Blade-Resolved CFD Simulations of a Periodic Array of NREL 5 MW Rotors with and without Towers

A fully resolved (FR) NREL 5 MW turbine model is employed in two unsteady Reynolds-averaged Navier–Stokes (URANS) simulations (one with and one without the turbine tower) of a periodic atmospheric boundary layer (ABL) to study the performance of an infinitely large wind farm. The results show that the power reduction due to the tower drag is about 5% under the assumption that the driving force of the ABL is unchanged. Two additional simulations using an actuator disc (AD) model are also conducted. The AD and FR results show nearly identical tower-induced reductions of the wind speed above the wind farm, supporting the argument that the AD model is sufficient to predict the wind farm blockage effect. We also investigate the feasibility of performing delayed-detached-eddy simulations (DDES) using the same FR turbine model and periodic domain setup. The results show complex turbulent flow characteristics within the farm, such as the interaction of large-scale hairpin-like vortices with smaller-scale blade-tip vortices. The computational cost of the DDES required for a given number of rotor revolutions is found to be similar to the corresponding URANS simulation, but the sampling period required to obtain meaningful time-averaged results seems much longer due to the existence of long-timescale fluctuations.

Machine Intelligent Hybrid Methods Based on Kalman Filter and Wavelet Transform for Short-Term Wind Speed Prediction

Wind power’s increasing penetration into the electricity grid poses several challenges for power system operators, primarily due to variability and unpredictability. Highly accurate wind predictions are needed to address this concern. Therefore, the performance of hybrid forecasting approaches combining autoregressive integrated moving average (ARIMA), machine learning models (SVR, RF), wavelet transform (WT), and Kalman filter (KF) techniques is essential to examine. Comparing the proposed hybrid methods with available state-of-the-art algorithms shows that the proposed approach provides more accurate prediction results. The best model is a hybrid of KF-WT-ML with an average R2 score of 0.99967 and RMSE of 0.03874, followed by ARIMA-WT-ML with an average R2 of 0.99796 and RMSE of 0.05863 over different datasets. Moreover, the KF-WT-ML model evaluated on different terrains, including offshore and hilly regions, reveals that the proposed KF based hybrid provides accurate wind speed forecasts for both onshore and offshore wind data.

Multi-Terminal DC Grid with Wind Power Injection

With the development of offshore wind generation, the interest in cross-country connections is also increasing, which requires models to study their complex static and dynamic behaviors. This paper presents the mathematical modeling of an offshore wind farm integrated into a cross-country HVDC network forming a multi-terminal high-voltage DC (MTDC) network. The voltage source converter models were added with the control of active power, reactive power, frequency, and DC link voltages at appropriate nodes in the MTDC, resembling a typical cross-country multi-terminal type of HVDC scenario. The mathematical model for the network together with the controllers were simulated in MATLABTM and experimentally verified using a real-time digital simulator hardware setup. The resulting static and dynamic responses from the hardware setup agreed well with those from simulations of the developed models.

Incorporating Public Participation in Offshore Wind Farm Siting in Greece

The public acceptance of Offshore Wind Farms (OWFs) is an important issue that is expected to depend highly on their site location. Public involvement in decision-making processes is recommended as it may contribute to the mitigation of opposing, delaying and even blocking OWF projects, as well as increasing future public confidence and support. The aim of this study is to identify the most suitable sites for OWFs deployment in Greece based on citizens’ preferences and judgments. The methodology consists of three phases: (i) identification of Eligible Marine Areas (EMAs) for OWF siting by deploying ten exclusion criteria, (ii) prioritization of six evaluation criteria and ranking of EMAs according to citizens’ judgments through an Online Questionnaire Survey (OQS) and (iii) overall prioritization of EMAs. The Analytic Hierarchy Process (AHP), supported by Geographic Information Systems (GIS) and the OQS are used for the analysis. The results illustrate the priority ranking of thirteen EMAs for OWFs deployment in the Greek marine environment under five different scenarios. The most suitable sites are located in the South-West zone offshore of Rhodes in all the examined scenarios. Sustainable development is a challenging social process, and the different preferences of the society should be integrated in planning processes.

Wind Power: An Important Source in Energy Systems

It is my great pleasure to welcome you to the inaugural issue of Wind [...]

Spatial-Economic Potential Analysis of Wind Power Plants in Germany

Before a new wind farm can be built, politics and regional planning must approve of the respective area as a suitable site. For this purpose, large-scale potential computations were carried out to identify suitable areas. The calculation of wind power plant potential usually focuses on capturing the highest energy potential. In Germany, due to an energy production reimbursement factor defined in the Renewable Energy Sources Act (“Erneuerbare-Energien-Gesetz”, EEG) in 2017, the influence of energy quantities on the power plant potential varies, economically and spatially. Therefore, in addition to the calculation of energy potentials, it was also necessary to perform a potential analysis in terms of economic efficiency. This allows, on the one hand, an economic review of the areas tendered by the regional planning and, on the other hand, a spatial-economic analysis that expands the parameters in the search for new areas. In this work, (a) potentials with regard to the levelized cost of electricity (LCOE) were calculated by the example of the electricity market in Germany, which were then (b) spatially and statistically processed on the level of the federal states.

Design, Construction and Evaluation of an Oscillating Vane Gust Generator for Atmospheric Flow Simulation

The study of unsteady aerodynamic phenomena in wind tunnels is supported by gust-generating devices capable of generating adjustable magnitude and periodicity velocity fluctuations in a flowfield. Gusts are typically generated actively by introducing moving vanes to direct the flow, or passively by tailoring the boundary layer growth and shape in the tunnel. The flow facility used here is a student-built closed-return low-speed wind tunnel, with a test section size of 750 mm × 750 mm and a maximum speed of 25 m/s. A two-vane gust generator utilizing NACA0018 airfoil sections of 150 mm chord length was designed and installed upstream of the test section. The flowfield was mapped with the installed vanes with and without gust actuation, utilizing a hot wire system. The tunnel with gust vanes exhibits a spatially uniform baseline turbulence intensity of 5%, with a steady state velocity deficit of 1 m/s in the vane–wake region. Upon introducing the gusting conditions at vane deflection angles of up to ±45°, velocity differences of up to 4 m/s were attained at 18 m/s freestream velocity at oscillation frequencies ranging between 1 Hz and 2 Hz.

The Benefit of Horizontal Photovoltaic Panels in Reducing Wind Loads on a Membrane Roofing System on a Flat Roof

The present paper proposes a measure for improving the wind-resistant performance of photovoltaic systems and mechanically attached single-ply membrane roofing systems installed on flat roofs by combining them together. Mechanically attached single-ply membrane roofing systems are often used in Japan. These roofing systems are often damaged by strong winds, because they are very sensitive to wind action. Recently, photovoltaic (PV) systems placed on flat roofs have become popular. They are also often damaged by strong winds directed onto the underside, which cause large wind forces onto the PV panels. For improving the wind resistance of these systems, we proposed to install PV panels horizontally with gaps between them. Such an installation may decrease the wind forces on the PV panels due to the pressure equalization effect as well as on the waterproofing membrane due to the shielding effect of the PV panels. This paper discusses the validity of such an idea. The pressure on the bottom surface of a PV panel, called the “layer pressure” here, was evaluated by a numerical simulation based on the unsteady Bernoulli equation. In the simulation, the time history of the external pressure coefficients, measured at many points on the roof in a wind tunnel, was employed. It was found that the wind forces, both on the PV panels and on the roofing system, were significantly reduced. The reduction was large near the roof’s corner, where large suction pressures were induced in oblique winds. Thus, the proposed method improved the wind resistance of both systems significantly.

Greenhouse Gas Savings Potential under Repowering of Onshore Wind Turbines and Climate Change: A Case Study from Germany

Wind energy is crucial in German energy and climate strategies as it substitutes carbon-intensive fossil fuels and achieves substantial greenhouse gas (GHG) reductions. However, wind energy deployment currently faces several problems: low expansion rates, wind turbines at the end of their service life, or the end of remuneration. Repowering is a vital strategy to overcome these problems. This study investigates future annual GHG payback times and emission savings of repowered wind turbines. In total, 96 repowering scenarios covering a broad range of climatological, technical, economic, and political factors affecting wind energy output in 2025–2049 were studied. The results indicate that due to more giant wind turbines and geographical restrictions, the amount of repowerable sites is reduced significantly. Consequently, in most scenarios, emission savings will dramatically diminish compared to current savings. Even in the best-case scenario, the highest emission savings’ growth is at 11%. The most meaningful drivers of GHG payback time and emission savings are wind turbine type, geographical restrictions, and GHG emissions. In contrast, climate change impact on the wind resource is only marginal. Although repowering alone is insufficient for achieving climate targets, it is a substantial part of the wind energy strategy. It could be improved by the synergies of different measures presented in this study. The results emphasize that a massive expansion of wind energy is required to establish it as a cornerstone of the future energy mix.