Biomass from farming is one of the sources of energy being considered for South Africa.
The potential of biomass as a feed for energy products in South Africa is limited due to arable land, rainfall and food security constraints. The best candidate feedstocks are urban organic waste and lignocellulose (comprising a mix of agricultural and forestry residue, and harvested invasive alien plants). It may be possible, with government assistance, to develop a sizeable energy crop industry for biodiesel manufacture based on subsistence farmland.
Bioenergy in South Africa has limited potential on account of relatively low primary productivity, largely constrained by rainfall and exacerbated by significant inter-annual variability. These factors, together with an inevitable focus on food security, combine to limit the attractiveness of energy derived from biomass.
Despite these constraints, some potential does exist. Technoeconomic assessment of options for biomass conversion to energy, and considerations such as job creation, impact on rural economies, greenhouse gas (GHG) mitigation and likely subsidies required to make energy products cost-competitive, were evaluated and resulted in the following set of feasible options for biomass utilisation:
Utilisation of all available urban domestic (household) organic waste, from solid waste and from wastewater, is the most feasible option, with an acceptable end-product cost. Upgrading to biomethane typically doubles the cost, and electricity generation will result in efficiency penalties.
The option requires intervention from government in respect of policy, accelerated permit processing for wastewater and solid waste facilities, and sponsoring of research and development of standardised large-scale digester and biogas upgrading technology. Some local authorities may elect to use wastewater biogas for in-situ electricity generation. Estimated contribution from feasible project options: up to 1 400MWe (electrical output of a power plant in megawatts).
Development of household or communal digesters in rural, unserviced areas in combination with cattle dung in areas where this is available. Government will have to identify and promote technology, implement programmes to promote acceptance and safe use, and possibly serve as a source of capital for initial investments. Estimated contribution from feasible project options: up to 250 MWe.
Combination of all available lignocellulose biomass. Invasive alien plants, plantation residues, sugar mill bagasse (what’s left from cane when the juice has been extracted) and agricultural residue can make a significant contribution to electricity generation in mid-size regional power stations (typical size 50-300MW). Projects may have a limited lifetime due to the objective of the eradication of invasive alien plants over a 20-year period. Some of the project options are in areas of poor electricity availability (rural Mpumalanga, Eastern Cape, KwaZulu-Natal) and will be able to underpin one or more rural electrification projects. Costs are comparable to new electricity from coal. Estimated contribution from feasible project options: up to 1 300MWe.
It may be possible to develop an energy crop industry on subsistence farmland as a measure to improve rural livelihoods. The most feasible option is for biodiesel manufactured from groundnut oil or sunflower oil, with byproduct sales offsetting the cost of final products. Due to the need for some form of subsidy, projects are unlikely to attract private capital. In addition, it is likely that significant effort will be required to transform rural agricultural practice. With an oil price in the order of $50 per barrel, these options are not attractive, but the situation might improve should oil prices rise to recent highs of $100 per barrel. Estimated contribution from feasible project options: 587MW, 235MWe as electricity equivalent, 570m l/a of biodiesel, approximately 5% of current diesel consumption.
1To benefit GHG emissions (greenhouse gas emissions), the eradicated biomass will have to be replaced. Options include managed Category 2 invasive plants (such as Eucalyptus) or restoration of indigenous vegetation.
2Sugar cane and sweet sorghum are attractive as energy crops due to high yields and large areas suitable for cultivation. Ethanol for E10 blends (5-10% ethanol added to petrol) needs to be near anhydrous (containing no water) and is expensive to produce, making it uncompetitive. E100 (95% ethanol and 5% water), as used in Brazil, is less expensive to produce but was not considered since it does not form part of the current Biofuels Strategy.
A number of project options for a variety of feedstock and processing combinations were evaluated. Not all of these combinations are feasible, generally since smaller facilities do not have the requisite economy of scale, or the combined feedstock and transport costs are too high. The feasible options identified generally minimise the cost of production based on feedstock input, transport costs and economy of scale, but in practice the logistics of supply and local variations in density and accessibility of feedstock might limit the size of such a facility.
Impacts of the most feasible options, as described above, were also assessed in terms of environmental considerations (GHG emission mitigation, invasive alien plant eradication, better utilisation of degraded land), and socioeconomic benefits (job creation, contribution to regional economy, and access to clean energy). It is clear from the assessment of these impacts that, in general, the following holds true:
The conversion of organic waste in urban areas to biogas and possible refinement to biomethane has positive GHG emission impacts, is price-competitive with alternatives, and will result in the creation of a small number of sustainable jobs.
The other options (based either on lignocellulose sources or on purposely cultivated energy crops) have limited or negative value in terms of GHG emission mitigation and the costs are the same or higher than those of fossil and renewable alternatives. Hence these projects will in all likelihood rather be undertaken in an effort to establish a national strategic intervention in rural areas that aims to:
-improve water availability through eradication of invasive alien plants;
-revitalise subsistence farming areas;
-create jobs in extraction, harvesting and processing of biomass;
-provide access to clean energy in some cases; and
– develop the rural economy.
Such a national scale strategic intervention would need to be integrated with existing government programmes (Agri-Parks, Working for Water, Working for Energy, Housing Subsidies, and programmes managed by the department of agriculture, forestry and fisheries).
To conclude, bioenergy is feasible in South Africa at a relatively small scale, involving mostly processing of organic waste, residues from forestry and agriculture, and eradication of invasive alien plants.
Feasible project options depend on the cost of feedstock, processing costs and transport costs. These factors are subject to economy of scale considerations. Furthermore, current low oil prices make bioenergy in general, and biofuel in particular, less attractive, with purposely cultivated crops being affected the most.
Despite this, it is possible to determine short-, medium- and long-term strategies for bioenergy generation, which, in total, may be able to contribute approximately 3 500MW of electricity equivalent to the national energy mix over the planning horizon of 20 years.Should accessible and sufficiently dense invasive alien plants be successfully eradicated over the planning horizon, it will have a significant impact on woody biomass availability and eventually reduce capacity by approximately 1 000 MWe. Negative greenhouse gas benefits ensue should the eradicated invasive alien plants not be replaced by more or less equally productive alternatives — either as managed short-rotation coppicing stands of Category 2 plants (such as Eucalyptus), or with indigenous species.