Modelling, simulation and optimization of a solar/battery Hybrid renewable energy system with maximum power point Tracking control strategy

Abstract

Solar energy is abundantly available and it is a choice to drive the energy transition in sub-Saharan Africa. However, harvesting the maximum power from the sun is challenging since it is not always available at all times. Also, the most commonly used perturb and observe technique for harvesting maximum power suffers from slow response time and oscillations around the maximum power point. In addition to that, batteries which are a popular option for energy storage for use in times of no sunshine are costly and have short life-cycle. Hence, they need to be effectively managed to extend their useful life. The main objective of this research was to model and simulate a solar/battery hybrid energy system with a Maximum Power Point Tracking (MPPT) control strategy and to optimize the battery charging/discharging cycle life. The specific objectives were to: analyse the daily energy supply (solar radiation levels) and energy consumption at the study site; model and simulate a solar/battery hybrid system; design and simulate a Maximum Power Point Tracking (MPPT) control strategy; and optimize the solar system performance and the battery charging/discharging cycle life. The research was based at Moi University. The solar radiation and temperature data were collected from the Moi University Meteorological Weather Station. The power consumption was measured using the PCE360 power analyzer. The solar battery hybrid systems were modelled and simulated using HOMER Pro version 3.10.3. The MPPT was designed and simulated in MATLAB/Simulink using Perturb and Observe (P&O) technique, which incorporated a Proportional Integral Derivative (PID) controller, tuned using metaheuristic GA. The efficiency of the tracker was calculated using the EN5030 European standard for converter efficiencies. The charging/discharging of the batteries was done using a bidirectional converter integrated with a GA tuned PID controller. The battery state of charge was steadily monitored and maintained at 30% minimum. The measured average solar radiation and temperature were 4.9 kWh/m2/day and 18oC, respectively. The daily peak power consumption for the Administration building and Library were 86 kW and 93 kW respectively. From the HOMER Pro simulations, the results obtained gave an optimal system size of 90 kW for the Administration Building and 100 kW for the Margaret Thatcher Library. Also, the net present costs were Ksh27,000,000 ($191,314) for the Administration building and Ksh32,000,000 ($226,743) for the Margaret Thatcher Library while the payback period in both cases was 6 years. The MPPT had a settling time of 0.025 seconds and a tracking efficiency of 99.5%. The study concluded that maximum power point tracking significantly enhances solar energy harvesting. It is recommended that the strategy for tracking the maximum power point be utilized to boost the output power from solar PV system in Moi university’s Administration and Library Buildings and any other similar institution.