NULIR
The National University of Lesotho Institutional Repository (NULIR) is a digital archive that collects, preserves, and provides open access to the scholarly and intellectual output of the University.
Recent Submissions
GIS-based electrification planning for Lesotho using ons SET/GEP
(National University of Lesotho, 2023) Letebele, Tsepo; Thamae, Leboli Zak
Universal access to clean and affordable modern electricity is a social and economic development challenge for many countries, especially in Sub-Saharan Africa. This study carries out an in-depth analysis of GIS-based electrification planning for Lesotho using OnSSET/GEP from 2020 to 2030 to support SDG 7. The analysis looks at how an electrification rate of 47.3% by 2020 can be improved to 100% by 2030 in order to contribute to the development of a visual, interactive and effective electrification master plan as part of a wider national integrated resources planning. The study results based on the LCOE calculations indicate that optimum electrification for Lesotho can be achieved using a blended mix of grid and off-grid technologies. Grid technology has an LCOE of around 0.087 US$/kWh while of-grid technologies have an LCOE in the range between 0.229 and 0.8 US$/kWh. The electrification technology mix from this study consists of existing and extended grid networks covering the majority of the lowlands and towns in the urban areas, stand-alone solar photovoltaic (PV) systems covering the majority of rural settlements, wind power mini-grids and hydropower mini-grids covering dense rural settlements.
The total investment required for Lesotho to attain universal access to electricity by 2030 is estimated at $401.54 million to be used for infrastructure, household connections and the generation of additional new capacity. Electrification through grid connections requires 65.81% of the total investment with off-grid technologies taking up the remaining 34.19% of the investment. Results further illustrate that stand-alone solar PV systems are the least-cost technology for off-grid connections that require around 95% of the total investment towards off-grid electrification technologies. The sensitivity analysis indicates that higher electricity demand and increased population growth rate require more electrification investments and usage of the grid and mini-grid technologies while lower demand requires less investment together with the usage of stand-alone solar PV systems. Moreover, reduced solar PV technology costs encourage the usage of solar PV systems, both stand-alone and mini-grids with less investment costs.
Formulating short-term electricity demand forecasting for Lesotho
(National University of Lesotho, 2020) Lefela, Lereko; Thamae, Leboli Zak
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.
Feasibility study of micro-hydropower resources at three selected mini-grids sites for potential integration of micro-hydro with solar mini-grids
(National University of Lesotho, 2022) Sekaleli, Mamokhomo Mateboho; Khaba, L; Makhele, M; Sahar, T
The study investigated the availability of water resources in three (3) sites earmarked for solar mini grids development for potential integration with micro-hydro power to form a hybrid system. Geographic Information System (GIS) together with other tools were used to select the study sites based on the availability of water resources, population size, accessibility, catchment area and availability of hydrometric stations. The three selected sites were Matsoaing, Sehonghong and Mashai. Flow rates data for the rivers near the study sites was acquired from the Department of Water Affairs (DWA) and Lesotho Highlands Development Authority (LHDA) and processed in Microsoft Excel to find the average flow rates for development of Flow Duration Curves and determination of design flows. Topographic maps, GIS and other GIS tools were used to evaluate the available heads at the three study sites. Based on the average flow rates, available heads, gravitational force and density of water, the maximum hydropower that can be produced in Matsoaing, Mashai and Sehonghong was found to be 171.71 kW, 44.15 kW and 3,112.63 kW, respectively. The study further assessed the possibility of hybridization of micro-hydropower with solar mini grids using Hybrid Optimization of Multiple Electric Renewables (HOMER). HOMER software assesses the feasibility and profitability of renewable energy systems. Net Present Cost (NPC) has been used as the main selection criteria for the optimum system. Based on the available solar radiation and water resources, system components costs and specifications, together with different sensitivity variable values, the NPC-optimized systems for all the three sites were found to be PV-hydro-diesel hybrid systems. The Levelized Cost of Electricity (LCOE) and NPC of the systems were found to be $0.184 and $79.184 for Matsoaing, $0.666 and $375,411 for Mashai and lastly $0.483 and $369,725 for Sehonghong.
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
Estimating hydropower generation potential of the Metolong dam
(National University of Lesotho, 2022) Moerane, Mokhothu Emmanuel
Metolong dam is located 30 km east of Maseru town, with the dam retaining wall built inside the
Phuthiatsana River. The purpose of the dam is to supply portable water to Maseru, Roma Mazenod, Morija and Teyateyaneng. The Instream Flow Requirement (IFR) given post Metolong dam construction and meant to sustain life downstream of the dam was used to estimate how much hydropower can be generated from IFR. Even though the study is aimed at assessing the hydropower generation potential of the dam, it did not address the sedimentation rate occurring inside the dam per year and how much storage capacity is lost due to sedimentation. Microsoft excel spreadsheet is used to estimate how much electricity can be generated from IFR and to examine how the water temperature affects the electricity projections.
The results show that the dam has the capacity to produce 65kW from In-stream flow requirement (IFR) in April, as a month with the highest IFR and 7 kW in September, as a month with the lowest IFR. These power production figures are studied together with the water temperature in three scenarios to observe the effects of water temperature on power production. The outcome is that they seem to have no significant effect. The power production is based on when a Radial flow PAT (Pump As Turbine) of 0.6 efficiency and, generator of 0.955 efficiency are attached at IFR release point. The dam head ranges between 23 m – 44 m for IFR, with water releases of 0.01 m3/s – 0.3 m3/s. This power can be used for distributed generation or net metering by the Water and Sewage Company (WASCO). The financing of the project is not expected to exceed $50 000 given the condition of the already installed penstock at the recovery period of less than 4 years factoring in fluctuations of power brought by those of IFR for environmental purposes downstream of Metolong dam.