Scielo RSS <![CDATA[Journal of Energy in Southern Africa]]> http://www.scielo.org.za/rss.php?pid=1021-447X20140002&lang=pt vol. 25 num. 2 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Challenges in household energisation and the poor</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2014000200001&lng=pt&nrm=iso&tlng=pt While the electrification of households in South Africa since 1994 has been impressive, many of the major energy services in poor households are still met by traditional fuels such as, on the Highveld, coal; in coastal regions, paraffin; and in rural areas by wood. Their use is associated with a range of challenges, from chronic respiratory tract infections to asphyxiation by carbon monoxide to massive fires that destroy not only homes but also lives. State interventions such as the provision of Free Basic Electricity are costly and do not appear to be contributing towards any solutions. The challenges are assessed, and a range of mitigations proposed. <![CDATA[<b>Design of a low voltage DC microgrid system for rural electrification in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2014000200002&lng=pt&nrm=iso&tlng=pt This project entails the design of a low voltage DC microgrid system for rural electrification in South Africa. Solar energy is freely available, environmental friendly and it is considered as a promising power generating source due to its availability and topological advantages for local power generation. Off-grid solar systems are perceived to be a viable means of power delivery to households in rural outlying areas in South Africa as solar panels can be used almost anywhere in the country. The design presented in this paper is based on the power demand estimation, photovoltaic panel selection, battery sizing and wire selection for the distribution system. <![CDATA[<b>South African renewable energy investment barriers: An investor perspective</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2014000200003&lng=pt&nrm=iso&tlng=pt As recently as the year 2010, renewable energy contributed less than 1% of all the energy sources in South Africa. Possible reasons include the lack of private sector investment in Renewable Energy technologies. By way of a structured interview methodology, this paper explores the reasons why private investors are reluctant to invest in renewables. The responses point to political, economic, social and technological barriers limiting private investment in renewable energy. Other barriers that were identified include poverty, low levels of education, limited technological readiness and access to the electricity grid. Some of these barriers are specific to the South African context. The paper concludes that a closer relationship between government and the private sector is required to stimulate innovation in the renewable energy sector. <![CDATA[<b>A PV power supply module for a portable Cubesat satellite ground station</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2014000200004&lng=pt&nrm=iso&tlng=pt This research focuses on the problem of powering a remote and mobile satellite ground station, where utility power is unavailable. It focuses on the use of photovoltaic energy, which is now widely accepted as an alternative source of energy. However, PV suffers from low conversion efficiency, non-linear I-V characteristics, which depend on temperature changes and the earth rotation. The research focuses on accurate determination of the ground station power budget whose total power demand involves an azimuth and rotator function and a current which varies depending on the stages of communication with the satellite. The power budget is used to determine the size, the ratings of solar generators, batteries and the system components. With the aid of a power logger, the PV voltage, the battery voltage, the AC voltage and PV power output is analysed for varying satellite loads. The data is analysed by taking into account the solar irradiation level on the day of measurement and the percentage cloud cover. This method is found to improve the reliability and can be adopted to improve reliability of standalone PV systems. The results are vital in PV power management and design. <![CDATA[<b>Optimization and effects of process variables on the production and properties of methyl ester biodiesel</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2014000200005&lng=pt&nrm=iso&tlng=pt Optimization of the production process in biodiesel production holds huge prospects. A reduced cost option is the optimization of process variables that affect yields and purity of biodiesel, which was achieved in this study. Optimized production and direct effects of process variables on the production and quality of methyl ester biodiesel fuels from the non-edible seed oils of sandbox seed was carried out. Catalyst nature and concentration, alcohol to triglyceride molar ratio, mixing speed, reaction time and temperature were taken into consideration as variables to their individual response on the yields, viscosity and specific gravity of the methyl esters produced. These are specific indispensable properties of biodiesel for use in compression ignition engines. Optimized concentrations were 0.3 to 1.5% w/v and two mole ratios of 3:1 and 6:1. Time of reaction was varied (5mins to 30mins) with temperatures (38oC and 55oC). Also, the effect of methanol in the range of 4:1and 6:1 (molar ratio) was investigated, keeping catalyst type, reaction time and temperatures constant. The effects of KOH and NaOH on the transesterification were investigated with concentration kept constant at 1%. The general response in this study was that at optimized rate of agitation (800rpm), optimized reaction time was as low as 5minutes, 1% catalyst concentration of NaOH was the optimal concentration, and 55oC was the optimal temperature with attendant high yields. However, there are variations with the nature of feedstock as the work further exposed. These high points are particularly of interest to guide against process backdrop. <![CDATA[<b>Voltage stability enhancement using an adaptive hysteresis controlled variable speed wind turbine driven EESG with MPPT</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2014000200006&lng=pt&nrm=iso&tlng=pt This paper investigates the enhancement in voltage stability achieved while connecting a variable speed wind turbine (VSWT) driven electrically excited synchronous generator (EESG) into power systems. The wind energy conversion system (WECS) uses an AC-DC-AC converter system with an uncontrolled rectifier, maximum power point tracking (MPPT) controlled dc-dc boost converter and adaptive hysteresis controlled voltage source converter (VSC). The MPPT controller senses the rectified voltage (VDC) and traces the maximum power point to effectively maximize the output power. With MPPT and adaptive hysteresis band current control in VSC, the DC link voltage is maintained constant under variable wind speeds and transient grid currents.The effectiveness of the proposed WECS in enhancing voltage stability is analysed on a standard IEEE 5 bus system, which includes examining the voltage magnitude, voltage collapse and reactive power injected by the systems. Simulation results show that the proposed WECS has the potential to improve the long-term voltage stability of the grid by injecting reactive power. The performance of this scheme is compared with a fixed speed squirrel cage induction generator (SCIG), a variable speed doubly-fed induction generator (DFIG) and a variable speed permanent magnet synchronous generator (PMSG). <![CDATA[<b>Use of hybrid solar-wind energy generation for remote area electrification in south-eastern Nigeria</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2014000200007&lng=pt&nrm=iso&tlng=pt This paper presents simulated hybridized solar-wind generation as an alternative for rural dwellers that do not have access to a conventional grid connection. Solar and wind were used as the main sources of energy with battery storage. Each power source has a DC-DC converter to control the power flow. An axial flux permanent magnet generator, which is suitable for a location with a low wind speed, was driven by the wind turbine. By using this generator, the efficiency of the system increased since certain losses were removed. The perturbation and observation method of MPPT is used to achieve maximum power extraction from the solar panel. The hybrid system was modelled in Matlab/Simulink software. A squirrel cage induction motor was used as the electrical load to the system load. The results obtained for the proposed hybrid system indicates that it can be used as an isolated power supply. By doing so, it improves the standard of living and hence, increasing total number of citizens using energy in the country. <![CDATA[<b>An analysis of the solar service provider industry in the Western Cape, South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2014000200008&lng=pt&nrm=iso&tlng=pt Scientists agree that rising electricity usage of the rapidly growing human race to improve its standard of living is negatively affecting the environment. To create a sustainable environment for future generations, renewable and environmentally friendly resources have to be exchanged for the present finite resources. In South Africa, coal plants are responsible for more than 90% of electricity production. This means that action has to be taken now to start a process of change to sustainable electricity resources. This paper focuses on the South African solar industry. Due to the high sun radiation levels, solar technology is one of the renewable energy sources with the greatest potential. The industry is in its infancy, characterised by accelerated growth expectancy and fuelled by factors such as government subsidies, the fluctuations of fossil fuel prices and the increasing focus on economical long-term sustainability. The expected growth necessitates a focus on the market positioning of solar service providers in the Western Cape, with the aim of taking full advantage of the opportunities associated with this industry. The main objective is to determine the current structure of the solar service provider value chain and subsequently areas of improvement to increase growth, stakeholder satisfaction and sustainability. A literature review was conducted to address the research objective, relevant approaches and the broader electricity industry. Porter's Value Chain approach was used as a foundation for the adaptation to the solar service provider value chain. Porter's Five Forces model was also used as a secondary approach, which analysed the competitive environment of the solar service provider industry in the Western Cape. The methodology entailed a qualitative research approach in the form of semi-structured interviews. All respondents were general managers or owners of a solar service provider, who were interviewed face to face. The research focused on the entire population of solar service providers in the Western Cape. Seventy-seven different service providers were targeted, of which 18 were interviewed. The interviews were transcribed and analysed using content and frequency analysis. To guarantee reliability, a pilot study was conducted to ensure that the respondents understood the questionnaire. The findings show that customer service is the foremost value driver for solar service providers. This entails the actual installation of the product as well as the people skills of the installation team. As most customers only have to be served once due to the long life span of the products, marketing also plays an obvious role in attracting new customers. The most important outcome of this paper is the determination and a better understanding of the solar service provider value chain in South Africa. The recommendations, especially with regard to marketing and service elements, could improve the performance of solar service providers. The consequence could be an increase in stakeholder satisfaction and an enhanced usage of solar energy in South Africa. Future research should focus on customers to reveal preferences and opportunities for marketing approaches. <![CDATA[<b>Performance of a compression ignition engine operated with sunflower ethyl ester under different engine loads</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2014000200009&lng=pt&nrm=iso&tlng=pt This study investigated the performance of a compression ignition engine operating with sunflower ethyl ester. A thermodynamic analysis, including energy and exergy analysis at different engine loads (20%, 40%, 60%, 80%, 100%), was conducted. The study calculated the first and second law efficiency, effective work, heat exergy losses and exergy destruction values at 10 different engine speeds for 5 loads. Maximum work, maximum thermal efficiency, maximum exergy efficiency and maximum volumetric efficiency are determined to be 6.45 kW, 0.26, 0.24 and 0.71 respectively. Finally, optimum operating conditions are discussed and it was determined that the engine should be operated at a lower engine speed for partial loads. <![CDATA[<b>A review on protective relays' developments and trends</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2014000200010&lng=pt&nrm=iso&tlng=pt One of the most complex disciplines in electrical engineering is power system protection which requires not only the proper understanding of the different components of a power system and their behaviours but also a good knowledge and analysis of the abnormal circumstances and failures that can occur in any element of a power system. Moreover, the rapid changing and development in relays principles as well as in their technologies are additional factors that oblige those people working in the field to expand and update continuously their knowledge. In this paper, we shed light in the evolution of protective relays since the onset of electrical energy to currently. We try also to foresee the future prospects and trends in this area. <![CDATA[<b>General aspects of carbon dioxide as a refrigerant</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2014000200011&lng=pt&nrm=iso&tlng=pt Carbon dioxide is an innocuous refrigerant for the environment. It is a substance of current interest in the refrigeration area. Its good thermodynamic and heat transfer properties have placed it in an excellent position for substituting refrigerants that contribute to global warming. This paper describes carbon dioxide as a refrigerant, the main characteristics that have made it a substance of current interest, its applications in subcritical and transcritical cycles, and a general vision of its usage at international level. Moreover, this paper presents the disadvantages of using this refrigerant and the upgrades made by the scientific community in order to improve the performance of those systems that work with this fluid. This paper is a reference for those interested in having a wider vision of frigorific technology based on carbon dioxide as a refrigerant. <![CDATA[<b>Investigation of fuel properties and engine analysis of Jatropha biodiesel of Kenyan origin</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2014000200012&lng=pt&nrm=iso&tlng=pt Biodiesel was produced from jatropha curcas oil of Kenyan origin through a two-step acid-base catalytic transesterification process. The relevant physico-chemical properties of the produced biodiesel were tested according to appropriate standards and were found to be within the requirements. Engine tests were carried out in an Audi, 1.9 litre, turbocharged direct injection, compression ignition engine at different loads. Emissions were measured by a Horiba emission analyser system while combustion data was collected by a data acquisition system, from which, cylinder pressure and rate of heat release of the test engine in every crank angle were calculated. Though the biodiesel had slightly higher brake specific fuel consumption when compared to fossil diesel, its emission behaviour was significantly better. The combustion characteristics were also slightly higher as compared to fossil diesel. This study therefore concluded that biodiesel derived from jat-ropha curcas of Kenyan origin can be utilized as a safe substitute for mineral diesel. <![CDATA[<b>A 2MW direct drive wind turbine; vector control and direct torque control techniques comparison</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2014000200013&lng=pt&nrm=iso&tlng=pt This paper presents a comparative study on the most popular control strategies used to control high power, Direct Drive Wind Turbines. The studied wind turbine is equipped with a supervision scheme in order to fulfil Grid connection requirements (GCR). For the generator-side converter, performances of the Field Oriented Control (FOC) and Direct Torque Control (DTC) are compared. Concerning the grid-side converter, Voltage Oriented Control (VOC) and Direct Power Control (DPC) are examined. The comparison is based on various criteria mainly, steady-state and transient performances. In addition, performances are evaluated in terms of low voltage ride through capabilities (LVRT), power limitation and reactive power control. It has been shown that best power quality features are given by vector control techniques. On the other hand, direct control offers the better dynamic response and power cross-coupling is substantially lower. Furthermore, during fault, the wind turbine does not trip for both techniques. However, vector control is better since it gives low power oscillations <![CDATA[<b>Erratum</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2014000200014&lng=pt&nrm=iso&tlng=pt This paper presents a comparative study on the most popular control strategies used to control high power, Direct Drive Wind Turbines. The studied wind turbine is equipped with a supervision scheme in order to fulfil Grid connection requirements (GCR). For the generator-side converter, performances of the Field Oriented Control (FOC) and Direct Torque Control (DTC) are compared. Concerning the grid-side converter, Voltage Oriented Control (VOC) and Direct Power Control (DPC) are examined. The comparison is based on various criteria mainly, steady-state and transient performances. In addition, performances are evaluated in terms of low voltage ride through capabilities (LVRT), power limitation and reactive power control. It has been shown that best power quality features are given by vector control techniques. On the other hand, direct control offers the better dynamic response and power cross-coupling is substantially lower. Furthermore, during fault, the wind turbine does not trip for both techniques. However, vector control is better since it gives low power oscillations