Browsing by Subject "Sustainable Energy Engineering"
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- ItemOpen AccessAn analysis of annual environmental conditions and heat gains, and theoretical assessment of approaches to improve summer thermal comfort, of the Energy Research Centre at the University of Cape Town(2017) Cunliffe, Guy Edward; Hibberd, Andrew; Moorlach, MaschaThe Energy Research Centre (ERC), a research centre located at the University of Cape Town (UCT), is considering retrofitting its offices with measures to improve its occupants' thermal comfort, particularly during Cape Town's summer months. While a simple solution would be to install an active cooling system, first consideration should be given to the deployment of preventative cooling measures and retrofits. By these means, the costs of an active cooling system would be reduced, as well as the building's relative increase in energy consumption and indirect greenhouse gas emissions. This dissertation examines internal thermal conditions of the ERC under current building conditions and predicts levels of thermal discomfort likely to be experienced by occupants, with emphasis on Cape Town's summer season. Heat gain components to the ERC are quantified, and a Base Case cooling scenario is determined; this characterises the peak cooling load and active annual cooling energy required to alleviate summer thermal discomfort, if no other interventions are implemented. Thereafter, the impacts of a selection of preventative cooling measures on the Base Case cooling scenario are assessed, and a theoretical payback period for each progressive measure is evaluated, relative to projected installation and operational costs of an active system designed to meet the Base Case. A model of the ERC offices is developed in DesignBuilder, which characterises thermal properties of the building envelope, thermal loads of lighting, electronic equipment and building occupants, and effects of prevailing weather patterns and solar radiation at the site of the building. Physical energy simulations of the model are run in EnergyPlus, which uses a series of algorithms based on the Heat Balance Method to quantify internal psychrometric conditions and heat gains in half-hourly iterations. An EnergyPlus Ideal Loads Air System component is input into the simulation to quantify the active cooling load required to maintain comfortable design conditions. The results indicate that 7 814.5 hours of thermal discomfort are experienced annually across the ERC (divided into eight thermal zones in the DesignBuilder model), with 37.6% of discomfort hours occurring between December and March, and 12.8% in February alone. Notably, a greater proportion of discomfort hours, 38.9%, were predicted for winter months (June through August). However winter thermal discomfort was not addressed in detail here, as the scope of the dissertation was limited to analysing ERC cooling only. Solar gains through external windows were found to be the largest single source of annual heat gain (20.65 MWhth), followed by heat gains due to lighting heat emissions (19.99 MWhth). Profiles during typical summer conditions showed significant heat gain also arises from conduction through the ceiling, due to existing but sporadic and thin layers of fibreglass ceiling insulation, with gaps that allow thermal bridging between the roof space and ERC thermal zones. The Base Case annual cooling requirements were determined to be 27.64 MWhth, while peak cooling load was found to be 66.87 kWth. Sensible cooling dominated total cooling loads in summer months. East and west facing thermal zones required the greatest cooling energy (normalised per floor area), having been shown to experience the greatest normalised solar and lighting heat gains. Inclusion of a 75 mm polyester fibre insulation layer above the ceiling boards would result in a 13.6% decrease in annual discomfort hours, relative to the current building condition, and reduced peak cooling load by 19% relative to the Base Case. Increasing thickness above 75 mm resulted in increased ceiling thermal resistance and further reduced annual discomfort hours. However, the marginal improvements in thermal comfort were found to decrease with increased insulation thickness. A 75 mm thickness of polyester fibre insulation was therefore selected as the first preventative measure to be considered for the ERC, and was included in all further assessment of additional preventative options. Lighting retrofits were also considered, by means of two progressive measures: Delamping – the removal of fluorescent luminaires from overly lit thermal zones – and Relamping – replacement of remaining fluorescents and light fixtures with more energy efficient technology (as well as the Delamping and Insulation measures). Delamping was found, from simulation analysis, to reduce lighting heat gains by 31%, relative to the Base Case and annual cooling requirements by 24%, with total projected costs after 10 years reduced by 15.6% relative to the Base Case. Relamping had a less pronounced impact on cooling requirements, but resulted in 15 % lower lighting energy use compared to Delamping only. The final measure considered was a Shading measure, whereby the replacement of the existing solar window film, currently fitted to each of the ERC's external windows, with internal adjustable shading. The Shading retrofit (in addition to all previous preventative measures) was found to cause a 35% reduction in annual cooling energy relative to the Base Case, as well as a 7% relative to the Relamping scenario. However, cost evaluation showed that costs of implementing the Shading retrofit significantly outweighed net incremental annual savings achieved under the measure, and was thus not recommended as a preventative option for the ERC. Alternative shading options, such as fixed external shading, may prove more cost effective in mitigating the ERC's solar heat gains, and should be considered in further research. From these results, it was concluded that a combination of insulation and lighting upgrades would provide the greatest benefit, in terms of thermal comfort, to the ERC, and would result in a more cost effective active cooling system, should one be proposed. The dissertation ended with recommendations for further work, including further analysis of ERC heating requirements in winter, and investigation into additional and alternative cooling methods, such as passive or solar cooling.
- ItemOpen AccessAssessing the energy implications of exploiting stormwater, through artificial aquifer recharge, as an alternative water source in the Cape Flats, South Africa(2018) Gobin, Aumashvini; Sparks, Debbie; Ahjum, Fadiel; Armitage, Neil PSouth Africa has been facing challenges in both its energy and water sectors over the past few years. They are heavily dependent on each other and a better understanding of the linkages between the two sectors is crucial for sustainable development and planning in both sectors. While the water-energy nexus has been widely explored in developed countries, there is a limited amount of literature found on the significance of the nexus in South Africa. With the current critical drought in the region, alternative water sources are being considered by the City of Cape Town including seawater desalination, water re-use and abstraction of groundwater, to increase potable water supplies. The Cape Flats Aquifer represents a significant water resource for Cape Town and its yield can be further augmented by using artificial recharge with stormwater. Due to the location and water quality of the resource, several possible approaches have been identified for its exploitation. This study investigates quantitatively the energy implications of the three selected approaches in order to exploit the Cape Flats Aquifer as an alternative water source for Cape Town and further provides the potential carbon emissions from their respective energy usages. The three approaches consist of a Centralised Approach to treat the abstracted water for potable uses at two existing Water Treatment Plants (Blackheath and Faure); a Decentralised Approach to supply neighbouring suburbs with minimally treated water for non-potable uses through four proposed treatment plants and a Desalination Approach to treat brackish groundwater to potable quality at a proposed desalination plant. The energy implications of the approaches were evaluated using both direct energy usage during the abstraction, conveyance and treatment stages and the embodied energy of the consumables used during the treatment processes. These were then used to compare the shares of direct electricity intensities and embodied energy intensities of the alternatives at each stage to determine their viability. The individual stages' and overall energy intensities were quantified in form of the total energy required to produce a kl of treated water. The minimum energy required to abstract and convey the water was estimated using basic hydraulic principles. The energy usage at treatment plant levels was computed using the installed electrical capacities at the two existing water treatments for the Centralised Approach while the Decentralised Approach's demand was estimated by determining the treatment processes required to produce non-potable water, which is fit for usage. Energy requirements at the desalination plant were estimated using the salinity levels of the brackish groundwater and target salinity concentration of the treated water. The energy intensities of the approaches were then used as a basis to calculate the current and future electricity costs and their associated carbon footprints using the CSIR (2016) least cost scenario and the IRP (2016) base case future electricity mixes, as the higher and lower threshold for electricity generation costs and carbon emissions. The study found that the electricity intensities of all three alternatives depended significantly on the spatial layout of their respective systems, that is, the topography, distance and extent of their transmission networks. However, the embodied energy intensity of the Centralised alternative was found to be comparable to its electricity intensity, since more chemicals were to purify the water to potable levels. The Decentralised Approach's extensive pumped transmission networks contributed the most to its electricity intensity during the treatment process. The Desalination option was found to be the most energy intensive alternative, with energy intensities ranging from 7.41 to 9.62 MJ/kl, of all three options (1.16 to 1.57 MJ/kl for the Centralised Approach and 3.57 to 7.31 MJ/kl for the Decentralised Approach) and had the highest costs and emissions intensities, mostly caused by the country's coal intensive electricity mix. The Centralised option was found to be the least energy and carbon intensive of the three options and the most viable approach investigated. Desalination, nonetheless, can still considered as an alternative, given the issue of water scarcity, to increase water supplies. Despite its high energy demands, its carbon footprint could potentially decrease with a larger uptake of renewable energy technologies as sources of electricity. The importance of holistic planning across sectors was brought out quantitatively by using current and future water and energy mixes, providing valuable insights on the water-energy nexus, in this study.
- ItemOpen AccessAssessing the potential for urban wind energy in Cape Town(2018) Gough, Matthew Brian; Madhlopa, Amos; Khan, Mohamed AzeemAs the demand for alternative and renewable sources of energy grows worldwide, it has been argued that small-scale Urban Wind Energy (UWE) could have the potential to provide a significant portion of the electricity demand for urban areas. However there is currently a lack of knowledge surrounding the realisable potential for UWE, especially in the South African context. In order to gain a better understanding of the potential for UWE and the barriers acting against its widespread uptake, it is essential to first quantify the resource potential. This study appraise and evaluate the UWE resource potential at six locations in Cape Town, South Africa in order to gain a solid understanding of the UWE resource potential and thus begin to build the knowledge base around UWE. In order to meet the research objectives, wind data was obtained from the South African Weather Service for six locations in Cape Town at five minute recording intervals for a period of two years. These locations were: The Royal Cape Yacht Club located in the Table Bay harbour, the Astronomical Observatory located in Observatory, and the Kirstenbosch Botanical Gardens located in Kirstenbosch, the Molteno reservoir located in Oranjezicht, the Automatic Weather station located near the Cape Town International Airport as well as the Cape Town Weather Office (WO) station which is also located at the Cape Town International Airport. The data sets are then analysed using a script written in the programming language R in order to quantify the wind energy resource potential of the chosen locations. The wind energy resource potential of each site was combined with four commercially available wind turbines power curves in order to calculate the expected annual energy production values of the various turbines at the each of the locations. Results from this study highlight the significant variability resource potential of the wind regime that occurs between the six locations. The lowest yearly average wind speed was 2.044m/s which was recorded at the Kirstenbosch recording station, while the highest average wind speed was 5.06m/s which was recorded at the WO station. The average of all six stations for the two year period was 3.24m/s. Therefore the WO station had the highest energy potential with a value of 1474 kWh/m²/year and the station with the lowest energy potential was the Kirstenbosch station with a value of 80 kWh/m²/year. Combining these resource potential values with power cures from four commercially available wind turbines yields the Annual Energy Production (AEP) values for the chosen site and wind turbine. These AEP values also varied drastically with the high of 4304 kWh/year being calculated for the SkyStream turbine at the WO station and a low of just 0.66 kWh/year being calculated at the Kirstenbosch station with the Turby turbine. This variability hampers the wide spread uptake of small scale wind power as the results from one area cannot be reliably used to infer the wind resource potential at another nearby site. Out of the six chosen locations in the Cape Town area, three of the locations (Royal Cape Yacht Club, the Automatic Weather Station (AWS), and the Cape Town Weather Office (WO)) showed potential for the installation of a small scale wind turbine, with the Horizontal Axis Wind Turbines (HAWTs) performing better than the Vertical Axis Wind Turbines (VAWTs). This is possibly due to the lower cut in wind speeds of the HAWTs compared to the cut in wind speeds for the VAWTs. The conclusions of this study show that the UWE resource potential in Cape Town is characterised by high resource variability between the various locations. Three of the six locations that were evaluated showed potential for UWE installations. This study has identified the major challenges associated with UWE to be the turbulence, lower hub heights of the wind turbines (this study used 20m as the standard hub height), and variability of the wind regime between locations.
- ItemOpen AccessAssessment of the potential contribution of biogas to mitigation of climate change in south africa(2014) Vanyaza, Sidwell Luvo; Madhlopa, AmosSouth Africa has its fair share in the global greenhouse gas (GHG) emissions, with recorded 2010 emissions per capita of 10tons/year. This is caused by the energy supply of the country which relies heavily on fossil fuels to drive its energy intensive economy. If this continues under “business as usual”, consequences like water and food shortage may be exacerbated. The waste sector has a share of 3 in national GHG emissions. These are caused by methane from biogas produced through anaerobic digestion of organic waste. The objective of this study was to assess the potential contribution that can be achieved in reducing the national GHG emissions by converting waste emissions into useful energy or capturing and destroying them. Three waste resources were investigated because of their abundance in the country: municipal solid waste, municipal wastewater and livestock manure. The national picture of municipal waste was extrapolated from the waste data available in 7 metros in the country (City of Cape Town, Johannesburg, Tshwane, Ekurhuleni, EThekwini, Nelson Mandela Bay, and Buffalo City municipalities). Projected GDP and population growths were used as indicators for extrapolating the national data. The total national organic waste derived from these waste categories was used to estimate their emission share in national GHG emissions and biogas generation in terms of methane production from each waste type. This was forecasted from 2010 to 2025. The methane gas production was optimised by assuming different waste combinations like: municipal solid waste and wastewater, wastewater and livestock manure, and remaining wastewater. In addition, the possible amount of electricity or heat produced from this biogas was estimated. This useful energy was used to evaluate the emission reduction potential (ERP) in the national GHG emissions of the country under “growth without constraints”. All these computations were performed by using MS Excel software. It was found that the total organic waste predicted during this period varied from 12 to 17Mton, with the waste emissions share being about 2 of the national GHG emission. Methane generated from this waste was about 644-1075Mm3 while the total optimal methane generated from these waste combinations was estimated to be 1770- 2650Mm3. In addition, 673-1123GWh of electricity and 1255-2150GWh of heat could be produced (without optimization) from methane over the same period of the forecast. For optimal methane production, the possible useful energy was estimated to be 1362-2037GWh of electricity and 2894- 4362GWh of heat. The ERP of methane capture and conversion to useful energy was about 2.1- 2.5. It is concluded that a) capturing and utilisation of methane gas from waste contributes to the reduction of the GHG emissions, b) optimisation of biogas production from waste increase methane yield and therefore useful energy, and c) the best contribution of biogas in climate change mitigation in South Africa would come from the optimal production of methane from waste.
- ItemMetadata onlyCharacterization of palm olein (oil) as base oil for biolubricant production(2016) Ugye, Rachel Serumun; Batidzira, Bothwell; Okoroigwe, EdmundThis research work is on the determination of the properties of palm oil as potential base oil for producing bio based lubricants. The samples analysed were obtained from the open markets in the South West, South East and South South zones of Nigeria. Some of the physical and chemical properties such as viscosity, flash point, pour point, cloud point, specific gravity, acid number, noack volatility and aniline point were analysed. The samples were degummed, neutralised and bleached to remove the red colour (carotene) and gummy materials. The bleached samples were tested to determine the above mentioned properties. Comparison of the crude palm oil and the bleached samples with the conventional lubricants Mobil Super SAE20W40 and Mobil gear oil SAE75W90 was made. Finally, it was observed that the crude palm oil and the bleached sample exhibit good lubricating characteristics to be used as base oils for formulation of bio-lubricants. Despite palm oil being a food crop, an abundance of available land and the scale of prospective market demand suggest that commercial cultivation is unlikely to negatively affect food cultivation and the prices of food products.
- ItemOpen AccessDetermining the impacts of selected energy policies on Gauteng's residential energy consumption and the associated emissions using LEAP as a tool for analysis : implications for sustainable livelihoods for the poor(2011) Senatla, Mamahloko; Hughes, AlisonEnergy is a key factor in economic growth and also central to meeting basic socio-economic goals. The use and production of energy in South Africa is associated with greenhouse gas (GHGs) emissions and pollution problems. Gauteng‘s residential sector is faced with a slowing rate of electrification due to high in-migration rates and high pollution levels in households that use coal to meet their energy needs. This study analyses whether the energy policies in Gauteng can help to steer Gauteng‘s residential sector toward sustainable use of energy by reducing the energy demand and associated GHG and pollutants emissions. Long range Energy Alternative Planning system (LEAP) was used as a tool for analysis.
- ItemOpen AccessEnergy efficiency in the South Africa crude oil refining industry drivers, barriers and opportunities(2012) Bergh, Caitlin; Cohen, BrettThis study has explored a range of barriers, drivers and opportunities to improving energy performance in the South African crude oil refining industry, thus providing information to further support energy efficiency improvement efforts. Energy efficiency is a cost effective means of reducing greenhouse gas emissions and energy costs, bringing additional quality and production benefits.
- ItemOpen AccessExploring the potential of nanofluids to enhance the productivity of solar stills(2019) Charitar, Deepti; Madhlopa, AmosDesalination technologies are being used to augment access to safe drinking water around the world. Nonetheless, most of these technologies are energy-intensive and driven by fossil fuels which emit greenhouse gases into the atmosphere, thereby contributing to climate change. Additionally, fossil fuels are non-renewable sources of energy and the exhaustion of such reserves can cause a threat to energy security. Consequently, exploitation of sustainable sources of energy for the desalination process has attracted a lot of attention. One such strategy is the use of a solar still which utilises solar energy to produce fresh water from saline or brackish water. However, the major drawback of a solar still lies in its low productivity. Many studies have investigated means of increasing the productivity of a solar still. One such technique which has recently been studied is to disperse nanoparticles into the impure water inside the basin of a solar still in order to obtain a nanofluid with enhanced optical and heat transfer characteristics. Since this is a relatively new topic, very few numerical studies on solar stills with nanofluids are available. Moreover, based on a literature review, no study examining the effect of nanoparticle size on the productivity of solar stills, and on the economic and environmental performance of solar stills was found. Additionally, the few available numerical studies on solar stills with nanofluids have not taken into account the view factor in the computation of the internal radiative heat transfer coefficient. Therefore, the aim of this study was to investigate both numerically and experimentally the effect of nanoparticle size on the performance of solar stills. Mathematical models with the view factor (Model 1) and without the view factor (Model 2) were developed for single slope solar stills, and a code was written in MATLAB software to solve a system of equations iteratively. Calculations were performed using climatic data from Stellenbosch (latitude 33.93°S, longitude 18.86°E) and University of Cape Town (latitude 33.96°S, longitude 18.46°E), South Africa, in order to evaluate the performance of solar stills with varying nanoparticle sizes. For the experimental phase, four identical solar stills were designed and built, and they were first tested with water only (base fluid) in all of them to test their performance and for calibration purposes. An Analysis of Variance (ANOVA) test was conducted on the experimental data collected from this first test. Subsequently, nanofluids containing aluminium oxide (Al2O3) nanoparticles of size 10 nm, 50 nm and 100 nm were used in three of the solar stills, with the other solar still containing the base fluid only. All the experiments were conducted at the University of Cape Town. The mathematical models were then validated using experimental data. Simulations in MATLAB based on Stellenbosch climatic data showed that for the month of January, which is a summer month in South Africa, the productivity of the solar still with the 10 nm, 50 nm and 100 nm Al2O3 nanoparticles was 9.01%, 8.94% and 8.89%, respectively higher than the productivity of the solar still with the base fluid only. On the other hand, for the month of July, which is a winter month in South Africa, the average productivity of the solar still with the 10 nm, 50 nm and 100 nm Al2O3 nanoparticles was 1.31%, 1.23% and 1.19%, respectively higher than the productivity of the solar still with base fluid only. In terms of the economic analysis, the simulations in MATLAB based on annual climatic data from Stellenbosch revealed that the cost of distilled water obtained from the solar still with the 10 nm, 50 nm and 100 nm Al2O3 nanoparticles was 10.42%, 6.21% and 3.51%, respectively higher than the cost of water obtained from the solar still with the base fluid only. Additionally, the payback period for the solar still with the 10 nm, 50 nm and 100 nm Al2O3 nanoparticles was 13.32%, 7.86% and 4.37%, respectively higher than the payback period for the solar still with the base fluid only. In terms of the environmental performance, the amount of carbon dioxide equivalent (CO2 equivalent) mitigated by the solar still with the 10 nm, 50 nm and 100 nm Al2O3 nanoparticles was 6.18%, 6.11% and 6.06%, respectively higher than the amount of CO2 equivalent mitigated by the solar still with the base fluid only. For the experimental phase, the ANOVA test based on the first set of experimental data (with base fluid only in all four solar stills) gave a probability-value (P-value) of 1.00. Moreover, experimental data collected from solar stills with base fluid and nanofluids revealed that the productivity of the solar still with nanoparticles of size 10 nm and 50 nm was 26.46% and 1.46%, respectively higher than the productivity of the solar still with base fluid only. On the other hand, the productivity of the solar still with nanoparticles of size 100 nm was 9.38% lower than that of the solar still with base fluid only. Furthermore, the root mean square error (RMSE) for the solar stills with nanofluids for Model 1 and Model 2 was 22.02% and 36.03%, respectively. It was confirmed that the performance of the calibrated solar stills was not significantly different. Moreover, the enhancement in the productivity of a solar still with nanofluids is much more distinct in summer than in winter. It was also demonstrated that the productivity of a solar still decreases with increasing nanoparticle size. Additionally, it was established that the cost of distilled water, the payback period and the amount of mitigated CO2 equivalent decrease with increasing nanoparticle size. Theoretically, the distillate yield and environmental performance of a solar still with nanofluids were marginally sensitive to the nanoparticle size while the cost of distilled water and payback period were significantly affected by the nanoparticle size. The effect of nanoparticle size on distillate yield was experimentally significant. Finally, it was demonstrated that the inclusion of the view factor improves the accuracy of modelling of solar stills with nanofluids.
- ItemOpen AccessFeasibility study of heat pumps for waste heat recovery in industry(2012) De Waal, Devin; Hibbard, AndrewA case study was thus carried out at an applicable local industry (brewery) to assess the feasibility of implementing the heat pump for waste heat recovery. Through analysis, the focus was narrowed down from a site wide audit, to a departmental breakdown and then eventually to a specific process; the wort boiler. Three different alternatives were investigated and the performance and economic viability compared; a simple waste heat recovery solution involving a vapour condenser (vq, a mechanical vapour recompression (MVR) heat pump and a thermal vapour recompression (TVR) heat pump. It was found that the MVR system yielded the greatest energy savings, followed by the VC and then the TVR system. All three systems had positive rates of return, with the VC and TVR systems being tied for first place.
- ItemOpen AccessGlobal review of CSP technologies(2011) Sikhosana, Qedile; Cowan, Bill; Bennett, KevinThis global review of concentrating solar power (CSP) technologies is based mainly on an assessment of available international literature, up to 31 October 2011. It includes a review of major CSP projects currently operating or under development at this time; the respective CSP technologies employed; and an assessment of the present and future economics of CSP relative to other conventional and renewable energy electricity-generating technologies. Global outlook scenarios for CSP are discussed, as well as specific conditions and proposals for CSP developments in South Africa. The economic analysis has been limited by several challenges. Since the CSP industry is new, there are few well-documented projects on which to base the analysis. Most of the projects referenced here are from the USA and Spain. As the CSP market rapidly expands, competition in the industry tends to restrict the disclosure of detailed financial/economic information for projects under development. In general, it has been difficult to compare the publicly available economic data, on a reliable basis, since the financial costing parameters used may vary from case to case. In addition, most of the economic forecasts, which have been reviewed, are based on forward modeling rather than practical proven costs. There are uncertainties and quite wide variations in such predictions. This dissertation concludes, however, that there is great optimism for the growing employment of CSP technology in the near future and that CSP electricity-generating costs, in areas with high solar energy resources, are expected to become competitive with levelised electricity generating costs from other conventional and renewable energy technologies. The cost reduction potentials for CSP lie mainly in expected technical research and development advances, and production economies of scale, achieved by high volume deployment, supported by mid-term investment incentives from governments and other agencies. Another cost reduction potential, especially in the South African context, lies in the localization of skills and local fabrication of some plant structures and components.
- ItemOpen AccessGreenhouse gas mitigation cost of energy from biogas : a techno-economic analysis of co-digestion of three types of waste in Cape Town(2011) Malla, Lesego; Hughes, Alison; Von Blottnitz, HarroThis paper investigates, in the context of Cape Town the emission reduction potential (ERP) of energy from biogas and related cost. Two project-scale models and a city-scale model were developed. Substrates for project model 1 were organic fraction of municipal solid waste (OFMSW) and primary sludge (PS) from sewage works. Project model 2 considered waste paper sludge (WPS) and PS. For the city-scale model, substrates for project model 1 were extended to include total amounts of OFMSW and PS generated in Cape Town. Financial results show that at the REFIT tariff model 1 would have a higher internal rate of return (20.5%) than model 2 (5.6%). The landfill ERP of the project-scale models is 98 600 CO2 equivalent tons per year, corresponding to a weighted average capital investment of R372 per CO2 equivalent ton saved in year 1. The results for the city-scale model indicate that a landfill ERP of 458 000 CO2 equivalent tons per year can be expected at an investment cost of R287 per CO2 equivalent ton saved in year 1. Energy emissions from fossil fuels at city-scale are most effectively mitigated if coal rather than other fossil fuel based power and heat generation are replaced.
- ItemOpen AccessAn investigation into increased productivity of small scale anaerobic digesters by means of temperature management(2018) Carolissen, Sanchez; Hughes, Alison; Von Blottnitz, HarroThe use of biological waste as a primary energy source for the production of biogas, by the process of anaerobic digestion, has been commonly used in the past by small communities and on a larger scale by waste water treatment plants. In the latter, the biogas is traditionally used for heating of the digesters in order to increase process performance. Smaller scale anaerobic digesters using food waste as a primary energy source for biogas production could be implemented for residences and restaurants. The biogas produced could be used for cooking and heating purposes. Whilst common designs for such smaller digesters do not provide for heating, there may be warm waste water on site to elevate the operating temperature and thus improve gas yield. This dissertation reports an experiment aimed at improving the performance of an existing anaerobic digester located at the Leo Marquard Hall (LMH) residence of the University of Cape Town. The 6 m³ digester has been operated using food waste as its sole substrate. The volume of gas produced is unknown as there are no gas measurement devices on site. In the past it has been roughly estimated from pressure readings before and after gas use. The digester operates at ambient temperature which averages 16 °C over the year, which is suboptimal. The anaerobic digester is not equipped with a temperature measurement device to monitor operating temperature. Two hypotheses were formulated and tested. The first stated that the temperature profile of the waste water leaving the LMH residence will have peaks in the morning and evening periods when the majority of students shower. The peak temperature periods will be in the morning before breakfast and in the evening after dinner. The temperature during these times is expected to be above 30 °C. In order to test the first hypothesis, a thermocouple with temperature data logger was installed to record the temperature of waste water in the manhole drain leaving the LMH residence. The temperature data recordings confirmed the temperature peak of waste water leaving LMH residence at an average temperature of 30.5 °C in the morning. However, a clear evening temperature peak was not identified. Thus the hypothesis was only true for the morning temperature peak of waste water leaving LMH residence for weekdays when lectures take place. The second hypothesis stated that, adding a portion of the 30 °C waste water into the LMH anaerobic digester will result in the digester running at 5 °C above the normal average operating temperature, and thus increase the productivity of the anaerobic digester. In order to test the second hypothesis the design and installation of a pumped pipe system was completed in order to pump waste water from the LMH residence waste water outlet manhole gravity sewer to the LMH anaerobic digester. By loading the LMH anaerobic digester with 600 ℓ of warm waste water, the maximum digester temperature increase obtained was 5 °C relative to the normal cold water operation. The maximum increases in total weekly biogas and methane production achieved were 238 % and 260 % respectively, relative to the average weekly cold water operation. The operating temperature of small scale anaerobic digesters is a very important factor for the performance of the anaerobic digester. This research shows that increasing the operating temperature of a small scale anaerobic digester by as little as 5 °C could double the performance of the anaerobic digester. The site location for the installation of small scale anaerobic digesters should be investigated at design stage by taking into consideration the operating temperature. The digester could be installed in close proximity to both an organic waste stream and warm waste water stream that could affect the feasibility of a particular project installation.
- ItemOpen AccessInvestigation of the use of biogas in a gas hob - and the feasibility of upgrading it on a household scale(2012) Trautmann, Christina; Von Blottnitz, HarroThe production and use of biogas on a household scale is becoming more common. The biogas is mainly used for lighting and cooking. Since some households may already be using sophisticated gas appliances prior to investing in an anaerobic digester and might not wish to downgrade to relatively simple and robust biogas appliances, a need to investigate the compatibility of biogas with a standard household appliance was identified. A gas hob was chosen.
- ItemOpen AccessNumerical study of a hybrid photovoltaic thermal desalination system(2016) Noble, Cole Douglas; Madhlopa, AmosThe world as we know it depends highly on fossil fuels. However, these resources are finite, and evidence suggests that their combustion contributes to climate change. In addition, fresh water supplies are becoming scarcer amidst instabilities in weather patterns and unsustainable water consumption levels. As such, photovoltaic (PV) systems have emerged as a potential off-grid alternative to traditional fossil fuel energy generation. However, their widespread proliferation is, in part, inhibited by their inefficiency as less than 20% of incident solar energy is converted to electrical energy. Hybrid photovoltaic thermal (PV/T) desalination systems have emerged as one way of improving the overall efficiency of PV panels as they make use of the waste heat from panels to aid the desalination process in solar stills. Solar stills have been modelled with software for the purpose of performance optimisation, but most of them do not account for the still's view factor in the calculation of internal radiative heat transfer coefficient. The aim of this study was to construct a numerical model for a hybrid PV/T desalination system and determine its accuracy. The modelling was undertaken in Matlab and was validated against experimental data from a previous study using Root Mean Square Error (RMSE) and correlation values. It was observed that the model performed adequately as a water yield RMSE value of 22.0% was found. Furthermore, it was found that the view factor reduces the RMSE of hourly water yield from 28.9% to 22.0% and improves the correlation factor from 0.9890 to 0.9896. Sensitivity analyses were performed with annual data from Stellenbosch, South Africa (33.935°S 18.7817°W) and indicated an optimal water depth of 0.02m for high water yield, and 0.04m for high electrical energy yield. Also, an optimal panel tilt angle of 30° was found for both water and electrical energy yields and optimal cover tilt angles of 40° and 60° were observed for maximum water and electrical yields respectively. The conclusion of this study was that the incorporation of a view factors does indeed improve the accuracy of hybrid PV/T desalination system models. Additionally, low basin water depth is favourable for high water yields and high basin water depth, for high electrical energy yields. Furthermore, a panel tilt angle of 30° is optimum for both types of yield. Finally, the still cover tilt angle should be set to 40° for optimal water yields, but should be as steep as possible for optimal electrical energy yields.
- ItemOpen AccessThe potential carbon dioxide emissions reduction when energy service interventions are applied to the current subsidised housing demand(2016) Krog, Petrus Jacobus; Trollip, Hilton; Boyd, Anya; Moolach, MaschaThis dissertation examines the role of subsidised housing in reducing carbon dioxide (CO₂) emissions in South Africa. Climate change is an occurring event and is largely caused by human activities, such as the production of energy from fossil fuels (NRC, 2010). Buildings are seen as one of the highest consuming sectors of energy and therefore present many potential climate change mitigation opportunities. The South African subsidised housing sector is expanding significantly and estimations made in the current study show that 2.8 million subsidised housing units can potentially reduce up to 3% of the total current CO₂ emissions from the residential sector. This demand for subsidised housing units can also potentially reduce up to 0.06% of South Africa's total annual CO₂ emissions.
- ItemOpen AccessThe potential of renewable energy for rural groundwater supply in the Elundini Municipality(2014) Kernick, Gordon; Hibberd, Andrew Charles Michael; Wlokas, HolleThe Elundini municipality, situated in the interior Eastern Cape of South Africa, as with many other municipalities with a large portion of rural inhabitants, is beset with the challenge of needing to provide clean drinking water to these far lying people in an efficient and cost effective manner. Due to the large distances between villages as well as from any town or major infrastructure, supplying water via traditional pipe networks is not feasible. Historically, groundwater has been the water source of choice and abstracted via the use of diesel powered borehole pumps. These pumps are however noisy, require constant maintenance and are associated with high running costs associated with the ever increasing price of fuel. Not only is the fuel expensive in itself, but it is also required to be transported long distance to the boreholes on a regular basis. This study then investigated how solar and wind powered borehole pumps compared with diesel powered options. This was done by assessing the natural resource potential of the region (wind and solar power) as well as the groundwater abstraction potential of a sample of villages. Notional solar, wind and diesel powered systems were then designed for each of the villages with each of their unique water supply requirements and then compared against one another with a life cycle cost analysis for each system being performed. The study found that, not unlike other similar studies in other regions of the world, that over their lifetime, wind and solar powered borehole pumps were cheaper than their diesel counterparts. This was especially true for solar powered options as the solar resource for the region is superior to that of wind. Although traditionally shunned due to high capital costs, solar powered pumps have been commercialized in recent years and are now only marginally more expensive than diesel options. Wind pump capital costs are still prohibitively high, although running and maintenance costs are low. For the Elundini municipality however, and its relatively poor wind resources, this would not be a recommended technology.
- ItemOpen AccessReducing industrial energy costs through energy efficiency measures in the South African foundry industry - evaluation and opportunities of a South African foundry(2016) Thiel, Dennis; Hibberd, AndrewDue to lack of generation capacity and high energy intensities South Africa's electricity supplier is forced to shut down high energy users frequently. Power cuts as well as escalating electricity prices threaten the country's steel industry. The objective of this study was to identify cost-effective energy efficiency improvements for the South African foundry industry. A lack of research in South African foundries was identified as existing literature on the topic was analysed. A large foundry operating an induction furnace in the Western Cape served as subjects to investigate the topic specifically in South Africa. The aim was to identify the energy intensity, evaluate already implemented energy efficiency measures and identify further opportunities to reduce energy cost of the foundry. The method followed for the data collection was much orientated on an industry energy audit. Types of energy, amounts and cost of energy usage were determined. The energy consumption and energy intensity of the foundry were analysed, based on meter readings, electricity bills and where necessarily a "bottom-up" approach for estimation was used. Results of the energy audit have shown that the foundry under review consumes about 127,000 MWh annually with a maximum demand of 26,500 kVA. The already implemented energy saving measures decreased the company's energy usage by 5% resulting in a current energy intensity of 1,493ZAR/ton. Further proposed energy efficiency measures included the compressed air system, preheating of the charge material and the reduction of the holding furnaces were analysed. The results of all evaluated measures, namely lighting, load-shifting and maximum demand management were cost effective solutions. Furthermore the recommended energy efficiency measures, namely reduction of compressed air leaks, reduction of holding furnaces as well as preheating of charge material, showed in theoretical calculations a reduction of carbon emissions as well as cost savings. This study offers an insightful view on energy intensity and energy efficiency opportunities in South African foundries, especially the ones operating an induction furnace.
- ItemOpen AccessReliability investigation of the South African power generation system with the inclusion of wind energy(2014) Maseela, Tiisetso; Merven, BrunoRenewable energy sources such as wind energy for electric power supply are receiving serious consideration around the world due to global environmental concerns associated with conventional generation and depleted conventional energy resources to meet increasing electricity demand. This is more than evident in South Africa, where the recently launched Renewable Energy Independent Procurement Program (REIPPPP) has a proposed capacity of 3725MW, allocating 1850MW to wind energy. This dissertation investigates the effects that geographical dispersion and penetration level have on the wind capacity credit and the reliability of the South African power generation system, by estimating the capacity credit. Some of the estimates are tested using a simplified dispatch model, which is also used to estimate other indicators such as the expected energy not served and CO2 emissions of the system for different wind configurations. The sensitivity of the capacity credit definition is further investigated through two definitions. Several scenarios are used to investigate the capacity credit of wind generation, based on the updated IRP base case scenario.
- ItemOpen AccessSite location and techno-economic analysis of utility-scale concentrating solar power plants in South Africa(2011) Brodrick, Joshua JL; Bennett, KevinThis dissertation comprises a two-part study concerned with the identification and quantification of potential Concentrating Solar Power (CSP) sites in South Africa; and the performance and cost modelling, optimisation and analysis of two CSP technologies in three locations. A further theme of the study is the consideration of the availability of water for plant cooling purposes, and hence the comparison between, and analysis of optimal CSP technologies and cooling methods for each location.
- ItemOpen AccessStudy into the feasibility and design of a renewable energy portfolio for the Klein Constantia Wine(2012) Leisegang, Derek Andrew Cecil; Hibberd, Andrew; Bennett, KevinThe South African wine industry has seen a growing interest in the field of renewable energy in recent years. This has been due, in part, to rising energy costs a long with increased public and consumer awareness around the issues of global warming and sustainability. This project was conceived in the light of these developments, and centres on an investigation into the feasibility and design of a renewable - energy portfolio for the Klein Constantia Wine Estate, located in the Western Cape. A literature survey was undertaken, shedding light on the common uses of energy on wine farms, renewable energy initiatives within the industry and the technologies available. A case study was then conducted using Klein Constanta Wine Estate as the subject. Physical measurements were taken where possible and, along with a combination of topographical, satellite and local climate data , were used to develop estimates f or the energy - generation potential of the farm's renewable resources and the cost implications thereof. Following this, a qualitative and quantitative analysis was conducted to determine the most favourable technologies from a portfolio design perspective. From these findings, three potential portfolio designs were developed, each covering varying degrees of the farm's energy consumption. Based on the se final designs, it was concluded that there was indeed significant potential for investment in renewable energy at Klein Constantia; and that the farm could more than cover its energy requirements. While the financial returns would be minimal, with relatively long payback - periods, the secondary benefits to the farm were considered to be sufficient to justify the investments. The final decision, however, would likely rest on the weight given to the secondary benefits by the farm owners. It was also determined that, in the case of Klein Constantia, the larger the investment the less secure it would be. This was primarily due to the need for higher - risk and more expensive technology options being required when the energy target was raised. With this in mind a renewable energy portfolio, covering only the farm's electricity use, was found to be the most favourable option available to the farm.