Exploring sustainable biofuel feedstock potential in Sub-Saharan Africa

The Worldwide Fund for Nature South Africa (WWF-SA) has commissioned IIASA to assess pathways towards large-scale, sustainable aviation biofuel deployment in Sub-Saharan Africa, and to address the complex interlinkages in different dimensions of the agriculture-energy-environment system.

The International Civil Aviation Organization has adopted the goal of carbon neutral growth from 2020 onwards (IATA, 2013). Large-scale aviation biofuels, including diverse agricultural feedstocks (i.e., raw materials), are anticipated to play a key role in achieving the target in the longer term.

Biofuels are produced from a range of diverse biomass types, including plant materials, vegetable oils, and starch. As biomass is a limited resource, the aviation sector will add to demand from food, feed, and other non-food agricultural products. To this end, the aviation industry called on the WWF-SA to embed and discuss the development of biomass for energy into a broader perspective of agricultural and socioeconomic development in Sub-Saharan Africa. The region is seen as one of the major expansion areas for the production of biofuel feedstocks.

The guiding principles used for the sustainability assessment were those developed by the Roundtable on Sustainable Biomaterials (RSB), an independent and global multi-stakeholder coalition. The IIASA ecological-economic modeling framework, which comprises the Food and Agriculture Organization of the United Nations (FAO)/IIASA Global Agro-ecological Zones and the IIASA World Food System model, was used to implement the RSB principles on food security, greenhouse gas (GHG) emission saving, environmental conservation, soils, and water management. The researchers defined exclusion layers such as food crops, livestock, safeguard areas of high value for biodiversity and the environment, and quantified them. This revealed some ‘unprotected’ grass- and shrubland areas that are potentially available for biofuel feedstock production. In addition to current land balances, development scenarios until 2050 evaluated future geospatial patterns of food production and associated land demand.

Once food security and environmental sustainability criteria were accounted for, the balance of remaining land (REMAIN land) was explored for its suitability and capacity to produce a variety of biofuel feedstocks, and assessed in relation to the GHG emissions saving criteria. The assessment included 11 feedstocks ranging from extensively employed, well established conversion pathways (e.g., sugar cane and cereals to bioethanol, or diverse vegetable oil crops to biodiesel) to novel crops (e.g., vegetable oil from solaris tobacco), and second-generation lignocellulosic biomass (i.e., all biomass that has a relatively high content of lignin and cellulose). This has been, and is still being extensively explored in a number of research and demonstration projects (e.g. miscanthus silvergrass).

Intensity and spatial distribution of REMAIN land in Sub-Saharan Africa, 2010.

The results of the study [1] indicate that about one third of REMAIN land, or 1.9 million km² are agro-ecologically very suitable, or suitable for the production of some annual or perennial biofuel feedstocks. However, exploitation of these land resources will require land conversion from natural shrub- and grasslands to cropland, followed by intensive feedstock cultivation practices. This will in turn result in substantial initial carbon debts due to the removal of the existing vegetation and the partial loss of soil carbon. The sustainability GHG emissions saving criteria set by the RSB requires at minimum a 60% saving relative to the fossil fuel comparator when using a 20-year accounting period. Adhering to this criterion implies that primarily perennial biofuel feedstocks requiring less frequent and less intensive cultivation of soils, can meet the criteria when conversion of natural grassland or shrubland is involved.

The sustainable production potential on prime land quality is restricted to miscanthus (silvergrass), palm oil, and sugarcane, and amounts to a current energy potential of some 6,000 petajoules. Over time, available REMAIN land shrinks because of additional cropland required for food production, which is projected to halve the current sustainable biofuel potential to about 3,000 petajoules by the 2050s. According to the results, annual feedstocks such as sweet sorghum would only be eligible under a less strict GHG criterion that uses a 60% GHG emission saving applied to the biofuel life cycle emissions in each year, and requires a payback period for additional emissions from direct land use change of less than ten years. In such a case, the current potential would increase to 12 thousand petajoules (biofuel equivalent).

In addition to the above, agricultural residues from food production could provide additional biomass for fuel production. When applied to 2010 data, the model shows that allowing 2 tons of crop residues per hectare to remain on the field to comply with the RSB principle on safeguarding soil fertility, results in a useable crop residue potential of 97 million tons (equivalent to 617 petajoules), thus increasing the potential from REMAIN land by 10%. Unlike REMAIN land, which will be decreasing towards the 2050’s, cultivated land for food production and associated crop residues will be increasing.

References

[1] Fischer G, Tramberend S, Van Velthuizen H, Bole-Rentel T, Reeler J. Sustainable Aviation Biofuel Feedstock Potential in Sub-Saharan Africa. A systems analysis investigation into the current and future potential for sustainable biofuel feedstock production. WWF and IIASA, forthcoming.

[2] IATA. 2013. Implementation of the Aviation Carbon-Neutral Growth (CNG2020) Strategy. [Online]. Cape Town: International Air Transport Association (IATA). [Accessed 12 Feb 2018 2018].