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CITATION: Votteler, R. G. & Brent, A. C. 2017. A mining perspective on the potential of renewable electricity sources for operations in South Africa Part I—the research approach and internal evaluation process. Journal of the Southern African Institute of Mining and Metallurgy, 117(3):285-297, doi:10.17159/2411-9717/2017/v117n3a10.

The research presented in this paper documents the implementation of an active hybrid energy storage system that combined a battery pack and an ultracapacitor bank. The implemented hybrid energy storage system was used to reduce the peak-power that the battery needs to provide to the load. An active topology utilising two direct current/direct current (DC/DC) converters and a switch was used to implement the hybrid energy storage system. Fuzzy logic was used as a close-loop control structure to control the DC/DC converters in the topology, whilst a rule-based control strategy was used to control the operating states of the hybrid energy storage system. Experimental implementation of the system showed that the system was able to actively control the energy flow throughout the hybrid energy storage system in order to limit the power drawn from the battery to a user-defined limit. The performance of the fuzzy logic controllers was also experimentally found to be sufficient when used in conjunction with the rule-based control strategy. The system allows one to utilize batteries that are optimized for energy density seeing that the system was able to actively limit the power drawn from the battery, whilst providing the required power to the load by utilising the ultracapacitor bank.

Abstract Grid-tied renewable energy sources (RES) with battery-behind-meter (BBM) architectures have successfully been used to ensure effective energy cooperation between the grid and RES-based microgrids. Such environments are quite stochastic, thus making power management very challenging. This paper presents the use of an asynchronous Q-learning in performing a power flow management task in a multi-source electric vehicle charging station with the integration of vehicle-to-microgrid technology. The power scheduling problem is first formulated as a Markov decision process. Asynchronous Q-learning is then used to solve it. The algorithm is tested with a typical charging station load profile over a 24-hour period and compared with a simple rule-based algorithm. Simulation results show that the proposed method is able to select a power schedule that reduces the energy cost with a better utilization of both the battery storage system and the vehicle to microgrid energy compared to the rule-based method.

Abstract This paper presents a near optimal hoist scheduling and control program for rock winders found in South African deep level mines in the context of demand side management and time-of-use (TOU) tariffs. The objective is to achieve a set hoist target at minimum energy cost within various system constraints. The development of a discrete dynamic and constrained mixed integer linear programming model for a twin rock winder system is presented on which a half-hourly model predictive control (MPC) algorithm containing an adapted branch and bound methodology is applied for near optimal scheduling. Simulation results illustrate the effectiveness of the control program by minimising the energy costs through scheduling according to the TOU tariff and controlling output and ore levels within their boundaries even in the case of significant random delays in the system. Scheduling according to the TOU tariff shows a possible 30.8% reduction in energy cost while approximately 6 h of delays in the system resulted in a mere 14% increase in energy cost.

Spider webs must be able to absorb the energy of impacting insects, and similarly, rock support must absorb the energy of ejected rock in rockbursts. A consideration of the properties of spider webs shows that spider silks (threads) are extremely strong, typically three times as strong as common steel. Spiders also construct their webs with yielding mechanisms to enhance their energy-absorbing capability. In this paper, the techniques employed in web construction are compared with those used in rock support in excavations prone to rockbursting. It is shown that the design of rockburst support could benefit from some of the capabilities used by spiders in the construction of their webs.

Ethanol is an attractive alternative fuel because it is a renewable bio-based resource and it is oxygenated, thereby providing the potential to reduce particulate emissions in compression-ignition engines. In this review the properties and specifications of ethanol blended with diesel fuel are discussed. Special emphasis is placed on the factors critical to the potential commercial use of these blends. These factors include blend properties such as stability, viscosity and lubricity, safety and materials compatibility. The effect of the fuel on engine performance, durability and emissions is also considered. The formulation of additives to correct certain key properties and maintain blend stability is suggested as a critical factor in ensuring fuel compatibility with engines. However, maintaining vehicle safety with these blends may entail fuel tank modifications. Further work is required in specifying acceptable fuel characteristics, confirming the long-term effects on engine durability, and ensuring safety in handling and storing ethanol-diesel blends.

The move towards renewable energy and technological advancements in the generation, distribution and transmission of electricity have increased the popularity of microgrids. The popularity of these decentralised applications has coincided with advancements in the field of telecommunications allowing for the efficient implementation of these applications. This convenience has, however, also coincided with an increase in the attack surface of these systems, resulting in an increase in the number of cyber-attacks against them. Preventative network security mechanisms alone are not enough to protect these systems as a critical design feature is system resilience, so intrusion detection and prevention system are required. The practical consideration for the implementation of the proposed schemes in practice is, however, neglected in the literature. This paper attempts to address this by generalising these considerations and using the lessons learned from water distribution systems as a case study. It was found that the considerations are similar irrespective of the application environment even though context-specific information is a requirement for effective deployment.

Within the context of the energy crisis in the Western Cape, the Provincial Government and Eskom (the South African power utility) embarked on a retrofit campaign to install 5 million compact fluorescent lamps (CFLs) in a desperate attempt to decrease the generation deficit. There is also increased pressure for investments in new generation capacity, with all options including the Pebble Bed Modular reactor (PBMR), the Open Cycle Gas Turbines (OCGT) as well as renewable resource technologies being pro-posed. Despite all these concerted efforts it is wide-ly regarded that demand-side technologies, with education programs, subsidies and research fund-ing, have greater scope for achieving success as they tackle the root cause rather than the symptom.The light emitting diode (LED) is a new energy efficient option in the lighting sector that has in recent times been deployed extensively by the City of Cape Town’s Transport Network Operations Department. The technology promises superior attributes that include a longer lifespan and higher energy conversion efficiencies, when compared to the traditional incandescents and fluorescents. This paper details the achievements of the LED in its brief history in the local traffic and signals industry as well as its projected impact on the city traffic light department’s future energy and mainte-nance budget. It is then proposed that these mono-chromatic signal LEDs, which is fast evolving into a white LED, holds the best promise in Cape Town as well as the Western Cape’s energy future if adopted for general lighting in the domestic, commercial and industrial market.