Optimization of a Hybrid Solar Pv-Hydro Power in Solution of Low Power Generation Considering Dry Seasons Effects in the Northern Province of Rwanda

Emile Niringiyimana

2019-2023

PhD in Renewable Energy and Clean Energy

ABSTRACT

Fossil fuels, such as coal, oil and gas, are by far the largest contributor to global climate change, accounting for over 75 percent of global greenhouse gas emissions and nearly 90 percent of all carbon dioxide emissions. It obvious that to avoid the worst impacts of climate change, emissions need to be reduced by almost half by 2030 and reach net-zero by 2050. To achieve this, we need to end our reliance on fossil fuels and invest in alternative sources of energy that are clean, accessible, affordable, sustainable, and reliable.

Standalone Hybrid RE systems are promising ways to provide consistent and continuous power for isolated areas. Renewable energy sources can effectively reduce carbon dioxide emissions while also reducing electricity shortages, especially in rural areas where the national grid is not extended. Modelling and optimization of a hybrid solar PV-hydropower system can be a useful solution for low power generation during dry seasons. The proposed system combines two renewable energy sources (solar PV and hydro) to increase the overall energy production and provide reliable power supply to Mutobo local community throughout the year. The first step of this work is to analyze the energy demand and the availability of the two energy sources. The solar PV panels generate electricity during the day when there is sunlight, while the hydro turbines generate electricity from the water flow in the river. The availability of solar PV and hydropower energy can vary depending on the weather and water levels, and this needs to be taken into account in the design of the system. The second step is to optimize the hybrid solar PV-hydropower system to maximize its efficiency and performance. This involves selecting the appropriate components such as solar panels, batteries, inverters, and turbines, as well as determining the optimal sizing and placement of these components.

This work developed the prospect and cost effectiveness hybrid system complementarity between a 100kW standalone solar PV system and a small-scale 200KW hydropower station with a pumped storage reservoir in Rwanda at Mutobo micro hydro power station. In order to establish the optimal size of a RE system with adequate sizing of system components, Scientific modeling methods are proposed. electricity demand, solar radiation, hydrology, climate data are utilized as system input. The average daily solar radiation in Mutobo is 5.6 KWh/m2 and average wind speed is 3.5 m/s. The ideal integrated RE system, according to HOMER optimization, consists of 91.21kW PV, 146kW hydropower, 12 x 24V li-ion batteries with a 20kW converter. The optimization method of the PV-hydro power hybrid systems control, sizing and choice of components is to decrease the system Net present cost, Cost of energy (COE), unmet load and reduction of CO2 using HOMER Pro optimization software and the incremental conductance algorithm.

In this study HOMER Pro software is used to find the optimal sizing of the hardware components due to its ease and fast searching ability and the system results was validated in Plexos9 software. PV modules are embedded with a modified incremental conductance algorithm based Maximum power point tracker power generation control to maximize the energy captured from the sun when the irradiance decreases. The power consumption varies according to the dominant source of energy in the system by controlling the energy compensation depending on the PV outputs (high or low) considering high/low peak hours. Mitigating the effects of dry seasons on the system, the capacity of the solar PV panels is increased to compensate for the lower hydro energy production during dry seasons and when the hydropower is supplying enough power to load, the generation from PV modules is stored as excess energy generated during the wet season for use during the dry season. Additionally, the control system is designed to prioritize the use of solar energy during the dry season when hydro energy is limited. By modelling and optimizing a hybrid solar PV-hydropower system can be an effective solution for low power generation considering dry season effects. The system can provide reliable and sustainable energy supply throughout the year, while minimizing the cost and environmental impact of energy production.

The power consumption varies according to dominant source of energy in the system by controlling the energy compensation depending on the generation capacity of each power source. The initial investment of the RE system is $977,689.25, and its operation and maintenance expenses is $142,769.39 over a 25-year period. Although the investment is very high, the targeted profits in future are huge, taking into consideration of high investment in rural electrification structure implementations, tied with an increase of electricity cost and the 5 years payback period. The study outcomes suggest that standalone hybrid solar PV-Hydropower system is feasible with zero pollution in Mutobo community.

According to part 5-2 of HOMER optimization results, validating the hybrid solar/hydropower system in Plexos9 demonstrated that the system is applicable in the north province of Rwanda. This is obtained from the figure 5-12 that shows the annual production of the solar PV array and hydropower station input to the transmission network where the power generated from the solar PV module is typically enough to satisfy the load demand.

The system was simulated in Matlab/Simulink to verify the feasibility of the hybrid system using the available data from the case study, the system parameters and settings selected from the Matlab/Simulink library. The results in show that the suggested hybrid system can be used in Mutobo village where the power generated from the PV array is enough to complement with the hydropower generation when the runoff river flowrate is decreases to the minimum rate to rotate the turbine.

Keys words: Hybrid Power System, hydropower, solar pv systems, pumped storage, HOMER optimization.