Development of a Wind-Solar PV Hybrid System for Small-Scale Power Generation in Low Wind Speed Regimes in Kenya

Abstract

Energy is a critical factor to society's economic growth. Increased energy demand has led to the usage of conventional energy sources such as coal, oil and natural gas, which pose ecological and health risks. Wind and solar resources are intermittent in nature, a condition that leads to fluctuations in their energies. Lack of continuous availability of these resources in nature has always brought stability challenges in power grids affecting the quality of electricity and lowering their reliability. Integration and optimization of wind and solar energy systems offer a solution. By integrating two or more energy resources through a hybrid technology, it is possible to minimize the effects caused by the intermittence of renewable energy resources. Much has been reported on solar and wind resources with little said on the viability of their complementary nature in low wind speed regime areas. This study aims at developing and optimizing a wind-solar hybrid energy system for electrification in low wind speed regimes where wind resource is rarely exploited to its full potential. Resource ground assessments were conducted using simulation and experimental methods. Wind distribution revealed Weibull’s shape (k) and scale (c) parameter values of 1.9 and 3.22 m/s, respectively. A WPD of 17 W/m2 at 20 m hub height and mean wind speed of 3.01 m/s has been reported. An average insolation of 5.84 kWh/m2 at 1 kWp capacity is reported. Wind and solar were found to have good complementarity increasing their viability in hybrid energy systems. Energy demand has been conducted using field surveys to establish the average load demand necessary to inform on appropriate system size. The energy demand analysis revealed a daily range of 0.052 to 4.23 kWh, where a daily average energy load of 0.582 kWh is reported. Based on these findings, a wind-solar hybrid system was developed. Turbine rotor blades were made from Styrofoam and aluminum, with a pitching allowed for energy optimization. Wind tunnel tests were done to a maximum wind speed of 20 m/s to determine TSR and CP at pitch angles between 0° and 40°. Analysis of the TSRs revealed a positively skewed pattern, implying good prospects for wind energy at low wind speeds. The foam blade performed best with a CP of 0.465 at a pitch angle of 20° and a TSR of 2.1. The CP translated to 238 W at a rated wind speed of 5 m/s. At a TSR of 1.9 and a pitch angle 15°, aluminum fared best with a CP of 0.431 which translated to 220 W at 5 m/s. Foam blades are more suitable for use in rotor blade fabrications. Field tests was conducted which revealed good wind-solar power integration in spite of time and weather changes. Vertical shear analysis revealed greater wind energy productivity at higher altitudes, where hub heights between 8 m and 50 m revealed WPD between 20 W/m2 and 79 W/m2, respectively. The hybrid system produced 143 W of solar power and 36 W of wind power at 8 m, which translate to 0.835 kWh for 5.84 peak sun hours and 0.864 kWh daily, respectively. Shear analysis provided the rated turbine wind speed of 5.0 m/s at hub height of 50 m, with a daily energy potential of 5.4 kWh. The findings revealed that the hybrid energy systems are viable for installation in rural households and small-scale utilities. Small-scale micro-grids, mini-grids, utilities, as well as the research communities exploring hybrid energy systems, could benefit from the findings and knowledge gained from this study.