Wind, Volume 2, Issue 1 (March 2022) – 10 articles

It is shown in the literature that wind turbine designs with different load distributions have different wake features. To systematically study how different load distributions affect turbine wakes, a method for designing variants of blades with different radial load distributions, but with approximately the same power ($C_P$) or thrust coefficient ($C_T$), is needed. In this work, an inverse design method based on the blade element momentum method and the multi-dimensional Newton’s method, with the normal and tangential force coefficients as the design objective and iterations for satisfying the $C_P$ or $C_T$ constraint, is developed. The proposed method is validated using the two-bladed small-scale NREL phase VI S809 wind turbine blade design and the three-bladed utility-scale NREL 5 MW wind turbine blade design. Four variants of the NREL 5 MW wind turbine, i.e., the Root-CP, Tip-CP, Root-CT, and Tip-CT designs, which represent the variants of the original design (NREL-Ori) with a higher load near the blade root and tip regions with approximately the same power coefficient ($C_P$) or thrust coefficient ($C_T$) as that of the NREL-Ori design, respectively, are then designed using the proposed method. At last, the flapwise blade bending moment and the power coefficients from different variants of the NREL 5 MW turbine are compared for different tip speed ratios, showing that the “Root” designs are featured by a wider chord near the root, lower blade bending moment, and higher power coefficients for tip-speed ratios greater than nine. Full article

The use of fossil fuels to generate energy is often associated with serious negative effects on the environment. The greenhouse gas emissions resulting from burning these fuels destroy the ozone layer and lead to global warming. As a strategic approach to the solution of this problem, calls for research and development, as well as the implementation of technologies associated with renewable energy sources within the European Union (EU), have intensified in recent years. One of the keys to a successful outcome from this intensified effort is to identify the challenges associated with the transfer of both intellectual property and technology rights in the renewable energy sector within the EU. The present paper contributes towards this direction. Firstly, data from the literature were used to identify contemporary trends within the European Union with regards to technology transfer and intellectual property within the sector of renewable energy. Then, a statistical analysis utilising an ordinary least squares (OLS) model was conducted to establish a correlation between renewable energy innovations (research and development) and the level of investment associated with renewable energy technologies. Finally, this correlation, along with the associated challenges, was then critically explored for four of the most popular renewable energy sources (namely solar energy, biomass, wind energy, and marine renewable energy), and conclusions are reported. Full article

Many residential houses with sloped roofs are equipped with photovoltaic (PV) systems. In Japan, PV systems are generally designed based on JIS C 8955, which specifies wind force coefficients for designing PV panels. However, no specification is provided to the PV panels installed near the roof edges where high suctions are induced. When installing PV panels in such high-suction zones, we need to evaluate the wind loads on the PV panels appropriately, usually by performing a wind tunnel experiment. However, it is difficult to make wind tunnel models of PV panels with the same geometric scale as that for the building, e.g., 1/100, because the thickness of PV panels and the distance between PV panels and a roof are both several centimeters. Therefore, in the present paper a numerical simulation is applied to the estimation of pressures in the space between the lower surface of PV panels and the roof surface, called “layer pressures”, using the unsteady Bernoulli equation and the time histories of external pressure coefficients obtained from a wind tunnel experiment. An assumption of the weak compressibility of the air and an adiabatic condition is made for predicting the layer pressures from the flow speed through the gaps. The simulation method is validated by a wind tunnel experiment using a model of square-roof building. Full article

Wind energy is an alternative source of clean energy to address the growing energy demand and provide pollution-free electricity. With the rapid development of urban areas, high wind energy resources such as high-rise building rooftops are excellent locations for urban wind turbine installation. One of the practical and simple urban wind turbines is the Savonius design. It has a simple design, easy to maintain, and is very affordable. This work focuses on the design evaluation of a Savonius wind turbine (SWT) by varying the rotor diameter, rotor height, and twist angle for urban applications. A transient computational fluid dynamics (CFD) approach is applied to assess the various design treatments using a space-filling design of experiments. To address the spaces in the hypercube statistical design, a sphere packing design method was adopted which suited the evaluation of computational simulations results such as that of the CFD. The Gaussian stochastic process model was applied to establish the trend of the parametric performance of the optimized SWT design through the model fitting. The results have shown that optimized SWT performs well with its self-starting capability compared to the traditional Savonius design. In addition, the optimized SWT has shown a better peak power coefficient compared with the results of previous works on the design of SWT. Full article

Wind-induced loss modeling plays a key role in insurance risk management. Hence, a flexible vulnerability framework is to be developed for residential and commercial buildings. This model predicts the losses induced by hurricane wind pressure, wind-borne debris and wind-driven rain. Twenty-five different key variables of the buildings and environment are used as attributes for the simulations. Model results are validated using the Florida Public Hurricane Loss Models (FPHLM) and HAZUS wind vulnerability functions. New contributions include (1) a Markovian roof-aging model to address decreases in roof performance due to aging, and (2) occupancy-specific interior value models based on FEMA Normative quantities for the systematic evaluation of interior value applicable to archetype buildings. A simple wind debris impact model and wind-driven rain intrusion model is also introduced. The influence of the number of stories, roof aging, and window vulnerability resulting in damage are investigated in this article to ensure consistency of the results. The proposed framework enables insurance loss modelers to make judicious choices of input variables based on partial or detailed knowledge about the building to model losses. Future research should focus on validation and calibration using good-quality insurance claims data. Full article

This paper proposed a standalone solar/wind/micro-hydro hybrid power generation system to electrify Ethiopian remote areas that are far from the national utility grid. The aim is that it will lead to the development of renewable energy sources, using a hybrid optimization model for energy renewables (HOMER) as an optimization and sensitivity tool and MATLAB as a design tool. The system uses 100% renewable energy. This system incorporated solar photo-voltaic (PV), wind turbines, micro-hydro systems, and battery systems. The net present cost of the system is $4,377,731, incorporating capital depreciation and levelized operation and maintenance costs. During the hybrid energy system’s lifetime, the cost of a grid extension power supply is $22.185 million, which is nearly $17,808,000 more than the cost of the proposed standalone system. So, developing solar/wind/micro-hydro hybrid power generation will save $17,808,000 versus extending the national utility grid. As a result of a thorough examination of renewable energy resources, standalone solar, wind, and micro-hydro hybrid power generation is a technically and economically viable option for the case study area of Maji town. Full article

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. Full article

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. Full article

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 MATLAB^TM 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. Full article

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. Full article