and glycerol
in the calculation gives an energy output to input ratio of around 3 to
1. This figure compares reasonably well with the ratio for fossil diesel
(which has been reported as 5 to 1, excluding energy used in oil exploration)
and there is potential to improve this ratio through modification of agricultural
practice and utilisation of rape straw.
Sheila Batchelor Scottish Agricultural College Aberdeen, Scotland
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