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
The impact of intermittent renewable energy generators on Lesotho National Electricity Grid
(National University of Lesotho, 2020) Mokeke, Sebota; Thamae, R
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 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.
The genderperspective of socio-economic determinants of household cooking energy consumption in Lesotho
(National University of Lesotho, 2023) Nkaile, Palesa; Mpholo, Moeketsi; Thamae, Retselisitsoe
Unveiling gender dynamics in household energy consumption is a pathway to empowerment and sustainable development since the inaccessibility of electricity perpetuates gender inequality due to women’s higher involvement in time-consuming and unproductive activities such as wood collection and cooking. This study investigates the variations in fuel consumption shares between female-headed and male-headed households and explores the determinants of these differences from a gender perspective. Using the Tobit regression model to analyse the 2017 Household Energy Consumption Survey (HECS) data, the study establishes the statistical significance of socioeconomic variables on household shares of biomass, paraffin, LPG, and electricity, assuming that the shares are left-censored. The findings reveal intriguing patterns, such as the increasing shares of dirty fuels with the age of the household head regardless of gender. However, education impacts female and male-headed households differently, with female-headed households generally increasing their share of high-end fuels while male-headed households opt for transition fuels. Increasing income and households in peri-urban and urban areas are also not discriminatory in terms of gender as both reduce the share of dirty fuels and rely more on cleaner alternatives. Conversely, increasing household size affects female-headed but not male-headed households as they are found to increase the shares of transition fuels in summer but reduce the share of cleaner fuels in winter. Therefore, the study emphasises the need for targeted education and economic empowerment programmes, awareness campaigns, and income-generating skills development policy interventions to foster clean energy access and improve the well-being of Basotho households.
Techno-economic analysis and policy design for PV electricity net-metering systems in Lesotho
(National University of Lesotho, 2025) Moleko, Lebohang Albert
Lesotho imported 65% of its electricity from Electricidade de Moçambique (EDM) and Electricity Supply Commission (ESKOM) in 2019/2020 (Lesotho Electricity Company (LEC), 2020). This is higher as compared to 59% in 2018/2019 ( Lesotho Electricity and Water Authority (LEWA), 2019). This shows that there is an increasing demand, but stagnant generation capacity hence the need for the security for the supply of electricity in Lesotho. Studies have shown that the interconnection of Solar Photovoltaic (PV) systems to the grid can reduce electricity imports amongst others. The objective of my study is to design optimum grid-connected solar PV systems for residential, commercial, industrial and institutional purposes; predict the system field performance and d o a cost-benefit analysis on net metering.
Optimal PV system is designed using the Typical Meteorological Year data closest to Maseru. PV power and inverter power outputs are calculated for each hour of the given typical year. The different load profiles from the utility are also used. Net metering policy options guidelines are designed such that PV electricity is sold to the grid at the utility retail price with no PV capacity cap for net metered systems. The benefits from net metered PV systems are calculated. These are from surplus sales, avoided energy savings and peak shaving in the billing period of 12 months.
The results show that with the current electricity tariffs, the PV system that gives the net electricity payments of zero at the end of the billing period for commercial and industrial customers results in negative NPV values which indicate that the system is not acceptable. On the contrary, the net-metered residential PV system offers the profitability index of 2.7643 at the discount rate of three percent (3%) which is very attractive for investment on the customer‟s perspective. The internal rate of return of the project is thirteen percent (13%). Based on these results, it is concluded that with the current tariff settings for residential customers, only the residential PV net metering is technically and economically viable. As for the commercial and industrial activities, PV net metering is technologically viable but not economically viable.
The changes in some variables such as dropping of solar PV systems‟ capital and the increase in energy charges to $0.0423 and $0.039 for commercial and industrial customers respectively, can make the systems acceptable. The reasonable Net Present Value (NPV) values are likely to increase the adoption rate of electricity net metering. H o w e v e r , to attract more investment into the net-metering system, the interest rate of the investment should always be greater than the inflation rate. The larger the range between the two, the more attractive the investment can be.
Solar water purification system for rural areas
(National University of Lesotho, 2025) Makebe, Rethabile; Jonathan, Enock; Kao, Moruti
This dissertation examines the design, efficacy, and viability of a hybrid solar photovoltaic-thermal (PVT) and ultraviolet (UV) water purification system specifically developed for rural Lesotho, featuring a case study in the Mohale Basin. The system incorporates thermal energy capture by the solar PVT array to preheat feedwater before reverse osmosis (RO) treatment, hence improving membrane efficiency and minimizing fouling hazards. The electricity produced by the PVT array energizes UV disinfection devices and water pumps, while battery storage guarantees continuous operation under low solar irradiance circumstances.
Two optimized setups, that is, 5.2 kWp and 14.4 kWp were simulated by PVsyst, underpinned by mathematical modelling and validated against DuPont WAVE software. The 14.4 kWp configuration exhibits enhanced energy reliability with feedwater preheating to 40 °C, recovery rates of 60%, and specific energy consumption as low as 1.06 kWh/m³. Comparative evaluations solar PV and solar PVT RO demonstrate that the incorporation of PVT preheating with dual-stage RO markedly decreases operating pressures and enhances water quality. Analysis indicated that the smaller 5.2 kWp system, despite its reduced initial expenditure, yields water at a higher Levelized Cost of Water (LCOW) of USD 1.25/m³. The larger 14.4 kWp system on the other hand attained a lower LCOW of USD 0.75/m³, illustrating the benefits of economies of scale in hybrid PVT-RO configurations.
This work demonstrates the viability of scalable solar-driven water purification systems for offgrid rural Lesotho, with implications for sustainable development and climate adaptation, providing a viable approach to furthering Sustainable Development Goals 6 (Clean Water and Sanitation) and 7 (Affordable and Clean Energy) in Lesotho.
Rehabilitation of Katse Dam mini-hydropower plant
(National University of Lesotho, 2022) Thamae, Ntoampe W; Makhele, Molefe; Khaba, Liphapang
The Katse Dam Mini-Hydropower station was designed to generate and supply electricity to auxiliary systems without connecting to the grid. This would increase the dam power supply and reliability thereby reducing the electricity bill incurred on the Lesotho Highland Water Project (LHWP) for operations. However, to date, the Mini-Hydropower station is not fully operational.
In this study, the decommissioned Katse Dam Mini-Hydropower plant’s rehabilitation is evaluated. Three significant activities characterized this rehabilitation process. The upgrading of electro-mechanical equipment or damaged parts, using condition assessment filters. Uprating is explored by flow duration plots for the possibility of increasing plant capacity. Lastly, the capacity dispatch (Integration) is studied intensively with computer software package (DigSilent Power Factory), for grid integration alternatives. In general, electrical equipment is the plant's most vulnerable to fatigue. Mechanical equipment is moderately damaged, with governor and guide bearing systems standing out.
Assessment of the potential of the plant’s capacity increase revealed that the reservoir compensation flow regime resulted in minimum design values of head and discharge being fulfilled 96% of the time. The Katse Dam load capacity is met 90% of the time, while the maximum single machine power is exceeded 84% of the time.
The Mini-Hydropower stable response to dam load growth and decline without a grid was shown in the grid integration option. However, there was a substantial deviation to a sudden loss of grid without load shedding, and the local bus voltage dropped below 6% tolerance.
The findings of this investigation demonstrated the need for this plant to be rehabilitated. All the necessary tests on relevant components point to the goals of the plant and the necessity for restoration. According to the economic study, implementing this project will result in a 9year return on investment and a 2.02 MWh annual energy guarantee, which is 54% of the yearly energy consumption of the auxiliary systems.