Renewable energy is harnessed from continuously replenishing natural processes. Some commonly known are sunlight, water, wind, tides, geothermal heat and various forms of biomass. The focus on renewable energy has over the past few decades intensified greatly. This thesis contributes to the research on developing renewable energy technologies, within the wind power, wave power and marine current power projects at the division of Electricity, Uppsala University. In this thesis grid connection of permanent magnet generator based renewable energy sources is evaluated. A tap transformer based grid connection system has been constructed and experimentally evaluated for a vertical axis wind turbine. Full range variable speed operation of the turbine is enabled by using the different step-up ratios of a tap transformer. This removes the need for a DC/DC step or an active rectifier on the generator side of the full frequency converter and thereby reduces system complexity. Experiments and simulations of the system for variable speed operation are done and efficiency and harmonic content are evaluated.  The work presented in the thesis has also contributed to the design, construction and evaluation of a full-scale offshore marine substation for wave power intended to grid connect a farm of wave energy converters. The function of the marine substation has been experimentally tested and the substation is ready for deployment. Results from the system verification are presented. Special focus is on the transformer losses and transformer in-rush currents. A control and grid connection system for a vertical axis marine current energy converter has been designed and constructed. The grid connection is done with a back-to-back 2L-3L system with a three level cascaded H-bridge converter grid side. The system has been tested in the laboratory and is ready to be installed at the experimental site. Results from the laboratory testing of the system are presented. / Wind Power / Wave Power / Marine Currnet Power

Several modifications have been implemented to numerical simulation codes based on blade element momentum theory (BEMT), for application to the design of ocean current turbine (OCT) blades. The modifications were applied in terms of section modulus and include adjustments due to core inclusion, buoyancy, and added mass. Hydrodynamic loads and mode shapes were calculated using the modified BEMT based analysis tools. A 3D model of the blade was developed using SolidWorks. The model was integrated with ANSYS and several loading scenarios, calculated from the modified simulation tools, were applied. A complete stress and failure analysis was then performed. Additionally, the rainflow counting method was used on ocean current velocity data to determine the loading histogram for fatigue analysis. A constant life diagram and cumulative fatigue damage model were used to predict the OCT blade life. Due to a critical area of fatigue failure being found in the blade adhesive joint, a statistical analysis was performed on experimental adhesive joint data. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection

In this study, the semi-empirical approach is introduced to accurately estimate the probability distribution of complex non-linear random variables in the field of wavestructure interaction. The structural form of the semi-empirical distribution is developed based on a mathematical representation of the process and the model parameters are estimated directly from utilization of the sample data. Here, three probability distributions are developed based on the quadratic transformation of the linear random variable. Assuming that the linear process follows a standard Gaussian distribution, the three-parameter Gaussian-Stokes model is derived for the second-order variables. Similarly, the three-parameter Rayleigh-Stokes model and the four-parameter Weibull- Stokes model are derived for the crests, troughs, and heights of non-linear process assuming that the linear variable has a Rayleigh distribution or a Weibull distribution. The model parameters are empirically estimated with the application of the conventional method of moments and the newer method of L-moments. Furthermore, the application of semi-empirical models in extreme analysis and estimation of extreme statistics is discussed. As a main part of this research study, the sensitivity of the model statistics to the variability of the model parameters as well as the variability in the samples is evaluated. In addition, the sample size effects on the performance of parameter estimation methods are studied. Utilizing illustrative examples, the application of semi-empirical probability distributions in the estimation of probability distribution of non-linear random variables is studied. The examples focused on the probability distribution of: wave elevations and wave crests of ocean waves and waves in the area close to an offshore structure, wave run-up over the vertical columns of an offshore structure, and ocean wave power resources. In each example, the performance of the semi-empirical model is compared with appropriate theoretical and empirical distribution models. It is observed that the semi-empirical models are successful in capturing the probability distribution of complex non-linear variables. The semi-empirical models are more flexible than the theoretical models in capturing the probability distribution of data and the models are generally more robust than the commonly used empirical models.

Ocean currents are an attractive source of clean energy due to their inherent reliability, persistence and sustainability. The Gulf Stream system is of particular interest as a potential energy resource to the United States with significant currents and proximity to the large population on the U.S. east coast. To assess the energy potential from ocean currents for the United States, the characterization of ocean currents along the U.S. coastline is performed in this dissertation. A GIS database that maps the ocean current energy resource distribution for the entire U.S. coastline and also provides joint velocity magnitude and direction probability histograms is developed. Having a geographical constraint by Florida and the Bahamas, the Florida Current has the largest ocean current resource which is fairly stable with prevalent seasonal variability in the upper layer of the water column (~200m). The core of the Florida Current features higher stability than the edges as a result of the meandering and seasonal broadening of the current flow. The variability of the Gulf Stream significantly increases as it flows past the Cape Hatteras. The theoretical energy balance in the Gulf Stream system is examined using the two-dimensional ocean circulation equations based on the assumptions of the Stommel model for quasi-geostrophic subtropical gyres. Additional turbine drag is formulated and incorporated in the model to represent power extraction by turbines. Parameters in the model are calibrated against ocean observational data such that the model can reproduce the volume and kinetic energy fluxes in the Gulf Stream. The results show that considering extraction over a region comprised of the entire Florida Current portion of the Gulf Stream system, the theoretical upper bound of averaged power dissipation is around 5.1 GW, or 45 TWh/yr. If the extraction area comprises the entire portion of the Gulf Stream within 200 miles of the U.S. coastline, the theoretical upper bound of averaged power dissipation becomes approximately 18.6 GW or 163 TWh/yr. The impact of the power extraction is primarily constrained in the vicinity of the turbine region, and includes a significant reduction of flow strength and water level drop in the power extraction site. The turbines also significantly reduce residual energy fluxes in the flow, and cause redirection of the Gulf Stream. A full numerical simulation of the ocean circulation in the Atlantic Ocean is performed using Hybrid Coordinate Ocean Model (HYCOM) and power extraction from the Florida Current is modeled as additional momentum sink. Effects of power extraction are shown to include flow rerouting from the Florida Strait channel to the east side of the Bahamas. Flow redirection is stronger during peak summer flow resulting in less seasonal variability in both power extraction and residual fluxes in the Florida Current. A significant water level drop is shown at the power extraction site, and so is a slight water level rise along the coasts of Florida and the Gulf. The sum of extracted power and the residual energy flux in the Florida Current is lower than the original energy flux in the baseline case, indicating a net loss of energy reserve in the Florida Current channel due to flow redirection. The impact from power extraction on the mean flow field is concentrated in the near field of the power extraction site, while shifts in the far flow field in time and space have little impact on the overall flow statistics.

Wave power is a renewable energy source with great potential, which is why there are more than a hundred ongoing wave power projects around the world. At the Division of Electricity, Uppsala University, a point-absorber type wave energy converter (WEC) has been proposed and developed. The WEC consists of a linear synchronous generator placed on the seabed, connected to a buoy floating on the surface. Power is absorbed by heave motion of the buoy, and converted into electric energy by the generator. The point-absorber WEC must be physically much smaller than the wavelength of the incoming waves, and can therefore not be scaled to very high power levels. Instead, the total power output is boosted by increasing the number of WECs, connecting them in wave power farms. To transfer the electric energy to the grid, an intermediate marine substation is proposed, where an AC/DC/AC conversion step is performed. Within this PhD-work, a full-scale offshore marine substation has been designed, constructed and experimentally evaluated. The substation is rated for grid-connection of seven WECs to the local 1kV-grid, and is placed on the seabed 3km off the coast at a depth of 25m. Various aspects of the substation design have been considered, including the mechanical and electrical systems, the WEC electrical interface, offshore operations and the automatic grid connection control system. A tap change circuit and different multilevel topologies have also been proposed. This dissertation has an experimental approach, validating a major part of the work with lab results. The final substation electrical circuit has been tested at rated grid voltage with a fluctuating input power source. The efficiency has been measured and the implemented functions are verified. Offshore operations have been successfully carried out and offshore wave farm data is expected in the nearby future.

Technologies exist that can capture and convert wave energy but there are few studies examining systemic integration of wave energy devices. This work examines the potential to use wave energy as a renewable energy resource on Vancouver Island, specifically in the Tofino/Ucluelet area. A model of a wave energy conversion (WEC) device was developed as a module within TRNSYS™ where it can be coupled to a load as well as to a storage medium. For this particular study, wave profiles generated from hourly average data for a location on the west coast of Vancouver Island are used as a resource input. An analysis of the potential to use wave energy is carried out with an emphasis on overall system efficiency and resulting device scaling. The results of the wave energy conversion with and without storage, as well as the general economics of these scenarios, are used to make recommendations regarding technical feasibility of wave power projects on Vancouver Island.

Eutrophication is one of the key environmental problems of today, both in terms of complexity and magnitude. For the Baltic Sea (BS), eutrophication is an acute problem, leading to hypoxic conditions at the bottom; a situation that is sustained and amplified, when phosphorus is released from hypoxic sediments. Reducing nutrient loading is a top political priority but the present situation is believed to require active measures within the catchments and recipients to reduce both loading and adverse effects. Implementation of effective and cost-efficient abatement methods requires understanding of natural processes in watersheds, streams and recipients as well as technological expertise in order to compare the effects of measures of different kinds and locations. This thesis tries to combine process understanding of catchment transport behaviour, especially in coastal zones, and feasibility of certain technologies for reducing nutrient loading and effects of eutrophication in-situ. The over-arching theme is the fate of the individual contaminant, from injection to removal. Transport and dispersion in catchments are investigated, combining physically-based, distributed, numerical groundwater models with Lagrangian stochastic advective reactive solute (LaSAR) transport modelling. The approach is powerful in the sense that it incorporates catchment structural, geomorphological dispersion in the numerical model with hydrodynamic and sub-scale dispersion as well as uncertainty in the LaSAR framework. The study exemplifies the complex nature of transport time distributions in catchments in general and when varying source size and location, importance of dispersion parameters and retention due to molecular diffusion. It is shown that geomorphological control on dispersion is present even for relatively heterogeneous systems and that neither the mean residence time nor a statistical distribution may provide accurate representations of hydrological systems. To combat internal loading of P from sediments in-situ, large-scale aeration of deep waters, halocline ventilation, has been suggested. This study further investigates the feasibility of wave-powered devices to meet the energy demands for such an operation. It is shown that the required amount of oxygen needed to keep the sediments at oxic conditions could be provided, cheaply and efficiently, through the use of wave power. / QC 20120511

To counteract one of the most urgent environmental issues in the Baltic Sea; eutrophication, excessivealgal blooms and hypoxia, a proposal to use wave energy to pump oxygen-rich surface water towardsthe sea bottom is investigated. Proposals have suggested that 100 kg of oxygen per second is needed tooxygenate bottom water and enhance binding of phosphorus to bottom sediments. This corresponds to 10 000 m3/s of oxygen-rich surface water. This thesis investigates a wave-powered device to facilitatethis oxygen ux. Results give expected water flow rates between 0.15 - 0.40 m3/s and meter breakwater.The mean specic wave power for the analyzed wave data is calculated to be between 3 - 4 kW/m wavecrest and the median to 1 kW/m. This study indicate, however, that the energy uxes in the BalticProper are signicantly higher. The study gives that the wave climate of the Baltic Sea is suffciently intense to facilitate vertical pumping with a feasible number of breakwaters. A full-scale implementationin the Baltic Sea would require some 300 to 1 200 oating breakwaters of a length of 50 m each. Thetotal cost is roughly estimated to 170 - 680 million EURO. The study also concludes that the interleavingof surface water should be constrained to a relatively small vertical distance from the outlet depth(20 - 30 m) and not stir up deep water to the surface. Wave modelling for the proposed pilot locationKanholmsfjärden indicate that this bay is not large enough to permanently produce a favorable waveclimate. It is, however, still an interesting location consistently to its vicinity to Stockholm and relativelylong measurement series.

This report presents a master's thesis conducted within the machine design track at KTH Royal Institute of Technology. The research work was undertaken in collaboration with Novige AB, who commissioned the project. Novige AB is in the development and testing phases of a wave energy converter (WEC) of which exhibits a large area of unutilized potential. This led to the purpose of this thesis, conceptualizing a support structure and expanding mechanism for solar panels to be mounted on the float of the WEC. Since no previous work related to the subject had been conducted, the objectives were to explore different solutions and present a detailed final concept, including initial finite element calculations from expected load cases. The work consisted of several concept phases to ensure a thorough design process and to be able to accurately evaluate each concept. The outcome of the project yielded a conceptual design, featuring stackable solar panel modules. Each module consisted of four panels arranged horizontally and three panels vertically, resulting in a total of 288 solar panels, when incorporating eight modules on each float. The cumulative potential maximum power output of the configuration was estimated to be approximately 115 kW. When harsh conditions would be detected, the outer modules would retract under the fixed center module. To support the outer modules, a telescope beam was incorporated, spanning the outermost points of the structure, while roller guides were utilized at the inner end. Moreover, the movement of the outer modules was facilitated by a chain mechanism, housed within a U-profile. Most components in the design were proposed to be manufactured using steel, supplemented with protective measures such as paint or coating to ensure durability in the oceanic environment. / Denna rapport presenterar ett mastersarbete som utförts inom maskinkonstruktionsspåret vid KTH Kungliga Tekniska Högskolan. Arbetet genomfördes i samarbete med Novige AB, som beställde projektet. Novige AB befinner sig i utvecklings- och testfaserna av ett vågkraftverk (WEC) som har en stor outnyttjad yta med potential. Detta ledde till syftet med detta arbete, att konceptualisering en stödstruktur och en expanderingsmekanism för solpaneler som ska monteras på flotten av WEC. Eftersom ingen tidigare forskning hade utförts på området var målet att utforska olika lösningar och presentera ett detaljerat slutkoncept, inklusive initiala beräkningar med FEM under förväntade lastningsfall. Arbetet bestod av flera konceptuella faser för att säkerställa en noggrann designprocess och för att kunna utvärdera varje koncept på ett genomgående sätt. Projektet resulterade i en konceptuell design med stapelbara solpanelesmoduler. Varje modul höll 12 solpaneler, fyra horisontellt och tre vertikalt med 3 moduler per struktur. Varje WEC kunde bära totalt 8 strukturer vilket ger 288 solpaneler per WEC. Den sammanlagda potentiella effekten för konfigurationen uppskattades till cirka 115 kW. Vid svåra väderförhållanden, skulle de yttre modulerna dras tillbaka under den fasta mittmodulen för att minska vindfånget. För att stödja de yttre modulerna inkluderades en teleskopisk balk som bär de yttersta punkterna på modulen, medan rullstöd användes i den inre delen. Dessutom utfördes rörelsen hos de yttre modulerna av en kedja-kuggmekanism som placerades inuti en U-profil. De flesta komponenter i designen föreslogs tillverkas av stål, kompletterat med skyddsåtgärder såsom färg eller beläggning för att minimera risken för korrosion i den marina miljön.

Detta projekt undersöker konstruktionsmöjligheterna för ett nivellerande vinschsystem till ett vågkraftverk. Kedjekonstruktionen till detta vinschsystem består av länkar med låg tolerans för vrid- och skjuvspänningar och har begränsad böjlighet vilket innebär att vinschsystemet behöver kunna vinkelkompensera för att kedjan inte ska brista. Initialt togs flera koncept fram genom att utvärdera en kravspecifikation och se vilka problem som fanns. Dessa konceptförslag modellerades sedan i Solid Edge och en ny utvärdering gjordes där förslagen utvärderades med avseende på komplexitet, vinkelstyrning, servicebarhet och energiåtgång från styrsystemen. Det förslag som var mest lovande utifrån denna utvärdering består av en vagga i vilken vinschtrumman är upphängd. Lutningen av denna vagga kan styras av två motorer och rotationsrörelsen styrs av ett rälssystem med boggier. Detta förslag vidareutvecklades sedan med hjälp av ANSYS Workbench för att göra konstruktionen lättare, undersöka utmattningsproblem samt se var spänningskoncentrationer uppstår. Från denna analys togs kravprofiler fram för ett antal komponenter som konstruktionen kräver för att kunna drivas. Vidare analys av växel, motor, lager samt energiåtgång kommer krävas för att utvärdera om hurvida konstruktionen är lönsam att bygga. / This project examines the design possiblilites for a self-leveling winch system for a wave power converter. The chain design for this winch consists of links with limited resistance to torsional shear and bending shear stress and with limited bending capabilities, which requires the winch construction to be able to compensate for angular changes to prevent the chain from breaking. Initially several designs were made by evaluating a specification of requirements and by examining the problems facing a winch based wave power converter. These designs were modelled in Solid Edge and evaluated based on complexity, angular steering, servicability and energy requirements for the control systems. The most promising of these designs is composed of a cradle in which the winch drum is mounted. The inclination of the cradle is controlled by electric motors and the rotation is controlled by a rail system with boggies. The design was then further improved upon by utilising ANSYS Workbench to decrease the mass of the design, examining problems related to fatigue failure, and studying stress concentrations. Based on this analysis a set of requirements were specified for a number of key components required for controlling the winch system. Further analysis of the transmission, motor, bearings and energy requirements for the control systems will be needed to evaluate wether the design is profitable to build.