Current and future technical, economic and environmental feasibility of maize and wheat residues supply for biomass energy application: Illustrated for South Africa

Residue availability and costs

At current conditions, the sustainable bioenergy potential from maize and wheat residues was estimated to be about 104 PJ. There is potential to increase the amount of crop residues to 238 PJ through measures such as no till cultivation and adopting improved cropping systems. These estimates were based on minimum residues requirements of 2 t ha⁻¹ for soil erosion control and additional residue amounts to maintain 2% SOC level.

At the farm gate, crop residues cost between 0.9 and 1.7 $ GJ⁻¹. About 96% of these residues are available below 1.5 $ GJ⁻¹. In the improved scenario, up to 85% of the biomass is below 1.3 $ GJ⁻¹. For biomass deliveries at the conversion plant, about 36% is below 5 $ GJ⁻¹ while in the optimised scenario, about 87% is delivered below 5$ GJ⁻¹. Co-firing residues with coal results in lower cost of electricity compared to other renewables and significant GHG (CO₂ eq) emissions reduction (up to 0.72 tons MWh⁻¹).

Outlook

Establishing sustainable crop residue supply systems in South Africa could start by utilising the existing agricultural infrastructure to secure supply and develop a functional market. It would then be necessary to incentivise improvements across the value chain