Scielo RSS <![CDATA[Journal of Energy in Southern Africa]]> http://www.scielo.org.za/rss.php?pid=1021-447X20150001&lang=es vol. 26 num. 1 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>SAURAN: A new resource for solar radiometric data in Southern Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2015000100001&lng=es&nrm=iso&tlng=es A new resource for sun strength data in Southern Africa has been established with the commissioning of a regional network of solar monitoring stations. The Southern African Universities Radiometric Network (SAURAN) is an initiative of Stellenbosch University and the University of KwaZulu-Natal (UKZN), and consists of an initial set of ten ground stations equipped with secondary standard thermopile radiometers. SAURAN's aim is to provide a long-term record of sun strength in a region that shows excellent potential for the deployment of solar energy technologies. Instruments measuring direct normal irradiance (DNI), diffuse horizontal irradiance (DHI) and global horizontal irradiance (GHI) feed time-averaged data over 1-minute, hourly and daily intervals to a central archive from where they are accessible to the public via a website interface. Meteorological data is also provided by most of the stations. This paper gives a brief background to the SAURAN project and describes the network's operation, coverage and future expansion. Examples of solar energy irradiance plots are also provided to illustrate the information available from the SAURAN database. <![CDATA[<b>The inter-relationships between regulation and competition enforcement in the South African liquid fuels industry</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2015000100002&lng=es&nrm=iso&tlng=es The competition authorities have devoted considerable time and energy to investigating anticompetitive conduct in the broad area of liquid fuel, gas and related products, where regulation sets rules for firm conduct. Competition cases have included the Sasol-Engen merger, collusive arrangements in gas distribution and the pricing of bitumen for road construction projects, and alleged coordination through information exchange in diesel. Drawing on a review of these matters we assess the inter-relationships between regulation and competition enforcement. We argue that regulation can be designed to enable greater competitive rivalry, while anti-competitive conduct can also be better remedied through recognition of the role of regulation. <![CDATA[<b>Investigation of common-mode voltage and ground leakage current of grid-connected transformerless PV inverter topology</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2015000100003&lng=es&nrm=iso&tlng=es The problems of increasing electricity demand by the unabated population and economy growth can be solved by employing sustainable distributed generation technologies. Convectional primary energy sources such as coal, liquid hydrocarbons' and natural gasses create environmental degradation and energy security problems. Even though the cost of solar energy is zero, the same cannot be said of a solar energy system. The system cost especially the initial capital investment has been hindering the rapid deployment of solar energy systems. One way of reducing the system cost of a solar energy system is to look into the constituent components and see where cost can be reduced without compromising the system efficiency and human safety. Eliminating the isolation transformer reduces the cost and increases the system overall efficiency. However, the galvanic connection between the PV array and the utility grid creates a safety problem for people and system equipment. We present a simplified model for the investigation of the common mode voltage and ground leakage current that can lead to electromagnetic interference. The leakage current level is used for the determination of the suitability of the investigated PV inverter topology for grid connection without isolation transformer. <![CDATA[<b>New markets for renewable industries: Developing countries - Turkey, its potential and policies</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2015000100004&lng=es&nrm=iso&tlng=es For today's world, energy is a huge requirement for economic, industrial and social life. The necessity of energy is increasing quite rapidly to keep pace with the technological and economical advancements and this brings about many energy problems like, dependence on energy importation, environmental pollution, global warming, increasing cost of energy expenses and inefficiency in energy use etc. Countries are working very hard to solve these problems. To supply the energy needs and protect our planet's future safety, it is very important to generate clean energies. In this context, governments give huge amounts of incentives for renewable energy generations and support related investments in many countries. In this study, the importance of renewable energy usage, recent incentives, renewable energy policies in Turkey and some developed countries are investigated and compared. It is also aimed to examine the real situation of renewables in Turkey by giving the latest numbers and make a contribution of future developments for these clean energies in Turkey. In this regard, some barriers and recommendations are also submitted. <![CDATA[<b>Production of biodiesel from chicken wastes by various alcohol-catalyst combinations</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2015000100005&lng=es&nrm=iso&tlng=es An environmentally friendly biorefinery process for producing biodiesel from chicken wastes was performed for this study. Low acid value (0.13±0.01 mg KOH/g) chicken oil was obtained by preparing chicken wastes with moderate heating and filtration processes that minimized damage to the lipids and thus facilitated subsequent reactions. Methanol-lipids in a molar ratio of 6:1 and a methanol-ethanol-lipids mixture in a molar ratio of 3:3:1 were both reacted with 1% KOH catalyst for transesterfication. Furthermore, ethanol-lipids in a molar ration of 6:1 were analogously transesterified with 1% sodium ethoxide. The amounts of biodiesel were 771.54 mg/mL±15.28, 722.98 mg/mL±37.38, and 714.86 mg/ mL±29.99 from methanol, ethanol, and a mixture of methanol/ethanol (3:3), respectively, after transesterification. The total amount of ethyl ester was comparable with the total amount of methyl ester. In addition, ethanol is a renewable resource and a biorefinery concept can be contributed for biodiesel production. Furthermore, transesterification of chicken oil with a mixture of methanol/ethanol (3:3) only needed a relatively short reaction time of an hour. Densities, viscosities, sulphur contents, acid values, and flash points of all esters were within the specifications of CNS 15072 and EN 14214. The transesterification system for chicken oil in ethanol and mixed methanol/ethanol (3:3) demonstrated in this study is a potential candidate for biodiesel production. <![CDATA[<b>Aggregate and regional demand for electricity in Malaysia</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2015000100006&lng=es&nrm=iso&tlng=es The main objective of this paper is the analysis of electricity consumption in Malaysia as a whole and its three regions, namely, Peninsular Malaysia, Sabah and Sarawak. This analysis has been carried out using distinguished data in sectoral level for 44 quarters (2000Q1-2010Q4). For this purpose, two log-log static and dynamic panel demand functions are estimated. The dynamic model, which is based on a partial adjustment approach, is used to compare with the static model. The aggregate and the three regional models are estimated based on their economic sectors in both the dynamic and static methods. This study seeks to reveal some features of electricity consumption in Malaysia and its regions. It is found that the short and long- run price elasticities of electricity demand in all regions of Malaysia are inelastic. Consumers' responsiveness to changes in electricity prices in the short-run is low, while they have a high response to the long-run changes in the entire Malaysian economy and its regions. This means that, while the short and long-run price elasticities of electricity demand are lower than one, the magnitudes of the long-run elasticities are greater than the short-run elasticities. Moreover, all elasticities in the dynamic models are smaller than the static models. The estimated short and long-run cross-price elasticities of Liquefied Petroleum Gas (LPG) are negative which suggests that LPG and electricity are complementary goods. <![CDATA[<b>Optimization analysis of solar-powered average temperature Stirling heat engine</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2015000100007&lng=es&nrm=iso&tlng=es This paper investigates the performance of the solar powered dish-Stirling engine using the non-linearized heat loss model of the solar dish collector and the irreversible cycle model of the Stirling engine. Finite time thermodynamic analysis is used to investigate the influence of the finite-rate heat transfer, operating temperatures, heat leak coefficient, and ratio of volume during regeneration processes, regenerator losses, thermal bridges losses on the maximum power output and the corresponding overall efficiency. The maximum overall system efficiency is 32% corresponding to absorber temperature and concentrating ratio of 850 K and 1300, respectively. The present analysis provides the basis for the design of a solar-powered mean temperature differential Stirling engine powered by solar dish system. <![CDATA[<b>Decomposition analysis of energy-related CO<sub>2</sub> emissions in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2015000100008&lng=es&nrm=iso&tlng=es South Africa has become one of the most developing countries in the world, and its economic growth has occurred along with rising energy-related CO2 emission levels. A deeper understanding of the driving forces governing energy-related CO2 emissions is very important in formulating future policies. The LMDI (Log Mean Divisia Index) method is used to analyse the contribution of the factors which influence energy-related CO2 emissions in South Africa over the period 1993-2011. The main conclusions drawn from the present study may be summarized as follows: the energy intensity effect plays the dominant role in decreasing of CO2 emission, followed by fossil energy structure effect and renewable energy structure effect; the economic activity is a critical factor in the growth of energy-related CO2 emission in South Africa. <![CDATA[<b>Assessing possible energy potential in a food and beverage industry: Application of the IDA-ANN-DEA approach</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2015000100009&lng=es&nrm=iso&tlng=es In the food and beverage industry, where growing, processing, packaging, distribution, storage, preparation, serving and disposing of food is the order of the day; energy consumption becomes an important input. Various energy models have been developed since the early 1970s, the period when energy caught the attention of policymakers due to the sudden price increase. Among the models are the index decomposition analysis (IDA), artificial neural network (ANN) and data envelopment analysis (DEA). The purpose of this study is to combine the strengths of these models, i.e., IDA, ANN and DEA, to allow biases in one model to offset biases in the other, so as to examine the effectiveness of energy management policies in a particular food and beverage industry. The integrated model applied to the food and beverage revealed that approximately 11% of energy consumed could be saved. <![CDATA[<b>Are solar tracking technologies feasible for domestic applications in rural tropical Africa?</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2015000100010&lng=es&nrm=iso&tlng=es That solar tracking improves energy yields from solar harvest systems is not debatable. Nor is the under powering of tropical Africa amidst plenty of energy resources - including solar. This paper presents a review of recent literature on tracking as applied to domestic solar harnessing devices. The purpose is to find basic requirements in design of a suitable solar tracker for the region's rural homes. It is concluded that Single axis passive trackers possibly will stand better chances of acceptability in the region. <![CDATA[<b>Performance optimization of an air source heat pump water heater using mathematical modelling</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2015000100011&lng=es&nrm=iso&tlng=es In South Africa, there is an ongoing constraint on the electricity supply at the national grid to meet the demand. Eskom is implementing various measures such as the Integrated Demand Management and the promotion and encouragement of the use of energy efficient devices like an Air Source Heat pump (ASHP) water heater to replace the high electrical energy consuming conventional geysers for sanitary hot water production. The ASHP water heater market is fast gaining maturity. A critical mathematical model can lead to performance optimization of the systems that will further result in the conservation of energy and significant reduction in global warming potential. The ASHP water heater comprises of an ASHP unit and a hot water storage tank. In this study, a data acquisition system (DAS) was designed and built which monitored the energy used by the geyser and the whole building, the temperature at the evaporator, condenser, tank outlet hot water, tank inlet cold water, the ambient temperature and relative humidity in the vicinity of the ASHP evaporator. It is also worthy to mention that the DAS also included to a flow meter and two additional temperature sensors that measured the volume of water heated and inlet and outlet water temperature of the ASHP. This work focused on using the mathematical equation for the Coefficient of Performance (COP) of an ideal Carnot's heat pump (CHP) water heater to develop basic computation in M-file of MATLAB software in order to model the system based on two reservoir temperatures: evaporator temperatures (Tevp) of 0°C to 40°C (approximated to ambient temperature, Ta) and condenser temperatures (T Con) set at 50°C, 55°C and 60°C (approximated to the hot water set temperature of 50°C, 55°C and 60°C) respectively. Finally, an analytical comparison of a CHP water heater to the practical ASHP water heater was conducted on a hot water set point temperature of 55°C. From the modelling results, it can be deduced that at 0°C Tevp, the COP was 5.96 and 2.63 for CHP and ASHP water heater respectively, at a hot water set temperature of 55°C. Above 20°C Tevp, the rate of change of COP increased exponentially for the ideal CHP system, but was constant at 0.01/°C for the practically modelled ASHP water heater. <![CDATA[<b>Performance of an autonomous solar powered absorption air conditioning system</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2015000100012&lng=es&nrm=iso&tlng=es The demand for air conditioning is increasing due to changing architectural trends and increased standards of living and indoor comfort conditions. Coupled to this, refrigerants used in conventional refrigeration systems have detrimental effects on the environment. As a result, there is an urgent need to implement environmentally cleaner ways of satisfying this air-conditioning demand. Absorption cooling systems have shown great potential to do so. In this study, system performance data for an autonomous solar heating and cooling system installed at the Vodafone Site System Innovation Centre, at the Vodacom Campus in Midrand was collected and analysed. The system comprises a 116 m² vacuum tube collector array, a 6.5 m³ hot water storage tank, a 35 kW LiBr-Water absorption chiller, 1 m³ of cold water storage, a dry cooler for the chiller, and two underground thermal stores to pre-cool the supply air to the building and the dry cooler respectively. System performance data was collected from the beginning of December 2011 to the end of January 2012 and used to estimate the system long term performance. The chiller has an average coefficient of performance (COP) of 0.51 whilst the solar COP has an average value of 0.24. The total installation cost is R2 822 436.89, with an annuity of R225 949.75 and a cost per kWh of R28.88. <![CDATA[<b>Theoretical investigation of a combined Kalina and vapour-absorption cycle</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2015000100013&lng=es&nrm=iso&tlng=es A program has been developed to calculate enthalpies at the salient points (later referred to as stations) of a combined power and cooling cycle provided pressure, temperature, mixture concentration and condition are known at these points. The ammonia-water mixture, which is taken as the working fluid, may be at one of the following seven conditions namely, superheated vapour mixture, mixture of superheated component of ammonia and pseudo vapour component of water, saturated vapour mixture, wet vapour mixture, saturated liquid mixture, mixture of subcooled water and pseudo liquid ammonia and subcooled mixture of sub-cooled components of ammonia and water. The mixture boiling-point temperature and dew-point temperature, needed to establish the condition of the working fluid, are functions of absolute pressure, critical pressure and critical temperature of the mixture; later two depend on the mixture concentration and the corresponding critical values of water at the given station. Using typical values of the variables as listed above, enthalpies at all stations are predicted. The predicted enthalpies are close (within 3%) to those available in the literature except at two stations where the mixture was weak in ammonia and its temperature was either in the near vicinity of the mixture boiling-point temperature or below the saturation temperature of pure ammonia at the concerned pressure. Using the predicted values of enthalpies, thermal efficiency of the combined power and cooling cycle has been calculated. <![CDATA[<b>A comparative study of the stochastic models and harmonically coupled stochastic models in the analysis and forecasting of solar radiation data</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-447X2015000100014&lng=es&nrm=iso&tlng=es Extra-terrestrially, there is no stochasticity in the solar irradiance, hence deterministic models are often used to model this data. At ground level, the Box-Jenkins Seasonal/Non-seasonal Autoregressive Integrated Moving Average (S/ARIMA) short memory stochastic models have been used to model such data with some degree of success. This success is attributable to its ability to capture the stochastic component of the irradiance series due to the effects of the ever-changing atmospheric conditions. However, irradiance data recorded at the earth's surface is rarely entirely stochastic but a mixture of both deterministic and stochastic components. One plausible modelling procedure is to couple sinusoidal predictors at determined harmonic (Fourier) frequencies to capture the inherent periodicities (seasonalities) due to the diurnal cycle, with SARI-MA models capturing the stochastic components. We construct such models which we term, harmonically coupled SARIMA (HCSARIMA) models and use them to empirically model the global horizontal irradiance (GHI) recorded at the earth's surface. Comparison of the two classes of models shows that HCSARIMA models generally out-compete SARI-MA models in the forecasting arena.