Skip to content
Skip to main content

About this free course

Download this course

Share this free course


Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

7 Biofuels: some of the issues

There are many issues to be considered and weighed up regarding the use of biofuels. The following points will help you to consider further the various implications of using trees, food crops and grasses as fuels.

How does the cost of biofuels compare with that of conventional fuels?

At present, the cost of producing biodiesel and bioethanol is approximately double that for conventional fossil fuels. The UK offers tax incentives to encourage fuel producers to make biofuel and there is also an incentive for consumers: the duty on petrol with 5% biofuel is, at the time of writing (2009), 20 p/litre less than that on ultra-low sulphur petrol.

A recent review has shown that biofuel production is a high-cost process overall; only the production of bioethanol from sugar cane was considered to be cost-effective. If, however, the price of crude oil rises then biofuels may start to become more competitive, although this would depend on fertiliser, and hence biofuel feedstock, prices remaining stable.

Does growing crops for fuel create higher food prices?

One point of view is that using land to grow crops for fuel rather than for food has led to increased food prices, which in turn impacts most on those in developing countries who have to spend a relatively large proportion of their income on food. In 2007, the United Nations Food and Agriculture Organisation (FAO) and the International Food Policy Research Institute (IFPRI) both released reports suggesting that rising food prices were due to the conversion of agricultural land from food to biofuel crops. Subsidies for the biofuel industry, quoted to be in the region of £5.6-6.1 billion per year (FAO), are believed to incentivise farmers to grow biofuel rather than food crops. However, those supporting biofuels hold the view that better production methods, which will use parts of the plant currently wasted in biofuel production, may be able to increase the efficiency of biofuel production.

Does growing biofuel crops result in more fertiliser and pesticide input?

The amount of fertiliser and pesticide input depends on the crop species grown; one criterion for a suitable biomass crop is that it has a low requirement for nutrients. Switch grass, for example, grows well in poor soil conditions and requires around two-thirds less fertiliser input than a food crop such as maize.

Is there a potential loss of biodiversity?

In some cases, the use of biofuels could increase biodiversity (the number of different species found within a given area), for example, by harvesting woodfuel and then replanting with mixed woodlands. Conversely, the increased use of soybeans for biofuel in the USA has caused soybean production to be increased in South America at the expense of Amazonian rainforest, which has been cut down to give more agricultural land. This has the potential to reduce biodiversity. Also, trees in rainforests help absorb CO2 (albeit not at the rate of newly planted forests) and so are believed to play a part in offsetting global warming.

Is the energy output greater than the energy input?

The overall energy balance, that is the net energy output compared to the input needed, is dependent on both the species of biomass crop and the type of biofuel being produced. The inputs to a biofuel crop include both the direct costs of growing, such as fertiliser, cultivation, harvest and labour, and the indirect costs, such as storage of the harvested crops. Processing inputs include pre-treatments, processing for energy release and the removal or reuse of residual waste. Ideal crops are being investigated that require low maintenance, need only low nutrients, grow quickly and can tolerate poor soil conditions. Switch grass is one such plant, and interestingly it has been shown that it is only energy efficient if it is used as a pelleted biomass for fuel rather than for bioethanol production.

Do biofuels reduce carbon emissions?

Burning biofuels does release CO2, but this is CO2 that has been removed from the atmosphere relatively recently, unlike the carbon in fossil fuels which has been removed from the atmosphere for many millions of years. Hence, biomass energy crops are deemed carbon neutral. However, some argue that nitrous oxide, which is 240 times more powerful as a greenhouse gas than CO2, is produced in greater quantities during the production of biogas than during the burning of fossil fuels. Also, biofuel production generates CO2 through the use of agricultural and haulage vehicles for growing and transporting the crop.

Question 22

At the start of this course you were introduced to the terms 'carbon offsetting' and 'carbon neutral'. Now that you have finished reading the course, explain in your own words the difference between the terms 'carbon offsetting' and 'carbon neutral' in the context of biofuels.


When biofuels are grown they take up a certain amount of carbon dioxide from the atmosphere and convert it into stored carbon compounds. When the biofuel is later burnt the carbon in these compounds is converted back into carbon dioxide which is released back into the atmosphere. The amount of carbon dioxide released during combustion is the same as that absorbed during plant growth so on the timescale of years biofuels do not change the amount of carbon dioxide in the atmosphere and so are said to be 'carbon neutral'.

The burning of fossil fuels releases into the atmosphere CO2 that was taken up by plants millions of years ago so increases the total amount of CO2 in the atmosphere. It is possible to calculate the number of new trees that would have to be planted to take up the equivalent amount of CO2 by photosynthesis. Funding the planting of these trees is said to 'offset' the amount of carbon that has been burnt by the use of fossil fuels. For example, when purchasing an airline ticket in 2010, it is possible to offset the carbon cost of the flight by paying for some trees to be planted.

Activity 2

Timing: 45 minutes

Task 1

In this activity you will listen to the audio slidecast in which Dr Angela Karp from Rothamsted Research discusses some of the issues relating to the use of biofuels in the UK.

Dr Angela Karp works at Rothamsted Research International, the largest horticultural research establishment in the UK. Her research group is particularly interested in looking at those plants species that grow well in the UK but which are not used as agricultural crops. They are investigating the ways of optimising how such crops can be utilised for use as liquid biofuels. Listen to the slidecast and then answer the following questions.

(You may find it helpful to listen all the way through once, then read the questions before going back to listen again, pausing where appropriate to make notes.)

Download this video clip.Video player: Video 1
Copy this transcript to the clipboard
Print this transcript
Show transcript|Hide transcript
Video 1
Interactive feature not available in single page view (see it in standard view).

Question 1

  1. What type of research is Angela Karp's group doing?
  2. What are the main difficulties in using woody crops as biofuels?
  3. Which polymers within the cell wall contain the sugars? What other component of the cell wall makes it particularly difficult to access the sugar-containing polymers?
  1. It is investigating woody crops (i.e. non-food crops) to see what their potential is for using as liquid transport biofuels. She is particularly interested in using different types of willow trees and researching how they use the sugar from photosynthesis to produce cell walls.
  2. The sugars contained within woody crops are locked away as components of the plant cell wall and this can make them difficult to access and to liberate.
  3. Both cellulose and hemicellulose (which is another type of cellulose) are polymers containing sugars (these sugars are composed of glucose monomers. Lignin is the polymer that made it difficult to access the sugar-containing polymers.

If you would like to know how Angela Karp became interested in plants, you can listen to another short audio clip.

Download this audio clip.Audio player: Audio 3
Copy this transcript to the clipboard
Print this transcript
Show transcript|Hide transcript
Audio 3
Interactive feature not available in single page view (see it in standard view).