Σκοπός αυτής της διπλωματικής εργασίας είναι η μελέτη όλων των στοιχείων που είναι αναγκαία για την κατασκευή ενός υπεράκτιου αιολικού πάρκου και της διασύνδεσης του στο δίκτυο μεταφορά και διανομής ηλεκτρικής ενέργειας. Γίνεται μια αναφορά στις ανεμογεννήτριες που υπάρχουν και μπορούν να τοποθετηθούν σε αντίστοιχες μελέτες. Επίσης οι τοπολογίες που μπορούν να στηρίξουν στη διασύνδεση των ανεμογεννητριών και να καταστήσουν δυνατή την δημιουργία ενός πάρκου ,αλλά και τα τεχνολογικά μέσα με τα οποία μπορούμε να μεταφέρουμε αυτή την ενέργεια στο δίκτυο διανομής και μεταφοράς ώστε να χρησιμοποιηθεί προς οποιαδήποτε κατεύθυνση. Τέλος παρουσιάζεται μια μελέτη ενός πάρκου σε μια παράκτια περιοχή της χώρας προσδίδοντας στοιχεία όμοια με τις περισσότερες περιοχές που μπορούν να δεχτούν μια τέτοια κατασκευή. Η μελέτη ολοκληρώνεται με μια προσομοίωση μιας ανεμογεννήτριας του τύπου που προτείνεται να εγκατασταθεί και παρουσιάζει τα αποτελέσματα λειτουργίας της στις αιολικές συνθήκες που επικρατούν το μεγαλύτερο διάστημα. / The aim of this dissertation was to present a project of an offshore wind farm including every point which is considered on a familiar construction and reviling the kinds of connections to the grid between that. There is a reference to the spices of wind turbines produced and used by the industry. Moreover the topologies of wind farms based on hvac or hvdc transmission systems, presenting categories with solutions for both cases. At the end a project of an offshore farm in the Greek coastline took place providing a solution to the majority of same areas around Greece with the same wind characteristics and depths. To sum up a simulation of a DFIG wind turbine functioned under the areas’ wind data giving an image of the pure power that is able to produce.

Η αντικεραυνική προστασία των αιολικών πάρκων αποτελεί ένα πρόβλημα με αρκετές ιδιαιτερότητες λόγω της μορφής και της τοποθέτησης αυτών των κατασκευών σε σημεία όπου είναι ευάλωτα σε κεραυνικά πλήγματα. Για αυτό τον λόγο, έχουν αναπτυχθεί διάφορες μέθοδοι για την προστασία των ανεμογεννητριών και διεξάγονται έρευνες για την αποτελεσματικότητα αυτών. Μία από τις μεθόδους που χρησιμοποιούνται είναι και η διασύνδεση των πλεγμάτων γείωσης των ανεμογεννητριών. Αντικείμενο, λοιπόν, της παρούσης εργασίας είναι η εξομοίωση της μεταβατικής συμπεριφοράς ενός συστήματος γείωσης ενός αιολικού πάρκου το οποίο αποτελείται από τέσσερεις ανεμογεννήτριες. Τα πλέγματα γείωσης των ανεμογεννητριών συνδέονται μέσω αγωγών γείωσης, με σκοπό την καταγραφή της συμπεριφοράς της τάσης σε διάφορα σημεία των πλεγμάτων. Στη συνέχεια, πραγματοποιείται σύγκριση των κυματομορφών των τάσεων στα διάφορα σημεία καθώς και σύγκριση για διαφορετικές διεγέρσεις και τιμές της ειδικής αντίστασης του εδάφους, στο χώρο όπου τοποθετούνται οι γειωμένοι αγωγοί διασύνδεσης. Επίσης γίνεται σύγκριση της συμπεριφοράς του διασυνδεδεμένου μέσω αγωγών γείωσης συστήματος με ένα σύστημα στο οποίο η διασύνδεση των γεννητριών γίνεται μέσω αγωγών οι οποίοι ακουμπάνε στο έδαφος. Για την εξομοίωση των συστημάτων γείωσης, χρησιμοποιήθηκε το μοντέλο της κυκλωματικής προσέγγισης σύμφωνα με το οποίο τα ηλεκτρόδια γείωσης παριστάνονται μέσω κατανεμημένων τμημάτων, τα οποία αποτελούνται από εν σειρά επαγωγές και αντιστάσεις, καθώς και εγκάρσιες αγωγιμότητες και χωρητικότητες. Το ισοδύναμο κύκλωμα δημιουργήθηκε στο πρόγραμμα εξομοίωσης ηλεκτρομαγνητικών φαινομένων EMTP και οι τιμές των διαφόρων μεγεθών υπολογίστηκαν με τη βοήθεια του Microsoft Excel. / Lightning protection of wind farms is a complex problem because of the shape and the placement of these structures in places where lightning strikes are very common. That's why many different methods for the protection of wind turbines have been developed and researches are done for their effectiveness. One of these methods uses the interconnection of the wind turbine's grounding grids for protection. In this thesis, a transient analysis of a grounding interconnected system of a wind farm, consisting of four wind turbines, is being conducted. The grounding grids of each wind turbine are interconnected through buried conductors for the recording of the voltage behaviour in different nodes of the grounding grids. Additionally, a comparison of the voltage waveforms in different nodes is being conducted, as well as a comparison for different injected currents and values of soil resistivity in the place where the interconnecting conductors are being placed. A comparison of the behaviour of an interconnected system using conductors placed on the ground is also being conducted. For the simulation of the grounding systems, the model of circuit approach was used. According to this, the grounding electrodes are modeled using series resistors and inductors and transverse conductivities and capacitancies. The equivalent circuit was created in the electromagnetic phenomena programm EMTP and the parameter values were calculated with the use of Microsoft Excel.

With the rising global warming issue and an ever-increasing dependency oil problem, wind power seems to be an alternative source of energy which is clean, non-polluting, and cost effective. The European 20-20-20 goals as well as national targets for the next ten years require a substantial increase in installed renewable capacity in France. Maïa Eolis is a leading French wind project developer and independent renewable energy producer which helps France to meet its new renewable energy targets. Even if the general opinion on wind energy is rather positive, developing a wind power project is a complex process in France because there are many regulations and new environmental constraints due to the Grenelle 2 law. Many administrative and legislative barriers consequently slow down every step of the development process. This includes handling and coordinating the permitting and application process, realizing pre-feasibility studies, and identifying the best suited sites for wind turbines, taking into account obstacles, aesthetics, and other environmental issues, in order to capture as much wind as possible. Ensuring local support is another key element of the success of a project in order to integrate it in the best possible way in its environment.

The UK has an abundant offshore wind resource with offshore wind farming set to grow rapidly over the coming years. Optimisation of energy production is of the utmost importance and accurate estimates of wind speed distributions are critical for the planning process. Synthetic aperture radar (SAR) data can provide synoptic, wide area wind field estimates at resolutions of a few kilometres and has great potential for wind resource assessment. This thesis addresses the key challenges for the operational implementation of SAR in this context; namely the accuracy of SAR wind retrievals and the ability of SAR to characterise the mean wind speed and wind power density. We consider the main stages of SAR wind retrieval; the retrieval algorithm; sources of a priori information; the optimal configuration of the retrieval system; and the challenges for and accuracy of SAR wind resource estimation. This study was conducted for the eastern Irish Sea in the UK, a region undergoing significant offshore wind energy development. A new wind retrieval algorithm was developed that implements a maximum a posterior probability (MAP) method drawn from Bayesian statistics. MAP was demonstrated to be less sensitive to input errors than the standard direction-based wind speed algorithm (DWSA) and provides a simple retrieval quality check via the error reduction ratio. Retrieval accuracy is strongly influenced by the quality of a priori information. The accuracy of two operationally viable a priori sources, mesoscale numerical weather prediction (NWP) data and WISAR image directions, was evaluated by comparison against in-situ wind observations and WERA coastal data. Results show that NWP wind speeds produce good wind speed and direction estimates with standard deviations of ¬±2 ms-1 and ±16o respectively. WISAR directions were less accurate producing standard deviations ranging from ±20o to ±29o, but were preferable when strong differences between NWP timesteps were observed. The accuracy of SAR wind retrievals was evaluated by comparison against in-situ wind observations. The MAP algorithm was found to provide modest improvements in retrieval accuracy over DWSA. Highest quality retrievals achieved using the CMOD5 forward model, producing wind speeds with a RMSE of 1.83 ms-1. Regarding the ability of SAR to estimate offshore wind resources, dataset density was found to be a controlling parameter. With 103 scenes available mean wind speeds were well characterised by comparison against in-situ observations and Wind Atlas results, while wind power density showed considerable errors. The accuracy of wind speed maps was further improved by accounting for wind direction and fetch effects upon the SAR wind distribution. A key strength of the SAR wind fields is their ability to identify the effect of mesoscale structures upon the surface wind field with atmospheric gravity waves observed in 30% of the images. These structures are shown to introduce wind speed fluctuations of up to ±2 ms-1 at scales of 5 to 10 km and may have significant implications for wind power prediction. These findings show that SAR may provide an important source of wide area wind speed observations as a complement to existing wind resource estimation techniques. SAR may be of particular use in coastal areas where complex wind fields are observed.

Growing concerns about the environmental impact of fossil fuel energy and improvements in both the cost and performance of wind turbine technologies has spurred a sharp expansion in wind energy generation. However, both the increasing size of wind farms and the increased contribution of wind energy to the overall electricity generation market has created new challenges. As wind farms grow in size and power density, the aerodynamic wake interactions that occur between neighboring turbines become increasingly important in characterizing the unsteady turbine loads and power output of the farm. Turbine wake interactions also impact variability of farm power generation, acting either to increase variability or decrease variability depending on the wind farm control algorithm. In this dissertation, both the unsteady vortex wake loading and the effect of wake interaction on farm power variability are investigated in order to better understand the fundamental physics that govern these processes and to better control wind farm operations to mitigate negative effects of wake interaction. The first part of the dissertation examines the effect of wake interactions between neighboring turbines on the variability in power output of a wind farm, demonstrating that turbine wake interactions can have a beneficial effect on reducing wind farm variability if the farm is properly controlled. In order to balance multiple objectives, such as maximizing farm power generation while reducing power variability, a model predictive control (MPC) technique with a novel farm power variability minimization objective function is utilized. The controller operation is influenced by a number of different time scales, including the MPC time horizon, the delay time between turbines, and the fluctuation time scales inherent in the incident wind. In the current research, a non-linear MPC technique is developed and used to investigate the effect of three time scales on wind farm operation and on variability in farm power output. The goal of the proposed controller is to explore the behavior of an "ideal" farm-level MPC controller with different wind, delay and horizon time scales and to examine the reduction of system power variability that is possible in such a controller by effective use of wake interactions. The second part of the dissertation addresses the unsteady vortex loading on a downstream turbine caused by the interaction of the turbine blades with coherent vortex structures found within the upstream turbine wake. Periodic, stochastic, and transient loads all have an impact on the lifetime of the wind turbine blades and drivetrain. Vortex cutting (or vortex chopping) is a type of stochastic load that is commonly observed when a propeller or blade passes through a vortex structure and the blade width is of the same order of magnitude as the vortex core diameter. A series of Navier-Stokes simulations of vortex cutting with and without axial flow are presented. The goal of this research is to better understand the challenging physics of vortex cutting by the blade rotor, as well as to develop a simple, physics-based, validated expression to characterize the unsteady force induced by vortex

The aim of this diploma thesis is to suggest the best locality in the CEE region for a prospective investment in wind farms for an undisclosed Czech company. This goal is to be achieved by comparison of generic projects that have the same technical specification, capital expenditures and operating expenses. These projects are investigated from different perspectives including wind conditions, financing terms, technology constraints and mainly the legal aspects of each respective country -- namely the regulatory environment for wind power-offtake either feed-in tariff or green certificate support schemes. The NPV of FCF and IRR (MIRR) are to be used for evaluation of these projects. Sensitivity analysis for key drivers will complement prior assumptions.

This thesis presents the concept of a "distributed HVDC converter" for offshore wind farms. The proposed converter topology allows series interconnection of wind turbines obviating the necessity of transformers and an offshore platform. Each wind turbine is equipped with a 5MW permanent-magnet synchronous generator and an ac-dc-dc converter. The converter topology is a diode rectifier (ac-dc) cascaded with a single-switch step-down converter (dc-dc). The dc-dc stage allows the current to flow at all times in the dc link while regulating generator torque. The receiving end is equipped with a conventional thyristor-based HVDC converter. The inverter station is located onshore and it regulates the dc link current to be constant. Stability of the configuration and independent operation of the wind turbines are validated through simulations using the PSCAD/EMTDC software package. Protection for some key dc fault scenarios are discussed and a possible protection strategy is proposed.

This thesis presents the concept of a "distributed HVDC converter" for offshore wind farms. The proposed converter topology allows series interconnection of wind turbines obviating the necessity of transformers and an offshore platform. Each wind turbine is equipped with a 5MW permanent-magnet synchronous generator and an ac-dc-dc converter. The converter topology is a diode rectifier (ac-dc) cascaded with a single-switch step-down converter (dc-dc). The dc-dc stage allows the current to flow at all times in the dc link while regulating generator torque. The receiving end is equipped with a conventional thyristor-based HVDC converter. The inverter station is located onshore and it regulates the dc link current to be constant. Stability of the configuration and independent operation of the wind turbines are validated through simulations using the PSCAD/EMTDC software package. Protection for some key dc fault scenarios are discussed and a possible protection strategy is proposed.

Reliance on foreign oil is a major problem facing the United States due to uncontrollable prices, dealing with hostile nations, and oil wars. Demographic variables, risk perception, community attachment, environmental knowledge, and environmental attitudes of Texans were examined to determine which factors influence attitudes toward the hard- and soft-energy path for ending the U.S. Reliance on foreign oil. The data for this study were collected through a mailed questionnaire which included 1,228 Texans in 12 counties over three ecological regions. The dependent measures, hard-energy path and soft-energy path, were regressed on the independent and control variables to determine which factors influenced energy-path preference. The results of the data analysis of Texans clearly demonstrated that environmental attitudes, and in the end, knowledge of energy solutions are the most powerful predictors of risk perception.

This thesis analyzes the feasibility of having an integrated wind and solar farm to optimize the use of land resources and capital investment by evaluating the effect that wind turbine shadows have on the area surrounding them. Two methods are used to predict shadow impact. The first method is based on the traditional textbook “Clear Sky” equations, which have maximum sensitivity to shadows because the method considers every day to be a perfect day. The second method uses measured global-horizontal and diffuse-horizontal solar radiation in units of W/m2, which take into account the true variations of daily conditions. The calculations are performed for 1 square meter surfaces, over different assumed areas of a wind power plant, for every second of the day. For purposes of shadow calculations, the tip-top height (i.e., tower height plus blade length) is used. All calculations are performed with the specifications of a GE 1.5 MW wind turbine, which is the most commonly used wind turbine in USA. / text