• Energy Research

The optimization of wind energy conversion efficiency has been recently boosting the technology improvement and the scientific comprehension of wind turbines. In this context, the yawing behavior of wind turbines has become a key topic: the yaw control can actually be exploited for optimization at the level of single wind turbine and of wind farm (for example, through active control of wakes). On these grounds, this work is devoted to the study of the yaw control optimization on a 2 MW wind turbine. The upgrade is estimated by analysing the difference between the measured post-upgrade power and a data driven model of the power according to the pre-upgrade behavior. Particular attention has therefore been devoted to the formulation of a reliable model for the pre-upgrade power of the wind turbine of interest, as a function of the operation variables of all the nearby wind turbines in the wind farm: the high correlation between the possible covariates of the model indicates that Principal Component Regression (PCR) is an adequate choice. Using this method, the obtained result for the selected test case is that the yaw control optimization provides a 1% of annual energy production improvement. This result indicates that wind turbine control optimization can non-negligibly improve the efficiency of wind turbine technology.

Abstract SCADA control systems are the keystone for reliable performance optimization of wind farms. Processing into knowledge the amount of information they spread is a challenging task, involving engineering, physics, statistics and computer science skills. This work deals with SCADA data analysis methods for assessing the importance of how wind turbines align in patterns to the wind direction. In particular it deals with the most common collective phenomenon causing clusters of turbines behaving as a whole, rather than as a collection of individuality: wake effects. The approach is based on the discretization of nacelle position measurements and subsequent post-processing through simple statistical methods. A cluster, severely affected by wakes, from an onshore wind farm, is selected as test case. The dominant alignment patterns of the cluster are identified and analyzed by the point of view of power output and efficiency. It is shown that non-trivial alignments with respect to the wind direction arise and important performance deviations occur among the most frequent configurations.

Abstract Wind turbines are an energy conversion system having a low density on the territory, and therefore needing accurate condition monitoring in the operative phase. Supervisory Control And Data Acquisition (SCADA) control systems have become ubiquitous in wind energy technology and they pose the challenge of extracting from them simple and explanatory information on goodness of operation and performance. In the present work, post processing methods are applied on the SCADA measurements of two onshore wind farms sited in southern Italy. Innovative and meaningful indicators of goodness of performance are formulated. The philosophy is a climax in the granularity of the analysis: first, Malfunctioning Indexes are proposed, which quantify goodness of merely operational behavior of the machine, irrespective of the quality of output. Subsequently the focus is shifted to the analysis of the farms in the productive phase: dependency of farm efficiency on wind direction is investigated through the polar plot, which is revisited in a novel way in order to make it consistent for onshore wind farms. Finally, the inability of the nacelle to optimally follow meandering wind due to wakes is analysed through a Stationarity Index and a Misalignment Index, which are shown to capture the relation between mechanical behavior of the turbine and degradation of the power output.

La conversión de energía eólica está contribuyendo significativamente a la nueva transición de energía limpia, pero, hasta ahora, dicha contribución está impulsada principalmente por grandes parques eólicos de varios MW. Por otro lado, las necesidades recientes en términos de producción de energía distribuida están revelando un nuevo interés en las tecnologías de conversión de energía eólica a pequeña escala para aplicaciones residenciales y urbanas. En este contexto, los aerogeneradores de eje vertical (VAWT) son a menudo la opción más válida desde el punto de vista de las posibilidades de integración de edificios, pero es bien sabido que sufren una brecha considerable en el rendimiento en comparación con las tecnologías de eje horizontal. Partiendo de estas premisas, en el presente trabajo se investigan algunas soluciones innovadoras para mejorar el rendimiento de un aerogenerador de eje vertical Darrieus a través de enfoques numéricos y de ingeniería. Las intervenciones investigadas incluyen la hibridación del rotor mediante el uso de una sección interna Savonius para mejorar el arranque de la máquina y la posible aplicación de hoyuelos para mejorar el rendimiento del perfil aerodinámico NACA 0021 en la sección externa del rotor. Los resultados demuestran la eficacia de las intervenciones en la obtención de un rotor con rendimientos estables en una gama muy amplia de regímenes de viento. La conversion de l'énergie éolienne contribue de manière significative à la nouvelle transition vers l'énergie propre, mais, jusqu'à présent, cette contribution est principalement due aux grands parcs éoliens de plusieurs MW. D'autre part, les besoins récents en termes de production d'énergie distribuée révèlent un nouvel intérêt pour les technologies de conversion de l'énergie éolienne à petite échelle pour des applications résidentielles et urbaines. Dans ce contexte, les éoliennes à axe vertical (VAWT) sont souvent le choix le plus valable du point de vue des possibilités d'intégration des bâtiments, mais il est bien connu qu'elles souffrent d'un écart de performance considérable par rapport aux technologies à axe horizontal. Sur la base de ces prémisses, dans le présent travail, certaines solutions innovantes pour améliorer les performances d'une éolienne à axe vertical Darrieus sont étudiées par des approches numériques et techniques. Les interventions étudiées comprennent l'hybridation du rotor par l'utilisation d'une section Savonius interne pour améliorer le démarrage de la machine et l'application éventuelle d'alvéoles pour améliorer les performances du profil aérodynamique NACA 0021 sur la section de rotor externe. Les résultats démontrent l'efficacité des interventions pour obtenir un rotor avec des performances stables dans une très large gamme de régimes de vent. Wind energy conversion is contributing significantly to the new clean energy transition but, up to now, such contribution is mainly driven by large multi-MW windfarms. On the other hand, the recent needs in terms of distributed energy production are revealing a new interest in small-scale wind energy conversion technologies for residential and urban applications. In this context, vertical axis wind turbines (VAWT) are often the most valid choice from the point of view of building integrating possibilities, but it is well known that they suffer a considerable gap in performance when compared to horizontal axis technologies. Based on these premises, in the present work some innovative solutions for improving the performance of a Darrieus vertical axis wind turbine are investigated through numerical and engineering approaches. The investigated interventions include rotor hybridization by the use of an inner Savonius section for improving the machine's start-up and the possible application of dimples for improving the NACA 0021 airfoil performances on the outer rotor section. Results demonstrate the effectiveness of the interventions in obtaining a rotor with stable performances in a very wide range of wind regimes. يساهم تحويل طاقة الرياح بشكل كبير في التحول الجديد للطاقة النظيفة، ولكن حتى الآن، فإن هذه المساهمة مدفوعة بشكل أساسي بمزارع الرياح الكبيرة التي تعمل بعدة ميجاوات. من ناحية أخرى، تكشف الاحتياجات الأخيرة من حيث إنتاج الطاقة الموزعة عن اهتمام جديد بتقنيات تحويل طاقة الرياح على نطاق صغير للتطبيقات السكنية والحضرية. في هذا السياق، غالبًا ما تكون توربينات الرياح ذات المحور الرأسي (VAWT) هي الخيار الأكثر صحة من وجهة نظر بناء إمكانيات التكامل، ولكن من المعروف جيدًا أنها تعاني من فجوة كبيرة في الأداء عند مقارنتها بتقنيات المحور الأفقي. بناءً على هذه الفرضيات، في العمل الحالي، يتم التحقيق في بعض الحلول المبتكرة لتحسين أداء توربينات الرياح ذات المحور الرأسي من Darrieus من خلال الأساليب العددية والهندسية. تشمل التدخلات التي تم التحقيق فيها تهجين الدوار من خلال استخدام قسم سافونيوس الداخلي لتحسين بدء تشغيل الماكينة والتطبيق المحتمل للدمامل لتحسين أداء الرقاقات الهوائية NACA 0021 على قسم الدوار الخارجي. تُظهر النتائج فعالية التدخلات في الحصول على دوار ذي أداء مستقر في مجموعة واسعة جدًا من أنظمة الرياح.

The electric generator is estimated to be among the top three contributors to the failure rates and downtime of wind turbines. For this reason, in the general context of increasing interest towards effective wind turbine condition monitoring techniques, fault diagnosis of electric generators is particularly important. The objective of this study is contributing to the techniques for wind turbine generator fault diagnosis through a supervisory control and data acquisition (SCADA) analysis method. The work is organized as a real-world test-case discussion, involving electric damage to the generator of a Vestas V52 wind turbine sited in southern Italy. SCADA data before and after the generator damage have been analyzed for the target wind turbine and for reference healthy wind turbines from the same site. By doing this, it has been possible to formulate a normal behavior model, based on principal component analysis and support vector regression, for the power and for the voltages and currents of the wind turbine. It is shown that the incipience of the fault can be individuated as a change in the behavior of the residuals between model estimates and measurements. This phenomenon was clearly visible approximately two weeks before the fault. Considering the fast evolution of electrical damage, this result is promising as regards the perspectives of exploiting SCADA data for individuating electric damage with an advance that can be useful for applications in wind energy practice.

Wind turbine upgrades have recently been spreading in the wind energy industry for optimizing the efficiency of the wind kinetic energy conversion. These interventions have material and labor costs; therefore, it is fundamental to estimate the production improvement realistically. Furthermore, the retrofitting of the wind turbines sited in complex environments might exacerbate the stress conditions to which those are subjected and consequently might affect the residual life. In this work, a two-step upgrade on a multimegawatt wind turbine is considered from a wind farm sited in complex terrain. First, vortex generators and passive flow control devices have been installed. Second, the management of the revolutions per minute has been optimized. In this work, a general method is formulated for assessing the wind turbine power upgrades using operational data. The method is based on the study of the residuals between the measured power output and a judicious model of the power output itself, before and after the upgrade. Therefore, properly selecting the model is fundamental. For this reason, an automatic feature selection algorithm is adopted, based on the stepwise multivariate regression. This allows identifying the most meaningful input variables for a multivariate linear model whose target is the power of the upgraded wind turbine. For the test case of interest, the adopted upgrade is estimated to increase the annual energy production to 2.6 ± 0.1%. The aerodynamic and control upgrades are estimated to be 1.8% and 0.8%, respectively, of the production improvement.

Despite their simplicity, photovoltaic (PV) modules are often arranged in structures that can be affected by severe and complex wind loads: in this context, the wind flow and the dynamic excitation induced by vortex shedding can introduce unexpected aeroelastic responses. This work introduces a novel wind tunnel application of experimental techniques to address this issue by the use of flow visualisation and video postprocessing, through the optical flow algorithm. Numerical simulations based on unsteady Reynolds-averaged Navier–Stokes (RANS) models are performed and compared against the experimental wind tunnel tests on a PV panel that was also instrumented with pressure taps. A setup with a 65∘ tilt angle was examined because, based on preliminary analyses, it was considered interesting for the free flow–wake transition associated with the dynamic response of the PV panel. The comparison of the experimental and numerical average wind fields supported that the proposed optical flow method was appropriate for characterising the wake of the panel, because there was enough seeding to perform the video postprocessing. Experiments and numerical predictions were compared as regards the average pressure distribution on the panel surfaces, and the average percentage was in the error of 7%; this supports that the URANS method was capable of reproducing the average behaviour of the panel, as well as for the selected configuration, which is particularly challenging. Furthermore, the simulated and measured power spectral densities of the wind speed were compared, and this resulted in the numerical model quite faithfully reproducing the frequency of the peak at 5 m/s, while the error was in the order of 20% for the 10 m/s case; this supports that, despite the URANS approach being affected by well-known critical points regarding the simulation of instantaneous quantities, it can be employed to elaborate information that can be particularly useful for the structural design of the panel. This kind of result can be considered as a first step, obtained with simplified and affordable methods, towards a characterisation of the dynamic behaviour of a PV panel in a real-world setup.