The aim of this section of the investigation is to quantify the amount of bio-ethanol that could be produced from the available land within the UK as worked out in the previous section.
To begin this analysis it is nessisary to assess the potential yields of the most suitable crops.
The two main energy crops which would be grown in the United Kingdom to produce bio-ethanol are sugar-beet and wheat crops. Ligno-cellulostic biomass (poplar and willow trees), waste straw and sawdust materials could also be used to produce bio-ethanol. However the technology and the chemical processes involved have not been proven for large-scale bio-ethanol production. For the purposes of this quantitative analysis, it has been assumed that the available land shall be split 50:50 for growing sugar-beet and wheat crops (although in real life this would not be the case).
Assuming that half of the 644,000 hectares of UK setaside land is used to produce bioethanol from wheat then:
Wheat Yield = 322,000 * 8 = 2,576,000 Tonnes per year
Bioethanol Yield From Wheat
Since bioethanol production is already a relatively mature technology, then to calculate the ethanol yield from wheat all that is required is to find what sort of yield levels existing plants achieve. The calculations that follow are based on the production yields of the Bioethanol Galicia Plant in Spain (ref16).
For Each tonne of wheat: 0.336m3 of bioethanol is produced.
From 2,576,000 tonnes of wheat:
Bioethanol Yield = 2,576,000 * 0.336 = 865,536 m3 (683,773 tonnes) per Year
= 865,536,000 Litres of Bioethanol per Year
Sugar Beet Yields
Assuming that the other half of the 644,000 hectares of UK setaside land is used to produce bioethanol from Sugar Beet then:
Sugar Beet Yield = 322,000 * 53 = 17,066,000 Tonnes per year
Bioethanol Yield From Sugar Beet
Similar to Wheat an empirical formula can be used to calculate the bioethanol yield:
For Each tonne of Sugarbeet: 0.108m3 of bioethanol is produced.
From 17,066,000 tonnes of Sugar Beet:
Bioethanol Yield = 17,066,000 * 0.108 = 1,843,128 m3 (1,456,071 tonnes) per Year
= 1,843,128,000 Litres of Bioethanol per Year
The total bioethanol production assuming use of 100% of the set aside land would be 2,708,664,000 Litres. For simplicity this can be rounded to 2.7 billion litres.
In 2002 the UK released for consumption 27.9 billion litres of petrol (ref18). By volume, the bioethanol produced from the set aside land could displace 9.7% of this petrol. This figure however is inaccurate unless the energy content of the fuel is taken into account.
Petrol has an energy content by volume of 31.5 MJ/L. Bioethanol has an energy content by volume of 21.1 MJ/L.
The total energy contained in 27.9 Billion litres of petrol:
= 27.9 billion * 31.5 = 878.85 billon MJ
The total energy contained in 2.7 billion litres of bioethanol:
= 2.7 billion * 21.1 = 56.97 billion MJ
This means that using all the setaside land to produce bioethanol could displace 56.97 billion MJ of the energy contained within the petrol, this is a 6.5% displacement by energy. 56.97 billion MJ of energy equates to 1.809 billion litres of petrol. Therefore 1.809 billion litres is the volume of petrol that would be saved over the year using all the setaside land.
Using all the set aside land to produce Bioethanol assuming a 50:50 split between wheat and sugar beet would result in:
If, for example, a 5% displacement by volume was required then we wouild require:
At this point it is worth noting some of the limitations and assumptions being made. As can be seen from the figures above bioethanol produced from Sugar beet results in a much greater yield, and so it would seem logical to produce bioethanol entirely from this source. There are however many other factors which should be considered. Firstly there is the problem of mono culture. When only one type of crop is grow on the same land for successive years then this crop will become very susceptible to certain pests and diseases as well as causing the depletion of certain minerals in the soil. The net result of these effects is a requirement for increased use of pesticides and fertilizers which due to their production process results in CO2 emissions. Sugar Beet yields are considerably higher than that of wheat and so fertilizer requirements are likely to be higher also, again causing increased emissions.
The best way to address this problem is with crop rotation. This technique of alternating between different crops helps alleviate the problems mentioned. For this reason it is necessary to use at least two different crops for producing bioethanol. If rapeseed, which is the crop used to produce biodiesel, is also added in then this will also help the problem. To gain a good understanding of what crops could be used and in what proportions would require a more detailed study in this area. This is outside the scope of this investigation and so a 50:50 wheat sugar beet ratio was assumed. Details of the limitations for biodiesel can be found here.