Wind farm layout optimization can greatly improve wind farm performance. However, past wind farm design has been limited in several ways. Wind farm design usually assumes that all the turbines throughout the farm should be exactly the same. Oftentimes, the location of every turbine is optimized individually, which is computationally expensive. Furthermore, designers fail to consider turbine loads during layout optimization. This dissertation presents four studies which provide partial solutions to these limitations and greatly improve wind farm layout optimization. Two studies explore differing turbine designs in wind farms. In these studies, Wind farm layouts are optimized simultaneously with turbine design. We found that for small rotor diameters and closely spaced wind turbines, wind farms with different heights have a 5–10% reduction in cost of energy compared to farms with all the same turbine height. Coupled optimization of turbine layout and full turbine design results in an 2–5% reduction in cost of energy compared to optimizing sequentially for wind farms with turbine spacings of 8.5–11 rotor diameters. Wind farms with tighter spacing benefit even more from coupled optimization. Furthermore, we found that heterogeneous turbine design can produce up to an additional 10% cost of energy reduction compared to wind farms with identical turbines throughout the farm, especially when the wind turbines are closely spaced. The third study presents the boundary-grid parameterization method to reduce the computational expense of optimizing wind farms. This parameterization uses only five variables to define the layout of a wind farm with any number of turbines. For a 100 turbine wind farm, we show that optimizing the five variables of the boundary-grid method produces wind farms that perform just as well as farms where the location of each turbine is optimized individually, which requires 200 design variables. The presented method facilitates the study for both gradient-free and gradient-based optimization of large wind farms. The final study presents a model to calculate fatigue damage caused by partial waking on a wind turbine which is computationally efficient and can be included in wind farm layout optimization. Compared to high fidelity simulation data, the model accurately predicts the damage trends of various waking conditions. We also perform a wind farm layout optimization with the presented model in which we maximize the annual energy production of a wind farm while constraining the damage of each turbine. The results of the optimization show that the turbine damage can be constrained with only a very small sacrifice of less than 1% to the annual energy production.

With the growing demand for electricity, renewable sources of energy have garnered a lot of support from all quarters. The problem with depending on these renewable sources is that the output from them is independent of the demand. Storage of electricity gives us an opportunity to effectively manage and balance the supply and demand of electricity. Fuel cells are a fast developing and market capturing technology that presents efficient means of storing electricity in the form of hydrogen. The aim of this research is to study the impact of integrating hydrogen fuel cell storage system with a wind farm to improve the reliability of the grid for allowing higher penetration of renewable energy sources in the power system. The installation of energy storage systems strongly depends on the economic viability of the storage system. We identified four types of fuel cells that could be used in a hydrogen fuel cell storage system. We bring together a range of estimates for each of the fuel cell systems for the economic analysis that is targeted towards the total capital costs and the total annualized costs for the storage system for individual applications like rapid reserve and load shifting. We performed sensitivity analysis to determine the effect of varying the rate of interest and cost of fuel cell on the total annualized cost of the storage system. Finally, we compared the costs of hydrogen based storage system with other storage technologies like flywheel, pumped hydro, CAES and batteries for the individual application cases.

Currently, most micrositing techniques aim to maximize annual energy production (AEP) or minimize cost of energy (COE) with no direct regard to revenue. This research study developed a method that utilizes the seasonal electricity price and wind data to microsite wind farms in terms of profitability. To accomplish this, six candidate wind farms with differing layouts and spacing were selected at a given location. They were then simulated using a wake modeling software to produce expected power outputs at different wind speeds, wind directions, and turbulence intensities. By interpolating the power output tables with wind data, a power time-series was created for each wind farm over a multi-year period. Electrical price was then incorporated with the power time-series to produce a revenue time-series of the revenue produced at each hour over the same time-period. Each relative wind farm was then rotated in increments to evaluate new candidate wind farms and revenue totals. This method is site specific and results may differ dependent on location and seasonal correlation between wind and electrical data. Overall, the method looks to exploit a different approach to the micrositing problem.

Modern power systems are characterized by an increasing penetration of renewable energy generating units. These aim to reduce the carbon emissions in the environment by replacing conventional energy generating units which rely on fossil fuels. In this new power systems composition, wind generators (WGs) dominate, being one of the largest and fastest-growing sources of renewable energy production. Nevertheless, their unpredictable and highly volatile power output hinders their efficient and secure large-scale deployment, and poses challenges for the transient stability of power systems. Given that, we identify two challenges in the operation of modern power systems: rendering WGs capable of reguating their power output while securing transient stabilization of conventional synchronous generators (SGs). This dissertation makes several contributions for effectively dealing with these major challenges by introducing new distributed control techniques for SGs, storage devices and state-of-the-art (SoA) WGs. Initially, this dissertation introduces a novel nonlinear control design which is able to coordinate a storage device and a SG to attain transient stabilization and concurrent voltage regulation on their terminal bus. Thereafter, it proposes control designs that SoA WGs can adopt to effectively regulate their power out- put to meet local or group objectives. In this context, the rst control design is a decentralized nonlinear energy-based control design, that can be employed by a wind double-fed induction generator (DFIG) with an incorporated energy storage device (namely a SoA WG) to regulate its power output by harnessing stored energy, with guaranteed performance for a wide-range of operating conditions. Recognizing that, today, albeit wind farms (WFs) are comprised of numerous WGs which are sparsely located in large geographical areas, they are required to respond rapidly and provide services to the grid in an efficient, reliable and timely fashion. To this end, this dissertation proposes distributed control methods for power output regulation of WFs comprised of SoA WGs. In particular, a novel distributed control design is proposed, which can be adopted by SoA WGs to continuously, dynamically and distributively self-organize and control their power outputs by leveraging limited peer-to-peer communication. By employing the proposed control design, WGs can exploit their storage devices in a fair load-sharing manner so that their total power output tracks a total power reference under highly dynamical conditions. Finally, this dissertation proposes a distributed control design for wind DFIGs without a storage device, the most common type of WGs deployed today. With this control design, wind DFIGs can dynamically, distributively and fairly self-dispatch and adjust the power they extract from the wind for the purpose of their total power tracking a dynamic reference. The effectiveness of the control designs proposed in this dissertation is illustrated through several case studies on a 3-bus power system and the IEEE 24-bus Reliability Test System.

Doctor of Philosophy / Department of Electrical and Computer Engineering / Anil Pahwa / Shelli K. Starrett / Analysis of power system voltage stability has practical value in increasing wind penetration levels. As wind penetration levels increase in power systems, voltage stability challenges arise due to locating wind resources far away from load centers. This dissertation presents several different voltage stability methods for sizing new wind farms. Power system wind penetration levels depend on the available voltage stability margins (VSMs) of the existing power system and system load characteristics. Three new iterative methods have been developed to maximize wind penetration level in weak power systems based on systems’ VSMs. The first two methods use an iterative approach for increasing the size of each wind farm until reaching the collapse point. Wind farms with less negative impact on system VSMs are sized larger than others. A third wind farm sizing method has been developed using modal analysis in conjunction with the traditional voltage stability method (Q-V method). Wind farms are placed at buses in the power system which have the lowest negative impact on voltage instability modes (strong wind injection buses). By placing the wind farms at the strongest wind injection buses, higher amounts of wind power can be injected into the power system. To further increase wind penetration in weak power systems, two additional techniques are introduced and applied to the western Kansas power system. The first technique uses modes of voltage instability to place voltage support equipment like static var compensators at locations in the power system where they provide the needed reactive power support for increasing levels of wind penetration. The second technique uses the fact that wind patterns at a wind farm site may rarely allow the wind farm to produce its maximum capacity during the peak loading hours. Wind farm maximum sizes can be increased above their maximum voltage stable size limit without driving the power system into becoming voltage unstable. Preventing voltage collapse for the additional increases in wind farm sizes is accomplished by disconnecting some wind turbines inside the wind farm during critical times to reduce its power output to a voltage stable level.

The offshore wind potential of the Caribbean Sea has barely been exploited. Currently, the offshore wind power industry in Latin America and the Caribbean region is still at very early stages, leaving aside an important resource that otherwise could contribute to satisfy the growing energy demand of the zone. In this study the possibilities arising from a massive exploitation of the wind resource in the Caribbean Sea are assessed. The objective is to investigate if the resources contained in it would be sufficient to satisfy the energy demand of Latin America and the Caribbean, which is foreseen to be about 1900 TWh/year by 2020. To address this question, the “Infinite wind farm” concept is used as a simple way to model the meteorological behaviour and the wind speed in the area. The model is utilized in combination with the bathymetric data of the Caribbean Sea and with a simple economic analysis, to evaluate what the requirements to satisfy the energy demand would be in terms of area, number of turbines, and levelized cost of energy (LCoE). The assessment is performed utilizing different turbine sizes, and inter-turbine separations to find the combination that minimizes the LCoE. It is found that the energy demand of Latin America and the Caribbean could be satisfied using only 125000 km2 (4.5% of the total Caribbean Sea area) of waters shallower than 25m at a cost of 69 €/MWh, if the turbines were separated 6.5D from one another and if they had a rotor diameter of 250m. In that case, 47760 turbines should be installed using only conventional monopile foundations.

SAMMANFATTNING Medvetenhet och oro kring miljöeffekter från utsläpp av växthusgaser och de minskande resurserna av icke förnybara energikällor har ökat de senaste årtiondena. Utvecklingen av ny teknologi för förnybar energi har drivits fram globalt som ett svar på denna oro. Det har skett stora framsteg i produktion av el och värme från sol, vind, hav, vattenkraft, biomassa, geotermiska resurser, biobränslen och väte. Följaktligen har utvecklingen av energi-lager blivit en viktig del för integration av förnybar energi i systemen. Det är gynnsamt för hela försörjningskedjan, för pålitlighet och bättre stabilitet i leveranser och distribution, och för ökad el-kvalitet. I uppsatsen undersöks en optimal energidesign för ett kombinerat system med vattenkraft och vindkraft inklusive ett lager i form av en damm. Vatten som pumpas upp till lagret har en stor och balanserande potential för att få in en högre grad förnybar energi i energisystemen. Detta är nödvändigt då dessa energikällor är intermittenta och variabla till sin natur. Ett av de studerade objekten är ett vattenkraftverk med pumpad damm, Tehri i Uttarakhand, Indien. Systemets totala verkningsgrad om 93 % diskuteras utifrån förluster såväl som potentialen för vind och dess inverkan. Vind-data är hämta från National Institute of Wind Energy (NIWE) och har analyserats med programmen MATLAB och WindPro. Det slutligen valda området för exploatering av vindkraft blev Ramakkalmedu, Idukki district, Kerala, Indien. Efter valet av plats valdes tre olika vindturbiner ut för analys; Siemens SWT-3.2-113 3.2 MW, Enercon E-126 4.2MW, och Enercon E-126 7.58MW. Analysen består av flera delar; vindparks-modellering, beräkning av buller-generering från vindkraften, beräkning av årlig energi-generering - Annual Energy Production (AEP), kapacitetsfaktor, vindparkens effektivitet med hänsyn tagen till lagret/dammens variation av bas-last. Resultat har erhållits från alla tre turbinerna och den övergripande slutsatsen är att kombinationen med vatten- och vindkraft med lagring av vatten som pumpas upp vid behov är en tillfredsställande metod för att möta belastningstoppar, vilket valideras av denna uppsats.   Nyckelord: pumpade vattenkraftdammar, vindkraftparker, energi lager, förnybar energi. / ABSTRACT  Awareness and concern regarding the environmental effects of greenhouse gas emissions and depletion of non-renewable energy sources has increased over the last decades. A considerable development of new technology for renewable energy has occurred globally as an answer to this concern. There has been a major progress in production of electricity and heat generated from solar, wind, ocean, hydropower, biomass, geothermal resources, and biofuels and hydrogen. Consequently, the development of energy storages has become an imperative part, for integration of renewable energy. It is beneficial for the entire supply chain, for dependability and better stability, and for enhanced quality of electrical power. This thesis is exploring an optimal energy design for a system of pumped hydro-wind power plants including storage. Solutions with Pumped Hydro Storages have a great potential for their balancing role necessary for a higher degree of renewable energy sources, RES, in the energy systems because of the intermittent and variable nature of these sources. Tehri pumped hydro storage plant, in Uttarakhand, India is one of the objects studied in this thesis. The systems total efficiency of 93%, calculated from head losses, is discussed as well as wind potential and its impact. Wind data is obtained from National Institute of Wind Energy (NIWE) and analysed using the software tools MATLAB and WindPro. The finally chosen area explored for wind potential is Ramakkalmedu, Idukki district, Kerala, India. After selection of site within the area, three different turbines; Siemens SWT-3.2-113 3.2 MW, Enercon E-126 4.2MW, and Enercon E-126 7.58MW were considered for analysis. The analysis consists of several parts; Wind farm modelling, Noise estimation of Wind Park, estimation of Annual Energy Production (AEP), Capacity factor, Wind park efficiency with respect to the storage/reservoir´s base load variation. Results are achieved for all three turbines. The overall conclusion is that combined hydro and wind power with a pumped storage, is a satisfactory method for bulk energy store to address peak loads, which is validated by this thesis.   Keywords: Pumped Hydro, Wind farm, Energy Storage, Renewable Energy.

This thesis focuses on providing the means to use vertical-axis wind turbines (VAWTs) in wind farms as an alternative form of harnessing wind energy in offshore and urban environments where both wake and acoustic effects of turbines are important considerations. In order for VAWTs to be used in wind farm layout analysis and optimization, a reduced-order wake model is needed to calculate velocities around a turbine quickly and accurately. However, a VAWT wake model has not been available to accomplish this task. Using vorticity data from computational fluid dynamic (CFD) simulations of VAWTs and cross-validated Gaussian distribution and polynomial surface fitting, a wake model is produced that can estimate a wake velocity deficit of an isolated VAWT at any downstream and lateral position based on nondimensional parameters describing the turbine speed and geometry. When compared to CFD, which takes over a day to run one simulation, the wake model predicts the velocity deficit at any location with a normalized root mean squared error of 0.059 in about 0.02 seconds. The model agrees with two experimental VAWT wake studies with a percent difference of the maximum wake deficit of 6.3% and 14.6%. Using the actuator cylinder model with predicted wake velocities of multiple turbines, aerodynamic loads can be calculated on the turbine blades to estimate the power production of a VAWT wind farm. As VAWTs could be used in urban environments near residential areas, the noise disturbance coming from the turbine blades is an important consideration in the layout of a wind farm. Noise restrictions may be imposed on a wind farm to limit the disturbance, often impacting the wind farm's power producing capability. Two specific horizontal-axis wind turbine farm designs are studied and optimized using the FLORIS wake model and an acoustic model based on semi-empirical turbine noise calculations to demonstrate the impact a noise level constraint has on maximizing wind farm power production. When a noise level constraint was not active, the average power production increased, up to 8.01% in one wind farm and 3.63% in the other. Including a noise restriction in the optimization had about a 5% impact on the optimal average power production over a 5 decibel range. By analyzing power and noise together, the multi-modality of the optimization problem can be used to find solutions were noise impact can be improved while still maximizing wind farm power production.

The number of integrated wind farms into the power system is increasing as well as the total installed wind power capacity, which may cause voltage stability concerns. Additionally, there are European Transmission System Operators (TSOs) that do notinvolve wind farms in contributing to the voltage control in any significant extent. In the on-going project by the European Network of Transmission System Operators for Electricity (ENTSO-E), to update the European grid requirements, this will probably be changed. The aim of this Master thesis is to demonstrate the voltage variations in the high voltage grid during different operational conditions. Thereafter, clarify when high voltages may occur at the connection point of the studied wind farm. Furthermore, it is investigated whether the wind farm is able to regulate the voltage in the cases when high voltages occur. The load flow and switching studies are performed with the software tool Power System Simulator for Engineering (PSS/E) version 32.1.1. The grid model represents a part of the Swedish high voltage grid. Since voltage stability often is a local issue, special modelling aspects has been performed at the hydropower generators in the close-located area of the wind farm. The main conclusions of this Master thesis are that high voltages is associated with low load situations, i.e., mostly during summer nights. Furthermore, the studied close-located reactor is not able to keep the voltage within desired level by itself. Finally, it has been shown that the wind farm is technically able to contribute to the voltage stability in the close-located area. But since wind power is an intermittent power source it makes the voltage regulating capacity less reliable compared to hydropower. The results and conclusions given in this Master thesis have also been summarized in a conference paper for The 11th International Workshop on Large-Scale Integration of Wind Power into Power Systems as well as on Transmission Networks for Offshore Wind Power Plants, see Lidström et al [35].

As wind exploitation gains prominence in the power industry, the extensive use of this intermittent source of power may heavily rely on our ability to select the best combination of wind farming sites that yields maximal reliability of power systems at minimal cost. This research proposes a general method to minimize the wind park global power output variance by optimally distributing a predetermined number of wind turbines over a preselected number of potential wind farming sites for which the wind patterns are statistically known. The objective is to demonstrate the benefits of diversification for the reliability of wind-sustained systems through the search for steadier overall power outputs. Three years of wind data from the recent NREL/3TIER study in the western US provides the statistics for evaluating each site for their mean power output, variance and correlation with each other so that the best allocations can be determined. Some traditional reliability indices such as the LOLP are computed by using sequential Monte Carlo simulations to emulate the behavior of a power system uniquely composed of wind turbines and a load modeled from the 1996 IEEE RTS. It is shown that configurations featuring minimal global power output variances generally prove the most reliable for moderate load cases, provided the sites are not significantly correlated with the modeled load. Under these conditions, the choice of uncorrelated/negatively correlated sites is favored. The correlations between the optimized global wind power outputs and the modeled load are studied as well.