How much biofuel is it feasible to produce sustainably? Part 2

The no-cultivation method:

Since large-scale biofuel cultivation expansion is most likely unfavourable at present, the IEA (2008) suggests that utilizing wastes, such as agricultural and forestry lignocellulosic residues, is a more realistic strategy in the short-term, as it will not require extra land to be converted to biofuel cultivation. The assumption used here was that 10% of the global forestry and 25% of the global agricultural residues are available for utilization as biofuels, assuming that the rest will be needed to be utilized for fertilizer, animal feed and domestic cooking fuel.

It was calculated that 10% of 2007’s agricultural and forestry residues would produce enough biosynthetic natural gas (Bio-SNG) and lignocellulosic ethanol to meet 4.2-6% of the energy needs for transport of 2007, while if 25% of residues are available, biofuels from residues would meet 10.5-14.9% of 2007’s global transport fuel demand.

The methods descibed in parts 1 and 2 combined:

A later study by Sandia (2009) has combined the energy produced from both, the future sustainable expansion of cultivated land and the use of residues, concluding that it will be feasible to be producing 21 billion gallons of cellulosic ethanol per year by 2022 without replacing food crops. This nearly meets the Renewable Fuel Standard’s (2007) target of 60 billion gallons a year by 2022 (Sandia, 2009). It also suggested that sustainably increasing the production to 90 billion gallons by 2030 is realistic, assuming the involvement of R&D, commercialization and supporting policies to ensure economic profitability. This was found to be no less competitive economically than continuing the energy production through fossil fuels. Additional benefits are that it was found to use less water than the current on-shore crude oil extraction and refining.

However, the calculations in the aforementioned reports are too simplistic, as they do not include the by-products, which can indirectly increase the amount of land available for biofuel production through decreasing the need for land for cultivating those other products. They also do not include the effect that multiple production pathways may have on how much biofuel is produced, as these methods may vary in efficiency. This therefore further adds to the uncertainty.