Small-scale Wind Turbine Research Articles

Identification of airfoil polars from uncertain experimental measurements

Abstract. A new method is described to identify the aerodynamic characteristics of blade airfoils directly from operational data of the turbine. Improving on a previously published approach, the present method is based on a new maximum likelihood formulation that includes errors in both the outputs and the inputs, generalizing the classical error-in-the-outputs-only formulation. Since many parameters are necessary to meaningfully represent the behavior of airfoil polars as functions of angle of attack and Reynolds number, the approach uses a singular value decomposition to solve for a reduced set of observable parameters. The new method is demonstrated by identifying high-quality polars for small-scale wind turbines used in wind tunnel experiments for wake and wind farm control research.

Vibration-based monitoring of a small-scale wind turbine blade under varying climate conditions. Part I: An experimental benchmark.

SummaryStructural health monitoring (SHM) has been increasingly exploited in recent years as a valuable tool for assessing performance throughout the life cycle of structural systems, as well as for supporting decision‐making and maintenance planning. Although a great assortment of SHM methods has been developed, only a limited number of studies exist serving as reference basis for the comparison of different techniques. In this paper, the vibration‐based assessment of a small‐scale wind turbine (WT) blade is experimentally investigated, with the aim of establishing a benchmark case study for the SHM community. The structure under consideration, provided by Sonkyo Energy as part of the Windspot 3.5 kW WT model, is tested in both healthy and damaged states under varying environmental, that is, temperature, conditions as imposed by means of a climatic chamber. This study offers a thorough documentation of the configuration of this experimental benchmark, including the types of deployed sensors, the nature of excitation and available measurements, and the investigated damage scenarios and environmental variations enforced. Lastly, an overview of the raw and processed measurement data, made available to researchers via an open access Zenodo repository, is herein provided.

Experimental and Numerical Investigation of the Influence of Leading Edge Tubercles on S823 Airfoil Behavior

Investigating the role of leading edge tubercles on the aerodynamic behavior of S823 airfoil tailored for wind turbine applications has been the forefront of the study. The aerodynamic characteristics of S823 airfoil effectuated by leading edge tubercles are ascertained at Reynolds number Re=200000 which is the usual operating range of most of the small-scale wind turbines. Firstly, the study elucidates the numerical investigation of baseline airfoil and later modified airfoils exhibiting different amplitude A and wavelength λ of the sinusoidal leading edge tubercles represented as A07W50, A12W50, and A07W25. The aerodynamic characteristics of the airfoils at Re=200000 and angles-of-attack ranging from 00 to 200 are evaluated numerically through k-ω SST turbulence model using ANSYS FLUENT® software package. A preliminary comparison of the computational data shows that the coefficient of lift Cl of all the modified airfoils was visibly superior to the baseline model across the angles tested. A07W50, A12W50 and A07W25 registered 20.6%, 26.2%, and 8.7% increase in the Cl values as compared to the baseline model. Contrasting to the Cl values, the aerodynamic efficiency Cl/Cd of the baseline model was slightly better but only across the pre-stall regime and later culminated with a sudden hard stall. Promisingly, this type of hard stall was not true for the tubercled models that demonstrated a more gradual and restrained stalling characteristic, thus showcasing superior performance in the post stall envelope that was never observed for the baseline model. Based on the outcomes, A07W50 model that displayed better aerodynamic characteristics was eventually fabricated and experimentally tested for its performance in a low speed wind tunnel. The numerical results of A07W50 were in good agreement with the experimental results. The overall results of the study prove beyond any point of doubt that tubercles indeed aid in improving the aerodynamic characteristics by enhancing the lift Coefficient Cl, rendering soft stalling nature and extending the scope of operation for the airfoil under study. Finally, the study positively confirms that leading edge tubercles very much play a significant role in passively augmenting the fluid dynamic characteristics of S823 airfoil and also qualify them to be a competitive passive flow control device.

Nacelle-to-Tower Multilevel IPT System for Small-Scale Wind Turbines

The use of small-scale wind turbines (SSWTs) in private households not only allows for increased renewable energy generation but also improved grid stability and resilience of individual regions. However, there are strict requirements regarding the efficiency, reliability, and electrical safety of SSWTs because of their low power levels, long payback period, and the fact that they are installed nearby residential areas. This article proposes a novel yaw inductive power transfer system based on a multilevel converter, which mitigates the main disadvantages of SSWTs—slip rings, low-voltage energy generation, etc. The system utilizes low-voltage mosfet s in multilevel boost-series resonant topology combined with zero-voltage switching techniques to maximize efficiency. The operating principle, switching waveforms, and behavior of the converter are described and analyzed. The cell voltage balancing algorithms are presented as well. Two different control techniques for power flow regulation have been introduced and compared. The effectiveness of the proposed solution has been verified by building a 3.3-kW prototype system and a comprehensive measuring of its performance. The experimental results show that the peak power transfer efficiency reaches 92.5% while converting generator voltage from 60 V dc to grid compatible 400 V dc.

Computational Analysis of an Optimized Curved-Bladed Small-Scale Horizontal Axis Wind Turbine

Abstract This article aims to study numerically the effect of curvature of linear blade profile on the performance of small-scale horizontal axis wind turbine (SSHAWT). Rotors with two curvature types, f forward angles 5 deg, 10 deg, 15 deg, 20 deg, 30 deg, and 45 deg and backward angles −5 deg, −10 deg, and −15 deg, are investigated. Furthermore, three curvature positions of r/R = 0.8, 0.9, and 0.95 are studied. The numerical simulations are performed on rotors of radius 0.5 m at different wind speeds. The results are compared with straight rotor of linear profiles of chord and twist, which is considered as base rotor. It is found that the rotor with forward curvature of 5 deg and r/R = 0.9 has the highest power coefficient compared with the other rotors. At the peak performance, the proposed rotor reduces the axial thrust by about 12.5% compared with the base rotor. The flow behavior represented by the streamlines contours is also discussed. In such case, the separation approximately disappeared for the tip speed ratios of 5 and 6, which is responsible for the performance peak.

Aerodynamic modeling of simplified wind turbine rotors targeting small-scale applications in Sri Lanka

A design and optimization procedure of simplified wind turbine rotors for small-scale applications is presented. The need for this research has arisen from the recent national initiative of the government of Sri Lanka titled ‘Battle for Wind Energy’ in promoting small scale grid connected wind plants for electricity customers under Net Metering scheme. The main objective of this research is to assist local developers to design optimum rotors for given electrical generators (as determined by customer requirements), suitable for wind characteristics at specific locations. Another objective is to enhance local manufacturing capabilities by providing a design option of a simplified rotor blade geometry. A study on the correlation between population density of electricity customers and wind energy potentials was carried out to categorize the demand centres based on wind energy potentials in proposing series of small-scale wind turbine designs. A unique and improved rotor design procedure is presented which attempts to match the point of maximum performance of a rotor (design tip speed ratio) with the design wind speed of a given location by considering generator performance. The new design procedure showed successful convergence on a unique blade diameter for each rotor configuration that allowed the design tip speed ratio to match the design wind speed. The performance evaluation of rotor designs showed that high solidity rotors work better on the low wind potential region while low solidity rotors dominate medium and high wind potential regions. The performance reductions of simplified rotor designs are not significant and therefore would be an effective way to enhance value addition through local manufacture. Problem statement•Lack of a rotor design procedure that considers generator performance.•Lack of a rotor design procedure for blades with an optimum simplified geometry.•Geographical mismatch between high resource sites and location of electricity consumers in Sri Lanka.•Lack of optimized small-scale wind turbine designs for sites with different wind potentials in Sri Lanka.•Limited opportunities for local manufacture in Sri Lanka. Major novel contributions•Identification of geographical locations most suitable for promoting small-scale wind turbines.•Creation of rotor design procedures for optimized and simplified blade geometries considering generator performance.•Creation of optimized and simplified wind turbine rotor designs for different wind potential regions in Sri Lanka.

A Proposal to Control Active and Reactive Power in Distributed Generation Systems Using Small Wind Turbines

This paper presents a proposal to control active and reactive power of small wind turbines employing permanent magnet synchronous generator (PMSG) in distributed generation systems. A three-phase AC-DC-AC electric power converter is employed to process the energy generated by the PMSG. Direct power control is applied to generate the PWM signals at the DC-DC converter, which allows controlling the active power through an adaptive PI controller by means of a gain scheduling adaptation mechanism. A voltage source inverter (VSI) is utilized to connect the machine to the electrical grid following stability and low harmonic distortion requirements. In addition, VSI has the role of controlling the reactive power exchanged with the grid. Simulation results have shown that the proposed system is reliable, leading to good results for a small-scale wind turbine. Moreover, direct power control is a strong and low-cost alternative for maximum power point tracking application. The reactive power control, in turns, adds a suitable extra degree of freedom to the system, which can be used to reduce the impact of voltage fluctuations and short-circuit on the grid.

Test campaign and application of a small-scale ducted wind turbine with analysis of yaw angle influence

This paper aims to investigate the innovative design of a ducted horizontal-axis wind turbine and to compare its energy production with a traditional free turbine for energy harvesting, both at laboratory and on relevant environment scales.The ducted wind turbine was designed considering a convergent-divergent duct, with the turbine in the throat section, where the velocity is maximum. The first part of the present paper describes the test rig and the experimental activities at the University of Genoa (Italy) wind tunnel, aimed comparing between the ducted and the traditional wind turbine at laboratory scale, considering the same rotor and comparing the power production. The second part describes the pre-commercial prototype of the ducted turbine (1 m rotor diameter), installed in the harbor of Genoa and tested under real conditions. The two experimental campaigns have shown a power increase up to 2.5 from the same rotor, compared to the free turbine configuration. In both experimental campaigns, the influence of the angle between the wind direction and the duct was investigated to determine the maximum power output of the turbine, corresponding to a yaw angle of 20°. As a final step, a possible application of this kind of ducted wind turbines is presented, investigating the case study of highway tunnel illumination: in this case, the presence of a yaw angle allows for reducing the number of turbines for the same energy production.

Nonlinear Optimal Control for PMSG-Based Wind Energy Conversion Systems

This paper presents the design of a nonlinear optimal control strategy for a wind energy generation system based on a small scale wind turbine, a permanent magnet synchronous generator, a back-to-back power converter, and an LCL filter interconnected with the grid. The main control objectives in this energy system involve the trajectory tracking and regulation of different system variables as generator angular speed, DC-link voltage and reactive power. In order to fulfill these objectives, the application of optimal controllers based on the state-dependent coefficient factorization technique is proposed for both the generator-side converter and the grid-side converter. The advantages of the proposed control scheme are to achieve a wide system operating range, due to the controller design takes into account the system nonlinearities, and in addition, an efficient trajectory tracking of time-varying references generated by a maximum power point tracking algorithm, which uses a wind speed estimator. Also, an LCL filter is used to attenuate the harmonic content of the injected current to the utility grid to satisfy interconnection standards, which requires a THD below 5%. The effectiveness of the proposed controllers is verified via simulations developed in Matlab/Simulink, where the variables to be controlled reach the desired references that ensure proper operation, maximum power extraction, and fulfillment of interconnection standards.

VISUAL ANALYTICS WEB PLATFORM FOR DETECTING HIGH WIND ENERGY POTENTIAL IN URBAN ENVIRONMENTS BY EMPLOYING OGC STANDARDS

Abstract. We propose a server-client web architecture identifying areas with high wind energy potential by employing 3D technologies and OGC standards. The assessment of a whole city or sub-regions will be supported by integrating Computational Fluid Dynamics (CFD) with historical wind sensor readings. The results, in 3D space, of such analysis could be used for locating installation points of small-scale vertical axis wind turbines in an urban area.

Energy harvesting via co-locating horizontal- and vertical-axis wind turbines

Co-locating horizontal- and vertical-axis wind turbines has been recently proposed as a possible approach to enhance the land-area power density of wind farms. In this work, we aim to study the benefits associated with such a co-location using large-eddy simulation (LES) and analytical wake models. In this regard, small-scale vertical-axis wind turbines (VAWTs) in triangular clusters are deployed within a finite-size wind farm consisting of horizontal-axis wind turbines (HAWTs). Wake flow within the wind farm and the effect of VAWTs on the overall wind-farm efficiency are investigated and quantified. The results show that the optimal deployment of small-scale VAWTs has a negligible impact on the performance of HAWT arrays while increasing the total power production. For the particular cases considered here, the power output of the co-located wind farm increases up to 21% compared to the baseline case in which only the HAWTs are present. Also, by comparing to the LES results, it is shown that the analytical framework proposed here is able to accurately predict the power production of wind farms including both HAWTs and VAWTs. Finally, as a real-world application, potential benefits of deploying small-scale VAWTs inside the Horns Rev 1 wind farm are explored for various wind directions using the calibrated wake model. The results show potential for about an 18% increase in the wind-farm power production, averaged over all wind directions, for a particular VAWT layout investigated in this study. The levelized cost of energy (LCoE) for the co-located wind farm is also assessed. The simulations finds that meanwhile the installation of VAWTs increases the annual energy production (AEP) of the wind farm, it also increases the LCoE, which is caused by a) lack of operational data, and b) a low TRL (Technology Readiness Levels) for VAWTs and floating foundations.

Pengaruh Panjang Batang dan Bentuk Daun Ekor pada Turbin Angin Sumbu Horizontal dengan Mekanisme Furling terhadap Performa Turbin

Small-scale wind turbines that operate at low wind speeds regularly will face yawing performance problems. The purpose of this study was to determine the effect of stem length and tail shape on turbine performance through the power generated and the yawing angle and furling angle that formed. An experimental method was used in this research. Tail stem length variations that used were 0.35 m, 0.53 m and 0.71 m. The tail shape varies Rectangular, Trapezoidal, Triangular, Up Rectangular, Down Rectangular, Up Trapezoidal, Down Trapezoidal, Up Triangular and Down Triangular. Wind speed used in this case is 4.3 m/s, 4.8 m/s and 5.2 m/s. The tests carried out at Marina Beach, Semarang. Power measurements using a digital multimeter. Yawing and furling angle measurements using video recordings and measured using Solidworks. Wind speed measurements using a digital anemometer. The results showed that the best configuration is the triangular tail shape with 0,53 m of tail stem length. The power generated of this configuration has increased from wind speed of 4.3 m/s (0.816 Watt) to 4.8 m/s (1.140 Watt) and decreased at a wind speed of 5.2 m/s (1.081 Watt). This phenomenon is related to the design where at wind speed above 5 m/s, the design of furling mechanism will work to reduce the capture of wind energy by diverting the direction of the rotor towards the wind direction. So that the damage of the blade due to higher wind pressure can be minimized.

Performance and Aeroacoustic Noise Prediction for an Array of Small-Scale Vertical Axis Wind Turbines

Small-scale vertical axis wind turbines are good candidates for urban area use where, due to various obstacles, the airflow is turbulent. In urban areas, air velocity is mostly low and site specific, so just in a few places, like tall buildings, there are suitable airflow situation in order to use turbine, so it is a good idea to install more than one turbine in such locations. On the other hand, acoustic noise that is emitted from turbines may bother people living in that area. In the current study, power performance of small-scale vertical axis wind turbines in a V-form array configuration is investigated using detached eddy simulation method. Also, Ffowcs Williams and Hawkings acoustic analogy formulation is conducted in order to predict the noise radiation level of turbines. Results showed that power performance of most of the turbines increased due to venturi effect that is made by low speed regions behind turbines. Acoustic noise analysis showed that there is a strong enhancement in sound pressure level in receivers compared with the isolated turbine.

The maximum power point tracking based-control system for small-scale wind turbine using fuzzy logic

This paper presents the research on small-scale wind turbine systems based on the Maximum Power Point Tracking (MPPT) algorithm. Then propose a new structure of a small-scale wind turbine system to simplify the structure of the system, making the system highly practical. This paper also presented an MPPT-Fuzzy controller design and proposed a control system using the wind speed sensor for small-scale wind turbines. Systems are simulated using Matlab/Simulink software to evaluate the feasibility of the proposed controller. As a result, the system with the MPPT-Fuzzy controller has much better quality than the traditional control system.

Performance analysis of a small horizontal axis wind turbine under the use of linear/nonlinear distributions for the chord and twist angle

The increase in efficiency, decrease in starting time, and ease in manufacturing of rotor blades are the most desirable aims of research in the design of small-scale wind turbines. A multi-objective optimization study is carried out to analyze the performance of a small horizontal axis wind turbine in terms of the output power and the starting time for four possible combinations of linear/nonlinear distributions of the chord length and twist angle along one-meter timber blades. The blade-element momentum theory is adopted for the calculation of the power coefficient and the starting time. The optimization is achieved through a genetic algorithm which simultaneously maximized the power coefficient and minimized the starting time. The most important contribution of this paper is the in-depth comparison of the linear and the nonlinear distributions for chord and twist angle subjected to the aforementioned optimization, which is not available in the existing literature in such detail. Results show that although the linear distributions have more deviation from the so-called ideal distributions, however, the output power performance of the blades with linear distributions is competitive with that of the nonlinear ones. Moreover, the results establish that the use of linear distribution can improve the starting performance at a lesser compromise of output power. This is of paramount importance, particularly to promote harnessing the wind energy in developing countries, as simpler distributions could facilitate the manufacturing of wind turbine blades. Apart from using the linear or nonlinear distributions for both the chord and the twist angle, two other cases are also investigated including the linear distribution for the chord and the nonlinear one for the twist and vice versa. The analysis of these cases shows that choosing the nonlinear distribution for the chord would improve the starting while using the linear one would lead to more powerful blades.

Exploring Solar and Wind Energy as a Power Generation Source for Solving the Electricity Crisis in Libya

The current study is focused on the economic and financial assessments of solar and wind power potential for nine selected regions in Libya for the first time. As the existing meteorological data, including wind speed and global solar radiation, are extremely limited due to the civil war in the country, it was therefore decided to use the NASA (National Aeronautics and Space Administration) database as a source of meteorological information to assess the wind and solar potential. The results showed that the country has huge solar energy potential compared to wind energy potential. Additionally, it is found that Al Kufrah is a suitable region for the future installation of the Photovoltaic (PV) power plant due to high annual solar radiation. Based on the actual wind speed analysis, Benghazi and Dernah are the best regions for large-scale wind farm installation in the future taking into account existing meteorological data limitations. The values of the wind power density in all regions are considerable and small-scale wind turbines can be used to generate electricity based on NASA average monthly wind data for 37 years (1982–2019). Moreover, this work aimed to evaluate the wind/PV systems technical and economically through RETScreen Expert (Version 6.0, CanmetENERGY Varennes Research Centre of Natural Resources Canada, Varennes, Canada). Focusing on the power supply crisis in the country, the potential of electricity production by 5 kW grid-connected residential/household rooftop PV in all regions is proposed and presented. Additionally, this paper evaluated a techno-economic analysis of the 50MW wind/PV system in suitable places. The performance of a 5 kW and 50 MW PV solar system with three PV technologies, namely mono-crystalline silicon, poly-crystalline silicon, and thin-film (CdTe), was also analyzed. The results demonstrated that the development of the wind/PV system in the selected regions is both technically and economically feasible. The outcomes of this study can help decision-makers in designing and installing PV power plants as an alternative source for the future.

Experimental study on novel curved blade vertical axis wind turbines

This paper presents the experimental study into the design and the electrical performance of a few novel curved blade vertical axis wind turbines. In the wind turbines, blade shape and quantity are crucial. In this study, curved wind blades are designed, fabricated, and used in developing the small-scale vertical axis wind turbines. Wind tunnel tests were carried out, and Results were presented for cases of vertical axis wind turbines with 2-blade, 3-blade, 4-blade configurations. Electrical parameters were monitored and compared for three different configurations. Results show that the curved blade wind turbine with a 3-blade configuration performs better when compared to the other two configurations.

The wind energy potential in Kudat Malaysia by considering the levelized cost of energy for combined wind turbine capacities

This paper presents the wind energy potential at Kudat Malaysia by considering the Levelized cost of energy (LCOE) model for combined wind turbine capacities. The combination of small- and utility-scale wind turbines is the key to the success of the operation of a wind park in the lower wind speed region. In a combination approach, the small-scale wind turbines provide the power required by the utility-scale wind turbines to start the blade rotation. For this reason, the particular closed-form equation was modified to determine the LCOE of a wind park with combined turbine capacities. The modified LCOE model can be used as a basis for setting tariff rates or define the economic feasibility of wind energy projects with combined wind turbine capacities.

Dynamic modelling and thermoeconomic analysis of micro wind turbines and building integrated photovoltaic panels

During the past few years a significant effort has been performed in order to promote the use of renewable energy sources. However, one of the main barriers for a mature commercialization is due to the unpredictability of the renewable power production, mainly in case of wind and solar energy. Unfortunately, electric storage devices are often poorly profitable. Therefore, some more stable renewable energy systems must be designed. In this framework, this paper presents a novel hybrid renewable system consisting of Building Integrated PhotoVoltaic panels and small-scale Wind Turbines and double-stage heat pumps. This combination is very promising since it reduces the typical fluctuations of solar or wind systems, achieving a more stable profile of the overall power production. A detailed dynamic simulation model is developed in TRNSYS environment, including validated models for all the components and a suitable thermoeconomic analysis. A case study is implemented for a hotel building, where the space heating and cooling energy is supplied by an electrically driven reversible air-to-water Heat Pump, supplied by the electricity produced by Building Integrated PhotoVoltaic panels and Wind Turbines. the thermal energy recovered from the HP desuperheater is coupled with the thermal energy produced by a two-stage cascade cycle Heat Pump to produce domestic hot water. Results are presented in terms of hourly, monthly and yearly system performance data as well as by discussing the results of a detailed sensitivity analysis performed to detect the optimum configuration and weather zone of this hybrid renewable system. An analysis of the building envelope features is also performed, according to the nearly zero energy buildings target. Results showed that the combination of photovoltaic and wind technologies allows one to significantly enhance the stability of the renewable power production. Results also show that the use of heat pumps leads to a reduction of the primary energy demand for building space heating/cooling and domestic hot water by 30%. A payback period of about 5.2 years is obtained and the optimum configuration suggests adopting one 20 kW Wind Turbine for the selected case study. • Building integrated photovoltaic panels coupled with small size wind turbines. • Dynamic simulation model developed with TRNSYS software. • Sensitivity analysis on the building envelope features and weather zones. • Simple payback period of about 4.4 years for two 20 kW wind turbines.

Computational fluid dynamics study of Savonius rotors using OpenFOAM

In this work, two-dimensional models of Savonius rotors are simulated using OpenFOAM® in order to predict the aerodynamic performance of small-scale vertical-axis wind turbines. The results are reported analyzing the aerodynamic performance and forces acting on the rotors. Power coefficient, [Formula: see text], is compared with experimental data for each operation point, and for three different geometries. Simulations with first- and second-order discretization schemes are carried out and compared, both quantitative and qualitative. Since usual grid dimensions result not to be suitable for simulations of Savonius rotors, an analysis of different domains is performed and compared. Finally, a set up for computational fluid dynamics simulation of two-dimensional Savonius rotors is proposed. The fluid–rotor interaction is analyzed and the vortex shedding is correlated with [Formula: see text] values and wake description.