By Antonio Ruffini, Editor, ESI Africa
Biogas has thus far received little attention in South Africa, considering that it has the potential to displace up to 2,500 MW of grid electricity and other thermal power supply options in the country.
There are an estimated 200 biogas digesters scattered across South Africa, most of these accounted for by small domestic units and a few non-government organisation (NGO) driven initiatives. In comparison there are 12 million biogas digesters in India and 17 million in China. Germany is building a commercial digester every eight hours and has an installed capacity of over 9,600 MW. In countries such as Germany, biogas technology is highly advanced and is applied primarily to produce green electricity in the megawatt range that is fed directly into the grid under a favourable renewable energy feed-in tariff (REFIT) structure. In developing countries such as India and China more basic technology is used to provide energy, mainly for cooking, with the feedstock for the digesters being human and animal waste.
Mark Tiepelt founded BiogasSA four years ago after he was unable to find a local company that could install a biogas digester at a reasonable price for his smallholding north of Johannesburg. He believes that if one considers some of the objectives of South Africa’s renewable energy programme, biogas should play a much more significant role as a viable source of renewable energy. “A biogas plant not only produces electricity, but the anaerobic digestion process converts the often environmentally hazardous waste material into organic fertiliser that can be used to increase the yield of planted crops. By running a large combined heat and power (CHP) generator, the process provides free thermal energy in the form of hot water at 85OC.
“Biogas in South Africa has much greater local job creation potential than other forms of renewable energy.” It is estimated that biogas as a renewable energy source has the potential to generate five times more permanent job opportunities than solar energy.
Biogas plants of less than 1.0 MW currently have an attractive rebate from Eskom. However, the National Energy Regulator of South Africa’s (Nersa’s) slashing of Eskom’s demand side management programme budget for the multiyear price determination (MYPD3) that extends until 2018 will undoubtedly have an impact going forward. The department of trade and industry (DTI) also has grants that could be accessed – both grants considerably improve the financial viability of such projects.
Biogas schemes are eligible for Clean Development Mechanism (CDM) rebates, as they remove methane production from the atmosphere, methane being 21 times more effective a greenhouse case than carbon dioxide. Increasingly CDM mechanisms are being evolved that allow the pooling of a number of small projects to gain credits, and biogas digesters ideally fit that model. Biogas can be used to generate power when it is required, unlike wind and solar energy (apart from concentrated solar power with storage). It means that industrial scale biogas plants could provide peaking power when required.
A number of reasons exist for why there are so few biogas digester plants in South Africa. These include public apathy (other sources of electricity are much less hassle), cheap electricity, limited grants or government incentives and no local technology providers. There is some degree of critical mass required in sourcing feedstock, to which a typical residential sector household is not suited. To produce 1.0 m3/day of biogas, which typically comprises 60% methane and 40% CO2 and some trace sulphur, one requires the black water from 15 to 20 people, or the manure from three cattle, or 10 pigs, or 1,000 chickens. That cubic metre of gas is sufficient to power a two-plate gas stove for a couple of hours.
Biogas has a lower calorific value than liquefied petroleum gas (LPG) or natural gas, which makes it less combustible, and it therefore cannot be used to run normal LPG gas appliances. Regular appliances can be modified to run on biogas by enlarging apertures, theoretically a simple process, but a lot more tricky in practice. Because of the negligible market in South Africa, biogas appliances currently have to be imported from countries such as China. A biogas digester for a smallholding costs in the region of R40,000.
The anaerobic process by which biogas is produced is very temperature sensitive, and the closer to 35OC the better. The retention time of the feedstock is typically 20 to 40 days, but a digester does start producing biogas almost immediately, though this ramps up over time and the ideal is to sustain a steady production. Unused biogas can be stored, but there is a cost balance effect which may see flaring the gas as more economical.
Biogas is not a new technology. The first street lights in London ran on methane collected from the underground sewerage tunnels. Any type of organic waste material that decomposes in the absence of oxygen (anaerobic process) will produce methane. As long as there is an airtight environment and a means to capture the biogas produced one has a functioning biogas digester. “In its most basic form, a biogas digester could be as simple as filling a black polyurethane bag with manure slurry and leaving it in the sun. As the manure begins to decompose, the gas produced inflates the bag, creating pressure that allows the gas to be tapped off,” Tiepelt says.
In fact biogas systems were first introduced to South Africa in 1957 by a pig farmer in the south of Johannesburg who turned his pig manure into energy. He ran a six-horse-power Lister engine on biogas for a number of years.
Biogas in South Africa has potential both on a small scale (domestic / smallholding / small farm) and on a commercial and industrial scale. Thousands of rural households have no access to electricity and no likelihood of receiving such in the near future. Most of these households have access to suitable feedstock (sewerage, animal manure, food / fruit / vegetable waste) that could provide energy for cooking and lighting. Large scale commercial digesters could be implemented at any number of municipal sewerage works, abattoirs, fruit and vegetable packaging plants, food processing plants, etc. and could typically provide 50% to 70% of the plant’s energy requirements. Normally only a Basic Assessment and not a full Environmental Impact Assessment (EIA) is required.
Speaking prior to the Nersa decision on Eskom’s funding for integrated demand management, Tiepelt said that the market could be about to take off in South Africa thanks to the utility’s incentive programmes. “Up until July 2012 the only incentive we could offer biogas projects was Industrial Development Corporation (IDC) soft loans. However, since July 2012 Eskom extended its standard offer rebate programme to include generating electricity from renewable sources and the DTI introduced a grant scheme that considerably improved the financial viability of projects. Eskom’s standard offer programme rebate of R1.2/kWh for biogas projects makes these viable and attractive.” According to the standard offer the rebate is offered between 6:00 AM and 10:00 PM on weekdays.
BiogasSA has undertaken a 500 kW project for an abattoir which will be able to generate 60% of its electricity from biogas (an estimated 1.4 GWh/year) fed by slaughter waste, thus solving two problems, the second being disposal of that waste material. “It amounts to a R14 million investment by the abattoir of which R5 million is covered by the standard offer rebate and it gives the company a four year payback on its investment.” The plant uses a 17 litre engine and has an energy efficiency of 40%. The plant also uses combined heat and power, with waste heat captured for water heating.
BiogasSA has been undertaking projects at a fruit packaging plant, a cattle feedlot, a tannery, a wine estate, a cheese factory, a pie factory and numerous dairies. Roughly speaking, electricity from biogas comes in at about R15 – R20 million per MW, but one has to take into account that it can be used as mid-merit or even baseload power, and at a cost of some R1.0/kWh will become economically viable in time. Then there are the greenhouse gas mitigation effects as well as waste disposal and the production of fertilisers which have some monetary value.
Perhaps the decider for biogas in South Africa might be the job creation impact of a large rollout of such technology. While the realistic actual figures for jobs created per megawatt of solar power in South Africa is 0.9 jobs per MW, biogas can create five jobs per MW, and there is the potential for thousands of biogas digesters to be established across the country.