Scielo RSS <![CDATA[Journal of Energy in Southern Africa]]> vol. 30 num. 1 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Influences of microalgae biomass on the thermal behaviour of waste coal fines</b>]]> For this study, waste coal fines were treated with live microalgae slurry at varying biomass ratios to form coal-microalgae blends. The parent samples and the coal-microalgae blends were analysed for their proximate, ultimate and calorific values. Thermogravimetric experiments were performed on the parent samples and coal-microalgae blends under inert conditions. The aim was to investigate the effects of loading live microalgae slurry onto the waste coals with respect to the overall chemical and thermal characteristics of the coal. Based on the analysed results, the blending of microalgae slurry with coal has been shown to enhance thermal decomposition of coal. Coal-microalgae blends have a higher hydrogen content and volatile matter content than coal. Moreover, the presence of microalgae results in faster rates of decomposition at lower temperatures (200-400 °C), and lower residual mass fraction. The blending of microalgae slurries with waste coal appears to be suitable for enhancing the thermal reactivity of waste coal as well as improving the thermal conversion of waste coal. Highlights • Enhance the ignitability and thermal conversion of the waste coal • Systematic increase in the hydrogen content • 10% loadings improve the thermal degradation of coal. • Microalgae facilitates the conversion of coal fines • Volatiles driven-off from microalgae biomass <![CDATA[<b>A ray tracer model for analysis of solar concentrating systems</b>]]> This study describes a 3D ray tracer model for analysis of a small-scale solar concentrating system where thermal heat is collected for cooking purposes. Emitted sun rays were traced from the source through all reflections until they intercepted with the receiver or were lost. The algorithm of the ray tracer and its implementation in MATLAB is clearly described. The ray tracer was programmed to contribute to the development of small-scale concentrating solar energy systems with integrated heat storage units. The ray tracer was demonstrated for selected cases where continuous reflecting surfaces and flat mirror-tiled surfaces were compared. Off-focus sensitivity analysis was shown and this could provide guidelines for the required solar tracking accuracy. The flux distribution on the absorber was analysed and found to be concentrated on a small area on the target for continuous reflecting surfaces and having high intensities. However, for reflectors with mirror tiles, an elongated image was formed centred on the focal point with low intensities. Small misalignment of the reflector in the order 0.2° had minimal impact on the interception ratio, but any further increase in the tracking errors caused a sudden drop in the interception ratio to zero. Results showed that there is close agreement in flux distribution and the tracking error impact on interception ratio, when compared with the literature. This model could be a useful tool when designing the reflection and absorption components of solar concentrators for complex systems with several components in a non-symmetric 3D arrangement. Highlights • An algorithm for a ray tracer was developed • Enlarged images centred on the focal point were formed for mirror-tiled reflectors • Small misalignment of the reflector had minimum impact on the interception ratio • The tracer model could be used as a design tool <![CDATA[<b>Inferential based statistical indicators for the assessment of solar resource data</b>]]> The drive to reduce fossil fuel dependency led to a surge in interest in renewable energy as a replacement fuel source, which provided research opportunities for vastly different domains. Statistical modelling was used extensively to assist in research. This study applied two statistical techniques that can be used in conjunction or independently to existing methods to validate solar resource data simulated from models. The case study, using a database from a Southern African Universities Radiometric Network, provided illustrative benefits to the methods proposed, while comparing them with some of the validation methods currently used. It was demonstrated that profile analysis plots are easy to interpret, as deviations between modelled and measured data over time are clearly observed, while traditional validation scatter plots are unable to distinguish these deviations. Highlights 1. Identified new statistical techniques to compare measured and modelled solar radiation data. 2. Multivariate technique used to assess the shape and trend of solar radiation data. 3. Developed a method to calculate interval estimate plots for the assessment of modelled data. 4. Both proposed methods provide adequate support for solar resource reliability. <![CDATA[<b>Reactive power and harmonic compensation: A case study for the coal-mining industry</b>]]> This study reports on a case study in Grootegeluk Mine: Exxaro Coal, Lephalale, South Africa, in terms of power factor correction (PFC), load flow, harmonic frequency scans and harmonic voltage distortion analyses. The DIgSilent PowerFactory software was used for network simulations. Harmonic and reactive power compensation techniques were compared in terms of filter type evolution and technology advancement, with the use of simple trade-off criteria such as cost-effectiveness versus performance. It was found that both passive and hybrid filters were more favourable and could effectively compensate all voltage and current harmonics and reactive power for large nonlinear loads. The installation of switched PFC filter banks tuned at the fifth harmonic order accommodates future network growth and this solution can be rolled out to any mining industry as a benchmark to lower energy cost and maximise savings achievable on the electricity bill. <![CDATA[<b>Development of a large-area, low-cost solar water-heating system for South Africa with a high thermal energy collection capacity</b>]]> A low-cost heat-exchanger system that can be used in high-pressure/low-pressure isolated solar water-heating systems in South Africa was developed for household applications. The combination of a copper coil and electrical heater allowed for isolation of the high-pressure and low-pressure sections of the system and enabled the utilisation of large low-cost solar heat-absorber platforms that operated at low pressure with a low risk of fouling and leaking. The design comprised a copper coil heat exchanger to be installed inside a conventional geyser, to replace the normal heating element and thermostat system in a conventional commercially available household geyser. The electric heating element still supplements the system in low solar energy conditions. The circulation in the system is created by a small separate photovoltaic panel and a circulation pump. An integrated switch allows the system to alternate between conventional electrical heating and solar water-heating according to prevailing weather conditions. Current tests show that the system of 15 m² area can be installed at a cost of approximately ZAR 10 000-12 000. The system can provide hot water at approximately 12 cents per kWh, with a total heat storage capacity of up to 10 kWh per day. This implies a saving to the customer of up to ZAR 600 per month. The accumulated saving to a household over the ten-year lifetime of the product is estimated at ZAR 200 000. As the thermal energy storage capacity of current systems as available on the local market is approximately 1 kWh per day for a 2 m² collector. A typical increase in thermal energy collection capacity of tenfold more than the capability of conventional systems on the market is hence achieved. The system offers implementation possibilities for South Africa's low-cost housing schemes and can provide for creating numerous new business and job opporiunities on the African continent with its abundant solar irradiation resources.