Scielo RSS <![CDATA[Journal of Energy in Southern Africa]]> vol. 31 num. 1 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Revisiting electric utilities' efficiency in the Southern African Power Pool, 1998-2009</b>]]> This study analyses the determinants of the technical efficiency performance for Southern African Power Pool (SAPP) power utilities in the period 1998-2009, excluding South Africa's Eskom. The study formulated an explicit model for technical inefficiency by considering the vertical structure of the utilities and the definition of the product, considering the specific characteristics of this sample. It was found that the most significant improvement in the average efficiency of the sample occurred from 2000 to 2002, coinciding with the first SAPP Energy Plan of2001. Density in consumption, control of corruption and load factor also contributed to the different levels of efficiency. The results provided a new empirical evidence that can be useful for the design of energy policy and incentive regulation. HIGHLIGHTS: • Significant improvement in the average efficiency of SAPP firms • A bad specification could lead to incorrect energy policy implications • Density and load factor contribute to explain efficiency levels • Institutional aspects represent a promising line of study <![CDATA[<b>Reclamation of ultra-fine coal with Scenedesmus microalgae and comprehensive combustion property of the Coalgae® composite</b>]]> Combustion of South African discard ultra-fine coal, charcoal, microalgae biomass, and composites of the three under air were studied. The objective of the study was to determine the effect of Scenedesmus microalgae biomass on the comprehensive combustion characteristics (CCC) of the ultra-fines. The composites were designed with Design Expert and, unlike blending with the dry microalgae biomass, fresh slurry was blended with the ultra-fine coal and charcoal. Non-isothermal combustion was carried out at heating rate of 15 °C/min at 40-900 °C and flow rate of 20 ml/min, oxygen/ carbon dioxide (O2/CO2) air. Combustion properties of composites were determined from thermogravimetric-differential thermogravimetric analysis and analysed using multiple regression. On combustion, the interaction of coal-charcoal-microalgae was antagonistic (b = -1069.49), while coal-microalgae (b = 39.17), and coal-charcoal (b = 80.37), were synergistic (p = 0.0061). The coal-mi-croalgae (Coalgae) indicated first order reaction mechanism, unlike coal and the charcoal. The CCC index of Coalgae, (S-value = 4.52E8) was superior relative to ultra-fine (S-value = 3.16E8), which indicated high-quality fuel. This approach to combusting ultra-fine coal with microalgae biomass is partly renewable, and it would advance the production of heat and electricity. HIGHLIGHTS: • Scenedesmus added value to reclamation and combustion of ultra-fine coal. • The interaction between coal dust and microalgae biomass was synergistic. • The derived response surface model could predict comprehensive combustion characteristics. • The combustion kinetic model of Coalgae deviated from first order reaction. <![CDATA[<b>Passive cooling for thermal comfort in informal housing</b>]]> Energy-poor households in Africa's burgeoning urban informal settlements are especially likely to suffer from heatwaves because of thermally inefficient dwellings and lack of affordable cooling options. This study utilised a controlled experiment to assess the effectiveness of passive cooling through specially formulated paints (cool coatings) in standard informal structures. The test structures were built to simulate typical shack dwellings in South Africa's urban informal settlements. Results showed that the mean daily maximum temperatures of the coated structure were up to 4.3 °C lower than those in the uncoated structure. The same cooling trend was observed for the minimum daily temperatures, which were lower by an average of 2.2 °C. Besides, the annual frequency of maximum temperature exceedances beyond the critical heat stroke value of 40 °C dropped from 19% for the uncoated structure to 1% for the coated structure. These temperature differences were found to be statistically and subjectively significant, implying that cool coatings may be effective in promoting thermal comfort and climate resilience in poor urban communities. It is recommended that governmental authorities and relevant role players invest in the production and assisted application of cool coatings in urban informal settlements. The interventions promise hope of reduced energy burden on poor households and could be implemented in parallel with ongoing efforts focused on the design and implementation of low-cost, durable and thermally comfortable houses for indigent communities. Ultimately, the endeavours could be a potential policy change to assist in expanding poor households' access to alternative and green energy resources. HIGHLIGHTS: • Energy-poor shack dwellers are frequently exposed to elevated summertime heat. • Passive cooling technologies are perhaps one economically viable option. • Experimental shacks coated with cool coatings showed lower indoor heat. • Cool coatings intervention can greatly improve survivability of shack dwellings. <![CDATA[<b>An intelligent alternating current-optimal power flow for reduction of pollutant gases with incorporation of variable generation resources</b>]]> Frequent escalations in fuel costs, environmental concerns, and the depletion of non-renewable fuel reserves have driven the power industry to significant utilisation of renewable energy resources. These resources cannot satisfy the entire system load demand because of the intermittent nature of variable generation resources (VGRs) such as wind and solar. Therefore, there is a need to optimally schedule the generating units (thermal and VGRs) to reduce the amount of fuel used and the level of emissions produced. In this study, an AC-power flow in conjunction with combined economic and environmental dispatch approach through the implementation of a modified constricted coefficient particle swarm optimisation was used to minimise the fuel cost and the level of emission gases produced. The approach was applied to the Institute of Electric and Electronic Engineers 30 bus test system through three different load conditions: base-load, increase-load and critical-load. The results showed the practicality of the proposed approach for the simultaneous reduction of the total generation cost and emission levels on a large electrical power grid while maintaining all the physical and operational constraints of the system. HIGHLIGHTS: • Considering several physical and environmental constraints of generating units. • Proposing a metaheuristic method based on swarm intelligence for solving AC-OPF problem. • Incorporation of variable generation resources in electricity spot markets. • Maximisation of social welfare and minimisation of total generation cost, while reducing the volume of pollutant gases. <![CDATA[<b>Effects of current mismatch due to uneven soiling on the performance of multi-crystalline silicon module strings</b>]]> Photovoltaic (PV) module operation is critical in PV systems for optimum generation of electrical power. Modules installed in the field suffer uneven soiling caused by bird droppings and dust build-up on their front surface. This study investigated the impact of partial shading caused by non-uniform soiling on the electrical characteristics of multi-crystalline silicon (mc-Si) modules and strings, and compared this with simulated I-V parameters. Light and heavy uneven soiling on mc-Si solar cells resulted in current mismatch which can be simulated. The effects of partial soiling on the I-V characteristics of mc-Si module strings were experimentally measured and agreed with the simulated results. <![CDATA[<b>Small signal stability analysis of a four-machine system with placement of multi-terminal high voltage direct current link</b>]]> Inter-area oscillation caused by weak interconnected lines or low generator inertia is a critical problem facing power systems. This study investigated the performance analysis of a multi-terminal high voltage direct current (MTDC) on the damping of inter-area oscillations of a modified two-area four-machine network. Two case studies were considered, utilising scenario 1: a double alternating current (AC) circuit in linking Bus_10 and Bus_11; and scenario 2: a three-terminal line commutated converter high voltage direct current system in linking Bus_6 and Bus_11 into Bus_9. It was found that scenario 2 utilising MTDC link with a robust controller provided quick support in minimising the network oscillations following a fault on the system. The MTDC converter controllers' setup offered sufficient support for the inertia of the AC system, thus providing efficient damping of the inter-area oscillation of the system.