The potential of biofuels to solve the world’s future energy requirements is explored by Carlton Wood, Chair of Plants and people (S173), a module which looks at the astonishing variety of uses that humans have found for plants.
A biofuel is a source of energy that is derived from material that was once living. This sounds simple enough, but there are so many ways of generating biofuels that things quickly get complicated.
In its simplest form, burning wood on a fire for warmth is using a biofuel. The wood was once alive and part of a living tree and it became ‘energy-rich’ through the process of photosynthesis. This, as many of us know, is where the plant uses the energy from sunlight to allow it to take carbon dioxide from the atmosphere and convert it into sugars, and ultimately into all the carbon-containing structures within the tree. These structures contain energy that has been converted from the sunlight.
Burning the wood allows this ‘trapped energy’ to be liberated as heat and also light. Indeed, any plant material that can be burnt can be used in a similar way.
You may not be aware that some of the electricity you use is produced by burning biomass. The largest power station in the UK, Drax in North Yorkshire, produces around seven per cent of the UK’s electricity and burns around 300,000 tonnes of biomass a year. It is looking to increase the amount of biofuel it uses to around 1.5 million tonnes, at the expense of the fossil fuel coal that it normally uses. But why?
There are advantages to using biofuels compared with fossil fuels such as coal that are derived from plants that were alive millions of years ago. To produce a fossil fuel, plants died, became buried and subsequently compressed and ultimately produced fossil fuels such as coal and oil, which are energy-rich in the same way as living plant material is.
Burning fossil fuels, however, releases both the energy and the carbon dioxide which was trapped millions of years before. The energy is useful, but the carbon dioxide is widely accepted to be a cause of global warming.
Burning a biofuel, however, releases carbon dioxide that was trapped only a few years prior. It is therefore classed as ‘carbon neutral’ and won’t cause an increase in global warming.
We have already seen that wood can be used as biofuel but there is a lot of interest in using certain types of grasses such as Miscanthus which can grow rapidly, using minimal inputs of fertiliser, and can be grown on land that is not used for growing agricultural crops. These last two points are important, as producing fertiliser requires energy and so it is nonsensical to use energy-requiring fertiliser to produce something that is going to be used as an energy source. Also, using land for growing biofuel that could be used for producing agricultural crops is hard to justify in a time of increasing food shortage.
Indeed, the increases in the global cost of wheat in 2008/09 were partly caused by poor worldwide harvests, but also by the USA using around 25 per cent of its harvest to produce biofuel for transport purposes.
The transport fuels petrol and diesel can both be substituted by liquid biofuels. Both the sugars and starches that are found in plants’ stems and seeds can be fermented to produce alcohol such as ethanol. This is what happens when beer is produced – barley seeds rich in starch have the starch converted to sugar and then yeasts break the sugar down to produce ethanol. In the case of beer, we drink the ethanol but it can be used to produce bioethanol and used as a replacement for petrol.
Biodiesel is produced in a slightly different way: the oils found in many seeds and nuts of plants such as sunflowers, oil seed rape or palm oil can be treated with chemicals to convert the energy-rich oils into biodiesel. The problem with using seeds and nuts is that you are using a potential food source for fuel purposes. Additionally, growing huge areas of plants such as palm oil, some of which is used for biofuel, has caused large tracts of biodiverse rainforest habitat to be cut down, threatening such species as the orangutan.
Scientists have found solutions to such problems. Some transport biofuels such as the biodiesel produced from the fruit of the Jatropha tree do not have such disadvantages. Jatropha fruit is inedible and, also importantly, the tree can tolerate drought conditions and grow on land unsuitable for agricultural crops. One example where Jatropha has been used successfully is in India where the diesel train that runs from Delhi to Mumbai uses 15 per cent biodiesel derived from Jatropha.
Biofuels, though, are not a full answer to our energy needs. Many experts believe that biofuels have an increasing and significant role to play in the generation of our fuels, but in the UK particularly there is extensive pressure on our land resource from population growth and the requirements for both housing and for food production. Biofuels are part of the answer, alongside other renewable sources of energy such as wind and solar power.
In some countries with greater land reserves than the UK, biofuels could be even more useful. In Brazil, for instance, 40 per cent of cars run on bioethanol and there are plans to increase this percentage.
The overall answer to our fuel issues is to use less fuel in the first instance, to decrease our reliance on fossil fuels, increase our reliance on biofuels and to work for a solution that requires global initiatives to maximise the use of non-agricultural land for producing biofuel crops.
Useful links
OpenLearn:biofuels heroes or villians?
The Energy and Environment Research Unit
