Scielo RSS <![CDATA[Journal of Energy in Southern Africa]]> vol. 24 num. 4 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>A cost-benefit analysis of concentrator photovoltaic technology use in South Africa: A case study</b>]]> The South African Government currently faces the dual problems of climate change mitigation and the rollout of electricity provision to rural, previously disadvantaged communities. This paper investigates the economic efficiency of the implementation of concentrator photovoltaic (CPV) technology in the Tyefu area in the Eastern Cape, South Africa, as a means of addressing these problems. Two cost-benefit analyses (CBA) are carried out in the study, namely a private CBA and a social CBA. The private CBA investigates the desirability of the CPV project from a private energy investor's perspective, whilst the social CBA investigates the desirability of the CPV project from society's perspective. The social CBA found that the project was socially viable and was, thus, an efficient allocation of government resources. The private CBA, on the other hand, found that investing in a CPV project was not financially viable for a private investor. With respect to the incentive scheme currently offered to private energy investors, it is recommended that the maximum bidding price of R2.85/kWh be increased. A sensitivity analysis of the bidding price showed that an increase of 300% is required to attract private investors into electricity generation projects. <![CDATA[<b>A possible design and justification for a biogas plant at Nyazura Adventist High School, Rusape, Zimbabwe</b>]]> The research study was carried out to assess the biogas potential at Nyazura Adventist High School, Rusape, Zimbabwe, a co-educational school with a total enrolment of 700 boarders. The school is connected to the national grid electricity. The electricity is in short supply due to long hours of load shedding. Firewood to be used for heating and cooking purposes is in short supply. The main objective of the study was to make an assessment of biogas potential at the school. The energy demand for the whole school was calculated and it was found to be 2 710 kWh per day. The biogas yields for the feedstocks at the school were estimated. The total biogas yield that could be obtained from the feedstocks was 50 m3 per day. The digesters volume for the feedstocks was estimated and the material requirements for the digesters were also determined. The techno-economic analysis of the proposed project was done. The results suggested that the proposed project was feasible, and it was concluded that the school is capable of producing enough biogas from its feedstocks to support a feasible project. The daily 50 m3 biogas yield is adequate to supply enough electricity for lighting purposes during the load shedding periods. <![CDATA[<b>Critical factors to be considered when planning the implementation of environmental improvements and energy saving</b>]]> To identify the critical success factors in the adoption of energy efficiency actions in Brazilian hospitals and describe their behaviour are the objectives of this paper. In order to achieve these goals, a literature review was performed on green management and energy efficiency. This was the basis to define the questions of the interview script applied to two hospitals located in the state of São Paulo, Brazil. The interview script application was complemented by secondary data and direct observation. The results showed that: a) the studied hospitals are embracing environmental management actions more often and, whenever possible, energy efficiency actions are taken as well; and b) in the cases analysed top management support, commitment with the environment, green process design and employee empowerment were some of the most relevant critical success factors to the accomplishment of energy efficiency actions. These findings may be of interest to emerging countries, including BRICS (Brazil, Russia, India, China and South Africa). <![CDATA[<b>Emissions analysis from combustion of eco-fuel briquettes for domestic applications</b>]]> In this study, flue gas emissions from combustion of eco-fuel briquettes in a ceramic lined stove were investigated. The eco-fuel briquettes were made of biomass such as spent coffee beans, mielie husks, saw dust, paper pulp and coal fines using a hand operated screw press. A combustion set-up consisting of digital weightometer, a ceramic lined stove and a complete chimney system was used. The emissions from the combustion process were measured using a Testo 350 gas analyser linked to the chimney system. The eco-fuel briquettes made from a mixture of biomass and coal fines burnt within the acceptable exposure limits as set out by the Occupational Safety and Health Agency (OSHA). The flue gas emissions from the combustion of eco-fuel briquettes were found to contain 74 parts per million (ppm) carbon monoxide (CO), 4.32 ppm hydrogen sulphide (H2S), 1.34ppm nitrogen oxides (NOx) and 3.67 ppm sulphur oxides (SOx). The measured gross calorific value was 18.9MJ/kg, with a burning rate of 2g/min. These properties make eco-fuel briquettes suitable for domestic applications. A survey conducted as part of this study also revealed a significant demand for eco-fuel briquettes in many informal settlements in Gauteng Province, South Africa, at a competitive selling price of R2.60/kg. <![CDATA[<b>Experimental study on natural convection greenhouse drying of papad</b>]]> In this paper, the convective heat transfer coefficients of papad for greenhouse drying under a natural convection mode are reported. Various experiments were conducted during the month of April 2010 at Guru Jambheshwar University of Science and Technology Hisar, India (29º5'5" N 75º45'55" E). Experimental data obtained for the natural convection greenhouse drying of papad was used to evaluate the constants in the Nusselt number expression by using simple linear regression analysis. These values of the constant were used further to determine the values of the convective heat transfer coefficient. The average value of a convective heat transfer coefficient was determined as 1.23 W/m2oC. The experimental error in terms of percent uncertainty was also evaluated. <![CDATA[<b>Dirt analysis on the performance of an engine cooling system</b>]]> This present work looked at the effect of sand blocking the heat transfer area of the radiator and its effect on the engine coolant through the conduct of experiments and a mathematical model developed. The results indicated that the percentage area covered resulted in a proportional increase of the inlet and outlet temperatures of the coolant in the radiator. The mathematically model developed also predicted the experimental data very well. Regression analysis pointed out that every 10% increase area of the radiator covered with silt soil resulted in an increase of about 1.7ºC of the outlet temperature of the radiator coolant. Similarly, using mud as a cover material, 10% of the area covered of the radiator resulted in an increase of about 2ºC of the outlet temperature of the radiator coolant. Statistical analysis pointed to the fact that the result obtained for mud, silt and the mathematical model were not significantly different. Thus, irrespective of the type of material that blocks the radiator surface area, the coolant rises proportional of the radiator covered. <![CDATA[<b>System and component modelling of a low temperature solar thermal energy conversion cycle</b>]]> Solar thermal energy (STE) technology refers to the conversion of solar energy to readily usable energy forms. The most important component of a STE technology is the collectors; these absorb the shorter wavelength solar energy (400-700nm) and convert it into usable, longer wavelength (about 10 times as long) heat energy. Depending on the quality (temperature and intensity) of the resulting thermal energy, further conversions to other energy forms such as electrical power may follow. Currently some high temperature STE technologies for electricity production have attained technical maturity; technologies such as parabolic dish (commercially available), parabolic trough and power tower are only hindered by unfavourable market factors including high maintenance and operating costs. Low temperature STEs have so far been restricted to water and space heating; however, owing to their lower running costs and almost maintenance free operation, although operating at lower efficiencies, may hold a key to future wider usage of solar energy. Low temperature STE conversion technology typically uses flat plate and low concentrating collectors such as parabolic troughs to harness solar energy for conversion to mechanical and/or electrical energy. These collector systems are relatively cheaper, simpler in construction and easier to operate due to the absence of complex solar tracking equipment. Low temperature STEs operate within temperatures ranges below 300oC. This research work is geared towards developing feasible low temperature STE conversion technology for electrical power generation. Preliminary small-scale concept plants have been designed at 500Wp and 10KWp. Mathematical models of the plant systems have been developed and simulated on the EES (Engineering Equation Solver) platform. Fourteen candidate working fluids and three cycle configurations have been analysed with the models. The analyses included a logic model selector through which an optimal conversion cycle configuration and working fluid mix was established. This was followed by detailed plant component modelling; the detailed component model for the solar field was completed and was based on 2-dimensional segmented thermal network, heat transfer and thermo fluid dynamics analyses. Input data such as solar insolation, ambient temperature and wind speed were obtained from the national meteorology databases. Detailed models of the other cycle components are to follow in next stage of the research. This paper presents findings of the system and solar field component. <![CDATA[<b>Modelling influence of temperature on daily peak electricity demand in South Africa</b>]]> The paper discusses the modelling of the influence of temperature on average daily electricity demand in South Africa using a piecewise linear regression model and the generalized extreme value theory approach for the period - 2000 to 2010. Empirical results show that electricity demand in South Africa is highly sensitive to cold temperatures. Extreme low average daily temperatures of the order of 8.20C are very rare in South Africa. They only occur about 8 times in a year and result in huge increases in electricity demand. <![CDATA[<b>Performance analysis of an air humidifier integrated gas turbine with film air cooling of turbine blade</b>]]> A computational analysis to investigate the effects of compressor pressure ratio, turbine inlet temperature, ambient relative humidity and ambient temperature on the performance parameters of an air cooled gas turbine cycle with evaporative cooling of inlet air has been presented. The blade cooling method selected is film cooling. The analysis indicates that the mass of coolant required for blade cooling is reduced with increase in temperature drop across the humidifier. Both decrease in ambient temperature and ambient relative humidity results in an increase in plant efficiency and plant specific work. The highest efficiency is obtained at a turbine inlet temperature of 1500 K for all range of ambient relative humidity and ambient temperature, beyond which it decreases. The compressor pressure ratio corresponding to the maximum plant specific work, however, varies with both ambient relative humidity and ambient temperature. The increase in specific work due to drop in ambient relative humidity is more pronounced at higher pressure ratios. Similarly, the increase in efficiency due to ambient temperature drop is prominent at higher turbine inlet temperatures. Finally, a design nomograph is presented to select the design parameters corresponding to best efficiency and specific work.