The suitability of vertical axis wind turbines (VAWTs) in harnessing energy within a complex wind environment has increased their renewed interest. However, there still exists a huge knowledge gap ...about the aerodynamic performance of VAWTs operating in a turbulent flow regime. In this paper, an experimental method is presented for a deeper understanding of unsteady rotor aerodynamics under turbulent flow operating conditions. To carry out the investigation, we developed and tested a small-scale Savonius turbine in a wind tunnel. A systematic analysis of torque and power coefficients, including their variations at uniform flow, was also presented to predict the power performance. A mechanism to generate a turbulent flow was then created to analyze the effect of induced turbulence intensity on the aerodynamics and performance of the VAWT. Results revealed that the turbulence of the inflow impacted fluctuating aerodynamic loads on the turbine blade and, ultimately, its aerodynamic performance. In addition, simulations using a CFD code were performed to compare numerical data with experimental measurements. This analysis shows the effect of turbulence intensity on performance of small wind turbines, and the aerodynamics that causes the behavior.
•A wind tunnel mechanism to generate turbulent inflow is developed.•Effect of induced turbulent intensity on VAWT aerodynamic performance is analyzed.•CFD simulations are performed to compare numerical data with experimental measurements.•Turbulent inflow impacts fluctuating aerodynamic loads on turbine blade.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Solar Photovoltaics is one of the budding technologies widely acknowledged as a solution to energy poverty. This is due to its high reliability, long life and automatic operation at low maintenance ...requirements even though handicapped by its low conversion efficiency and high capital costs. This study investigates the influence of wind profiles, relative humidity and module siting on dust deposition on the surfaces of photovoltaic modules hence its overall performance in an outdoor setup. A significant decrease in short circuit current density (JSC), maximum current density (JMPP), and voltage at maximum power point (VMPP) due to dust deposits on the surface of the PV module are observed. The modules peak power (Pmax) degradation rate after a fortnight is observed to be higher (4.4 %) for sites experiencing a higher temperature coefficient (Tc) for VMPP as a consequence of temperature effects of soiling, lower wind speeds and a higher relative humidity. A lower deposition rate is observed in sites experiencing higher wind speeds and a higher module’s tilt angle thus experiencing a lower effect on the reduction of current and voltage parameters. Similarly, the site-specific average wind speeds were inadequate for complete particulate resuspension of small sized particles (less than 500μm) adhering to PV module surface. Therefore, dust accumulations on the surface of PV modules have significant deleterious effects on the current and voltage parameters.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Integration of intermittent renewable energy resources provides the potential to mitigate the impact of the variability of independent sources. The intermittent nature creates stability, reliability ...and power quality problems in power grids. Wind and solar energies are the most viable resources whose complementarity could be deployed in the development of hybrid renewable energy systems to enhance their performance. In this study, wind-solar resource complementarity is investigated to establish its viability in hybrid energy systems in Machakos, a rural-urban town whose geographical location is 1°31′S, 37,016′E in the Eastern region of Kenya. The study findings could be fundamental in energy planning and developments in the area to provide more flexible and dependable hybrid energy systems which would supply energy services under constantly changing conditions. Ground measurements included PVGIS simulation and experimental tools installed at a height of 20 m. Weibull's distribution model and energy potential of wind resource are investigated to characterize wind resource for energy generation. The Wind distribution revealed a positively skewed profile with scale (c) and shape (k) parameter values of 2.68 m/s (≈ 3.0 m/s) and 1.9 at a mean wind speed of 2.47 m/s, respectively. The findings revealed a wind power density of 17 W/m2 at an average wind speed of 3.0 m/s. Further, an annual solar insolation of 2130 kWh/m2 with monthly average of 178 kWh/m2 translating to daily insolation of 5.8 kWh/m2 at an installation capacity of 1 kWp is reported. The months with minimum and maximum solar insolation were July and March which recorded monthly averages of 145 kWh/m2 and 213 kWh/m2 translating to a daily average of 4.7 kWh/m2 and 6.9 kWh/m2, respectively. The understanding gained from this study could be useful to the renewable energy research community and can be extended to stakeholders in PV and wind energy systems for micro grids and utility applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Wind tunnel investigation is performed on small-scale vertical axis wind turbine rotors.•The aerodynamics characteristics are analyzed on Darrieus and Savonius-type VAWT configurations.•Compared to ...Savonius rotor, Darrieus rotor attains higher power coefficient across all tested wind speeds.•The results give useful insights to aerodynamic performance characteristics of small-scale wind turbine rotors.
The effects of flow regime and rotor configuration strongly influence the power performance of vertical axis wind turbines (VAWTs). Yet, there exits few experimental investigations from literature that have been carried to explain this effect. This could be attributable to huge wind tunneling cost requirement and an array of design skills required including time constrains. The balance between cost and power performance has limited development of VAWTs towards utility scale type. In this paper therefore, we seek to investigate in detail the performance characteristics of vertical axis wind rotors in a wind tunnel environment. The H-Darrieus and Savonius-type VAWT configurations have been utilized to carry out the investigation. A systematic analysis of effect of blade number, rotor configuration, and flow regime including comparison of the two configurations was presented to predict the power performance using a rotary sensor. Results revealed a significant impact of flow field regime on power performance of the VAWT models, with the Savonius-type rotor attaining lower power coefficient (CP) than the Darrieus-type rotor across all the tested wind speeds. In addition, increase in number of blades for Darrieus-type rotor revealed narrower negative CP band that decreased with increase in wind speeds. In both configurations, the CP decreased at low tip speed ratios while an increase in CP was revealed at high tip speed ratios. The understanding gained from the results could be useful to the VAWT research community, and the findings can be extended to the design of wind turbines for mini-grid and utility scale applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PV module exposure to ambient environmental factors, such as dust deposits, have negative effects on the module's peak power (Pmax) and overall power conversion efficiency (η). In this study the ...ideal counter-acting force needed to remove adhered dust particles on PV modules is investigated. An automated self-cleaning system that uses fluid velocities to suspend adhered dust particles on the PV module surface at a reduced induced static charge induction is designed. The automated system produces lift and drag forces of 3.973 N and 4.563 N per square metre, respectively, which are strong enough to loosen stuck-on dust particles on solar PV surfaces. The model's net present value (NPV) of $ 2383.71 with a dynamic payback period of 1.95 years and profitability index of 1.78 indicate that the investment in the self-cleaning model is financially feasible even for small-scale installations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
During sudden wind speed changes, the response time of the wind turbine rotor is essential so that optimum operating condition always governs. As a result, wind turbine rotors especially the blades ...are the most delicate parts in a fluctuating wind condition posing a challenge for their effective operation. This paper focuses on gain scheduling pitch and MPPT control for a small H-type Darrieus vertical axis wind turbine (VAWT) with respect to the power output. A gain scheduled controller is designed by solving Linear matrix inequalities (LMIs) and used for stability control of the Darrieus VAWT rotor in an urban wind condition. A NACA 0018 airfoil is used to demonstrate the wind speed variations and nonlinear aerodynamic rotor behavior. The Stochastic Differential Equations (SDEs) as a function of a random number are imposed in Simulink using MATLAB R2018b. The proposed gain scheduled controller is found to be stable and achieves better performance under a gusty and turbulent wind condition compared to conventional controllers. The simulations are consistent to published experimental and numerical findings such that the system behaves as closely as possible to the real H-Darrieus turbine.
•Pitch angle control increases efficiency of a small vertical axis wind turbines.•Gain scheduling guarantees desirable performance for small scale vertical axis wind turbines.•Gain scheduling control provides better quick response to wind gusts.•Pitch angle control is limited by its nonlinear relationship with the power coefficient.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Exposure of PV modules to ambient environmental conditions like dust deposits, has some deleterious effects on peak power (Pmax) and overall conversion efficiency (η). This study investigates the ...effect of module height, tilt, and orientation on the rate of dust deposition on the surfaces of PV modules. Consequently, the effect of different dust categories on Pmax and η are investigated. North facing module surfaces are observed to exhibit higher deposition rates in southerly winds. A significant decrease in conversion efficiency of 1.30%, 1.74%, 4.05%, 2.74% and 1.38% after a fortnight are observed in modules installed in five randomly selected study sites. A higher decrease in efficiency on average after a fortnight is observed in sites having traces of anthropogenic particles on dust samples collected from the PV surfaces with minimal effects observed in sites having biogenic and geogenic particles. Abundance of anthropogenic dust particles coupled with mild tilt and leeward orientation led to a higher maximum power and efficiency degradation rate.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Machakos is an area characterized by low wind speeds in the range of 0.5 m/s to 5 m/s with an annual average wind speed of 3.5 m/s. Maximum power generation from wind requires the appropriate design ...of the conversion system. In this study, two HAWT rotor blades were fabricated using Styrofoam and aluminium with a pitching mechanism to maximize power. The system was tested in a wind tunnel environment at a wind speed range of 0 m/s−20 m/s. RPMs and torque were measured and then used to calculate the TSR and power coefficients at different pitching angles. Energy optimization was performed by varying the pitch angles from 0 to 40 degree and rotational speeds, blade shape, and also a variation of blade materials. The analysis of tip speed ratios showed positive skewness implying high potential for significant energy generation at low wind speeds. At the rated wind speed of 5 m/s, Styrofoam blades performed optimally at a pitch angle of 20 degree with a tip speed ratio (TSR) of 2.1 corresponding to a Cp of 0.465. This translates to 238 W of power. Aluminium type performed optimally at a pitch angle of 15 degree with a TSR of 1.9 corresponding to a CP of 0.431, a power estimate of 220 W. These findings showed that Styrofoam blades were more effective and thus suitable for application in wind systems. The understanding gained from this study could be useful to the HAWT research community and can be extended to the turbine designs for small-scale microgrids and utility applications.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Kenya's energy depends on fossil fuels and the country is yet to embrace alternative sources that are environmentally friendly. In this paper, empirical and computational approaches are presented to ...investigate aerodynamic performance of Small Wind Turbine (SWT) operation at arid rural Mwingi-Kitui plateau region, Kenya. We used empirical statistics to represent wind resource, and Computational Fluid Dynamics (CFD) to address SWT aerodynamic performance at the site. The numerical simulations, employing Transition Shear Stress Transport (SST) model and fully mesh resolved rotor, were performed and results obtained compared with empirical methods. From the Wind Power Density (WPD) values, 44.50–85.48 W/m2 between turbine hub heights 20 and 60 m, the site corresponds to wind class ≈1; hence unsuitable for grid-connected power generation. In addition, the numerical findings give useful insights to SWT aerodynamic performance with respect to empirical approach at a plateau terrain wind regime.
•Small wind turbine aerodynamic performance is analysed at a plateau terrain.•The CFD and empirical approaches are employed for the small wind turbine analysis.•Compared to the empirical methods, the CFD model application is found appropriate.•The Mwingi-Kitui plateau is found unsuitable for grid-connected power generation.•The results give useful insights to SWT aerodynamic performance in a plateau terrain.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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