Theses and Dissertations

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Application of solution state NMR to structural problems in chemistry
(Durham University, 2006-09) Khoabane, Ntai Martin; Dr. Sanderson, John; Dr. Grayson, Elizabeth; Dr. Natrajan, Louise; Mr. McKeag, Ian; Mrs. Heffernan, Catherine
First and foremost I would like to thank the Lord almighty for the life he has given me. My stay and study at Durham University was funded and supported by Canon Collins Trust to whom I am very thankful. I would also like to pass my gratitude to the National University of Lesotho for releasing me on staff development leave, my dependants’ allowance, and funding my travel both ways. I would like to thank my supervisory team: Dr. Alan M. Kenwright for his supervision and training and demonstrated kindness and patience. He motivated and encouradme during this period. I am also grateful to him for coming up with original ideas of a project on which I worked. Dr. John Sanderson cannot be forgotten for his co-supervisory role. I am also grateful to Dr. Elizabeth Grayson for the supervision in chemistry and for the protection and deprotection of the mannoside compounds. Dr. Louise Natrajan, I thank you for the lanthanide complexes I worked on. I would also like to thank Mr. Ian McKeag and Mrs Catherine Heffernan who contributed a lot to my training in solution state NMR. Other groups of people who contributed to my training need to be mentioned: all my lectures in the taught modules, the mass spectrometry facility and all the Chemistry Department staff. Last but not least my family members. Most importantly my wife and son who suffered the loneliness of my being thousands of miles away from them without complaint. Nuclear Magnetic Resonance (NMR) spectroscopy is a robust, non invasive technique applicable in structure determination as well as in the study of dynamic behaviour of chemical compounds. This thesis is in two sections, the first dealing mainly with a structure determination application of NMR and the second dealing mainly with a study of dynamic behaviour. Section 1 NMR characterisation of carbohydrates has proved challenging because of the limited chemical shift ranges of both the proton and carbon signals. The broad signals due to the labile hydroxyl protons cause further complications by overlapping proton signals from the ring. Protecting group chemistry is vital in the preparation and manipulation of synthetic carbohydrates and can potentially help with the assignment of the (otherwise extremely complicated) NMR spectra of carbohydrates. However, the widely used benzyl protecting group can make the spectrum more difficult to interpret because the benzyl CH2 proton signals often come in the same region of the spectrum as the anomeric protons, usually used as reporter groups of carbohydrates and the benzyl CH2 carbon signals come in the same region as the carbohydrate ring carbons. This section reports the invetsigation and application of a family of alternative protecting groups, namely various fluorobenzyl groups, which have not been used in carbohydrate chemistry before. With pentafluorobenzyl, the proton chemical shift dispersion is improved, and the CH2 and carbohydrate ring carbon signals are shifted to lower frequency, considerably simplifying the task of assigning the carbon spectrum, facilitating the interpretation of all 1H-13C correlation experiments (HSQC, HMQC, HMBC). Section 2 Cyclen complexes of lanthanide (III) ions have found use in magnetic resonance imaging (MRI), luminescence imaging and assay studies. In particular, europium (III) complexes have potential in anlytical, forensic, and biomedical applications based on their impressive emissive properties. However, the emissive properties are modulated by the thermodynamic stability and kinetic inertness of the complexes. For biomedical applications, chelation is necessary to avoid europium toxicity that may be triggerd by accidental dissociation of the complex and release of the metal in vivo. A new cyclen europium(III) complex with pyridyl pendant ligands instead of the usual acetate groups has been synthesised by a group at Manchester University. The pyridyl ligands confer higher emmisive intensities to the complex, to enable applicability of the complex in time gated measurements. The chemical structure determination of the compound was accomplished by 1H, 13C, COSY, HMQC / HSQC and EXSY NMR experiments. Selective inversion experiments data were evaluated using the CIFIT simulation program, and showed that in aqueous solutions from -0.2º C to 107.6º C the dominant dynamic process is flipping of the pendant (pyridyl) arms, and isomerism is biased towards the twisted square antiprism (TSAP).
Characterisation and Application of Municipal Sewage Sludge to Agricultural Land in the Maseru Metropolitan Area
(National University of Lesotho, 2011) Khesa, Makhale E; Tanor, E.B.
The nutrient content and other important properties of the sewage sludge from the Wastewater Treatment Plant at Ha Ratjamose in Maseru were determined. In addition, the sludge was characterised in terms of its, pH, salinity, TDS and temperature. The sludge was found to contain 0.011 - 0.013 (wt%) PO43- and 0.018 - 0.070 (wt%)NO3- with D/R 2000 Spectrophotometer. The values for some important physical properties were found to be as follows: pH,( 6.35-6.59); conductivity,( 335- 1674μScm-1) , salinity,( 0.00-0.6) , total dissolved solids (TDS) ,( 355-1576mgL-1) and temperature ,( 24.1-25.5˚C). The sludge was found to contain considerable amounts of nutrients, but lower than those found in commercial chemical fertilizers. It was also slightly acidic, hence it can be more appropriate if applied to strongly alkaline soils or be stabilized with alkalis if it is to be applied to neutral of acidic soils.
The Effect of Phosphate Detergents Discharges and the Application of Fertilizers on the Water Quality of Liphiring River
(National University of Lesotho, 2011-04) Tlali, A.R; Dr Tanor, E.B.
Sewage from the waste treatment ponds serving the university community in Roma, water samples from the Liphiring River and soil samples from the croplands along the river banks were analyzed for some selected parameters. The values for the physical parameters pH, temperature, conductivity, total dissolved solids and turbidity suggest that the discharge of the wastewater into the river does have much negative impact on the water quality. Also, the levels of chemical parameters suggest some degree of contamination. The levels of nitrites and sulphates are higher in the sewage thus the effluent discharge contributes to levels in the river. The levels of phosphates and nitrates are higher in soil thus the soil contributes to levels in river water due to leaching and run-offs.
Synthesis and characteristics of Phthalocyanines
(National University of Lesotho, 2011-05) Ts'enoli, Sidwell; Dr. Sekota, M;
The phthalocyanine compounds K2[(CN)2FePc], K2[(CN)2CoPc], FePc(Py)2 and CoPc(Py)2 were successfully synthesized and characterized by UV-Visible and IR spectrometry. This was done for application of these compounds as electrode modifiers and as chemical sensors. These coordination compounds were synthesized by the synthesis of the metal-free phthalocyanines followed by the introduction of the axial ligands. The characteristic UV-Visible and IR spectral bands were observed for the four complexes. Therefore it can be concluded that the complexes were successfully synthesized.
Moisture Absorption, Dimensional Stability Properties and Applications of Composites made from Thermosetting Resins, Reinforced with Sandstone, Diorite, and Corn Stalk.
(National University of Lesotho, 2011-05) Osiki, I.O; Dr. Thamae, T.
Moisture absorption and dimensional stability of materials is one major concern in any engineering design, as well as in any environment. This is because moisture absorption and poor dimensional stabilities in any material is capable of leading to the degradation and ultimate failure of such a material. The purpose of this research however, was to study the moisture absorption as well as dimensional stability properties of composites made from thermosetting polymers, reinforced with diorite, sandstone, and cornstalk. Other objectives of the research were to determine possible applications of the different composite materials as well as determine which of the thermosetting polymer resins would be most applicable as matrix material. Moisture absorption was carried out using the long term immersion procedure based on the ASTM D 570 - 98 standard. From the results of moisture absorption, the corn stalk-polyester composite was found to absorb more moisture than the other synthesized composite. The diorite-polyester composite absorbed the least moisture and results indicate that moisture decreases with increasing amount of the diorite filler added. The dimensional stability tests indicate that the sandstone-polyester composite is the most dimensionally stable of all the composite materials made in this research, and comparism of this composite with the water based acrylic resinsandstone composite indicates that the polyester composite is the preferable choice of polymer resin as matrix material for the production of composites. This conclusion was based on facts obtained from dimensional stability tests that indicate that the polyester resin is more stable dimensionally when filled with sandstone. Finally, designs were made from the various composites and this include table tops made from polyester-diorite composites, wall tiles made from polyester-sandstone composite, artifacts made from polyester-cornstalk composite, and wall tiles were also made using the water-based acrylic resin. A cost analysis was also carried out and although cornstalk was estimated as possible material for production of cost effective composites but its undesirable properties such as high moisture intake , made the sandstone a preferable choice of filler material for production of cost effective materials.
Synthesis and Characterization of Erbium and Neodymium Oxide doped Titanium Oxide Nanocomposites and their Application in Visible Light Photocatalysis of Congo red
(National University of Lesotho, 2011-05) Alotsi, Ntjamang Daniel; Prof. Alemu, Hailmichael
Nanocomposites (NCs) of Titanium dioxide doped with Erbium and Neodymium oxides, ( TiO2[Er2O3 ]x and TiO2[Er2O3 ]x, x=0.1,0.2) were prepared both by chemical co-precipitation followed by hydrolysis (CPH) as well as the solid-state reaction (SSR). The CPH synthesized NCs were obtained with particle sizes in the range (10nm-30nm). TiO2 was also synthesized using precipitation followed by hydrolysis method. All the NCs were investigated for their capability of degrading a dye, Congo Red (CR) using visible light and about 99.6% of CR was degraded. Throughout the entire research, all the chemically synthesized NCs showed high photocatalytic activity and this is attributed to smaller particle size of the NCs as compared to those NCs prepared by the SSR method. This directly reflects that photosensitization is major route of photocatalytic degradation mediated on TiO2 NCs. On comparison with the synthesized TiO2, the doped NCs revealed no greater photocatalytic activity than the synthesized TiO2, however this is apparent since TiO2 was synthesized with similar method to CPH method.
Detection and Estimation of Aflitoxins in Groundnut and Groundnut Materials
(National University of Lesotho, 2011-05) Nkhabu, Rethabile A; Prof. Alemayehu, G.C
The aflatoxins are well suited for analysis by Thin Layer Chromatography (TLC) since most of the compounds fluoresce under long wave ultraviolet (UV) light. The TLC technique serves as both purification and quantitation step. Before the TLC analysis, the peanut butter and crushed groundnut (peanuts) samples were separately de-fatted with light petroleum (boiling point 40 to 600C, ant the toxins within the samples were extracted from the de-fatted samples with methanol, and the extracts were purified by repetition solvent partition technique. The solvents used in the former technique were water-methanol mixture and chloroform, and aflatoxins have high affinity for chloroform. The obtained extracts were diluted to desirable concentrations and were then used for TLC analysis using silica gel Kieselgel G chromatoplate, and the mobile phase as the methanol-chloroform combinations. The quantitation of the results obtained was by fluorescence using fluorescent lamp (365 nm).
Voltammetric Determination of Paracetamol with Poly (3, 4-Ethylenedioxythiophene) PEDOT modified Glassy Carbon Electrode
(National University of Lesotho, 2011-05) Setubatuba, T.A; PROF. Alemu, H.
The voltammetric oxidation of paracetamol on poly (3, 4-Ethylenedioxythiophene) PEDOT modified glassy carbon electrode was explored in 0.1M sodium acetate buffer solution by using cyclic and differential pulse viltammetry. Cyclic and differential pulse voltammetry studies indicated that oxidation of paracetamol at the electrode surface as a two-electron reversible step and fundamentally controlled by diffusion. A quasi-reversible redox process of paracetamol at modified electrode was obtained and the over-potential of paracetamol decreased significantly compared with that at bare electrode. PEDOT modified electrode showed excellent performance for detecting paracetamol in the linear detection range between 9.99 x 10-6 to 3.38 x 10-4 M, with a detection limit of 4.7 x 10-6 M and a sensitivity of 0.043 A/M. The method was then successfully utilised for the determination of paracetamol in a real samples of Panado tablets and Ibupain capsule with recoveries of 99.1% and 80.7% respectively for each sample.
Catalytic Behaviour of Anionic Metalloporphyrins towards the Synthesis of Water- Soluble Polyaniline
(National University of Lesotho, 2011-05) Phooko, Mathese Palesa; Ass.Prof. Sekota, M.
In this study, metalloderivates of anionic tetrasulphonated tetraphenyl porphyrin (MTPPS4, where M= Ru(III) and Rh(III)) were synthesized and characterized and later utilized in the synthesis of water-soluble Polyaniline (PANi). The selected metalloporphyrins were synthesized with very low percentage yields. It was found that the RUTPPS4 was more effective as the homogeneous catalyst than RhTPPS4 as it showed a high turnover. This was attributed to the size of Ru3+ and the relative ease of oxidation of Ru(III) to Ru(IV). The synthesis and properties of PANi prepared are reported. The processabilty of the polymer was examined and it was found to be soluble in water and polar aprotic solvents like dimethyl formamide (DMF). The clewed nanostructured porous PANi exhibited rich electrochemical features which are interesting in the field of sensors and actuators.
Isolation,Charactorisation and electrochemistry of geshoidin from rhamnus prinoides
(National University of Lesotho, 2011-05) Malataliana, T. F; Professor G. C., Alemayehu; Professor H., Alemu
The leaves and the stems of Rhamnus Prinoides (Amharic name, Gesho and Sesotho name, Mofifi) are used as traditional medicine to treat pneumonia, gonorrhea, rheumatism, stomach-ache, as a gargle and so many more. In some countries such as Ethiopia, the leave and stems are used in traditional fermented beverages such as Tella and Tej. Chemical investigation on the leaves resulted in the isolation of a characteristic bitter principle known as naphthalenic compound β-sorigenin-8-O-β-D-glucoside. Then, the name Geshoidin was proposed for this novel glucoside. The structure of Geshoidin was established from the spectroscopic analysis of natural products. The electrochemical behaviour of Geshoidin was investigated at a glassy carbon electrode in mixtures of citric acid and di-sodium hydrogen orthophosphate aqueous buffer system over a wide pH range (pH 2-11) using cyclic voltammetry. Chemically irreversible single oxidation and reduction peaks were obtained in the potential and pH region investigated. Variations in the peak potential and peak current of the oxidation peak have been observed as function of pH. The wave characteristics, the reversibility of the reactions, the diffusion coefficient and the number of electrons transferred have been studied. Linear sweep voltammetry was applied for the voltammetric determination of Geshoidin and a linear calibration curve over the range 1.00 x 10-6 - 1.00 x 10-4 mol dm-3 Geshoidin was achieved. The detection limit was found to be 5.00 x 10-7 mol dm-3 Geshoidin. For eight successive determinations of 1 x 10-5 mol dm-3 Geshoidin, a relative standard deviation (RSD) of 3.2% was obtained. Thabang Fernando
Formulating short-term electricity demand forecasting for Lesotho
(National University of Lesotho, 2020) Lefela, Lereko; Prof Thamae, L. Z.
Electricity demand forecasting is an important process in the planning and operation of the electricity industry. Providing uninterrupted energy to consumers requires electricity demand to be predicted accurately. This study utilizes ABB Nostradamus short-term demand forecasting software, which accepts historical demand data, days of the week, time of the year and Lesotho public holidays for electricity demand forecasting. It produced day-ahead, week-ahead and hourahead electricity demand forecasting results with 3.06%, 4.06% and 5.09% accuracy. These MAPE results are close to or within the acceptable 5% accuracy for short-term demand forecasting, and provide crucial confidence levels for LEC to engage in power pool trading in the SAPP market for optimal power procurement. LEC utilizes bilateral agreements with LHDA, Eskom and EDM to supply the electricity demand. During the high demand season, bilateral imports from Eskom and EDM costs LEC around 3.27 Million US Dollars (M49 Million) which is twice the money incurred (1.60 Million US Dollars (M24 Million)) during the low demand season. Compared to the average SAPP DAM, IDM and FPM-W prices, Eskom’s 20 USc/kWh peak cost is higher than SAPP’s 12 USc/kWh DAM and IDM, and 13 USc/kWh FPM-W peak charges. Again, EDM’s 4 USc/kWh off-peak cost is higher than SAPP’s 3 USc/ kWh DAM, IDM and FPM-W off-peak charges. The study therefore recommends bilateral contracts use to meet intermediate demand of around 103 MW. For demand above 103 MW, utilizing SAPP market can assist to reduce bulk purchases costs.
Optimization of Mantsonyane and Semonkong mini hydro power stations by hybridization
(National University of Lesotho, 2020) Lepheane, Bahlakoana David; Thamae, L. Z.
This paper shows the optimized design and performance of a hybrid energy system for the following study sites, Mantsonyane and Semonkong in Lesotho. The main objective is to design a hybrid system with Low Cost of Energy (LCOE), high Renewable Fraction (RF) and reduced carbon emissions from a diesel generator at Semonkong hydro-diesel hybrid system. This study employs HOMER Pro simulation software to demonstrate the performance of the Mantsonyane and Semonkong hybrid renewable energy systems. The proposed Semonkong system design is made up of 360 kW of solar PV array, 100 kW wind turbine, 500 kW inverter, 1 MWh battery storage, 180 kW mini hydro and 410 kW diesel generator with a Load Following (LF) dispatch strategy. The simulation results indicate the environmentally friendly system with a renewable fraction of 97.3% which also reflects the high utilization of renewable energy in the system and the remaining small portion is diesel generator. The total energy produced is 1,978,099 kWh per year out of which 25.2% is contributed by wind turbines, hydro power generation contributed 41.8% while solar PV supplied 31.6% and diesel generator injected only 1.42%. The LCOE for this system is $0.129/kWh and these results are taken at the solar irradiation of 5.44 kWh/m2, wind speed of 9.71 m/s, average flow rate of 1,595 L/s and the diesel price of $1.00/L. The project would demand an initial capital contribution of roughly $1.25M with a total NPC of $2.65M. The proposed Mantsonyane system design comprises of twenty-five wind turbines with a total capacity of 7.5 MW, one unit of 1MWh battery storage, 2 MW mini hydro turbine and a 2 MW converter. The simulation results show that the renewable fraction for the most cost effective system configuration is 100% with the LCOE of $0.149/kWh. The results were taken at the solar irradiation of 5.44 kWh/m2, wind speed of 9.71 m/s, and average flow rate of 1,731 L/s. This project would demand an initial capital contribution of roughly $22.8M with a total NPC of $45.2M. Sensitivity analysis is used to investigate the impact of variation in wind speed, solar radiation and river flow rates at Mantsonyane. The analysis indicates that a high COE is experienced when the plant is operating at a very low load with comparatively low O&M costs. It is also found that good river flow rates and high wind speeds result in a more affordable unit price. As for Semonkong site, the optimal solution shows a minimal impact from the instability of diesel price, river flow rate and solar radiation. The LCOE drops with the increasing wind speed and river flow rates. However, the diesel generator will remain part of the system in order to boost generation during dry season from July to September.
Analysis of Quthing River and Letseng-laLetsie for Hydropower Potential
(National University of Lesotho, 2020) Lekhanya, Liteboho; Dr Khaba, L.; Dr Makhele, M.
This dissertation presents the analysis of Quthing River and Letseng-la-Letsie for hydropower potential in Quthing district in Lesotho. Electrical power deficit in the country is more prominent in rural areas like Quthing District. This calls for assessment of electrical sources in the vicinity of rural area load centers to inform policies for electrical production so as to curb power deficit problem. Mountain Rivers like Quthing River with steep slopes or gradients naturally provide good head which needs to be assessed along with its flow rates. Furthermore elevated dams like Letseng-la-Letsie can also provide a natural good head which needs to be assessed alongside with its discharge rates. The assessment was carried out by employing catchment area method to asses flow rates since the abstraction points of the study areas were ungaged and lacks data. The maps in association with QGIS were used to evaluate heads of the study areas and lastly TURBNPRO was used to determine power outputs from the study areas. The resultant net head for Quthing River was found to be 164.15 m while the net head for Letsengla-Letsie was 159.23 m. The design flow rate of Quthing River was found to be 0.58 m3/s while that of Letseng-la-Letsie was 0.1 16 m3/s. The results from TURBNPRO showed that the power output for Quthing River turbine was 815 kW while the power output for Letseng-la-Letsie turbine was 221 kW. Using typical hydro-electric generators efficiency of 99% and typical capacity factor for Africa of 0.49, the capacity from Quthing River was found to be 807 kW with annual energy of 3.46 MWh. The capacity for Letseng-la-Letsie was found to be 0.22 MW with annual energy of 0.95 MWh.
Evaluation and optimisation ofsolar water pumping systems for Lesotho
(National University of Lesotho, 2020) Moholo, Itumeleng Moses
Water and energy are the key drivers of sustainable development, yet the world is facing severe energy and water crisis. Photovoltaic water pumping system (PVWPS) is a mature technology that conserves both energy and water for sustainable applications. However the wider application of this technology is affected by improper system designs wider application of this technology is affected by improper system designs, high initial costs lack and of predictability . This study aims to evaluate critical factors for optimal sizing and performance prediction of PVWPS at the least cost of pumping. First objective of this study is to develop the meteorological parameters interpolated grid data base for Lesotho. Solar and ambient temperature data are recorded for 0.25 ×0.25 longitude and latitude interval for the range 27.00 East to 30.00 East and 28.00 South to 31.00 South. The range defines the extreme longitude and latitude boundaries of Lesotho. Grid data is interpolated and implemented into the computer program, hence meteorological parameters variations are automatically read at any point in Lesotho. Another objective is to develop a flow-power function, which comprehensively takes into account the instantaneous variation of ambient temperatures and solar irradiance and their effect on the pump system flow-rate and the system resistance. The flow-power function expresses the flow output of the solar pumping system as a function of the dynamic variation of the photovoltaic array power output, for a given pump and pipe parameters. The PVWPS components namely, the pump; solar photovoltaic array; pipeline system and the water storage are sized in an integrated fashion. The model is especially suitable for long pipelines where the PV array power required to deliver a demanded daily volume of water significantly decreases as the pumping main pipe diameter is increased. From the factory gate to site of installation the relative specific costs of PV array, pump and pipe differ from place to place. As a final objective an economical optimum combination of these sub system components, which meet the required daily demand of water at the least cost of pumping, is attained. Applying a time-step balance of the hourly pump flow output with the hourly water demand also enables a more precise estimation of the required balancing storage, by applying the mass-balance-curve approach. This study shows; how does the time step variation in meteorological parameters for a specified water requirement affect PVWP systems design and efficiencies; and how can the different pump-pipe combinations of PVWP systems be optimized from an integrated system perspective to arrive at the least cost of pumping. The applied method is technical accurate for sizing and also more economical thus proves to be a significant improvement to the traditional simplified approach of sizing solar pumping systems. It can result in significantly reduced unit cost of pumping. In the case study for Tosing, Lesotho (27.90 longitude 30.36 latitude) potable water demand of 350m3/ day. The design overall system efficiency is 7.1% the required PV array power was reduced by 25.8 % and the required water storage capacity reduced by 50% when compared to their respective values prescribed by the traditional sizing method.
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.
The Impact of Intermittent Renewable Energy Generators on Lesotho National Electricity Grid
(National University of Lesotho, 2020) Mokeke, Sebota; Prof Thamae, L. Z.
Lesotho is confronted with huge challenge of low electricity access, with 63.9 % of the population lacking access to electricity. Lack of electricity impedes both economic and social development. However, Lesotho has abundant renewable energy resources that can be exploited through large integration of renewable energy sources. The inherent variability and uncertainty of renewable energy sources (solar-PV and wind) creates both operational and planning challenges for the power system. This results in the reluctance of the power system operators integrating largescale renewables to the national grid due to the power system stability problems. The characteristics of the intermittent renewable energy generators mandates that careful grid impact studies be performed in ensuring that the power grid is operated stably. The thesis focuses on the impact of the Intermittent Renewable Energy Generators (IREGs) on the power stability of Lesotho electrical grid considering both solar photovoltaic (PV) and wind generation at Ha-Ramarothole and Letseng respectively. The integration of IREGs involves both steady state and dynamic analysis of the electrical network. To this aim, the thesis assesses the impact of the IREGs on the stability of Lesotho electrical network at transmission level. In addition, maximum allowable penetration levels were determined at the point of interconnection. Load flow simulations were performed to assess the steady state performance of the electrical network. Furthermore, the transient analysis was performed by applying the 3-phase short circuit at the critical points of the network and observing how voltage, frequency and rotor angle stability were affected and evaluated against grid code of Lesotho. The simulations were performed using DigSILENT PowerFactory software, which was used to model the electrical network of Lesotho. The maximum allowable penetrations for solar was about 19 % at substation at Ramarothole while for the wind it was found to be 27 % at Letseng substation. The simulations revealed that increased penetration of the IREGs led to grid instability. For all the simulations, frequency stability was observed except for the penetration of 36 MW for solar farm. The voltage ii violations at the Tlokoeng substation of 1.051 p.u. resulted from penetration limit of 52 MW capacity of the wind farm at Letseng. The solar penetration limit resulted from the rotor angle instability as increased penetration resulted in large rotor angle oscillations.
Construction of a long-term hourly electricity demand curve and peak load using MAED-EL for Lesotho
(National University of Lesotho, 2020) Kente, Leana
At the time that this study was undertaken, Lesotho Electrical Company (LEC) had no longterm hourly load curve forecast for electricity consumption. This makes it difficult for the utility to plan for future power plants and cost effective bilateral agreements as well as policy maker to make informed decision and for Independent Power Producers (IPPs) to be developed by investor. Therefore, this study aimed to construct a long-term hourly load curve for future electricity consumption in Lesotho starting with 2018 as the base year, followed by five-year long intervals from 2020 to 2040. The Model for Analysis of Energy Demand (MAED-EL) was used to calculate future hourly load curves for electricity and it uses the end-use approach when calculating the energy projections. Three scenarios were considered in this study to model possible trajectories of future electricity consumption, namely: Business-as-Usual (BAU), Low Economy Scenario (LE) and High Economy Scenario (HE). The annual growth rates of electricity consumption were estimated to be 4.3% for BAU, 2.4% for LE and 6.3% for HE. The projected peak demand for each scenario occurs during winter season (June to July). It was anticipated that the peak load will grow by 224% 123% and 54% for HE, BAU and LE scenarios from 2020 to 2040 while the energy consumption will increase by 223%, 122% and 53% for HE, BAU and LE from 2020 to 2040. The base load was predicted to grow from 58.77 MW,56.79 MW and 54.74 MW for HE,BAU and LE to 190.05 MW, 126.29 and 84.29 in for HE,BAU and LE respectevely in 2040 . Due to growth of electrical energy load the power deficit which was already high in 2018 at 94.44 MW would increase to 539.92 MW, 330.1 MW and 196.44 MW for HE, BAU and LE respectively in 2040. The Peak Load of the system was equal or above 75% of system peak load for 20% of the available time of the year.
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.
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.
Determination of Cost-Reflective Feed-in Tariff for Grid Connected Solar PV Systems in Lesotho
(National University of Lesotho, 2020-05) Kokome, Limpho
Lesotho needs a feed-in tariff policy that can help accelerate integration of renewable energy in its electricity grid. In this study a method to determine the feed-in tariff for grid connected solar Photovoltaic (PV) systems was developed. The necessity to set different tariffs for different locations in terms of the solar PV array yield 𝑌, and different tariffs for different installed capacities were examined. Location specific tariffs were examined because given a particular solar module, the array yield 𝑌 could vary with location because of different ambient temperature and radiation, while size specific tariffs were examined because solar PV systems have different specific costs for different system sizes. In order to determine the cost reflective feed-in tariff, the Levelized Cost of Electricity (LCOE) was used as the objective function. With this approach the feed-in tariff was set as the price for selling electricity that is reasonably above the unit cost of production. A custom spreadsheet model was used to calculate the solar PV array yield 𝑌 over Lesotho. This array yield was used to divide Lesotho into two regions, low yield regions, and high yield regions. Representative systems were chosen and the feed-in tariff for different solar PV installed capacities in both regions were determined. The study found that the feed-in tariff varies with location and system size as follows; System Category FiT ($/kWh) Low Array Yield Region High Array Yield Region 30 kWp Roof Mount 0.1778 0.1616 500 kWp Roof Mount 0.1597 0.1451 30 kWp Ground Mount 0.1740 0.1581 500 kWp Groun Mount 0.1453 0.1321 10 000 kWp Ground Mount 0.1138 0.1034 The study recommends a feed-in tariff that is both location and size specific. The feed-in tariff depends on duration of the tariff with shorter periods resulting in higher feed-in tariff. A 20-year duration of the feed-in tariff is therefore recommended by this study. The method used in this study to determine the feed-in tariff included the impact of inflation in the analysis and therefore a fixed feed-in tariff (that is not indexed to inflation) is recommended. The energy regulator, and theministry responsible for energy policy setting can make use of this study in setting out feed-in tariff policy.

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