Introduction
With the need to reduce carbon emissions, and the
dwindling reserves of crude oil, liquid fuels derived from
plant material – biofuels – are an attractive source of
energy. Moreover, in comparison with other forms of
renewable energy such as wind, tidal, and solar, liquid
biofuels allow solar energy to be stored, and also to be
used directly in existing engines and transport infrastructure.
Currently, bio-ethanol from, for example, corn
starch, sugar cane or sugar beet, and biodiesel from oil
crops such as palm and oilseed rape, are the most widely
available forms of biofuel. However, there are two major
issues over the sustainability of these first generation
biofuels [1,2]. Firstly, to provide a significant proportion of transport fuel, the growth of these crops would compete
for arable land with food crops. In 2008, the UK used
an estimated 47 billion liters of transport fuel, 53% of
which was diesel [3]. If this were met using biodiesel from
oilseed rape, it would require 17.5 Mha (Table 1), more
than half the land area of the UK. Secondly, the overall
savings in energy and greenhouse gas emissions over the
lifecycle of the biofuel may be less than anticipated; for
example for biodiesel from oilseed rape [2] and soya [1]
the input of energy required over the life-cycle is 50% of
the energy contained in the fuel.