Design and Optimization of a Solar Photovoltaic Mini-Grid: Case Study of Rwumba Village of Nyamasheke District, Rwanda
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Universal access to clean energy is very paramount and brings along with it a lot of socio-economic benefits to the citizens in terms of poverty reduction, cost effectiveness and safeguarding the environment. However, most rural areas in developing countries have no access to electricity due to the high cost of power transmission and this hinders their development. In this perceptive, Rwumba Village of Nyamasheke district of Rwanda has no access to electricity from the grid. This research focused on the design of an optimum solar photovoltaic (PV) mini-grid system that can provide the required power and energy to the village. The solar PV mini-grid was designed and optimized using HOMER software. To achieve good results, two sites were visited and specific data were collected for each site by means of questionnaires. The first site visited is an existing standalone solar PV system known as Banda solar PV mini-grid and the second site is Rwumba village which is the case under study. The data collected from the existing Banda solar mini-grid include among others installed capacity and size of various system components, load data, energy and power requirements. Analysis of these data showed that this system is not optimum. The PV panels were found to be oversized whereas the storage batteries are undersized. Thus, using HOMER software, a model for optimizing this existing mini-grid was developed, simulated and validated using the data collected from the same mini-grid. The software simulated the combinations of inputs (PV panel, battery, power inverter and cost) at different capacity shortages and proposed the most optimum combinations. The best results corresponding to the optimum PV mini-grid were obtained at the capacity shortage of 3% which means that the mini-grid can meet the load at the reliability of 97% throughout the year. The estimated peak power and daily energy requirement was found to be about 7.5 kW and 51 kWh respectively. This is to be provided by PV panel capacity of 16 kW, battery bank storage of nominal capacity of 192 kWh that will be able to store energy for 3 days during cloudy days and power inverter of 12 kW. Then, the same procedure was followed to achieve most optimum results for Rwumba solar PV mini-grid. The optimum system size was found to have PV Panel capacity of 34 kW, a battery bank storage of 384 kWh nominal capacity, and power inverter of 15 kW serving an estimated daily load of 111 kWh. The power distribution system for the mini-grid was designed to be single phase supply two wire with distribution voltage of 230 V. The layout of households in the village dedicated the power to be distributed using three feeders from the power generation point. Feeder 1 is 0.4 km long, with power demand of 4.2 kW and a voltage drop of 4.5%; feeder 2 is 0.45 km long, power demand of 3.9 kW and voltage drop of 4.7% while feeder 3 is 0.45 km long, power demand of 5.9 kW and voltage drop of 4.4%. These results revealed that, the same size of the conductor present different voltage drop and power losses depending on the power demand and the location distance of the load being electrified from the generation plant. Economic analysis of the designed system was done using the life cycle cost technique. An annual interest rate of 6% and 20 years project life were used. The initial capital was found to be about USD 143,660. The payback period was found to be around 10 years at the system’s annual cash inflow of USD 13,435 and cost of energy of USD 0.419 per kWh. This means that there will be around 10 years of realizing the profit. Therefore, it was concluded that the project is financially feasible since the payback period is less than the project lifetime.