A new Markov chain based energy storage model to evaluate the power supply availability of microgrids with renewable energy generation for critical loads is proposed. Since critical loads require above-average availability to ensure reliable operation during extreme events, e.g., natural disasters, using renewable energy generation has been considered to diversify sources. However, the low availability and high variability of renewable energy sources bring a challenge in achieving the required availability for critical loads. Hence, adding energy storage systems to renewable energy generation becomes vital for ensuring the generation of enough power during natural disasters. Although adding energy storage systems would instantaneously increase power supply availability, there is another critical aspect that should be carefully considered; energy storage sizing to meet certain availability must be taken into account in order to avoid oversizing or undersizing capacity, which are two undesirable conditions leading to inadequate availability or increased system cost, respectively. This dissertation proposes to develop a power supply availability framework for renewable energy generation in a given location and to suggest the optimal size of energy storage for the required availability to power critical loads. In particular, a new Markov chain based energy storage model is presented in order to model energy states in energy storage system, which provides an understanding of the nature of charge and discharge rates for energy storage that affect the system's power output. Practical applications of the model are exemplified using electrical vehicles with photovoltaic roofs. Moreover, the minimal cut sets method is used to analyze the effects of microgrid architectures on availability characteristics of the microgrid power supply in the presence of renewable energy sources and energy storage. In addition, design considerations for energy storage power electronics interfaces and a comparison of various energy storage methods are also presented. / text

Renewable Natural Gas (RNG) is a low-carbon fuel source that is derived from the anaerobic digestion (AD) or thermal gasification (TG) of biomass, or produced using renewable electricity through the methanation of carbon dioxide. This thesis uses a thermodynamic balance to determine the total technical potential of RNG in the United States, as well as the future technical potential of methanation-derived RNG based on growth curves for renewable electricity. Furthermore, this work establishes an analytic decision-making framework for determining on a rolling basis, from an economic standpoint, whether to sell electricity directly to the grid, or produce and sell methanation-derived RNG. This framework is used to establish the economic potential of RNG, based on Texas wind resources. This work details the formulation of a model that determines which production option generates more marginal profit, based on fluctuating electricity and gas prices. The model also aggregates the total amount of electricity and RNG sold, assuming that the main objective is to maximize the marginal profit of integrated wind- and methanation facilities. This work concludes that the annual technical potential of methanation-derived RNG nationally was 1.03 Quads in 2011. The technical potential of biomass-derived RNG was 9.5 Quads. Thus, the total 2011 technical potential of RNG in the United States was 10.5 Quads, or equal to roughly 43% of the total US consumption of natural gas that year. Assuming a constant, 80% electrolyser efficiency, the technical potential of methanation-derived RNG is expected to rise at an average rate of 1.4% per year, following growth curves for renewable power, until the year 2040, when it will be 1.54 Quads. The 2011 economic potential of methanation-derived RNG in Texas was between 2.06×10⁷ MMBTU and 3.19×10⁷ MMBTU, or between 19.4% and 30.1% of the corresponding annual technical potential. Furthermore, the total marginal profit increase from introducing the option of producing and selling methanation-derived RNG was around $366 million, given a ‘best case scenario’ for the state of Texas. / text

Bakgrund och problem: Vindkraftens tillförlitliga fastställelse av lönsamhet påverkas av olika osäkerheter, främst vindförhållanden men även ekonomiska faktorer. Vanligtvis används de traditionella metoderna så som nuvärdesmetoden, pay-back metoden och IRR för att värdera en investerings lönsamhet. Dessa metoder är dock otillräckliga vid värdering av riskfyllda projekt. Reala optioner tar hänsyn till flexibilitetens värde och är en komplettering till de traditionella metoderna vid värdering av riskfylla investeringar. Reala optioner möjliggör att fatta beslut efter iakttagelser av hur utvecklingen utvecklas. Genom flexibilitet kan osäkerhet minskas. Syfte: Syftet är att beskriva och analysera hur reala optioner tar sig uttryck i vindkraftsprojekt i Sverige. Detta för att skapa förståelse för om reala optioner används för att hantera den osäkerhet som föreligger i vindkraftsprojekt. Metod: Studien kännetecknas av en metod som är av hermeneutik, induktiv och kvalitativ karaktär. Studien blir därmed av tolkande art och vi utgår från empiri i studien. Semistrukturerade intervjuer har genomförts med tre bolag i vindkraftsbranschen. Slutsats: Utifrån vår forskningsfråga: ”Hur tar sig reala optioner uttryck i vindkraftsprojekt?” kunde vi finna tre av fem reala optioner i de studerade bolagen. Dessa är: optionen att skjuta upp investeringar, optionen att göra stegvisa investeringar och optionen att expandera. Trots att begreppet reala optioner inte används i de studerade bolagen kan slutsatser ändå dras att reala optioner existerar i vindkraftsprojekt. Uppsatsens bidrag: Vår förhoppning med uppsatsen är bland annat att den ska bidra med ökad förståelse för användningen av reala optioner i vindkraftsprojekt. Förslag till framtida forskning: Vår studie behandlar fem reala optioner. Trigeorgis (2005) redogör åtta reala optioner i artikeln: Making use of real options simple: an overview and applications in flexible/modular decision making. En studie som inkluderar alla åtta reala optioner i vindkraftsprojekt hade varit intressant. Detta för att undersöka om det finns fler reala optioner än de tre denna studie identifierat i vindkraftsprojekt. / Background and problem: The reliable determination of the wind power profitability is affected by various uncertainties, mainly wind conditions but also economic factors. Generally the traditional methods are used, such as net present value method, the pay-back method and the IRR when it comes to evaluate an investment's profitability. These methods are insufficient to valuing risky projects. Real options considering the value of flexibility and is a complement to the traditional methods when it comes to valuation of risky investments. Real options allow making decisions based on observations of how the evolution develops. Through flexibility, the uncertainty can be reduced. Purpose: The purpose is to describe and analyze how the real options are reflected in windpower projects in Sweden. This is to create an understanding if the real options are used to manage the uncertainty that exists in wind power projects. Method: The study is characterized by a method of hermeneutic, inductive and qualitative character. The study is therefore interpretive and the starting point of the study is empirical data. Semi-structured interviews were conducted with three companies in the wind power industry. Conclusion: Based on our research question: "How do the real options find their expression in wind power projects?" are we able to find three of the five real options in the studied companies. These are: the option to defer investment, the option to stage investment and the option to expand. Although the concept of real options is not used in the studied companies, conclusions can still be drawn that real options exists in wind power projects. The grants in the essay: Our hope, among other things, is that the essay will contribute to increased understanding for the use of real options in wind power projects. Proposals for future research: Our study deals with five real options. Trigeorgis (2005) describes eight real options in the article: Making Use of Real Options Simple: an overviewand applications into flexible/modular decision making. A study that includes all eight real options in wind power projects would be interesting. This is to investigate whether there are more real options than the three this study identifies in wind power projects.

Due to growth of wind power, system operators are being challenged by the integration of large wind farms into their electrical power systems. Large scale wind farm integration has adverse effects on the power system due to its variable characteristic. These effects include two main aspects: voltage stability and active line flow. In this thesis, a novel techniques to forecast active line flow and select pilot bus are introduced with wind power integration. First, this thesis introduces a methodology to forecast congestion in the transmission line with high wind penetration. Since most wind resources tend to be located far away form the load center, the active line flow is one of the most significant aspects when wind farm is connected to electrical grid. By providing the information about the line flow which can contribute to transmission line congestion, the system operators would be able to respond such as by requesting wind power or load reduction. The second objective of this thesis is to select the weakest bus, called pilot bus, among all load buses. System reliability, especially voltage stability, can be adversely affected by wind variability. In order to ensure reliable operation of power systems with wind power integration, the index to select the pilot bus is developed, and further prediction of voltage profile at the pilot bus is fulfilled. The objective function to select the pilot bus takes account of the N-1 contingency analysis, loading margin, and reactive power sensitivity. Through on the objective function, the pilot bus is representative of all load buses as well as controllable by reactive power regulation. Predicting the voltage profile at the pilot bus is also useful for system operators to determine wind power output. / text

Στις μέρες μας οι συνεχώς αυξανόμενες ενεργειακές ανάγκες, καθώς και η απαίτηση των κοινωνιών για ένα πιο καθαρό περιβάλλον, έχουν κάνει τις ανανεώσιμες πηγές ενέργειας όλο και πιο ελκυστικές ως προς την εκμετάλλευση τους. Η αξιοποίηση της αιολικής ενέργειας στην παραγωγή ηλεκτρικής ενέργειας κερδίζει όλο και περισσότερο έδαφος. Η τεχνολογία των αιολικών συστημάτων αναπτύσσεται συνεχώς ,με αποτέλεσμα να υπάρχουν διάφορες κατηγορίες αυτών, ανάλογα με τη χρήση για την οποία προορίζονται. Στην παρούσα διπλωματική μου εργασία, μελετάται ένα αιολικό σύστημα μεταβλητών στροφών που χρησιμοποιεί μία παραλλαγή της επαγωγικής μηχανής Διπλής Τροφοδοσίας. Η διαφοροποίηση του έγκειται στον επιπλέον dc/ac μετατροπέα που χρησιμοποιείται, προκειμένου να ελέγξουμε την τάση που μπορεί να δει ο στάτης. Μ΄ αυτό τον τρόπο, το αιολικό σύστημα μιας γεννήτριας διπλής τροφοδοσίας γίνεται ακόμα πιο αξιόπιστο, συνεχίζοντας την παραγωγή ισχύος και παραμένοντας συνδεδεμένο με το δίκτυο σε περίπτωση σφάλματος στην πλευρά του δικτύου. Στη μελέτη αυτή, αφού εξαγάγαμε το μαθηματικό μοντέλο του συστήματος και το προσομοιώσαμε σε περιβάλλον Matlab - Simulink, δοκιμάσαμε το σύστημα σε συνθήκες ύπαρξης σφάλματος στο δίκτυο. Στο σύστημα εφαρμόστηκαν κλασικές τεχνικές ελέγχου,με στόχο τη διατήρηση της μέγιστης απομάστευσης ισχύος από το σύστημα, την αύξηση της αντοχής του σε σφάλματα από την πλευρά του δικτύου, καθώς και τη μη αποσύνδεση του συστήματος από το δίκτυο σε μία τέτοια περίπτωση. Τέλος, συγκρίναμε τη συμπεριφορά αυτού του συστήματος με τη συμπεριφορά ενός κλασικού αιολικού συστήματος με επαγωγική γεννήτρια Διπλής Τροφοδοσίας και παραθέσαμε τις διαφορές. / The increasingly energy demands in our days and also the modern societies demand for a greener environment, have made the electrical energy production from renewable energy sources more attractive. The use of wind energy in the electrical energy production is having more and more fervent supporters. The technology and the types of the wind systems varies, depending on the use and the environmental conditions. In my diploma thesis I designed, we will study a variation of a wind system with a variable speed operation with a Doubly Fed Induction Generator. In this system we also use a dc/ac converter in order to control the voltage which the stator can “see”. Using this converter the wind system with a DFIG is more reliable and remains connected to the ac grid, maintaining the maximum power production, in case of a fault on grid side. In this thesis, after we made the mathematical model with a great accuracy and simulated using Matlab - Simulink, we tested it under conditions of different voltage sags from the side of the grid. In order to control the system and maintaining the power production power at the maximum level, we used classic control methods, and as a result, we achieved to keep the maximum level of power production and to keep the wind system connected to the grid in a scenario of a grid side fault. Finally, we compared the behavior of the system we designed with the wind system with the classic DFIG and we presented the differences.

Baigiamajame magistro darbe nagrinėjamas dviejų vėjo jėgainių parkų keliamas triukšmas. Analizuojami triukšmo susidarymo ypatumai vėjo jėgainių parkų viduje bei sklaida parko išorėje. Vertinamos infragarso bei žemo dažnio garso dažninės charakteristikos vėjo jėgainių parkų aplinkoje. Darbą sudaro 4 skyriai. Pirmajame skyriuje apžvelgiama garso fizikinė prasmė, triukšmo šaltiniai, problema bei keliamo triukšmo poveikis žmonėms. Antrajame skyriuje aprašomi tyrimo objektai bei eksperimentinė vėjo jėgainių keliamo triukšmo tyrimų metodika. Trečiajame skyriuje pateikiami dviejų vėjo jėgainių parkų keliamo triukšmo tyrimų rezultatai bei analizė. Dviejų vėjo jėgainių parko Anužių kaime bei šešių vėjo jėgainių parko „Liepynė“ Kretingos rajone. Ketvirtajame skyriuje pateikiamas vėjo jėgainių parkų keliamo triukšmo modeliavimo rezultatai taikant „CadnaA“ modeliavimo programą. Taip pat pateikiamos bendros išvados, rekomendacijos, literatūros sąrašas ir publikacijų sąrašas šio darbo tema. Darbo apimtis – 103 p. teksto be priedų, 72 iliustr., 5 lent., 84 bibliografiniai šaltiniai. / In this master analyzing of noise dispersion around two wind farms. Analyzing the noise generation and dissemination characteristics of wind farms within and outside the park. Assessed infrasound and low frequency sound frequency response in the places around of wind farms. The master consists of 4 chapters. The first chapter provides an overview of sound physical meaning, sources of noise, the problem and the noise impact to people. The second section describes the objects of research, experimental wind noise research methodology. The third section presents the research results and analysis of two wind parks. Wind farm of two wind turbines in Anužiai village and wind farm of six wind turbines in „Liepynė“ Kretingos district. The fourth section describes the modeling results of wind park using simulation program „CadnaA“ . Also provides an overall conclusion, recommendations, bibliography and list of publications of this master. The volume of master – 103 pages text without attachments, 72 pictures, 5 tables, 84 references.

This thesis presents a comprehensive procedure to study sub-synchronous interactions in wind integrated power systems effectively and efficiently. The proposed procedure involves a screening phase and a detailed analysis phase. The screening is performed using a frequency scan and the detailed analysis is performed using small signal stability analysis. To facilitate the small signal analysis, a detailed linearized model of a Type 3 wind power plant is presented in this thesis. The model presented includes the generator, a three-mass drive train model, rotor and grid side converter controller models, converter transformer model and the pitch controller model. To accurately capture the effects of sub-synchronous interactions, the ac network is modelled using dynamic phasors. It is shown that using the proposed procedure, the sub-synchronous interaction between a Type 3 wind power plant and a series compensated line is due to an electrical resonance between the wind power plant generator and the series capacitor. It is also shown that this interaction is highly controllable through the rotor side converter current controllers. This fact will be proven by studying the sub-synchronous interactions in a single machine power system as well as in multi machine power systems. This thesis also presents a sub-synchronous interaction mitigation method using network devices. The performance of an SVC and a STATCOM is evaluated in this thesis. A small signal stability analysis based method will be used to design a sub-synchronous damping controller. A method will be presented to estimate the damping controller parameters systematically to obtain the desired performance using small signal stability analysis results. Furthermore, it will be shown that by strongly controlling the voltage of the point of common coupling, the damping of the oscillations produced by the sub-synchronous interaction between the wind power plant and the series compensated line can be improved. Based on the findings of this research, the thesis proposes a number of recommendations to be adopted when studying the sub-synchronous interactions in wind integrated power systems. These recommendations will facilitate to do such studies effectively and pinpoint the root cause of the sub-synchronous interactions.

The increased fatigue loads and decreased power output of a wind turbine placed in the wake of another turbine is a well-known problem when building new wind-power farms and a subject of intensive research. These problems are caused by the velocity gradients and high turbulence levels present in the wake of a turbine. In order to better estimate the total power output and life time of a wind-power farm, knowledge about the development and stability of wind-turbine wakes is crucial. In the present thesis, the flow field around small-scale model wind turbines has been investigated experimentally in two wind tunnels. The flow velocity was measured with both hot-wire anemometry and particle image velocimetry. To monitor the turbine performance, the rotational frequency, the power output and the total drag force on the turbine were also measured. The power and thrust coefficients for different tip-speed ratios were calculated and compared to the blade element momentum method, with a reasonable agreement. The same method was also used to design and manufacture new turbine blades, which gave an estimate of the distribution of the lift and drag forces along the blades. The influence of the inlet conditions on the turbine and the wake properties was studied by subjecting the turbine to both uniform in flow and different types of boundary layer in flows. In order to study the stability and development of the tip vortices shed from the turbine blades, a new experimental setup for phase-locked measurements was constructed. The setup made it possible to introduce perturbations of different frequencies and amplitudes, located in the rear part of the nacelle. With a newly developed method, it was possible to characterize the vortices and follow their development downstream, using only the streamwise velocity component. Measurements were also performed on porous discs placed in different configurations. The results highlighted the importance of turbine spacings. Both the measurements on the turbine and the discs were also used to compare with large eddy simulations using the actuator disc method. The simulations managed to predict the mean velocity fairly well in both cases, while larger discrepancies were seen in the turbulence intensity. / <p>QC 20140424</p>

Nyckeln till ett framgångsrikt och värdefullt företag är att göra bra investeringar eftersom det är investeringarna som skapar den avkastning som dess ägare får som ersättning (Froot, et al., 1994). Om företaget strävar efter att göra värdemaximerande investeringar måste de därför bedöma vilka investeringar som kan tänkas generera en avkastning som är större än kostnaden för kapitalet som investeras (Brealey, et al., 2014). Detta är den teoretiska grundregeln för all investeringsbedömning (Brealey, et al., 2014). Men eftersom framtiden är fylld av risk och osäkerhet är bedömningen av en investerings ekonomiska värde ingen enkel sak (Sandahl &amp; Sjögren, 2005). I företagens strävan att tämja denna risk och osäkerhet har Mikes (2009;2011) identifierat två olika kulturer, den beräknande kulturen och den visualiserande kulturen. Dessa kulturer präglas av sin syn på vad som är meningsfullt att sannolikhets bedöma och vad som inte är meningsfullt att sannolikhets bedöma (Mikes, 2011). Synen på vad som är risk och osäkerhet kan också kopplas ihop med Knights (1964) definition av begreppen där risk är det mätbara och osäkerhet det omätbara. Med utgångspunkt i Knights (1964) definition av risk och osäkerhet försöker vi i denna studie förstå hur bedömningen av vindkraftsinvesteringar påverkas av företagens syn på risk och osäkerhet. Vi söker förståelsen genom att studera tre olika företag som på olika sätt kan kopplas samman med investeringar i vindkraft. De tre perspektiv vi studerar är dels bankens som lånar ut, dels den privata aktören som enbart investerar i vindkraft och dels den kommunala aktören där investeringar i vindkraft inte tillhör kärnverksamheten.  Vår studie tyder på att de flesta risker som ingår vid bedömning av ett vindkraftverks ekonomiska värde uppfattas som osäkra. Den enda faktor som företagen försöker mäta och sannolikhets bedöma är vinden, detta är därför den enda faktor som kan anses vara en kvantifierbar riskfaktor enlighet Knights definition. Osäkerhetsfaktorerna som det framtida priset på el och elcertifikat hanteras istället med hjälp av kvalitativa metoder. Även om vinden verkar uppfattas som den viktigaste faktorn kan man därför argumentera för att den slutliga bedömningen av det ekonomiska värdet framför allt är en kvalitativ bedömning där erfarenhet och intuition spelar en avgörande roll. De studerade vindkraftsexploatörerna verkar därför tillhöra den visualiserande kulturen. / The key to a successful and valuable business is to make good investments because it is investment that creates the returns that its owner receives as compensation (Froot et al., 1994). If the company strives to make value -maximizing investments they must therefore assess which investments may generate a return greater than the cost of capital invested (Brealey et al., 2014). This is the theoretical basic rule of any investment decision (Brealey et al., 2014). But since the future is fraught with risk and uncertainty assessment of an investment's economic value is not straightforward (Sandahl &amp; Sjögren, 2005). In the companies' efforts to tame this risk and uncertainty Mike (2009: 2011) identifies two different cultures, the calculative culture and the envisioning culture. These cultures are characterized by their view of which areas it is meaningful to assess the probability for and for which areas it is not meaningful to assess the probability (Mikes, 2011). Views on what is risk and uncertainty can be paired with Knights (1964) definition of the concepts in which the risk is measurable and the uncertainty is unmeasurable. Based on Knights (1964) definition of risk and uncertainty, this study tries to understand how investments in wind power plants are affected by the companies’ view of risk and uncertainty. We seek understanding by studying three different companies who in different ways can be linked to investments in wind power plants. The three perspective we study is; the bank who is financing wind power investments, the private company who only make wind power investments, and the municipal where investments in wind power does not belong to the core business. Our study suggests that most of the factors included in the assessment of the wind power economic value are perceived as uncertain. The only factor that the companies are trying to measure and make probabilities about is in their assessment of the wind. We therefore conclude that this is the only factor that can be considered as a quantifiable risk factor according to Knights definition. The uncertainties like that of the future price of electricity and electricity certificates is instead handled using qualitative methods. Although the wind seems to be perceived as the most important factor we therefore argue that the final assessment of the economic value is primarily a qualitative assessment where experience and intuition plays a crucial role. The studied companies therefore seem to belong to the visualization culture.

This thesis examines the design of supervisory controllers for windfarms of pitch-controlled wind turbines. The control objectives are the maximisation of the financial income from the generated electricity and the minimisation of the turbines' fatigue damage. The design exploits the wide variations in the ratio of financial income to fatigue damage which are found both spatially across windfarms and as a function of time. The supervisory control strategy makes use of the ability of pitch-controlled turbines to operate with variable power set points; a capability which is rarely exploited in practice. A windfarm simulation which has been developed for the purposes of testing supervisory controllers is described. It is shown that the simulation is a suitable test-bed for this application. Results are presented which demonstrate how the fatigue damage of a turbine's gearbox and structural components vary as functions of the mean wind-speed, turbulence intensity and power set point, both for isolated turbines and for turbines experiencing wake effects. A lifetime performance function is proposed and 'ideal' power set point curves are evaluated using a genetic search algorithm. It is shown that significant improvements in performance can be achieved if the operation of the turbines is altered to take account of variable electricity tariffs. A windfarm control strategy that splits the turbines into interacting and non-interacting categories is found to give good results. Using data generated by the simulation, it is shown that simple cost functions can be developed for non-interacting turbines which, when used in a controller, give performance that is close to the 'ideal'. A similar cost function is applied to a group of three interacting turbines, and it is found that substantial reductions in all measures of total annual fatigue damage are achieved for a small reduction in total annual financial income. The on-line implementation of windfarm supervisory controllers is discussed and the behaviour of a simple hill-climbing algorithm is examined using a simulated group of three interacting turbines.