1,720,956 research outputs found
Great expectations for offshore wind turbines: Emulation of wind farm design to anticipate their value for customers
No full textTo date, the technical feasibility of making electricity from offshore wind energy has been convincingly proven. However, the current challenge is to reduce the costs of this form of energy. One of the aspects playing a role in cost reduction is the optimisation of the wind turbine. The wind turbine influences the costs of various elements of an offshore wind farm, such as the structure on which it will be built, the electrical cabling, the installation, maintenance and, last but not least, the electricity production. The extent of this influence is hard to determine during the design of the wind turbine. In this research a method is developed to assess the effects of a wind turbine on the costs and performance of an offshore wind farm. Core of the method is a software program that automatically designs a wind farm for a turbine for which the user provides the inputs. By varying the inputs, the user can find the turbine design for which the cost of energy would be lowest. The method has been tested with a case study and with industrial users. The case study shows that the method can indeed lead to a better wind turbine design and the test-users confirm the utility of the program. Using the program stimulates further cooperation between the marketing and engineering departments, which may require a different way of working for some companies. The thesis provides a more extensive summary.Aerodynamics, Wind Energy, Flight Performance and PropulsionAerospace Engineerin
Effects on support structure design due to wake-generated turbulence
No full textAs the world demands cleaner, sustainable and economical energy sources, the wind energy academia and industry battles to increase performance and reduce costs. One of the promising fields of study is wind turbine wakes in wind farms. The position of the turbines within the layout affects the intensity of their wake effects, such as reduced wind speed or turbulence, therefore the choice of its position has an impact on wake losses and fatigue damage induced by wake-generated turbulence on the components. In this work, the possibility of wind turbine’s support structure cost reduction is explored by studying the effect on its design (and cost) caused by wake-generated turbulence. Furthermore, layout optimization considering wake losses and the wake-affected support structure cost was studied. To obtain insights about these effects, the turbulence intensity calculation and a simple support structure design were implemented into the wind farm design tool TeamPlay (by M. Zaaijer in the Wind Energy Research Group at TU Delft) and used to perform a series of case studies. The turbulence calculation was implemented following the IEC guidelines for any layout and wind direction distribution. The simple support structure design approach used in this work is based on two key aspects: (1) a base design obtained from Teamplay which does not account for fatigue and (2) the assumption of proportionality between fatigue equivalent load and turbulence. By using these tools, a location-specific support structure design within the wind farm was performed. Further, the weight and cost of the support structures was compared with the case in which all support structures have the same design obtained from the worst turbulence regime. It was found that wake-induced fatigue and its effect on the support structure design is not relevant for layout-spacing optimization because wake losses dominate the cost changes due to layout changes. Moreover, it was found that location-specific support structure design, according to their specific turbulence regime, would result in cost reductions that could account, as an upper limit, between 0.3 % and 0.7 % of the total capital costs in the studied cases. Finally, the cost reduction share of the total capital cost increases with increasing support structure size.Aerospace EngineeringSustainable Energy Technolog
The nonlinear effect of combining uncertainties on the energy yield of an offshore wind farm
No full textOffshore wind energy is expected to grow in the coming years: future plans for offshore wind farms total more than 98 GW. Financing is needed to realise these plans. Investment decisions partly depend on the uncertainty in energy yield predictions. It is therefore important that these energy yield predictions and their corresponding uncertainty are determined as accurately as possible. Current methods for determining annual energy production assume that there is a linear relation between input uncertainties and output uncertainty, allowing the use of simple methods for determining annual energy production and its uncertainty. It is however known that this assumption is incorrect: nonlinear relations do exist. This means that it is unclear whether the use of these simple methods can be justified. This thesis has developed a methodology that can be used to determine if, and how, the nonlinear effect of combining two uncertainty sources should be incorporated in the energy yield prediction. This has been done by investigating the case study of the nonlinear effect of combining array efficiency and availability. The investigation was split up in five main steps. First, the physical relations between array efficiency and availability have been explored, revealing that downtime of a turbine affects the array efficiency of a wind farm. Figuring out the state-of-the-art methods pointed out that this interdependency is currently not taken into account. By adjusting the current models, an adapted model was developed that is able to consider this effect. Simulations have been performed on both the current and the adapted model. The results show that for a typical mean availability value of 96.2%, the differences between the current and the adapted model are smaller than 1%. This means that the current methods used by industry can be justified. However, if availability values drop, the difference between both models becomes significant. Due to the high development and computational time of the adapted model, an approximation of the mean annual energy production was developed that uses existing tools. This approximation yields accurate results: the difference between the approximation and the results of the adapted model is lower than 0.5%. Since the approach that was used in this research has proven to be successful, it can be translated to a generic methodology. This methodology can be followed to determine the nonlinear effect of two other uncertainty sources.Wind EnergyAerospace Engineerin
Offshore wind farm optimization, investigation of unconventional and random layouts
No full textThis project aims at investigating whether or not unconventional and/or random offshore wind farm layouts lead to better performance of the farm. The determination of each solution is based on the estimated value of the Levelized Production Cost, thus the cost per produced unit of energy (i.e., ecents/kWh). For the purposes of the current research a previously developed Matlab code is used. Due to some restrictions that had been adopted by the original composer of the code, the tool was updated and extended so that it is able to evaluate more random-shaped offshore wind farms. The optimization of an offshore wind farm layout is a multidisciplinary problem, which includes several design variables. In addition various restrictions should be considered if the purpose of setting the problem on a more realistic basis is desired. In this study due to the limited time as well as narrow computational resources, only some of these parameters are considered. Among others they include, the wake effect, electrical losses and a site specific wind rose. A reference offshore wind farm is set, and in detail is investigated, by a deterministic and stochastic approach, the effect of a) different separation distance for each row and column of the wind farm, b) displacement of individual wind turbine(s), c) discard of specific wind turbine(s). These alterations try to achieve the increase of the energy production, either by maximizing the energy output of the wind turbines, due to the decrease of the losses caused by the wake effect, or by minimizing the electrical losses. Moreover, a better layout design could be realized by reducing the costs which refer to the overall project. In addition to the aforementioned listed alterations the case of the Horns Rev offshore wind farm is studied. This case is investigated by the deterministic and stochastic approaches, as the previous cases and the results are compared to the ones included in already published bibliography. Overall, it was shown that the layout design according to the characteristics adopted in this research could lead to a more efficient offshore wind farm. In the majority of the cases it is seen that the decrease of the LPC is mainly a result of the cable cost and losses. When the small test wind farm is considered, it is noticed that the structured approach of unconventional layouts resulted in better values for the LPC in comparison with the more random approach.Applied SciencesSustainable Energy Technolog
Development of a design tool for offshore wind farm layout optimization: Consideration of wake effects and electrical infrastructure costs and losses
No full textA design tool has been developed with the aim of helping in the wind farm design process. The tool is able to handle rectangular layouts with any number of turbines. Wind farm power, as well as wind and site conditions can be specified by the user. The main tool models are described and the developing steps have been detailed. Results of tool functionality are presented and compared with other tools or real case studies. The two modes of operation are explained: the separation distance sweep mode and the optimization function mode. Besides, the advantage and limitations of the optimization mode are indicated. The main lessons learnt during the developing of this tool are described for each developing stage. The most relevant is that the optimum layout dimensions should be found using the separation distance sweep mode rather than the optimization function. As a main conclusion, the implemented design tool can be helpful for the design process of offshore wind farms. The tool allows the user to define turbine, wind and site conditions and wind farm layout properties. Based on these properties, the tool delivers the optimum layout dimensions considering the effects of wake losses and electrical cable losses and costs. Additional conclusions and recommendations are summarized together with some future work possibilities.Aerospace EngineeringSustainable Energy Technolog
What is the ideal powercurve?: Optimizing the powercurve above rated wind speed for large offshore wind turbines
No full textCurrent large offshore wind turbine design practice is using a powercurve that is flat above rated wind speed. The most important reason for this is generator and electric system costs, while another reason is that parts such as blades and tower are not designed for higher loads. In this report, it is investigated which other possibilities are present than a flat powercurve. These possibilities include a maximum thrust-designed, maximum torquedesigned, and fatigue damage-designed powercurve. Furthermore, the NREL 5 MW powercurve is optimized using part-wise engineering-based cost functions. For this turbine, 5% of the levelized cost of energy is saved if the powercurve is adjusted. The main proposed changes are peak shaving, a rotor speed increase and a power decrease at high wind speeds.Aerospace EngineeringSustainable Energy Technolog
Adhesive bonded towers for wind turbines: Design, Optimization and Cost Analysis
No full textIn an increasingly competitive energy market, the cost of a wind power plant has become more important. A tubular steel tower supporting a wind turbine can amount to up to 20% of the overall turbine costs and its optimization may lead to substantial savings with regard to the costs and the use of materials. One important aspect of the design is connections between the tower’s sections and between the cans. The towers usually consist of steel segments, made of several welded cans (conical subsections), which are further connected by welded flanges. The welded connections have high risk of fatigue failure leading to the thick tower wall. Also, the flanges are very expensive. This research is focused on improving wind turbine towers by using adhesive bonded joints instead of welded joints and flanges. This idea is investigated and the principles of bonded connection are presented. Fatigue resistance is treated as the main discerning factor between the existing design and the proposed solution in this study. The first part of the project focuses on providing a design solution for replacing the bottom-most flange with the bonded joints. A comparative cost study of the proposed solution is also provided in this project. In the second part, optimization of the thickness has been investigated for the entire tower when the cans are bonded circumferentially using adhesives instead of welds. For the cost analysis of the proposed solution, an 80m reference tower was designed based on the stability and the fatigue assessment of the welds. The approach is use a reference 3MW wind turbine model in GH Bladed. The proposed bonded joint is a tubular-single lap joint based on implementation of simple analytical Volkersen Model. A design guideline for the adhesive bonded joint is presented. Furthermore, particular focus was given to the factors affecting a joint strength and their behavior in a bonded joint. Finally, the benefits in terms of fatigue strength, design simplicity, and cost savings are addressed in detail. According to this study, the replacement of the bottom-most flanges with an adhesive bonded joint provides a maximum cost reduction of 17%. This seems to be an economically feasible assembly solution. For the bonding of entire cans in the tower, only the top two cans can be bonded economically, keeping the remaining cans to be welded to each other. The replacement of welds in the entire tower by bonded joints is possible, however, in comparison to the existing solution it is not a feasible solution in terms of material and cost saving.Aerospace EngineeringWind EnergySustainable Energy Technolog
Root Blade Load Estimation by Measurement Database for the Implementation in a SCADA System
No full textAerospace EngineeringWind EnergySustainable Energy Technolog
Design concepts for offshore wind turbines: a technical and economical study on the trade between stall and pitch controlled systems
No full textMaintenance of offshore wind turbines is much more expensive than that of onshore machines. Several suggestions have been made in this respect to reduce operation and maintenance costs by employing simpler turbine concepts with higher reliability. Particularly, stall-controlled machines have been suggested as robust and reliable options that could lower operation and maintenance costs, due to the lack of a pitch mechanism and its control system and because of the lower failure rates they seem to have. This turbine concept, however, trades-off turbine performance against operation and maintenance costs. The focus of this thesis is to determine the possible gains regarding operation and maintenance and the losses in power performance resulting from changing turbine concept from pitch to stall control. To do so a design assessment of a baseline, pitchcontrolled turbine and an alternative, stall-controlled one is carried out. The turbines are designed for an IEC class IA and aimed for a specific location in the North Sea. The designs are then compared and evaluated according to their technical and economical performance. Qualitative as well as quantitative comparisons are pursued to get insight in the advantages and disadvantages of each concept when intended for offshore locations. The energy yield, availability, operation and maintenance and levelised production costs associated to each turbine design are estimated to identify which turbine option could lead to the most benefits in the case of an offshore wind farm. From the analysis made it can be observed that the use of a stall-controlled scheme does contribute in reducing the operation and maintenance expenses of an offshore wind farm project. The loss in performance, however, surpasses the gains in maintenance and availability attained.Aerospace EngineeringWind EnergySustainable Energy Technolog
Design aspects of integrated navigation for an unmanned Ballistocraft for Acceleration Research
No full textFor scientific experiments it is sometimes desirable to eliminate the earth gravity partially or entirely. It is possible to create this 'microgravity' with the use of a droptower, a spacevehicle or an aeroplane. Because the existing facilities for this kind of research are very expensive, have long waiting periods (space vehicle, aeroplane) or provide very short duration of microgravity (droptower), there is a need for a new system. Using an Unmanned AirVehicle (UAV) it is possible to solve the larger part of the problems mentioned before. This vehicle should be cheap, with a high availability and should be able to fly parabolic trajectories to create the microgravity. The UAV combines the relatively long duration of the microgravity in an aeroplane with the cheap and easy availability that is obtained in a drop tower…Applied SciencesElectrical EngineeringTelecommunications and Traffic Control Systems Grou
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