Potential order-of-magnitude enhancement of wind farm power density via counter-rotating vertical-axis wind turbine arrays

This paper introduces the GWIT EHD VAWT and the logic and history behind its development. We develop a simplified model to compare the performance of EHD VAWTs with conventional propeller machines. GWIT is engaged on a path to optimize the performance of its wind turbines in a wind farm setting. The paper details the characteristics of its first two prototypes - JJ and JJ3. The turbines are designed to meet the atmospheric conditions prevailing in China. While the EHD VAWT concept can be implemented in many configurations, GWIT has developed its turbines to operate over the broadest possible atmospheric conditions with an absolute minimum of moving mechanical components. We focus on turbine designs that more than double energy capture from the wind site. More than 90% of the turbine's content is of local manufacture. I. HISTORY OF THE EHD VAWT Wind turbines can trace their origins thousands of years into the past. Modern wind turbines can trace their current mission - the conversion of wind energy into electricity-back to the closing days of World War II when some Northern Continental European nations first converted some of their water pumping and grain milling wind turbines into producers of electricity. Since that time European nations began to devote significant research efforts into developing efficient machines to produce grid usable electricity from their abundant wind resources. More recently these efforts have been joined by North American and Asian nations. While some effort was devoted to the development of vertical axis wind turbines (VAWTs) almost all European research efforts were devoted to horizontal axis wind turbines (HAWTs). In Canada and the United States significant efforts were made to develop VAWTs, but the vast majority of wind energy research was devoted to HAWTs. By 1980 European designed HAWTs were focusing on economic parameters while Canadian and American efforts were still attempting to demonstrate feasibility. Numerous HAWT powered wind farms emerged but only two VAWT powered wind farms were in development or operation. Rely- ing on a Sandia National Laboratories design, FloWind fielded 512 170 kW F-17 and 300 kW F-19 VAWTs on two wind farms in California. Both wind farms operated successfully until they were replaced with Micon HAWTs between 1998 and 2002.

Co-locating horizontal- and vertical-axis wind turbines has been recently proposed as a possible approach to enhance the land-area power density of wind farms. In this work, we aim to study the benefits associated with such a co-location using large-eddy simulation (LES) and analytical wake models. In this regard, small-scale vertical-axis wind turbines (VAWTs) in triangular clusters are deployed within a finite-size wind farm consisting of horizontal-axis wind turbines (HAWTs). Wake flow within the wind farm and the effect of VAWTs on the overall wind-farm efficiency are investigated and quantified. The results show that the optimal deployment of small-scale VAWTs has a negligible impact on the performance of HAWT arrays while increasing the total power production. For the particular cases considered here, the power output of the co-located wind farm increases up to 21% compared to the baseline case in which only the HAWTs are present. Also, by comparing to the LES results, it is shown that the analytical framework proposed here is able to accurately predict the power production of wind farms including both HAWTs and VAWTs. Finally, as a real-world application, potential benefits of deploying small-scale VAWTs inside the Horns Rev 1 wind farm are explored for various wind directions using the calibrated wake model. The results show potential for about an 18% increase in the wind-farm power production, averaged over all wind directions, for a particular VAWT layout investigated in this study. The levelized cost of energy (LCoE) for the co-located wind farm is also assessed. The simulations finds that meanwhile the installation of VAWTs increases the annual energy production (AEP) of the wind farm, it also increases the LCoE, which is caused by a) lack of operational data, and b) a low TRL (Technology Readiness Levels) for VAWTs and floating foundations.

Vertical Axis Wind Turbines (VAWTs) are not mature enough yet for offshore wind farms, but they offer benefits compared to conventional Horizontal Axis Wind Turbines (HAWTs). Higher power densities, reduced wakes, lower center of mass, and different power and thrust curves make VAWTs an interesting option to complement existing wind farms. The optimization of wind farm layouts—finding the optimal positions of wind turbines in a park—has proven crucial to extract more energy from conventional wind farms. In this study, we build an optimizer for VAWTs that can consider arbitrarily shaped layouts as well as obstacles in the area. We adapt a recent model for the wakes of VAWTs considering a Troposkien design. We can then model and optimize a large VAWT park in a real wind scenario and assess for the first time its performance operating Troposkien VAWTs. In addition, we present a novel model for wind farm optimization that considers the clockwise and counterclockwise rotation of turbines. This optimization exploits the asymmetric wakes of VAWTs, thus increasing the total energy production. We benchmark our optimization on realistic instances and compare VAWTs and HAWTs wind farm layouts, showing that VAWTs can achieve higher density and power production than HAWTs in the same area. Finally, the wake loss reduction is compared to the literature.

Review on the technical perspectives and commercial viability of vertical axis wind turbines

Renewable are seen as next generation sources of energy for meeting rising energy demands and depleting fossil fuels. Solar, biomass, geothermal, hydro-electric and wind are the renewables which can produce huge megawatts of power. Among all this, wind is the cheapest renewable source of energy. This fast growing wind energy source needs to be utilised. On the basis of structure, wind turbines are broadly classified as Horizontal Axis Wind Turbine (HAWT) and Vertical Axis Wind Turbine (VAWT). VAWT can tap wind energy from any direction, while HAWT can tap wind from only one direction. But still HAWT are being researched upon and used more as it taps more wind energy as compared to VAWT. Traditional HAWT have unreasonable efficiencies so focus has slightly shifted to VAWT. Economically HAWT are better than VAWT but VAWT are more portable in nature. This paper deals with the different classification of turbines, relative comparison between them and development of mathematical modelling of wind turbines.

Compounded energy gains in collocated wind plants: Energy balance quantification and wake morphology description

Large fixed and floating wind farms are planned in the US, the first of which will come on stream along the East Coast, and then possibly followed by the West Coast in deepwater. However, there are other regions in North and South America, and even the Caribbean that are rapidly aiming for offshore wind farms. One of those locations, offshore Texas, may develop ahead of the West Coast by taking advantage of the unparalleled expertise in ocean engineering in Texas gained through over 40 years of offshore oil and gas developments. In addition, Texas has regional competitive advantages that could result in another offshore boom for the region. Texas is the leading state for onshore wind power and consequently has some highly innovative research institutions and initiatives that could further push Texas to the forefront of regional, if not global, offshore wind technology development and deployment. The additional advantages that Texas can provide to wind farm developers based on its proximity to the Caribbean and South American offshore wind markets are also presented. As an example of innovation in Texas, the University of Texas at Dallas, DOE ARPA-E (Department of Energy Advanced Research Projects Agency – Energy) funded vertical axis wind turbine (VAWT) development is summarized (ARPA-E, 2020). While elements of VAWT technology are transferable to horizontal axis wind turbine (HAWT) technology to improve HAWT performance, more generally, the deployment of VAWTs overcomes many logistical and performance problems inherent in deploying HAWTs offshore. Such VAWT advantages are discussed. Two cases are presented comparing HAWT versus VAWT floating wind farms. The technology and execution differences of the two cases are compared and the net present value and internal rate of return are calculated conserving the technology differences. Discussion of forthcoming additional financing opportunities is also presented to illustrate how even in low-cost electric rate markets, offshore wind can still be feasible.

Experimental characterisation of the wake behind paired vertical-axis wind turbines

Background: In a wind farm, the wind speed of the downstream wind turbine will be lower than the wind speed of the upstream wind turbine due to the influence of the wake. Therefore, the wake of wind turbines is one of the uncertain factors predicting the annual power generation of the wind farms. The study on the wake can effectively improve the efficiency of power generation. The arrangement of vertical axis wind turbines in wind farms is rarely studied. Therefore, it is important to study the vertical layout of wind turbines under the influence of wakes to obtain the best layout and unit spacing. Objective: The objective of this study is to obtain the optimal layout and unit distance of wind turbines in Senegal wind farms by studying the arrangement of Senegal vertical axis wind turbines in wind farms. Methods: Based on the ANSYS CFX flow field calculation module, the fluid dynamics model of the Senegal fan was established and the flow field simulation analysis was carried out. Based on the Jensen wake model and its improved model, three layout methods for the wind farm wind turbines were proposed: two units were arranged in series, two units were arranged in parallel, and three units were staggered. Through the simulation model, the wind energy utilization coefficient and wind speed of the wind turbine in the wind farm were obtained. Results: The optimal separation distance between the units was analyzed from four different angles: wind energy utilization coefficient, torque analysis, downstream tail flow and wind speed cloud contour. Finally, based on the optimal arrangement and unit distance, a triangular staggered wind farm composed of 10 units was established, and the integrated flow field characteristics of the whole wind farm were simulated and analyzed. The integrated flow field wake characteristics of the wind farm were obtained. Conclusion: In all the three arrangements, the optimum distance between the units must be three times the diameter of the wind turbine. This arrangement ensures that most of the units are unaffected by the wake, the area affected by the low-velocity wake of the wind farm is small, and the area affected by the high-speed wake is large.

The aerodynamic interaction between wind turbines grouped in wind farms results in wake-induced power loss and fatigue loads of wind turbines. To mitigate these, wind farm control should be able to account for those interactions, typically using model-based approaches. Such model-based control approaches benefit from computationally fast, linear models and therefore, in this work, we introduce the Dynamic Flow Predictor. It is a fast, control-oriented, dynamic, linear model of wind farm flow and operation that provides predictions of wind speed and turbine power. The model estimates wind turbine aerodynamic interaction using a linearized engineering wake model in combination with a delay process. The Dynamic Flow Predictor was tested on a two-turbine array to illustrate its main characteristics and on a large-scale wind farm, comparable to modern offshore wind farms, to illustrate its scalability and accuracy in a more realistic scale. The simulations were performed in SimWindFarm with wind turbines represented using the NREL 5 MW model. The results showed the suitability, accuracy, and computational speed of the modeling approach. In the study on the large-scale wind farm, rotor effective wind speed was estimated with a root-mean-square error ranging between 0.8% and 4.1%. In the same study, the computation time per iteration of the model was, on average, 2.1 × 10 − 5 s. It is therefore concluded that the presented modeling approach is well suited for use in wind farm control.

The need for energy and electricity has been increasing globally, and this means more power is required from the power plants. Power plants, however, will then continue harming the earth because of the greenhouse gasses produced while generating energies that contribute to global warming. Using renewable sources to produce clean energies is one of the sustainable methods to deal with such challenges. Wind energy is one of the renewable sources, which is accessible anywhere on earth, creating green energy. Wind turbines are mainly categorized into Horizontal Axis Wind Turbines (HAWT) and Vertical Axis Wind Turbines (VAWT). This paper firstly presents a general comparison between the HAWTs and VAWTs. Then, it presents mathematical modelling for the aerodynamic factors of HAWT and Darrieus VAWT to assist the researchers to understand some key design aspects of wind turbines, such as lift/drag ratio, tip speed ratio, power coefficient, and torque coefficient. Also, this paper presents a review of the aerodynamic performance of the recent VAWT designs to help researchers to identify and choose the best model among the Savonius and Darrieus rotors for further development or designing a new model at different wind conditions. This comparison review shows that for a large scale HAWT upwind 3 bladed wind turbines are the most optimum. The helical Savonius rotors perform better by having positive torque coefficient at all azimuth angles. Moreover, helical Darrieus was found to produce lesser noise and suitable for conventional areas. hybrid Savonius-Darrieus rotors can solve the self-starting challenge of the VAWTs, and they are suitable at low wind speeds. At last, this review shows some of the recent hybrid Savonius-Darrieus rotors which would help to solve the low efficiency of Savonius rotor and self-starting challenge of Darrieus rotors.

The offshore wind sector is expanding to deep water locations through floating platforms. This poses challenges to horizontal axis wind turbines (HAWTs) due to the ever growing size of blades and floating support structures. As such, maintaining the structural integrity and reducing the levelised cost of energy (LCoE) of floating HAWTs seems increasingly difficult. An alternative to these challenges could be found in floating offshore vertical axis wind turbines (VAWTs). It is known that VAWTs have certain advantages over HAWTs, and in fact, some small-scale developers have successfully commercialised their onshore prototypes. In contrast, it remains unknown whether VAWTs can offer an advantage for deep water floating offshore wind farms. Therefore, here we present a multi-criteria review of different aspects of VAWTs to address this question. It is found that wind farm power density and reliability could be decisive factors to make VAWTs a feasible alternative for deep water floating arrays. Finally, we propose a way forward based on the findings of this review.

A review on the wake aerodynamics of H-rotor vertical axis wind turbines

A double-multiple-streamtube vertical axis wind turbine simulation and design module has been integrated within the open-source wind turbine simulator QBlade. QBlade also contains the XFOIL airfoil analysis functionalities, which makes the software a single tool that comprises all functionality needed for the design and simulation of vertical or horizontal axis wind turbines. The functionality includes two dimensional airfoil design and analysis, lift and drag polar extrapolation, rotor blade design and wind turbine performance simulation. The QBlade software also inherits a generator module, pitch and rotational speed controllers, geometry export functionality and the simulation of rotor characteristics maps. Besides that, QBlade serves as a tool to compare different blade designs and their performance and to thoroughly investigate the distribution of all relevant variables along the rotor in an included post processor. The benefits of this code will be illustrated with two different case studies. The first case deals with the effect of stall delaying vortex generators on a vertical axis wind turbine rotor. The second case outlines the impact of helical blades and blade number on the time varying loads of a vertical axis wind turbine.

Optimization of H-Rotor Darrieus turbines' mutual interaction in staggered arrangements