Scielo RSS <![CDATA[Journal of Energy in Southern Africa]]> vol. 28 num. 3 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[<b>Bioethanol production from lignocellulosic sugarcane leaves and tops</b>]]> Bioethanol production is one of the most promising possible substitutes for fossil-based fuels, but there is a need to make available cost-effective methods of production if it is to be successful. Various methods for the production of bioethanol using different feedstocks have been explored. Bioethanol synthesis from sugarcane, their tops and leaves have generally been regarded as waste and discarded. This investigation examined the use of lignocellulosic sugarcane leaves and tops as biomass and evaluated their hydrolysate content. The leaves and tops were hydrolysed using concentrated and dilute sulphuric acid and compared with a combination of oxidative alkali-peroxide pre-treatment with enzyme hydrolysis using the enzyme cellulysin® cel-lulase. Subsequent fermentation of the hydrolysates into bioethanol was done using the yeast saccha-romyces cerevisae. The problem of acid hydrolysis to produce inhibitors was eliminated by overliming using calcium hydroxide and this treatment was subsequently compared with sodium hydroxide neutralisation. It was found that oxidative alkali pre-treatment with enzyme hydrolysis gave the highest yield of fermentable sugars of 38% (g/g) for 7% (v/v) peroxide pretreated biomass than 36% (g/g) for 5% (v/v) with the least inhibitors. Concentrated and dilute acid hydrolysis each gave yields of 25% (g/g) and 22% (g/g) respectively, although the acid required a neutralisation step, resulting in dilution. Alkaline neutralisation of acid hydrolysates using sodium hydroxide resulted in less dilution and loss of fermentable sugars, compared with overliming. Higher yields of bioethanol of 13.7 g/l were obtained from enzyme hydrolysates than the 6.9 g/l ethanol from dilute acid hydrolysates. There was more bioethanol yield of 13.7 g/l after 72 hours of fermentation with the yeast than the 7.0 g/l bioethanol after 24 hours.This research showed that it is possible to use sugarcane waste material to supplement biofuel requirements and that combining the chemical and biological methods of pretreat-ments can give higher yields at a faster rate. <![CDATA[<b>Reducing energy poverty through carbon tax revenues in South Africa</b>]]> How much can poverty be reduced through carbon tax revenue? This study analyses specific programmes, with carbon taxes generating revenues and equivalent spending on programmes to reduce energy poverty. The twin challenges of development and climate change could be addressed in this way in South Africa. A simple spreadsheet model was used to estimate revenue available from a carbon tax, given different tax rates and emission projections. Four programmes to reduce energy poverty were quantified: electrification, extended free basic energy, scaling-up sustainable housing, and subsidising rooftop solar for poor households. Matching carbon revenue with equivalent expenditure, the study found that applying all carbon revenue to a single programme could fund the national budget for electrification. Hundreds of thousands, and up to tens of millions, of households could receive free energy in the form of 5 kg of liquefied petroleum gas every month, as well as better houses that are warmer in winter and with fewer health impacts from indoor air pollution. Carbon revenues could fund at least a few hundred thousand improved homes, or subsidies for at least 100 000 rooftop solar systems per year to poor households. Institutional and other constraints would have to be addressed. Carbon revenue could fully fund all four programmes combined into an integrated strategy, in three of the four scenarios. The results suggested that full funding could be available from 2019 or from 2025, dependent on carbon tax revenue scenario. Energy poverty can be reduced by expenditure of carbon tax revenues. Highlights: • Energy poverty can be reduced by expenditure using carbon tax revenues. • Paper estimates revenues across a range of carbon tax rates. • Revenues can fund large-scale programmes to reduce energy poverty: electrification, LPG, sustainable housing, rooftop solar. • Integrated energy poverty strategy can be funded in three of four carbon revenue scenarios. • Tax revenue could be available from 2019 to 2025. <![CDATA[<b>The impact of political objectives on optimal electricity generation and transmission in the Southern African Power Pool</b>]]> Southern Africa's electrification is at odds with United Nations goals to provide modern energy for all by 2030. Electricity planning, a crucial tool to optimally match future supply and demand, has largely focused on minimising costs in southern Africa, sometimes complemented by a discussion of a discrete set of environmental scenarios. Political objectives, although their significance is well documented, have been overlooked in Southern African Power Pool (SAPP) quantitative electrification planning research. This study created a novel geo-refer-enced, multi-objective linear programming (MOLP) model that combined continuous cost and carbon dioxide (CO2) emission minimisation objectives with the political goal of achieving national electricity self-sufficiency, yielding the optimal trade-off between these three objectives. It solved the MOLP for three different political risk scenarios in order to examine a further political objective. The results revealed a sharp monetary trade-off between CO2 emission reductions and national electricity sovereignty objectives in the SAPP. Furthermore, curtailing international political risks has significant consequences for trade and the optimal generation mix. While the optimal size of the frequently recommended Grand Inga dam in the Democratic Republic of Congo was considerably reduced when either national electricity sovereignty or political risk constraints were imposed on the model, solar energy shares increased significantly in both cases. This was the case especially when CO2 emissions were simultaneously curtailed. Increased technological, institutional and policy-making efforts to implement solar PV at scale would therefore imply immediate political and environmental merits for national governments in the SAPP, and present a sustainable development opportunity for the region. Highlights: • Multi-criteria optimisation of Southern African Power Pool energy network reveals novel insights. • Sharp monetary trade-off between CO2 reduction and national electricity sovereignty. • Electricity sovereignty and political risk restrictions greatly affect generation mix. • Solar energy meets electricity sovereignty goals and decreases political risks. <![CDATA[<b>What role can African cities play in low-carbon development? A multilevel governance perspective of Ghana, Uganda and South Africa</b>]]> Cities' ability to mainstream climate goals into their activities is, to a large extent, influenced by the vertical divisions of responsibilities across different levels of government. This study examined how cities' agency to steer low-carbon urban development is enabled or constrained by multi-level governance arrangements in Jinja in Uganda, Ga East in Ghana, and Polokwane in South Africa. In both Uganda and Ghana, uneven progress with implementing decentralisation reforms greatly limited local government action, and there was poor alignment of sectors they could influence and those with significant emissions reduction potential. In Polokwane, however, a highly devolved governance structure afforded the municipality authority and autonomy over a much wider range of functions. Across all three cases, however, systemic capacity and resource constraints constrained the potential to develop proactive climate governance. Highlights: • In Uganda and Ghana, uneven progress with implementing decentralisation reforms greatly limits local government action. • South Africa's highly devolved governance structure and supportive national frameworks support greater local governance of low-carbon development. • Systemic capacity and resource constraints within municipalities suggest a more collaborative mode of climate governance is required in African cities. <![CDATA[<b>Optimising concentrated thermal photovoltaic energy systems for green and sustainable energy generation</b>]]> Electricity generated from a concentrated thermal photovoltaic system can be improved upon for optimum output. This investigation considered the various options of optimising system operation via effective control of the operating conditions. It examined various options of varying the system configurations for optimised system efficiency and power output and at minimum operating costs. The number of mirrors and photovoltaic cells for use in the concentrated thermal photovoltaic system were set at eight as standard for the system operation. This number was varied down and up (from eight to six and then from eight to ten) to study the effects of these variations on the concentrated thermal photovoltaic system efficiency and generated power output. A novel thermal model was built in two dimensions and was used to simulate the thermal performance of the concentrated thermal photovoltaic modules. The parameters used for the materials involved were defined and the appropriate physics applied in the study of various operating conditions that affected the system performance for the two-dimensional system were stated. The results showed that temperature rise was least in the ten mirrors configuration and highest in the six mirrors configuration. The six PV cells-mirrors configuration, however, generated the highest power output of the three different configurations considered. The six PV cells/mirrors configuration utilised the least numbers of mirrors and PV cells out of the three configurations, ultimately translating to reduced-materials cost for the operation. Based on these findings, the choice of the lower number of six mirrors and six PV cells was considered the most economical and, therefore, most desirable. <![CDATA[<b>Characterisation of wind speed series and power in Durban</b>]]> Both the planning and operating of a wind farm demand an appropriate wind speed model of its location. The model also helps predict the dynamic behaviour of wind turbines and wind power potential in the location. This study characterises the wind speed series and power in Durban (29.9560°S, 30.9730Έ), South Africa, using Markov chain and Weibull distribution. Comparison of statistical quantities of measured and Markov model-generated wind speed series revealed that the model accurately represented the measured wind speed series. The Markov model and Weibull distribution were also compared through their corresponding probability density functions. The root mean square error of the Markov model against the measured wind speed series was nearly one-tenth that of the Weibull distribution, indicating the effectiveness of the former. Finally, the analysis of wind power density showed that Durban and its environs need large wind turbines with hub heights greater than 85 m for efficient utilisation of the available wind energy. Highlights: • Wind speed series in Durban can be characterised using the Markov chain model, and the corresponding power can be fairly predicted using the model. • Compared to the conventional Weibull distribution, the Markov chain model accurately represents the wind speed series in Durban. • Durban and its environs require wind turbines with heights higher than 85 m for efficient operation. <![CDATA[<b>Numerical optimisation of a small-scale wind turbine through the use of surrogate modelling</b>]]> Wind conditions in South Africa are suitable for small-scale wind turbines, with wind speeds below 7 m.s-1. This investigation is about a methodology to optimise a full wind turbine using a surrogate model. A previously optimised turbine was further optimised over a range of wind speeds in terms of a new parameterisation methodology for the aerodynamic profile of the turbine blades, using non-uniform rational B-splines to encompass a wide range of possible shapes. The optimisation process used a genetic algorithm to evaluate an input vector of 61 variables, which fully described the geometry, wind conditions and rotational speed of the turbine. The optimal performance was assessed according to a weighted coefficient of power, which rated the turbine blade's ability to extract power from the available wind stream. This methodology was validated using XFOIL to assess the final solution. The results showed that the surrogate model was successful in providing an optimised solution and, with further refinement, could increase the coefficient of power obtained. <![CDATA[<b>Characteristics of selected non-woody invasive alien plants in South Africa and an evaluation of their potential for electricity generation</b>]]> Alien invasive plants (AIPs) pose a threat to the existence of plant and animal biodiversity in the ecosystems they invade. They need to be cleared, monitored and eventually eradicated from the landscape. The potential and the economic viability to supply non-woody AIP biomass for electricity generation were assessed in this study, which was conducted on samples from 13 common non-woody AIPs in South Africa, namely: Arundo donax (giant reed), Lantana camara (lantana), Pontederia cordata (pickerel weed), Ricinus communis (castor-oil plant), Opuntia ficus-indica (sweet prickly pear), Solanum mauritia-num (bugweed), Atriplex nummularia (saltbush), Cestrum laevigatum (inkberry), Senna didy-mobotrya (peanut butter cassia), Chromoleana odo-rata (chromoleana), Eichhornia crassipes (water hyacinth), Cerus jamacaru (queen of the night) and Agave sisilana (sisal plant). Proximate and ultimate analysis was made in order to assess the suitability of the biomass for different thermo-chemical conversion techniques for electricity generation. A financial evaluation of the costs to supply biomass to the plant gate was performed by combining the harvesting, chipping and transport costs. The results showed that the biomass of giant reed, lantana, bugweed, saltbush, inkberry, cassia and Chromoleana may be used to generate electricity through combustion, although the total average cost was approximately 50% higher than that of woody biomass feedstock, requiring a 'fuel cost subsidy' to justify their utilisation for energy production. Highlights: • Physical and chemical properties make some non-woody alien invasive plants suitable for electricity generation. • Economic analysis showed that, without subsidy, some non-woody alien invasive plants are not suitable as feedstock. <![CDATA[<b>Long-term temperature measurement: Biogas digesters fermenting slurry</b>]]> This paper reports the results of the temperature profile of the unheated and unstirred continuous fermenting bio-slurry in a fixed-dome Deenbandhu 2000 model. The digester is a brick-built system of bulk size 6 m³. The digester was monitored for eight months, measuring internal bio-slurry temperature. A K-type nickel chromium-nickel temperature sensor with a sensitivity of approximately 41 μV °C and response time of 0.8s in liquids was positioned at the centre of the digester to measure the slurry temperature. The sensor was connected to the data logger and programmed to record temperature readings every second for the entire study period. The study results reported give a clear indication about the reaction of bio-slurry temperature in the digester at a local level, particularly for the eight months' period, which covered all seasons. The calculated values of the daily average temperature reveal that the digester was operating within the range of psychro-philic 10.32 °C and mesophilic 28.80 °C, although it sometimes operated at 35 °C and above during certain hours in summer. This study is useful for anaerobic digestion processes for biogas production. The results obtained can be used as a basis to estimate the amount of heat required to raise the temperature of digesters to reach an optimum temperature of mesophilic digesters. Highlights: • The measurements rely on the K-type nickel chromium-nickel temperature sensors. • The temperature is measured at the centre of the digester. • The digester considered is a fixed-dome, brick-built Deenbandhu 2000 model. • The digester is unheated, unstirred and buried underground. • The soil pH at 0.0 cm is 5.0 in potassium chlorine. <![CDATA[<b>Knowledge, attitudes and perceptions of stakeholders on biofuels as an enabler in a South African bio-based economy</b>]]> This study investigates stakeholder knowledge, attitudes, and public perception concerning biofuels as an enabler towards a bio-based economy. In innovation and adoption studies, perceptions play a critical role in the acceptance of a technology. Biofuels have been touted as a clean fuel with an ability to reduce greenhouse gas emissions while simultaneously creating employment and growing economies. South Africa is in the process of transitioning towards a bio-based economy. Accordingly, policies and institutions have been developed to promote biofuels production and distribution. Knowledge, attitude and perception (KAP) surveys were carried out to deepen knowledge and understanding of the stakeholder's KAP. Emails as well as telephonic and group interviews based on open questions and social media were used to gather data. The study employed cluster, purposive random and snowball sampling to select the participants with descriptive statistics, thematic analysis and discourse analysis used to analyse the data. The study found that the introduction of biofuels presents many opportunities and benefits for the economy and unlocking the potentials for rural entrepreneurs. Stakeholders have concerns and issues regarding the use of biofuels on their internal combustion engines. The study recommends proper communication and education should be done on the benefits of biofuels in a bio-based economy.