Theses and Dissertations

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https://hdl.handle.net/20.500.14155/200

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Browsing Theses and Dissertations by Author "Hove, Tawanda"

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    Development of solar radiation database and its integration into solar process applications in Lesotho
    (National University of Lesotho, 2020-05) Bulane, Lebohang; Hove, Tawanda
    Solar energy is a viable alternative source of energy for socio-development of a developing country like Lesotho. Investment in solar process applications, requires a accurate solar radiation data for the successful implementation of solar process projects. However, in Lesotho measured solar radiation datasets are not sufficient both temporally and spatially as there are only seven solar radiation measuring sites, two of which are not reliably operational. This study solves the problem of the scarcity of solar radiation data in Lesotho, by developing a solar radiation database for the country. It has a primary objective of developing an accurate solar radiation database for Lesotho. This is achieved by merging ground measured solar radiation data with satellite – derived solar radiation data. The merged data is complimented by solar radiation data derived from sunshine duration data. Merging solar radiation datasets is important because ground measured data are sparsely distributed and cannot be interpolated accurately to represent solar radiation at any location. Although satellite – derived datasets are spatially continuous, they are not accurate as they are inferred from extra- terrestrial solar radiation modified with atmospheric models. As a result, each of the databases cannot be relied up unilaterally. Measured ground data is from five stations and sunshine duration derived solar radiation is form twelve stations. The improved database is validated using a leave one out cross validation technique. Its reliability in estimating ground solar radiation is tested by relative bias error (rBE), relative mean bias error (rMBE) and normalized root mean square error (NRMSE). Results show that the database is credible as it has a maximum error of 2.7 % which is comparable to other studies of similar nature in Africa. An interpolation tool, increases the accuracy and reliability of interpolated solar radiation as compared to manual reading of data from solar radiation maps. It has an accuracy of 99.54%. The improved database and interpolation tool can confidently be used in any solar application process design and sizing in the country.
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    Energy Audit and Management Opportunities for a Diamond Mine: A case for Lets’eng Diamond Mine
    (National University of Lesotho, 2020) Ntelekoa, Masiane; Hove, Tawanda
    The mining sector is highly energy intensive. Undertaking mining activities at a geographic location bearing extremely cold temperatures like Lets’eng in Lesotho exacerbates the situation as abundant energy is required to provide the comfort needed by employees. Nonetheless, there exists ample waste in energy use within the mining sector which can be avoided by bringing forth energy management strategies. The study firstly identifies areas of energy waste and their cause. Both simple and technical energy management strategies are employed in correcting ways of energy use in order to utilise the least possible energy. The aim of the study is to minimize energy costs at the mine and reduce environmental damage associated with electrical energy use while also integrating renewable energy technologies where it is possible to do so. Monthly energy consumption profiles from electrical meters at the mine were used to analyse the consumption patterns of different energy processes. The study identified energy management opportunities in the energy processes of lighting, space heating, water heating and poor power factor. Energy management interventions for all the opportunities identified were economically assessed in terms of their cost of implementation and operation against the associated energy savings they would yield. All the recommendations proved to be economically viable as they resulted in a positive Net Present Value (NPV) and all Payback Period in years were within the remaining life of the mine which spans until 2034. Modelling gives a total of 41 903.14 tonnes of greenhouse gases averted from emission to the environment as a result of implementation of energy management opportunities.
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    Investigating viability of using solar
    (National University of Lesotho, 2021-04) Lesenyeho, Tabempe Edgar; Hove, Tawanda
    Selection of the solar thermal collector using the energy per dollar matrix, prevailing interest rate and the prevailing inflation rate is of paramount importance for decision-making for investment in solar-assisted biodigesters. This paper presents a comprehensive computer-based excel model on investigating the viability of using solar thermal energy for optimizing the biogas yields in Lesotho. The excel based model is used to analyze both the thermal and economic performance of the solar-assisted biogas digester.The model determines solar thermal performance,solar thermal collector size, solar storage size, as well as the surface area over which the heat losses occur in both the solar water heater and biodigester tank.It will further look into economic analysis of the system. In order to ensure maximum benefits, sizing of the solar thermal system has been carried out to give the optimum solution. Simulations have been performed on an hourly time step. Comparison of production of biogas with solar thermal energy and production of biogas without solar thermal energy were undertaken to find the effects of temperature on the production of biogas. It was found that the production of biogas is optimum at the mesophilic temperatures of 180 C to 300 C. Different collectors, both evacuated tube collectors and flat plate collectors which are valued by Solar Ratings & Certificate Corporation are ranked using energy per dollar matrix. The Sun power evacuated tube collector is the best collector used for system design since it has high energy per dollar of 25.3 kWh and low heat loss parameters. The Net Present Value is the objective function to optimize for the solar thermal system. The optimum collector area to deploy for 5𝑚3 biodigester is 16𝑚2, the optimum solar storage tank of 800 liters is required. The total cost of buying the collector and the solar storage tank is $1744.In Lesotho 1𝑚3 of biodigester requires a solar v thermal collector area of about 3𝑚2.The optimum collector area gives a maximum Net Present Value of $1854.Moreover, the biogas produced is 396𝑚3 per annum with the percentage increase of extra biogas as 11.5% per annum. The project is economically viable with a Net Present Value of $1854, an Internal Rate of Return of 10.36%, a Payback period of 9 years, and a Benefit-Cost Ratio of 2.01. The project lifetime is 20 years.
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    Optimal sizing, performance prediction and economic appraisal of off-Grid Solar PV hybrid power systems in Lesotho: A reliability–cost approach
    (National University of Lesotho, 2020) Lepolesa, Selone Augustinus; Hove, Tawanda
    This dissertation reports about the development of and the application of a simple spreadsheet-based mathematical model for the sizing, the performance prediction, and the economic analysis of a PV-Diesel-Battery autonomous power supply system. The main objective was to find appropriate reliability level required of a mini-grid system in Lesotho that minimized the Levelized Cost of Energy (LCOE), and at the same time, supplied a satisfactory energy service. The goal was to determine the costeffective level to set for the energy reliability for mini-grids in Lesotho, such that the LCOE would not increase disproportionately with the marginal increase in the reliability level. The method used was to find the reliability at the minimum cost using the elbow of the graph. The simulation and performance analysis showed that there was an infinite number of combinations of battery, PV array and diesel generator size required to achieve a given supply reliability. It was observed that the conditions for minimum LCOE may not correspond to highest reliability and satisfactory energy service.
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    Optimization of the choice of solar minigrid architecture and management in Lesotho
    (National University of Lesotho, 2020) Kao, Moruti Clement; Hove, Tawanda
    Installation and maintenance of the solar photovoltaic systems for power generation is highly discouraged by the high costs of storage units resulting from the traditional approach of sizing the systems. In order to reduce these costs, Solar PV systems sizing using a time-step approach is used in this study as opposed to traditional approach. Comparison of the traditional and timestep approaches used for sizing solar PV systems was performed and showed that time-step approach is the most cost-effective way of sizing the PV systems. The time-step approach is very important in this study since it addresses the country’s lack of progress in mini-grid establishment regarding appropriate mini-grids architectural combinations versus costs best for Lesotho. The primary aim of this research work was to develop a comprehensive computer-based model to be used for performance and optimization of mini-grid systems in order to reduce the system costs, operation costs as well as enhancing the systems reliability. This involved developing an approach to modelling hourly load profile in the absence of historical consumption data and finally determine the best mini-grid system architectural combination which should be used in Lesotho, based on considerations of reliability and cost of energy. The current work successfully developed a simple computer-based program for optimally sizing, performance prediction and economic analysis of mini-grids systems. It shows how optimally sized solar mini-grid systems are determined by the model. The only data required to differentiate between mini-grid systems is the daily energy load as well as its hourly distribution and the desired supply reliability. The current work uses Sehong-hong mini-grid among sites identified by Sustainable Energy for All (SE4ALL) in Lesotho’s mountainous districts and the objective function used for determining the cost effective solar mini-grid architectural combination best for Lesotho is the Levelized Cost ofEnergy (LCOE). The study also explores several diesel dispatch strategies on system performance and energy cost. The study presents an optimised design and performance of solar mini-grid architectural configurations comprising solar PV array, solar inverter, battery bank, battery chargers as well as diesel generator. In this study, system component sizing is defined in terms of daily-energyload related dimensionless variables, 𝑃𝑃 for PV array size, 𝐵���𝐿�� for battery size and 𝑄��𝐿 for diesel generator size. This allows generalization of the design for similar locations and similar hourly load profiles. Results of simulations using the study method show that the ii most cost-effective configuration for mini-grid systems in Lesotho comprises a PV array, a battery and a diesel generator, and should operate at a high solar fraction. For 100% supply reliability, the optimum system comprises solar PV array size (𝑃𝑃 = 11.2), battery bank size (𝐵���𝐿�� = 1.8) and diesel generator size (𝑄��𝐿 = 2.2), operating at 83 % solar fraction and at LCOE of 0.62 USD/kWh. For 99% supply reliability, the optimum system has 𝑃𝑃 = 3.9, 𝐵���𝐿�� = 0.292 and (𝑄��𝐿 = 2.2), operating at 85% solar fraction and at LCOE of 0.30 USD/kWh. It is opined to go for 99% reliability ahead of 100% reliability as only a 1% increase in reliability results in 54% cost increase. The used dispatch strategy in this study for the diesel generator is charge cycling strategy.