Abstract
This study assessed the feasibility of mobilising maize and wheat residues for large-scale bioenergy applications in South Africa by establishing sustainable residue removal rates and cost of supply based on different production regions. A key objective was to refine the methodology for estimating crop residue harvesting for bioenergy use, while maintaining soil productivity and avoiding displacement of competing residue uses. 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). 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.
Highlights
IntroductionIn Europe, Denmark pioneered large scale power generation using straw and has commercialised the technology since 1989 [1,11]
Key differences in Greenhouse gas emissions (GHG) emissions for the biomass scenarios are related to second transport (raw bales incur about 2.5 times more GHGs (CO2 eq.) compared to pre-treated biomass) and pre-treatment
There is potential to mobilise about 300 PJ from sugar cane residues, forestry residues and waste as well as municipal solid waste e which is about 10% of total coal used for power generation in South Africa
Summary
In Europe, Denmark pioneered large scale power generation using straw and has commercialised the technology since 1989 [1,11]. A key advantage of using crop residues is that their use leads to minimal to no land use change impacts (compared to energy crops). According to the Intergovernmental Panel on Climate Change (IPCC) biomass energy deployment scenarios [6], agricultural residues are likely to play an important role in future energy systems contributing between 15 and 70 EJ to long term global energy supply. Agricultural residues are considered to be less contentious, low cost, carry few risks [6,12,13] and represent an important energy resource for countries with a large agricultural production base
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