Theses and Dissertations

Permanent URI for this collection

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

Browse

Now showing 1 - 15 of 15

Open Access
Analysis of the viability of using solar thermal energy for Maluti Mountain Brewery
(National University of Lesotho, 2021) Lillane, Malillane; Hove, Tawanda; Mpholo, M
It has been established by literature that there is worldly movement towards renewable energy usage because of global warming. Solar energy among many is one form of renewable energy that can be used to reduce conventional energy usage. This study realized an opportunity to reduce the conventional energy (coal) use at Maluti Mountain Brewery (MMB); a brewery in Lesotho by preheating the boiler make up water. The boiler at MMB is serviced by condensate (70°C) and the cold water from the tap. The cold makeup water mixes with the condensate prior to the being carried into the boiler and thus reducing the efficiency of the boiler. This is because the boiler in turn demands a lot of coal to heat up the boiler feed water. A retrofitted solar thermal system into the existing system at MMB was done. This system was aimed at preheating the cold make up water before it mixes with the hot condensate in order to avoid the makeup water from reducing the condensate temperature. An Excel based model was made in order to design a solar thermal system that is cost effective and technically viable. The designed system is an active solar thermal system composed of evacuated tube collector with the EPD of 18 kWh/$), collector area of 80 m2 which was decided upon by the required maximum storage tank temperature of 100 °C. The storage tank size of the system was found to be 2110 Liters. A tank of such size could not be found on the market; therefore, a 2500 Liters storage tank would be ideal for the purpose. The actual collector area decided upon according to the collector aperture area of 2.998 was found to be 81 m2. The system was found to be able to preheat 54% of the makeup water (12 % of the boiler feed water is the makeup water). The amount of coal used by MMB would be reduced by 11% and therefore saving the company as the NPVSS is positive, amounting to $25044 for over 20 years.
Open Access
Design and analysis for a feasibility study of a floating solar PV power system for Metolong Dam
(National University of Lesotho, 2022) Moqulo, Rorisang Christopher; Thamae, Leboli Zak; Hove, Tawanda
Over the past years, an increasing capacity of floating solar photovoltaic (FSPV) technology utilizing water bodies to install solar power has been implemented, showing an alternative for countries where land use is constrained, land is not easily accessible, or land leasing is expensive. In addition to reducing land use competition, FSPV is promoted as a more efficient solar technology, bringing with it additional benefits such as reduced water evaporation and decreased algae growth. Based on previous field studies and industry insights, this study aims to analyse whether an FSPV project can be a feasible and cost-effective option for electricity generation and usage at Metolong Dam and water treatment works (WTW) located in Maseru district, Lesotho. Furthermore, PV module temperature analysis is another critical area, governing the efficiency performance of solar cells. In this study, the initial approach entailed the modelling of the Metolong reservoir water temperature (using Microsoft Excel) due to insufficient water temperature data at a selected location (since simulation software does not have features for FSPV). Then water temperature was used to investigate the photovoltaic (PV) module temperature on water bodies. The optimal sizing and performance prediction of a proposed power plant was modelled using a set of mathematical equations in a spreadsheet application (Microsoft Excel) and PVSyst software. Both models were compared to analyse the difference in annual electricity generation. Then, an economic analysis was performed to showcase the Levelized Cost of Electricity (LCOE) and Net Present Value (NPV). Finally, an evaporation model was proposed with the objective to quantify the potential savings an FSPV could provide using the calculations adapted from the Penman-Monteith model. The results indicated that this FSPV power plant would significantly contribute to the reduction of carbon dioxide (CO2) emissions. The recommended FSPV, with total installed capacity of 7.8 MWp, would consist of 3 platforms with an installed power of 2.6 MWp each. The study reveals that the proposed FSPV energy generation system is about 3.4% higher than ground-mounted PV (GMPV) generation system predicted by the PVSyst software due to the cooling effect provided by water just below the panels. From the simulation results, the value of performance ratio (PR) comes out as 90%, and the capacity utilization factor (CUF) value is 15.21% with a total effective energy generation at the output of the array of 17,345 MWh per year. The system could meet up to 70% of load demand during a typical day in winter months at the selected facilities. The FSPV system could cost US$ 10 Million with a payback period of 13 years, where the largest contributors to this cost are related to the floating structures and anchoring system of this plant. The proposed FSPV plant will substantially reduce the cost of energy as the plant cost is expected to be considerably reduced based on the low LCOE of 36.4 $/MWh. The economic feasibility of a FSPV system on a Metolong reservoir was thus established, and may be considered an efficient use option for electricity generation in Lesotho. Additionally, the shading provided by the FSPV system can save up to 84,136 m3 of water annually. The annual reduction of greenhouse gas (GHG) emissions was analyzed and found to be 17,329 tCO2 per year. Future studies should include more in-depth research into factors such as the impact of substation upgrade costs, variable interest rates, economies and environmental impacts.
Open Access
Determination of cost-reflective feed-in tariff for grid connected solar PV systems in Lesotho
(National University of Lesotho, 2020) Kokome, Limpho; Hove, Tawanda
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 the ministry responsible for energy policy setting can make use of this study in setting out feed-in tariff policy.
Open Access
Development of solar radiation database and its integration into solar process applications in Lesotho
(National University of Lesotho, 2020) 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 2.67 % 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.
Open Access
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.
Open Access
Economic comparison between solar PV and diesel operated system for irrigation application in Lesotho
(National University of Lesotho, 2023) Tukula, Mafa; Makhele, Molefe; Mokeke, Sebota; Hove, Tawanda
Access to electricity is improving in Lesotho although the use of energy for economic growth is still stagnant. Sustainable economic growth is essential for improving livelihoods; however, this is difficult to achieve in rural areas where agriculture is the main industry. Hence in this study, an innovative economic analysis of solar and diesel-operated pumping devices for irrigation application in Lesotho is put forth. The main objective of the study is to scrutinize the concepts related to the effective characteristics of irrigation pumps, their design, selection, installation, and possible diagnosis of their problems in order to assist farmers and stakeholders. Furthermore, the aim is to compare the economic costs of solar and diesel-pumping systems. Several novel solar photovoltaic models and solutions have been proposed in an effort to circumvent some of the challenges. In addition, a recent intervention that serves as an example of the new study technique is discussed. A thorough technique for sizing and performance forecasting of photovoltaic (PV) solar pumps and a diesel generator is also given. The empirical data on the performance of the solar pump, the prescribed model of sizing, and the performance extrapolation approach made use of data on solar radiation and ambient temperature of the location. The empirical functions of the flow rate, as opposed to solar power, were similarly derived for different pipe size diameters of 63 mm, 75 mm, 90 mm, and 110 mm. Additionally, depending on the pump, pipe diameter, and PV array size that resulted in the lowest pumping cost per unit of energy, the optimum solar pumping system was chosen. This method of designing solar pumping systems was advised because it produced significantly different and more accurate results than the frequently employed straightforward method, which ignored the fact that the total dynamic head (TDH) fluctuated as the solar irradiance deviated. The simulation results drawn indicated that the best system configuration that resulted in the least unit cost of pumping is comprised of a 4 kW Lorentz PS2-4000-CS-F32-20-2 centrifugal solar surface pump, a 110 mm pipe size, and a 2110 watt PV array. As a stipulation, it is important to point out that solar photovoltaic (PV) seems to be a promising energy alternative to support irrigation development in Lesotho. In that matter, the unit cost of pumping for a solar PV-operated pump for irrigation application is 3.58 USD cents/ m³ while for a diesel generator it is 16.1 USD cents/ m³. Based on the life cycle cost analysis (LCCA) of both systems, the annualized cost of solar PV at a 10% discount rate is $1263.00 and that of a diesel generator is $5517.00, with 35314 m³ of water pumped per annum. The cost of solar PV per watt, including installation at the initial stage is 0.42, $/watt, while for the diesel generator it is 0.41 $/watt. However, for a long run, solar PV is more cost effective as compared to diesel generator. The proposed system was also found to be not only cost-effective but similarly environmentally friendly, as it emits zero amounts of greenhouse gases (GHG). The amount of greenhouse gases to be emitted as per simulation when using a diesel generator for irrigation purposes is 32.3 tons of carbon dioxide (𝐶2) per year.
Open Access
Energy audit and management apportunities for a 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.
Open Access
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.
Open Access
Evaluation and optimisation of solar water pumping systems for Lesotho
(National University of Lesotho, 2020) Moholo, Itumeleng Moses; Hove, Tawanda
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. Keywords: meteorological grid data base, dynamic variations, photovoltaic water pumping system (PVWPS), flow-power function, optimal sizing, least cost of pumping
Open Access
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.
Open Access
Investigating viability of using solar thermal energy for optimizing the gas yields for biogas in Lesotho
(National University of Lesotho, 2021) 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 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.
Open Access
Optimal sizing, performance prediction and economic appraisal of off-grid solar PV hybrid power systems in Lesotho
(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.
Open Access
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.
Open Access
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 of Energy (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, 𝑃⁄𝑃0 for PV array size, 𝐵𝑐𝑎𝑝⁄𝐿𝑑𝑎𝑦 for battery size and 𝑄𝐷𝐺⁄𝐿̅ 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 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 (𝑃⁄𝑃0 = 11.2), battery bank size (𝐵𝑐𝑎𝑝⁄𝐿𝑑𝑎𝑦 = 1.8) and diesel generator size (𝑄𝐷𝐺⁄𝐿̅ = 2.2), operating at 83 % solar fraction and at LCOE of 0.62 USD/kWh. For 99% supply reliability, the optimum system has 𝑃⁄𝑃0 = 3.9, 𝐵𝑐𝑎𝑝⁄𝐿𝑑𝑎𝑦 = 0.292 and (𝑄𝐷𝐺⁄𝐿̅ = 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.
Open Access
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.

Browse

Browsing Theses and Dissertations by Author "Hove, Tawanda"

Results Per Page

Sort Options