Increase In Annual Energy Production Research Articles

Exploring cooperation between wind farms: a wake steering optimization study of the Belgian offshore wind farm cluster

In recent years, significant research efforts have focused on increasing power extraction using wake steering through yaw misalignment. In the current work, we evaluate the potential increase in annual energy production (AEP) for the Belgian offshore wind farm cluster using the FLORIS framework. The 2.2 GW Belgian cluster is an excellent test case to explore cooperation between wind farms as the concession zone is split into nine individual farms, resulting in a mix of intra- and inter-farm wakes to be considered in one of the largest wind farm clusters operational to date. Furthermore, the cluster high power density with relatively low turbine spacings is found to be responsive to wake mitigation strategies. Three different cost functions are compared. The first one is the complete cluster yaw angles optimization. The other two are farm-based optimizations seeking to maximize either their own AEP or the cluster AEP. Results show that all wind farms benefit from every optimization, encouraging operators to implement this strategy. The cluster optimization is found to be the one providing the best AEP increase for all wind farms individually and thus for the cluster. The farm-based function optimizing the cluster AEP is in second place, encouraging wind farm operators to collaborate for their own profits.

Performance Analysis of Ultra-Scale Downwind Wind Turbine Based on Rotor Cone Angle Control

The theoretical feasibility of the power output strategy based on rotor cone angle control for ultra-scale downwind wind turbines is studied in this paper via the Open FAST simulation platform. The performance of five cases, namely UW, DW, DWC, DW6, and DW6IC, which have different rotor parameters or control strategies compared with the reference DTU 10 MW wind turbine, are calculated and analyzed. It is found that the downwind rotors have significant advantages in reducing the blade root load. The DW case reduces the peak load at the blade root by 22.54% at the cost of 1.57% annual energy production loss. By extending the length and redesigning the stiffness of the blade, the DW6 case achieves 14.82% reduction in the peak load at the blade root and 1.67% increase in the annual energy production under the same blade weight as that of the UW. The DWC case with rotor cone angle control has the same aerodynamic performance as the DW case with the same blade parameters. However, when the wind speed achieves or exceeds the rated speed, the blade root load decreases at a greater rate with the increasing wind speeds, and achieves minimum load with a wind speed of 16 m/s. Compared with the UW case, the DW6IC case with the improved rotor cone angle control reduces the peak load of the blade root by 22.54%, leading to an increase in annual energy production by 1.12% accordingly.

Interrelationship between variables for wave direction-dependent WEC/site-configuration pairs using the CapEx method

Renewable energies are mostly compared using the Levelised Cost of Energy (LCoE). Two major components of LCoE are of interest in this study, the others being still experimental: the Annual Energy Production (AEP) and the Capital Expenditure (CapEx). Since many Wave Energy Converters (WECs), including Wavepiston, are wave direction-dependent, this research investigates the wave direction impact on the relationship between the site-configurations (site characteristics and wave climates), WEC-configurations and power, alongside AEP and CapEx. Wave climate and WEC power are expressed in 3-dimension by adding the wave direction to the common 2-dimensional space of wave height and period. Wavepiston's WEF costs are calculated using the CapEx method. Assessing the relationship between the diverse sources of AEP/CapEx variations, enabled the development of the Cost-AEP Threshold Criterion (CAEPTC) to determine the threshold where an increase in AEP becomes negligible compared to CapEx increase. CAEPTC is perhaps a better alternative to LCoE for enhanced WEC/site-configuration pairing. Based on this Criterion and the limited dataset (a challenge to most wave companies), it was apparent that the best WEC/site-configuration pairs came from configurations with the highest yearly energy production, which is not necessarily the most expensive, and for sites with lower wave energy.

Site-specific Modeling of self-reacting point absorber in real wave spectrum

Power performance of floating wave energy converters is typically performed under regular wave conditions or using standard ocean spectrum models with one peak. We explore the effect of device geometry of a self-reacting point absorber (SRPA) for real wave spectrum having multiple peaks. Different float and torus designs are evaluated to alter the cut-off frequency of the SRPA to extract more power in operating wave periods representative of two real ocean sites. A float with a damping plate was more suitable for higher wave periods, while a slender body float was preferred for lower wave periods. Increasing the torus outer diameter increased the absorbed power by 20% for low wave period while the absorbed power was reduced by 5% for a high wave period site. The modified SRPA with slender body float showed a four-fold increase in annual energy production when compared to regular wave conditions for the low wave period site. For the high wave period sea site, a modified SRPA with a damping plate showed a 6% increase in annual energy production. The study shows that while the geometry of the SRPA determines the operating period, the PTO damping can be varied to determine the operating bandwidth.

Aerodynamic Optimization of a Wind Turbine Blade for Maximum Annual Energy Production at Manjil Wind Farm

To keep pace with current trends in the wind industry, this paper aims at the improvement of the annual energy production of a horizontal axis wind turbine by aerodynamic optimization of blades at the wind conditions of the Manjil site. To achieve this goal, the Riso wind turbine, whose characteristics are publicly available, is selected, and its twist angle and chord length distributions along the blades are optimized. The blade element momentum theory with appropriate corrections is used to predict the turbine output power. The genetic algorithm optimization tool, and Weibull probability density function, for wind regime representation, are also utilized in this work. Optimization results show a 9.4% and 11.6% increase in annual energy production, respectively, for the blade with optimal twist angle and the blade with optimal chord length and twist angle distributions. Finally, the superiority of selecting annual energy production as the objective function is assessed in comparison with other objective functions.

On the Use of Modern Engineering Codes for Designing a Small Wind Turbine: An Annotated Case Study

While most wind energy comes from large utility-scale machines, small wind turbines (SWTs) can still play a role in off-grid installations or in the context of distributed production and smart energy systems. Over the years, these small machines have not received the same level of aerodynamic refinement of their larger counterparts, resulting in a notably lower efficiency and, therefore, a higher cost per installed kilowatt. In an effort to reduce this gap during the design of a new SWT, the scope of the study was twofold. First, it aimed to show how to combine and best exploit the modern engineering methods and codes available in order to provide the scientific and industrial community with an annotated procedure for a full preliminary design process. Secondly, special focus was put on the regulation methods, which are often some of the critical points of a real design. A dedicated sensitivity analysis for a proper setting is provided, both for the pitch-to-feather and the stall regulation methods. In particular, it is shown that stall regulation (which is usually preferred in SWTs) may be a cost-effective and simple solution, but it can require significant aerodynamic compromises and results in a lower annual energy output in respect to a turbine making use of modern stall-regulation strategies. Results of the selected case study showed how an increase in annual energy production (AEP) of over 12% can be achieved by a proper aerodynamic optimization coupled with pitch-to-feather regulation with respect to a conventional approach.

An initial study into the potential of wind farm control to reduce fatigue loads and extend asset life

A quasi-static open loop wind farm control approach is considered, where optimisation is carried out offline in a simulation environment to create a lookup table of yaw setpoints implemented by a central wind farm controller. The objective of the optimisation is to reduce blade root bending moment for all turbines on the site, thereby increasing the asset life, and this is achieved by querying a fatigue loads database in DNV GL’s LongSim software for wind farm control design, optimisation and verification. The Lillgrund 48-turbine layout is used for this example. The optimisation results in a small increase in annual energy production of 0.13% which is combined with a 0.4% increase in blade life, which is translated to an increase in asset life to yield a 0.5% increase in energy production over the farm lifetime. In this case we make the simplistic assumption that blades have the minimum life of all turbine components, and limit fatigue life. The results are a step towards wind farm control techniques which maintain and extend wind farm life, whilst simultaneously increasing energy production.

Wind energy at remote islands in arctic region—A case study of Solovetsky islands

This paper describes a case study of wind resource assessment and wind park design at the Solovetsky Islands, which are located in the Arctic region of northern Russia. The Solovetsky historical and cultural complex has been included in the list of UNESCO's World Heritage Sites. 18 years of data of wind climatology from the NASA Langley Research Center are used for wind resource assessment at the Solovetsky Islands for two different wind park locations. Computational fluid dynamics based numerical simulations are carried out for wind resource assessment and for the estimation of the resultant annual energy production (AEP) for both locations. To better understand wind flow physics and the effects of wind turbine wake effects, three different wake models are used for the numerical simulations. Analyses of seasonal weather effects on energy production show that wind power production at the Solovetsky Islands is higher during the winter period compared to the summer period, mainly due to higher wind speeds and air density at cold winter conditions. A preliminary case study about wind park layout optimization has also been carried out, where the results show an increase in AEP with the optimization of the wind park layout.

Evaluation of wind energy potential and estimation of wind turbine characteristics for two different sites

In this study, a novel approach is discussed to study wind speed characteristics and wind turbine (WT) characteristics. This paper focuses on the study of estimation of wind resource potential and WT characteristics at higher hub height. A detailed wind resource assessment analysis and selection of WT are discussed for estimating capacity factor and harnessing maximum wind power at MANIT and Mamatkheda. The selection procedures of the efficient WT of (class II) for the site, according to IEC 61400, are thoroughly investigated. It is observed from the investigation that generalised gamma distribution produces accurate results to estimate annual energy production (AEP). This study also reveals that MANIT has a very low wind potential at a height of 80 m; therefore, it is not a suitable location for a class IV WT, whereas Mamatkheda has a high wind potential which results in a significant increase in AEP.

Extending the life of wind turbine blade leading edges by reducing the tip speed during extreme precipitation events

Abstract. Impact fatigue caused by collision with rain droplets, hail stones and other airborne particles, also known as leading-edge erosion, is a severe problem for wind turbine blades. Each impact on the leading edge adds an increment to the accumulated damage in the material. After a number of impacts the leading-edge material will crack. This paper presents and supports the hypothesis that the vast majority of the damage accumulated in the leading edge is imposed at extreme precipitation condition events, which occur during a very small fraction of the turbine's operation life. By reducing the tip speed of the blades during these events, the service life of the leading edges significantly increases from a few years to the full expected lifetime of the wind turbine. This life extension may cost a negligible reduction in annual energy production (AEP) in the worst case, and in the best case a significant increase in AEP will be achieved.

Effect of airfoil profile on aerodynamic performance and economic assessment of H-rotor vertical axis wind turbines

This research focuses on the effects of the asymmetric airfoil profiles on aerodynamic performance and economic evolution of a vertical axis wind turbine (VAWT) at different blade heights, solidities, and tip speed ratios (TSR or λ). The aerodynamic performance of six asymmetric airfoils, S809, S814, RISØ-A1-24, Du 93-W-210, FFA-W3-241, and FX66-S196-V1, was calculated using double multiple-stream tube (DMST) theory and blade element methods for determination of their performance for tip speed ratios from 1 to 12, and solidities of 0.2–0.6, were considered for this study. All calculations focused on the Khaf area (rural zone) in Iran and considered two heights: 10 m and 40 m. To verify the performance of the developed code, results were compared with experimental power coefficient data for NACA0012 airfoil. For FFA-W3-241 airfoil, maximum power coefficient was obtained at solidity of 0.5 and tip-speed ratio of 4. This aerodynamic excellence resulted in 22.4% and 21.9% increase in annual energy production at hub heights (h) of 10 m and 40 m, respectively, while keeping the total investment costs constant. Moreover, the ratio of wind-generated electric power sales to the total investment cost was found to be 4.33 (0.15/0.0346) for 15 years of operation.

Study of wind farm control potential based on SCADA data

In this work, a control-oriented wind farm model is validated against SCADA data from a typical on-shore wind farm, without additional instrumentation available. The comparison of model-predicted and measured power deficits due to wake impingement shows good agreement. Furthermore, the model is used to compute optimum yaw misalignments for yaw-induced wake steering, leading to an estimated 1.7% increase in annual energy production by mitigation of wake losses. Results show that wake steering based on standard SCADA data, which is usually available in operational wind farms, has promising potential for open-loop model-based wind farm control.

Experimental study of surface curvature effects on aerodynamic performance of a low Reynolds number airfoil for use in small wind turbines

This paper presents the wind tunnel experimental results to investigate the effects of surface gradient-of-curvature on aerodynamic performance of a low Reynolds number airfoil Eppler 387 for use in small-scale wind turbines. The prescribed surface curvature distribution blade design method is applied to the airfoil E387 to remove the gradient-of-curvature discontinuities and the redesigned airfoil is denoted as A7. Both airfoils are manufactured with high precision to reflect the design. Low-speed wind tunnel experiments are conducted to both airfoils at chord based Reynolds numbers 100 000, 200 000, and 300 000. Surface pressure measurements are used to calculate the lift and pitching-moment data, and the wake survey method is applied to obtain the drag data. The experimental results of E387 are compared with NASA Low Turbulence Pressure Tunnel (LTPT) results for validation. The gradient-of-curvature discontinuities of E387 result in a larger laminar separation bubble which causes higher drag at lower angles of attack. As the angle of attack increases the separation bubble of the airfoil E387 moves faster towards the leading edge than that of A7, resulting in a premature bubble bursting and earlier stall on E387. The impact of the gradient-of-curvature distribution on the airfoil performance is more profound at higher angles of attack and lower Reynolds number. The aerodynamic improvements are integrated over the 3D geometry of a 3 kW small wind turbine, resulting in up to 10% increase in instantaneous power and 1.6% increase in annual energy production. It is experimentally concluded that an improved curvature distribution results in a better airfoil performance, leading to higher energy output efficiency.

Power performance optimization and loads alleviation with active flaps using individual flap control

The present article investigates the potential of Active Trailing Edge Flaps (ATEF) in terms of increase in annual energy production (AEP) as well as reduction of fatigue loads. The basis for this study is the DTU 10 MW Reference Wind Turbine (RWT) simulated using the aeroelastic code HAWC2. In an industrial-oriented manner the baseline rotor is upscaled by 5% and the ATEFs are implemented in the outer 30% of the blades. The flap system is kept simple and robust with a single flap section and control with wind speed, rotor azimuth, root bending moments and angle of attack in flap's mid-section being the sensor inputs. The AEP is increased due to the upscaling but also further due to the flap system while the fatigue loads in components of interest (blade, tower, nacelle and main bearing) are reduced close to the level of the original turbine. The aim of this study is to demonstrate a simple and applicable method that can be a technology enabler for rotor upscaling and lowering cost of energy.

Comparison of Airfoil Precomputational Analysis Methods for Optimization of Wind Turbine Blades

The objective of this research was to develop and compare various airfoil precomputational parameterization and analysis techniques for aerostructural optimization of wind turbine blades. The airfoils along the blade were added as optimization design variables through precomputational parameterization methods using thickness-to-chord ratios and blended airfoil family factors. The airfoils’ aerodynamic performance was analyzed with three methods of increasing fidelity: a panel method (XFOIL), Navier–Stokes-based computational fluid dynamics (RANS CFD), and wind tunnel data. The optimizations minimized mass over annual energy production ( $m/AEP$ ) and thereby approximated the minimization of cost of energy. The results were compared to the NREL 5-MW reference turbine and a conventional optimization where the airfoils were fixed. Results showed an average $m/AEP$ reduction of 1.7% over conventional optimization methods. The primary benefit in adding the airfoil shape was through an increase in annual energy production (1.6%) with a similar decrease in turbine mass (1.8%). Using the precomputational airfoil parameterization methods provided significant reductions in the cost of energy with relatively minor additional computational cost.

Exploring the Potential for Increased Production from the Wave Energy Converter Lifesaver by Reactive Control

Fred Olsen is currently testing their latest wave energy converter (WEC), Lifesaver, outside of Falmouth Bay in England, preparing it for commercial operation at the Wavehub test site. Previous studies, mostly focusing on hydrodynamics and peak to average power reduction, have shown that this device has potential for increased power extraction using reactive control. This article extends those analyses, adding a detailed model of the all-electric power take-off (PTO) system, consisting of a permanent magnet synchronous generator, inverter and DC-link. Time domain simulations are performed to evaluate the PTO capabilities of the modeled WEC. However, when tuned towards reactive control, the generator losses become large, giving a very low overall system efficiency. Optimal control with respect to electrical output power is found to occur with low added mass, and when compared to pure passive loading, a 1% increase in annual energy production is estimated. The main factor reducing the effect of reactive control is found to be the minimum load-force constraint of the device. These results suggest that the Lifesaver has limited potential for increased production by reactive control. This analysis is nevertheless valuable, as it demonstrates how a wave-to-wire model can be used for investigation of PTO potential, annual energy production estimations and evaluations of different control techniques for a given WEC device.

Prototyping a series of bi-directional horizontal axis tidal turbines for optimum energy conversion

A series of bi-directional horizontal axis tidal turbine (HATT) rotors was prototyped. The geometry and motion parameters of the turbine series cover a wide range of tidal turbine operating conditions targeted to the tidal flow speed probability distribution of the Bay of Fundy, NS Canada. A generic yet novel wind/tidal turbine rotor design and optimization procedure was developed and used for the optimization process. In the process, optimum annual energy production, as a benchmark, was obtained and used for comparison by taking into account both rotor hydrodynamic power production performance characteristics and annual tidal inflow speed probability distribution. The diameter of the full-scale bi-directional HATT rotor series developed is 20-m. Optimum values of various variables were obtained for maximum annual energy production. These optimum values include: uniform pitch-diameter-ratio (p/D) distributions, nominal pitch values with different curve forms of non-uniform p/D distributions, shaft rotational speeds under fixed rotor diameter, diameter at fixed tip-speed-ratio (TSR), a combination of optimum shaft speeds at corresponding inflow speeds and optimum uniform p/D distribution at a fixed rotor diameter, number of rotor blades at fixed chord length, rotor solidity at fixed number of blades, and the combination of number of blades and solidity for both optimum constant pitch distribution and optimum linear pitch distribution. For the 20-m bi-directional HATT, a substantial improvement in power coefficient Cpow was obtained, from 0.28, as a result of the primary optimization process (for both optimum uniform p/D distribution and shaft speed n), to the final maximum of 0.43. This corresponds to a 56% increase in annual energy production of 1230MWh, from 2188 to 3418MWh, an improved energy production equivalent to the energy generated from 600tonnes of coal (at 2kWh per 1kg coal from a standard thermal power plant). The annual energy production from the optimized 20-m bi-directional HATT before the deduction of mechanical and electrical conversion loses, is 3418MWh, equivalent to the electric energy generated from 1550tonnes of coal.