Cut-in Wind Speed Research Articles

Numerical investigation of vertical axis c-shaped Savonius wind turbine

In recent decades, the use of wind turbines has been successfully increasing in power generation. Various types of wind turbine configurations as well as possible blade geometries are been proposed and are still under development for extracting the maximum possible energy extraction. Vertical axis wind turbine (VAWT) found to have enhanced adaptable physiognomies to the unsteady wind of urban terrains. These turbines can yield electricity from the wind of any direction with low-slung cut-in wind speed. These turbines are ominously quieter than the old-fashioned HAWTs, light-weight, and can be straightforwardly unified into buildings. Hence, the main idea of the present work to numerically evaluate the design performance of a C-shaped Savonius turbine for wind-energy conversion thus obtaining a higher output. During computational fluid dynamic (CFD) simulations, 3 different symmetric and non-symmetric airfoils are examined. After authenticating the numerical procedure against experimental measurements, precise CFD simulations of the unsteady flow around an H-rotor Darrieus turbine have been carried out and presented here. Based on the various configuration of the H-rotor Darrieus turbine tested the DU-06-W-200 found to be capable of wind energy generation, particularly in urban areas.

A comb-like beam based piezoelectric system for galloping energy harvesting

This paper proposes a comb-like beam (CombBeam) based piezoelectric energy harvester (PEH) for harvesting wind energy by exploiting the galloping mechanism. The CombBeam-based PEH consists of a series of parasitic beams being mounted to a conventional cantilever beam with a piezoelectric transducer. A theoretical modelling method is established to simplify the proposed CombBeam-based PEH as a multiple-degree-of-freedom (MDOF) system. The conventional beam PEH is first represented as a single-degree-of-freedom (SDOF) system and the parasitic beam is then also converted into an equivalent SDOF system. A factor is derived to correct the reaction force of the SDOF model of the parasitic beam to address the force interaction between the host beam and the parasitic beam and a scaling factor is introduced to reflect the effect of the parasitic beam when being mounted onto the host beam at different positions. The complete mathematical formulations of the MDOF model for the CombBeam-based PEH under the base excitation and the aerodynamic force excitation are developed. Under the base excitation, a finite element model is built to first verify the MDOF model of the proposed CombBeam-based PEH in terms of derived equivalent lumped parameters, correction factors and scaling factor. A physical prototype of the proposed CombBeam PEH is then fabricated and the wind tunnel experiment is conducted to validate the MDOF model for predicting the energy harvesting performance under aerodynamic force excitation. The PEH undergoing galloping is referred as CombBeam-based GPEH to distinguish it with that under the base excitation. The results show that the CombBeam-based GPEH has the advantages over a conventional beam GPEH in reducing the cut-in wind speed from 2.24 m/s to 1.96 m/s and enhancing the power output around the optimal resistance for about 171.2% under a specific wind speed of 3 m/s.

Wind Energy Potential and Economic Assessment of Southeast of Pakistan

ABSTRACT This study aims to evaluate wind resource potential and analyze the performance of wind turbines for six onshore and near-coast sites (three commercial power plants and three new potential sites) of Pakistan. The technical and economic performance analysis of more than 200 commercially available turbines suitable for weak wind regions is performed, 20 turbines were selected based on performance. The percentage increase in annual Capacity Factor (CF) and decrease in Levelized Cost of Electricity (LCOE) for commercial sites using proposed turbine is 42–61% and 30–38% respectively compared to installed turbines on the sites. Three potential sites have wind power density as 155, 203, and 237 W/m2 and corresponding wind power class as poor, marginal and marginal respectively. The CF and LCOE of potential sites having marginal power class using PT10 turbine (Goldwind GW140/3.0) is up to 50% and 5.5 US¢/kWh respectively so these two sites are economically feasible for future wind projects. The CF and LCOE of potential sites having poor power class using PT10 turbine is 34% and 7.2 US¢/kWh. The wind turbines having lower cut-in wind speed and lower-rated wind speeds are economically feasible for sites having poor wind power class.

Estimation of the wind energy potential for coastal locations in India using the Weibull model

Abstract Wind energy has exhibited the fastest growth of all renewable energy sources. Available wind energy potential for use by wind turbines has been found to be highly overestimated by existing methodologies when the wind energy potential is assessed from the total wind speed data because the wind turbine operates between cut-in and cut-out wind speeds. While applying existing methodologies, wind power density is overestimated on average by nearly 25% compared to the actual wind power available to a wind turbine. Hence, for estimating wind energy potential, availability factors and wind energy between cut-in and rated wind speeds should be properly estimated using Weibull models. The appropriateness of different methods of estimating Weibull parameters are site specific. In this article, a novel method has been developed for estimating the actual wind power available to the wind turbine. The parent two-parameter Weibull model can be used to determine the availability factor, whereas when determining the available wind energy between the cut-in and rated wind speeds, wind speed data should be refitted in the range defined by the cut-in and rated wind speeds using a three-parameter Weibull model, where the location parameter can be equated to the cut-in wind speed.

Validation of Numerical Models of the Offshore Wind Turbine From the Alpha Ventus Wind Farm Against Full-Scale Measurements Within OC5 Phase III

Abstract The main objective of the Offshore Code Comparison Collaboration Continuation, with Correlation (OC5) project is validation of aero-hydro-servo-elastic simulation tools for offshore wind turbines (OWTs) through comparison of simulated results to the response data of physical systems. Phase III of the OC5 project validates OWT models against the measurements recorded on a Senvion 5M wind turbine supported by the OWEC Quattropod from the alpha ventus offshore wind farm. The following operating conditions of the wind turbine were chosen for the validation: (1) idling below the cut-in wind speed, (2) rotor-nacelle assembly (RNA) rotation maneuver below the cut-in wind speed, (3) power production below and above the rated wind speed, and (4) shutdown. A number of validation load cases were defined based on these operating conditions. The following measurements were used for validation: (1) strains and accelerations recorded on the support structure and (2) pitch, yaw, and azimuth angles, generator speed, and electrical power recorded from the RNA. Strains were not directly available from the majority of the OWT simulation tools; therefore, strains were calculated based on out-of-plane bending moments, axial forces, and cross-sectional properties of the structural members. The simulation results and measurements were compared in terms of time series, discrete Fourier transforms, power spectral densities, and probability density functions of strains and accelerometers. A good match was achieved between the measurements and models setup by OC5 Phase III participants.

Switching strategy of the low wind speed wind turbine based on real-time wind process prediction for the integration of wind power and EVs

Utilizing the secondary wind resources in cities and countryside is a significant way to promote wind power consumption and sustainable transportation. However, the probability of wind speed near the cut-in wind speed increases in such area and resulting in frequent on/off switches as well as large fatigue load of the wind turbine. To address these problems, this paper proposes a switching strategy of the low wind speed wind turbine based on real-time wind process prediction. First, the wavelet decomposition and neural network are employed to predict the time series of wind speed in a real-time manner. Second, based on the historical and predicted wind speed, the typical wind processes are extracted by using the x-means algorithm. Third, seven indexes are defined to quantify the characteristics of the wind process set before developing the corresponding switching strategy for each type of it. Data from NREL are used to validate the proposed models. The results show that, the proposed strategy increases the energy yield, reduces the number of wind turbine switches as well as the power fluctuation. Therefore, the proposed strategy is beneficial to both wind power projects development and electric vehicles charging.

Study on Wind Energy Harvesting Effect of a Vehicle-Mounted Piezo-Electromagnetic Hybrid Energy Harvester

To realize the self-power of the vehicle micro-sensors, a piezo-electromagnetic hybrid vehicle-mounted energy harvester is proposed to recover the wind and vibration energy generated during driving. This energy harvester includes a flutter piezoelectric energy harvesting structure (FPEH) and an electromagnetic vibration energy harvester structure (EVEH). The combination of the two structures can improve the energy harvesting effect and reduce the cut-in wind speed. The coupled vibration mathematical model is established to predict the output performance of the wind energy harvesting effect. The effects of the different distances between magnets on the output are discussed. And the vibration characteristics of piezoelectric and electromagnetic vibrators are analyzed. Results show that the energy-harvesting effect is the best when the distance between magnets is 30mm. At the same time, the numerical simulation proves that the wind energy harvesting effect of the hybrid structure is better than the classic flutter structure. The experimental verification is carried out, and the experimental results are consistent with the theoretical prediction results, which verified the correctness of the theory. The optimal load of FPEH is 70kΩ , and the optimal load of EVEH is 60Ω. Under these conditions, when the wind speed is 18m/s, the peak output power of FPEH is 14.5mW, and that of EVEH is 31.8mW.

Study on the Critical Wind Speed of a Resonant Cavity Piezoelectric Energy Harvester Driven by Driving Wind Pressure.

In order to solve the problem of continuous and stable power supply for vehicle sensors, a resonant cavity piezoelectric energy harvester driven by driving wind pressure was designed. The harvester has an effective working range of wind speed. According to the energy conservation law, the cut-in (initial) wind speed of the harvester was solved. The pressure distribution law of the elastic beam in the flow field was studied by the Fluent software package, and the results were loaded into a finite element model with a method of partition loading. The relationship between the wind speed and the maximum principal stress of the piezoelectric cantilever beam was analyzed, and the critical stress method was used to study the cut-out wind speed of the energy harvester. The results show that the cut-in wind speed of the piezoelectric energy harvester is 5.29 m/s, and the cut-out wind speed is 24 m/s. Finally, an experiment on the power generation performance of the energy harvester was carried out. The experimental results show that the cut-in and cut-out wind speeds of the piezoelectric energy harvester are 5 m/s and 24 m/s, respectively, and the best matching load is 60 kΩ. The average output power, generated by the harvester when the driving wind speed is 22 m/s, is 0.145 mW, and the corresponding power density is 1.2 mW/cm3.

Enhanced performance of piezoelectric wind energy harvester by a curved plate

Piezoelectric wind energy harvesting is a promising strategy for developing self-powered small electromechanical systems. In this paper, a curved-plate bluff body is studied for enhancing the performance of piezoelectric wind energy harvester based on galloping phenomenon. The proposed curved-plate bluff body seems to have more design flexibility and the possibility of improving aerodynamic performance. A lumped parameter theoretical model is given and verified by experiments. The numerical research has shown that the curved-plate bluff body can obtain high lift and negative pressure in the inner circulation, which are the key drivers for the vibration of the piezoelectric beam based on galloping phenomenon. Experimental results show that the piezoelectric wind energy harvester with the curved-plate bluff body (WEHC) can generate higher output voltage than the conventional cross-section (square, regular-triangle, and D-shaped) bluff bodies, and has a lower cut-in wind speed. When an external load resistance of 820 KΩ is connected and the arc length is 45 mm, the piezoelectric wind energy harvester with curved-plate bluff body generates an average power of 35.6 μW.

Performance enhancement of wind energy harvester utilizing wake flow induced by double upstream flat-plates

Small-scale wind energy harvesting system is being considered to provide green long-term electric power to unattended sensor network nodes which are widely used in urban and natural environments. This paper proposes that placing a double-plate structure upstream of the bluff body in the wind energy harvesting system can significantly improve the output performance. At a certain wind speed, two wake flow zones with low-pressure are formed behind two upstream side-by-side plates, which induced the bluff body at the downstream intermediate position to deviate to both sides. Even at a low wind speed, the vibration of bluff body can still occur because the pressure fluctuation of the wake zone disturb the static equilibrium. Placing the double plates upstream of a wind energy harvester with a cylinder can change the vibration response from VIV (vortex-induced vibration) to galloping. Moreover, when the ratios of the horizontal and vertical distances to the windward width of the cylinder are 1 and 0.5, respectively, the cut-in wind speed is as low as 1.5 m/s. For the galloping-based wind energy harvester with a square prism, after the double plates are placed upstream, the cut-in wind speed decreases from 3.5 m/s to 1 m/s and the output voltage increases from 1 V to 12 V at 1.5 m/s. The increase of voltage caused by the addition of double plates to the upstream of six different bluff bodies indicates the good adaptability of this structure. The higher voltage output capability by this method at low wind speed significantly expands the application scope of wind energy harvesters.

The Potential Wind Power Resource in Central-South of the Constanta County

Abstract Usually, wind turbine generator’s structures or radio masts are located in wind exposed sites. The paper aims to investigate the wind conditions in the nearby area of Cobadin Commune, Constanta County, Romania at heights of 150-200m above the surface using global reanalysis data sets CFSR, ERA 5, ERA I and MERRA 2. Using the extreme value theory and the physical models of the datasets, the research focuses on the assessment of the maximum values that are expected for the wind speeds, but the wind statistics created can be used for a further wind or energy yield calculation. Without reaching the survival wind speed for wind turbine generators, with mean wind speed values higher than 7 m/s and considering the cut-in and cut-out wind speeds of 3 m/s, respectively 25 m/s, the site can be exploited in more than 90% of the time to generate electricity, thus, the paper is addressed to the investors in the energy of renewable sources. At the same time, the insights of the wind characteristics and the knowledge of the extreme values of the wind speed can be useful, not just for the designers, in the rational assessment of the structural safety of wind turbines, but also those evaluating the insured losses.

On the need for the development of low wind speed turbine generator system

The study focused on the need for the development of a low cut-in wind speed turbine system with a view to challenge for concerted efforts towards improvement in design in such a way that favours operation at wind speeds as low as 1.5 to 2.0 m/s. It reviewed some existing reports on rotor designs with major focus on improved blade design for enhanced turbine performance and structural integrity. It found that despite the advances in turbine blade designs, there is the need to further the design to include those that can drive generators not just for small wind turbine applications but also for operation under lower cut-in speeds (less than 2.0 m/s). It further demonstrated the need to have improvement in wind turbine generator design that eliminates/reduce lubrication parts and possibly employ electro-magneto-mechanical principles for operation.

Investigation of a small Horizontal–Axis wind turbine performance with and without winglet

The objective of this study is to demonstrate computationally the effect of winglet length and cant angle on the performance of a small horizontal-axis wind turbine. The computational study was done using the ANSYS Fluent 15 software for a steady-state flow. Different designs of winglet with different lengths and cant angles were numerically studied and optimized using Artificial Neural Network (ANN). The winglet length was changed from 1% to 7% of the wind turbine rotor radius with cant angles from 150 to 900. The parameters of the wind turbine performance, which are power coefficient and thrust force coefficient were investigated for different winglet configurations. This was carried out from cut-in wind speed (3.12 m/s) to wind speed (12 m/s). It demonstrated that, there were noticeable enhancements in power and thrust coefficients in the presence of winglet. The best improvement in the performance was achieved when winglet length was 6.32% and cant angle 48.30. At this case, the percentage increase in power coefficient equals to the percentage increase in thrust coefficient which was 8.787%.

Analysis of tension-tunable clamped–clamped piezoelectric beams for harvesting energy from wind and vibration

This article presents a nonlinear structural modeling framework to analyze a tensioned doubly clamped energy harvesting device. The device is investigated for energy harvesting under base excitation loading, where the structure undergoes bending motion and aerodynamic loading, where the structure undergoes combined bending–torsion motion. Transfer-matrix method for analyzing torsional motion is modified to include the effects of applied axial preload tension. The tension-modulated mode shapes and natural frequencies of the structure, obtained using transfer-matrix method, are found to be in good agreement with the results obtained using a commercially available Finite Element software. Under base excitation loading, it is shown that the effects of tension on electromechanical coupling and stiffness create competing influences on the power efficiency of the system. For aerodynamic loading, increasing preload tension increases the cut-in wind speed of the device. However, beyond the cut-in wind speed, with proper selection of the preload tension, the tensioned structure can produce an order of magnitude more power than the untensioned case at the same flow speed.

Effects of Electrical and Electromechanical Parameters on Performance of Galloping-Based Wind Energy Harvester with Piezoelectric and Electromagnetic Transductions

This paper presents an analysis of galloping-based wind energy harvesters with piezoelectric and electromagnetic transductions. The lumped parameter models of the galloping-based piezoelectric energy harvester (GPEH) and galloping-based electromagnetic energy harvester (GEMEH) are developed and the approximate analytical solutions of the equations are derived using the harmonic balance method (HBM). The accuracy of the approximate analytical solutions is validated by the numerical solutions. A parametric study is then conducted based on the validated models and solutions to understand the effects of the dimensionless load resistance, r, and electromechanical coupling strength (EMCS) on various quantities indicating the performance of the harvesters, including the dimensionless oscillating frequency, cut-in wind speed, displacement, and average power output. The results show that both r and EMCS can affect the dimensionless oscillating frequencies of the GPEH and GEMEH in a narrow frequency range around the natural frequency. A significant decrease in the displacement around r = 1 for GEPH and at a low r for GEMEH indicates the damping effect induced by the increase in EMCS. There are two optimal r to achieve the maximal power output for GPEH given strong EMCS while there is only one optimal r for GEMEH. Both GPEH and GEMEH show similar characteristics in that the optimal power outputs can reach saturation with an increase of the EMCS. The findings from the parametric study provide useful guidelines for the design of galloping-based energy harvesters with different energy conversion mechanisms.

Potential and economic viability of green hydrogen production by water electrolysis using wind energy resources in South Africa

In recent times, more attention is given to renewable and clean energy sources that could ameliorate the current shortage of electricity plaguing South Africa. Due to the comparable use of hydrogen to fossil fuel in the transportation, industrial and electricity sector, hydrogen could be a potential solution to the current energy crises especially when produced from a clean and sustainable source. One of the most appropriate methods of green hydrogen production is the use of wind energy via water electrolysis. This paper therefore investigates the capability and viability of hydrogen production from the wind energy resources of South Africa using the actual wind speed obtained at 60 m anemometer height. Sensitivity analyses are also conducted to gain insight into the possible influences of wind turbine operating parameters on the cost of hydrogen production. Wind regime of fifteen (15) different sites across five (5) major provinces are analysed for possible wind-hydrogen production using eleven (11) different off-the-shelf wind turbines ranging from small to large categories. Some of the key results revealed that the mean wind speed (Vm) varies from 5.07 m/s in Eston (S12) to 8.10 m/s in Napier (S5). Wind turbine WT9 (ServionSE MM100) with rated wind power of 2 MW, cut-in wind speed of 2 m/s, rated wind speed of 11 m/s, cut-out wind speed of 22 m/s and turbine hub-height of 100 m has the highest capacity factor (Cf) across all the sites with the values that range from 24.04% in Eston (S12) to 54.55% in Napier. Site S5 presents the best hydrogen production potential with annual hydrogen production that ranges between 6.51 metric-tons with turbine WT1 and 226.82 metric-tons of hydrogen with turbine WT11. Wind turbine WT9 has the least cost of electricity generation ranging from 0.23$/kwh at site S5 to 0.42 $/kwh at site S13. Also, the cost of hydrogen is lowest at site S5 and ranges between 39.55 $/kg using wind turbine WT1 and 1.4 $/kg using wind turbine WT11. The sensitivity analysis conducted revealed that rated wind speed has significant effect on the cost of hydrogen production compared to other wind turbine parameters.

Wind Turbines for Electricity Generation Operating in the Low Wind Velocity Regime

Wind turbines are simple and eco-friendly means of generating electricity. This review paper introduces the challenges in harvesting maximum energy at low wind velocities (typically around 3 m/s, the cut-in wind speed for most of the turbines). The recent research works carried out with regards to design and operation of the wind turbines at low wind velocities are summarized. With respect to design, optimizing blade geometry, improving the starting characteristics, addition of flow augmentation devices and electrical efficiency improvement are explained. Regarding the operation of low wind velocity turbines, some novel means of improving the operational performance and some unconventional modes of operation have been discussed thoroughly. The current study on low speed wind turbines has ascertained that there is a great potential for energy harvesting at low wind velocities with significant possible improvement in energy conversion efficiency. Finally, few potential areas of research in the area of low speed wind turbines have been pointed out.

Wind energy resource assessment for Suva, Fiji, with accurate Weibull parameters

Wind resource assessment is carried out for Suva, the capital of the Republic of Fiji Islands. The wind speeds at 34 m and 20 m above ground level, wind direction, atmospheric pressure, and temperature were measured for more than five years and were statistically analyzed. The daily, monthly, yearly, and seasonal averages were estimated. For the site, the overall average wind speed at 34 m above ground level is found to be 5.18 m/s. The occurrence of effective wind (between the cut-in and cut-off wind speeds of the selected turbine) is predominantly from the east. An effective wind speed of 74.175% was recorded which can be used for power generation. The turbulence intensity and wind shear coefficient are estimated. The site’s overall turbulence intensities are 12.5% and 13.72% at 34 m and 20 m above ground level, respectively. The diurnal wind shear correlated with the temperature variation very well. The overall and seasonal wind distributions are analyzed, which shows that the wind speed in Suva is mostly between 3 m/s and 9 m/s although the winter season has higher wind speeds. The Weibull parameters and the wind power density were found using 10 different methods. The wind power density is estimated to be 159 W/m2 using the best method, which is found to be the empirical method of Justus. A high-resolution map around the site is digitized and the wind power density resource map is generated using wind atlas analysis and application program. From the wind atlas analysis and application program analysis, it is seen that Suva has high potential for power generation. Five possible locations are selected for installing wind turbines and the annual energy production is estimated using wind atlas analysis and application program. The total annual energy production from the five sites is 1950 MWh. The average capacity factor of the five turbines is 17%. An economic analysis is performed which showed a payback period of 10.83 years.

Dynamics and performance of a two degree-of-freedom galloping-based piezoelectric energy harvester

To improve the performance of the galloping based piezoelectric energy harvester (GEPH), this paper analytically investigates the potential advantages of the 2-degree-of-freedom (2-DOF) GPEHs over the conventional 1-DOF GPEH. Firstly, two different configurations of 2-DOF GPEH are proposed and the corresponding governing equations are presented. The approximate analytical solutions to both configurations are derived by using the harmonic balance method. Numerical simulations are conducted to verify the accuracy of these analytical solutions. Subsequently, comparisons are conducted between the 1-DOF GPEH and the 2-DOF GPEHs in terms of the cut-in wind speeds and output powers. It is demonstrated, both analytically and numerically, that the second configuration of 2-DOF GPEH can easily and remarkably reduce the cut-in wind speed and improve the output power from galloping phenomenon. Finally, a parametric study is performed to ascertain the effects of the mechanical parameters of the second configuration on the energy harvesting performance. Based on the results from the parametric study, design guidelines for tuning the mechanical parameters are provided to achieve performance enhancement.

The optimization and the application for the wind turbine power-wind speed curve

An optimized wind turbine power-wind speed curve (P-v curve) was presented in this paper to solve the problems in the low-wind-speed regions like the large wind speed variation and the low wind turbine efficiency. When the wind speed was lower than the cut-in wind speed, the operation mode of the wind turbine was changed by the extra power supplied by the motor excitation source to keep the wind turbine operating. The application condition of the optimized P-v curve was derived and calculated. The effects of various wind speeds on the powers and the power generation of the wind turbine were analyzed by comparison with and without the improvement. The results indicated that the prolonged working period, the improved efficiency of the wind turbine and the incremental power generation were induced by the usage of the optimized P-v curve. The cut-in wind speed was declined by 42.8%. The power generation was enhanced by 73.4% at the actual wind condition of some wind field. The motor power was augmented with the huge amplitude of the wind speed. Compared with the traditional P-v curve, the optimized P-v curve was more suitable for the lower average and larger amplitude of the wind speed.