Exploring densification and pyrolysis as alternative energy recovery solutions for crop residues in Africa

Africa faces challenges with low access to electricity, resulting in many relying heavily on firewood and charcoal to meet their household energy needs. Of note, large quantities of raw crop wastes and by-products (collectively called ‘residues’) are generated daily from agricultural production. A large proportion of these is, however, underutilised and/or improperly managed. This study thus provides, for the first time, a continent-wide assessment of the energy recovery potential of underutilised crop residues across all 54 African countries, based on FAO statistical harvest data for the 2011 to 2021 period for 34 crops and 59 residue types. This assessment covers a significantly broader scope than do previously reported country- or region-specific studies. Estimates of potentially available residues for energy recovery were derived using residue-to-product ratios (RPR), surplus availability factors (SAF), and an assumed average moisture content of 25%, parameters commonly applied in biomass assessments, but that are inherently subject to variability across local contexts. Based on these inputs, the analysis indicates that the quantity of residues potentially available for energy recovery averages ~1.01 billion tons on a dry basis. This includes 0.53 billion tons of surplus primary residues and 0.16 billion tons of surplus secondary residues, which are available after meeting the demand for all existing competing uses. To beneficiate these residues into fuels, densification and pyrolysis, both recognised for their ability to transform raw biomass into high-value energy products are considered. Both conversion routes are reviewed to assess the energy potential of their resulting products and to identify their most suitable operating conditions. In conclusion, this study showed that implementing certain technologies could elevate the technical energy recovery potential for Africa to 8.60–9.61 exajoules per year. Finally, a greenhouse gas (GHG) emission analysis indicated that converting 100% of secondary residues into biofuels could reduce Africa’s GHG emissions by up to 14.57 mega tons of CO₂ equivalent, as compared to direct combustion, which is currently the most widely used method for residue management. While these findings highlight significant opportunities, they rely on literature-based assumptions and average values, which represents an inherent limitation and underscores the need for region-specific analyses.