Scielo RSS <![CDATA[Journal of Energy in Southern Africa]]> vol. 23 num. 3 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>A techno-economic study of energy efficiency technologies for supermarkets in South Africa</b>]]> The food retail sector is energy intensive, consuming large amounts of electricity for refrigeration, air-conditioning and cooking. Retailers are aiming to reduce their electricity consumption in supermarkets and thus their carbon footprint using energy efficiency technologies. This paper reports on a techno-economic analysis of energy efficient technologies to recommend to the food retail sector for use in supermarkets. The targets and needs of food retail companies were surveyed and thereafter, the retailers were divided into three categories. Category 1 retailer had the highest targets for electricity and carbon reduction and was willing to take on more risk. Category 2 retailer had intermediate targets and would only use developed technologies, while category 3 retailer would only invest in developed technologies if they were proven to show significant long term saving with short pay back periods. The analysis showed that closed refrigerators had the highest electricity/carbon savings and the highest profit (NPV), followed by heat reclamation from refrigeration. Both these technologies were recommended for category 1 retailers. A combination of heat reclamation, energy efficient lights, fridge curtains, electronic controls for refrigerators and POS power management systems were recommended for category 3 retailers. A combination of the two recommendations was identified for category 2 retailers. Behavioural changes of all staff were identified as important for energy efficiency technologies to work at optimum levels. <![CDATA[<b>Efficiency and cost analysis of a designed in-line water heating system compared to a conventional water heating system in South Africa</b>]]> In this paper, the authors compares the efficiency and cost of a designed in-line water heating system with a conventional water heating system (geyser) in South Africa. The paper provides an overview on water heating systems and heating elements and provides the typical water consumption required by an average household in South Africa. A summary on the design of the in-line water heating system together with a system cost analysis is provided. The designed in-line water heating system takes the energy consumption, temperature and pressure into account during operation. The energy consumption and cost of the designed in-line water heating system is compared to a conventional water geyser. A cost analysis on the designed in-line water heating system, heat pumps and solar water heating systems are also provided. The energy consumption results showed that the conventional water geyser on average consumes 2.5% more energy to heat one litre of water from 15 °C to 60 °C, than the designed in-line water heating system to supply one litre of water at 60°C. <![CDATA[<b>Performance of A R22 split-air-conditioner when retrofitted with ozone friendly refrigerants (R410A and R417A)</b>]]> R22 that has been used predominantly in air conditioning and in medium and low-temperature applications contains ozone depleting chlorine atoms and hence will be phased out eventually. This paper presents the experimental performance study of a split-air-conditioner using ozone friendly alternative refrigerants. The existing split-air-conditioner originally designed for R22 as the working fluid was retrofitted with R410A and R417A respectively, and the performance of the system was evaluated and compared with its performance when R22 was used. Experimental results showed that with R417A, the system had 1.9% higher refrigeration capacity and 14.2% lower with R410A when compared to that of R22. The average discharge pressure of the compressor obtained with R417A and R410A were 3.8% lower and 10.3% higher, respectively, than with R22. The lowest compressor power consumption and pressure ratio were obtained with the R417A retrofitted system. The average coefficient of performance (COP) obtained using R417A is 2.9% higher, while that of R410A is 8.4% lower than that of R22. Generally, with R417A the system consistently had the best performance in comparison to both R22 and R410A, indicating that R417A would be a better choice for retrofitting existing split-air-conditioners originally designed to use R22 as working fluid. <![CDATA[<b>Regression-SARIMA modelling of daily peak electricity demand in South Africa</b>]]> In this paper, seasonal autoregressive integrated moving average (SARIMA) and regression with SARIMA errors (regression-SARIMA) models are developed to predict daily peak electricity demand in South Africa using data for the period 1996 to 2009. The performance of the developed models is evaluated by comparing them with Winter's triple exponential smoothing model. Empirical results from the study show that the SARIMA model produces more accurate short-term forecasts. The regression-SARIMA modelling framework captures important drivers of electricity demand. These results are important to decision makers, load forecasters and systems operators in load flow analysis and scheduling of electricity. <![CDATA[<b>Reliability worth assessment of electricity consumers: A South African case study</b>]]> This paper discusses the results obtained from a customer survey conducted in Cape Town, South Africa, using in-person interviews with approximately 275 sample business customers. The survey included customer interruption cost estimation questions based on the direct costing method. The results obtained show that customer interruption cost for business customers varies with duration and time of occurrence of power interruptions. The variation was shown to be dependent on customer segment. Furthermore, it revealed that business customers can be grouped in terms of the investment they make to mitigate the impact of power interruptions on their activities, such as the use of backup power supplies. <![CDATA[<b>Comparing performance of MLP and RBF neural network models for predicting South Africa's energy consumption</b>]]> In view of the close association between energy and economic growth, South Africa's aspirations for higher growth, more energy is required; formulating a long-term economic development plan and implementing an energy strategy for a country /industry necessitates establishing the correct relationship between energy and the economy. As insufficient energy or a lack thereof is reported to be a major cause of social and economic poverty, it is very important to select a model to forecast the consumption of energy reasonably accurately. This study presents techniques based on the development of multilayer perceptron (MLP) and radial basis function (RBF) of artificial neural network (ANN) models, for calculating the energy consumption of South Africa's industrial sector between 1993 and 2000. The approach examines the energy consumption in relation to the gross domestic product. The results indicate a strong agreement between model predictions and observed values, since the mean absolute percentage error is below 5%. When performance indices are compared, the RBF-based model is a more accurate predictor than the MLP model. <![CDATA[<b>Generation, characteristics and energy potential of solid municipal waste in Nigeria</b>]]> The generation, characteristics and energy potential of municipal solid waste for power generation in Nigeria is presented in this paper. Nigeria generates 0.44-0.66 kg/capita/day of MSW with a waste density of 200-400 kg/m³ leading to large volumes of poorly managed waste. The direct burning of these wastes as a waste management option in the open air at elevated temperatures liberates heat energy, inert gases and ash which can be conveniently used for power generation and other applications. The net energy yield depends upon the density and composition of the waste; relative percentage of moisture and inert materials, size and shape of the constituents and design of the combustion system. MSW samples used in this study were obtained randomly from different dump sites in selected state capitals, at least one from each of the six geopolitical zones in Nigeria based on the spot sampling method of Corbit. An average calorific value of 17.23 MJ/kg with variable high water content of 20-49% was determined for MSW using a bomb calorimeter and on the basis of an incineration plant of capacity 1500 ton of MSW/day, 700kW/day of power can be generated. <![CDATA[<b>A specification of a flywheel battery for a rural South African village</b>]]> The strong growth rates in the installed capacities of renewable energy technologies that have been posted in recent years demonstrate their capacity in the mitigation of green house gas emissions and climate change. The majority of these growths, however, have been realised in grid connected first world programs and do not require provision for energy storage. Most African rural areas are still far from the grid. Many upcoming developments such as cellular network repeater stations and health clinics must be operated from independent off grid PV installations. The intermittence of the resources dictates that reliable energy storage must be provided. The lead acid battery is currently the only available option but has well documented maintenance and disposal problems. The flywheel battery is an old technology that is re-emerging with a strong promise and could address the shortcomings of the lead acid battery. In this paper, a case study of a rural South African village load is depicted. Using a real utility database a possible specification for an electromechanical battery is derived. The authors further highlight the areas that will need future developments.