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  • 1.
    Ahmad, Haseeb
    Gotland University, School of Culture, Energy and Environment.
    Offshore Wind Park Connection to an HVDC Platform, without using an AC Collector Platform2012Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This thesis investigates the comparison between two different alternating current topologies of an offshore wind farms connection to an offshore high voltage direct current (HVDC) converter platform. The offshore high voltage direct current converter platform converts alternating current into direct current. Two different topologies will be investigated.

    In the first topology, the offshore wind farms are connected to an HVDC converter platform through offshore AC collector platform. An offshore AC collector platform is used to collect energy from the wind farm and step up the voltages for transmission to HVDC convertor platform. The offshore AC collector platforms contribute significantly in the total cost and technical complexity of the HVDC connection.

    In the second topology, the offshore AC collector platform is removed from the circuit and the offshore wind farms are connected directly to offshore HVDC converter platform.

    In this thesis, short circuit analysis and loss analysis of an offshore wind farm cluster connected to an offshore HVDC converter platform is conducted for the two topologies described above.

    Two wind turbine generator types i.e. doubly fed induction generator and full conversion generator is compared for two different topologies. The effect of changing the distance between wind farms and offshore HVDC converter platform on short circuit currents in the absence of AC collector platform is presented for the second configuration. Two internal voltage levels i.e. 33 kV and 66kV of wind farms are compared for short circuit currents in the absence of AC collector platform. DIgSILENT software is used to perform short circuit calculations.

    The thesis is done in collaboration with “Offshore Wind Connections” department ABB, Sweden. The idea is still under development however this study will serve as good starting point to figure out the cost efficient AC topology of an offshore wind park HVDC connection.

  • 2.
    Ahnesjö, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Andersson, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Le Corre, Jean-Marie
    Westinghouse Electric Sweden AB.
    Andersson, Stig
    Westinghouse Electric Sweden AB.
    Tomographic reconstructions and predictions of radial void distribution in BWR fuel bundle with part-length rods2015Conference paper (Refereed)
    Abstract [en]

    The Westinghouse FRIGG facility, in Västerås/Sweden, is dedicated to the measurement of critical power,stability and pressure drop in fuel rod bundles under BWR operating conditions (steady-state andtransient). Capability to measure cross-sectional void and radial void distributions during steady-stateoperation was already considered when the facility was built in the late 1960s, using gamma transmissionmeasurements. In the 1990s, redesigned equipment was installed to allow for full 2D tomography andsome test campaigns were successfully run where the void was measured in the Westinghouse SVEA-96fuel bundle geometry with and without part-length rods.

    In this paper, the tomographic raw data from the SVEA-96 void measurement campaigns are revisitedusing various tomographic reconstruction techniques. This includes an algebraic method and a filteredback-projection method. Challenges, for example due to artifacts created by high difference in gammaabsorption, or to accurately identify the location of the bundle structure, are resolved. The resultingdetailed void distributions are then averaged over entire sub-channels or within the steam core only, forcomparison against sub-channel simulations.

    The resulting void distributions are compared against sub-channel void predictions using the VIPREW/MEFISTO code. The region downstream the part-length rods are of particular interest to investigatehow the void in the steam core is redistributed within the open region of the bundle. The comparisonshows a reasonable agreement between the measurements and the predictions.

  • 3.
    Alm, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Energieffektivisering av Saltsjöbaden Grand Hotell2017Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In a hotel building there are many processes which consume energy, such as lightning and drive fan motor in the ventilation system. These processes needs supplied with electricity. The building is a big consumer of heat. The heating system is supplied with heat pumps and oil. The consumption of electricity is about 1700 MWh and 350 MWh of oil. This thesis affects an energy saving investigation for a hotel and the purpose is to find measures to reduce the energy consumption for this building. The method for the investigation consisted of three steps. First step was to establish how much energy the building consumes today. Second step was to find measures which could be implemented and the third was to calculate the energy saving potential for each measure. If all investigated measures will be implemented the Hotel could save up to 40 % energy. If only the economical and easy measures would be implemented the hotel could save 30 % energy. The easiest measure was to change some parameters in the control system so the oil burners did not go at all times. With that change and a change in the control system for ventilation to reduce the hours the ventilation are on gave reduced energy consumption with 20 %. The economical investments were converting one of the oil burners to an extra heat pump and to change all old lighting to a new LED-Lighting.

  • 4. Andersson, Hjalmar
    et al.
    Zdansky Cottle, Leo
    Claesson, Melker
    Karlsson, Nils
    Stenhammar, Oscar
    Insamling av drift- och produktionsdata från energiteknik vid Ihus anläggning på Vaksala-Eke2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    För att minska den globala uppvärmningen bär utbyggnaden av förnybar energiproduktion en stor vikt i dagens samhälle. Av den anledningen är det av stor betydelse som nya tekniker för energiproduktion testas. För att undersöka huruvida dessa tekniker är effektiva och lönsamma är det viktigt att deras produktionsdata publiceras och görs tillgänglig för allmänheten. Det är anledningen till att det här projektet beställts från Ihus via STUNS energi.

    Projektidén var att samla in högfrekvent uppmätt produktionsdata från en soltracker, ett vindkraftverk och ett batterilager. Dessutom skulle väderdata samlas från en väderstation och solinstrålningsmätare för att sedan offentliggöra datan via STUNS Energiportal.

    För genomförandet av projektet användes en enklare dator för att ta emot information från olika sensorer. För att kommunicera med enheterna användes olika standardiserade kommunikationsprotokoll. Enheterna konfigurerades och kopplades in i datorn. Den insamlade datan bearbetades med en programmerad kod. Programmet sände iväg datan till en molnlagringsplattform för att sedan publicera den.

    Uppkoppling mot soltrackerns växelriktare samt pyranometern lyckades. Den insamlade informationen från de två enheterna publicerades sedan på Energiportalen. Väderstationen producerade data men kommunikation med det ursprungligt tänkta protokollet lyckades inte att upprättas. Genom ett annat protokoll erhölls värden, men inte genom den implementerade koden. Dessutom uppstod problem med batterilagret och vindkraftverket. Ingen information lyckades hämtas från någon av dem.

    I projektets gång har det samlats in mätpunkter var femte sekund för respektive enhet. Utifrån det erhållna resultatet kan de konstateras att vid högfrekvent insamling av väder- och produktionsdata, blir viktig information tydligare för vardera energiproduktionsenhet. Denna information kan gå förlorad vid lågfrekvent datainsamling. Det beror på vädrets hastiga fluktuation. En lågfrekventare datainsamling ger således en sämre uppfattning av hur värdena egentligen ändras med tiden.

  • 5.
    Andersson, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Energy storage solutions for electric bus fast charging stations: Cost optimization of grid connection and grid reinforcements2017Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This study investigates the economic benefits of installing a lithium-ion battery storage (lithium iron phosphate, LFP and lithium titanate, LTO) at an electric bus fast charging station.  It is conducted on a potential electric bus system in the Swedish city Västerås, and based on the existing bus schedules and routes as well as the local distribution system. The size of the energy storage as well as the maximum power outtake from the grid is optimized in order to minimize the total annual cost of the connection. The assessment of the distribution system shows that implementing an electric bus system based on opportunity charging in Västerås does not cause over-capacity in the 10 kV grid during normal feeding mode. However, grid reinforcements might become necessary to guarantee potential backup feeding modes. Batteries are not a cost effective option to decrease grid owner investments in new transformers. However, battery energy storage have the possibility to decrease the annual cost of connecting a fast charging station to the low-voltage grid. The main advantage of the storage system is to decrease the fees to the grid owner. Of the studied batteries, LTO is the most cost effective solution because of its larger possible depth-of-discharge for a given cycle life. The most important characteristics, that determine if a fast charging station could benefit economically from an energy storage, is the bus frequency. The longer the time in between buses and the higher the power demand, the more advantageous is the energy storage.

  • 6.
    Andersson, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Mårtensson, Gustav
    Mycronic AB, Täby.; Chalmers Univ Technol, MC2, EMSL, Gothenburg.
    Klintberg, Lena
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Flowing and pressurizing a solid-liquid two phase monodispersed fluid with high solid content in a transparent microfluidic high-pressure chip2017In: 28TH MICROMECHANICS AND MICROSYSTEMS EUROPE WORKSHOP, IOP PUBLISHING LTD , 2017, article id UNSP 012010Conference paper (Refereed)
    Abstract [en]

    Handling highly concentrated solid-liquid two-phase fluids in microfluidics is challenging. In this paper, we present the first studies of flowing solder paste with a high solid content in a transparent high-pressure tolerant glass chip, thereby increasing the understanding of how multiphase liquids with high density difference between the phases behave in small channels (840 mu m in diameter). The system, including a custom made high-pressure, low resistance, interface, was continuously operated at pressures up to of 6 MPa and devices where shown to have pressure tolerance up to 17 MPa. During flow through the chip, the packing density of the solder balls displayed inhomogeneity over the channel where chains of solder balls in contact with each other were formed together with voids. These in-homogeneities persisted along the channel during flow. The flow rate of the paste through the chip oscillated between 63 to 350 mu m/s when pumping at constant volume rate of 30 mu l/min. When a pressure of 2 MPa was applied, the volume of the solder paste particle segment decreased 1.6%, and 0.1% was elastically recovered when the pressure was released. It is concluded that this transparent microfluidic high-pressure glass chip with the special developed interface is suitable for flow studies of solder paste with a high solid content.

  • 7.
    Andersson, Peter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Holcombe, Scott
    OECD Halden Reactor Project.
    Tverberg, Terje
    Halden Reactor Project.
    Quantitative Gamma Emission Tomography Inspection of LOCA rod IFA-650.152017In: EHPG, 2017Conference paper (Refereed)
  • 8.
    Antonelli, Jacopo
    Gotland University, School of Culture, Energy and Environment.
    Reduced order modeling of wind turbines in MatLab for grid integration and control studies2012Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The current trend in the wind power industry is to develop wind turbines of constantly increasing size and rated power, as well as wind farms of growing size and installed wind power. A careful study of the behaviour of the wind turbines during their operation is of crucial importance in the planning phase and in the design stage of a wind farm, in order to minimize the risks deriving from a non accurate prediction of their impact in the electric grid causing sensible faults of the system.

    To analyze the impact of the wind turbines in the system, motivates the development of accurate yet simple models.

    To be able to practically deal with this topics, a simple model of a wind turbine system is investigated and developed; it has the aim to describe the behaviour of a wind turbine in operation on a mechanical standpoint.

    The same reduced order simple model can also be employed for control system studies; the control system model that can’t be used in generation, can use the reduced model. Together with the analytical description of such model, is realized a MatLab code to numerically analyse the response of the system, and the results of the simulation through such code are presented.

    The objective of this thesis has been to provide a simple benchmark tool in MatLab for grid integration and control studies for interested researchers.

  • 9.
    Ardo, Shane
    et al.
    Univ Calif Irvine, Dept Chem, Irvine, CA 92697 USA;Univ Calif Irvine, Dept Chem Engn & Mat Sci, Irvine, CA 92697 USA;US DOE, Off Energy Efficiency & Renewable Energy EERE, Fuel Cell Technol Off, EE-3F,1000 Independence Ave SW, Washington, DC 20585 USA.
    Rivas, David Fernandez
    Univ Twente, MESA Inst Nanotechnol, Mesoscale Chem Syst Grp, Enschede, Netherlands.
    Modestino, Miguel A.
    NYU, Dept Chem & Biomol Engn, Brooklyn, NY 11201 USA.
    Greiving, Verena Schulze
    Univ Twente, Dept Sci Technol & Policy Studies, Enschede, Netherlands.
    Abdi, Fatwa F.
    Helmholtz Zentrum Berlin Mat & Energie GmbH, Inst Solar Fuels, Berlin, Germany.
    Llado, Esther Alarcon
    Amolf Inst, Ctr Nanophoton, Amsterdam, Netherlands.
    Artero, Vincent
    Univ Grenoble Alpes, CNRS, CEA, Lab Chim & Biol Metaux, Grenoble, France.
    Ayers, Katherine
    Proton OnSite, Wallingford, CT 06492 USA.
    Battaglia, Corsin
    Empa, Swiss Fed Labs Mat Sci & Technol, Dubendorf, Switzerland.
    Becker, Jan-Philipp
    Forschungszentrum Julich, IEK Photovolta 5, Julich, Germany.
    Bederak, Dmytro
    Univ Groningen, Zernike Inst Adv Mat, Nijenborgh 4, NL-9747 AG Groningen, Netherlands.
    Berger, Alan
    Air Prod & Chem Inc, Allentown, PA 18195 USA.
    Buda, Francesco
    Leiden Univ, Leiden Inst Chem, Leiden, Netherlands.
    Chinello, Enrico
    Ecole Polytech Fed Lausanne, LAPD, Lausanne, Switzerland.
    Dam, Bernard
    Delft Univ Technol, MECS, Dept Chem Engn, Maasweg 9, NL-2629 HZ Delft, Netherlands.
    Di Palma, Valerio
    Eindhoven Univ Technol, Dept Appl Phys, Eindhoven, Netherlands.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Fujii, Katsushi
    Univ Kitakyushu, Inst Environm Sci & Technol, Wakamatsu Ku, Kitakyushu, Fukuoka, Japan.
    Gardeniers, Han
    Univ Twente, MESA Inst Nanotechnol, Mesoscale Chem Syst Grp, Enschede, Netherlands.
    Geerlings, Hans
    Delft Univ Technol, MECS, Dept Chem Engn, Maasweg 9, NL-2629 HZ Delft, Netherlands.
    Hashemi, S. Mohammad H.
    Ecole Polytech Fed Lausanne, Opt Lab LO, Lausanne, Switzerland.
    Haussener, Sophia
    Ecole Polytech Fed Lausanne, LRESE, Lausanne, Switzerland.
    Houle, Frances
    Lawrence Berkeley Natl Lab, Joint Ctr Artificial Photosynthesis & Chem Sci Di, Berkeley, CA 94720 USA.
    Huskens, Jurriaan
    Univ Twente, MESA Inst Nanotechnol, Mol Nanofabricat Grp, Enschede, Netherlands.
    James, Brian D.
    Strateg Anal Inc, Arlington, VA 22203 USA.
    Konrad, Kornelia
    Univ Twente, Dept Sci Technol & Policy Studies, Enschede, Netherlands.
    Kudo, Akihiko
    Tokyo Univ Sci, Fac Sci, Dept Appl Chem, Tokyo 1628601, Japan.
    Kunturu, Pramod Patil
    Univ Twente, MESA Inst Nanotechnol, Mol Nanofabricat Grp, Enschede, Netherlands.
    Lohse, Detlef
    Univ Twente, MESA Inst Nanotechnol, Phys Fluids Grp, Enschede, Netherlands.
    Mei, Bastian
    Univ Twente, MESA Inst Nanotechnol, Photocatalyt Synth Grp, Enschede, Netherlands.
    Miller, Eric L.
    Moore, Gary F.
    Arizona State Univ, Sch Mol Sci, Biodesign Ctr Appl Struct Discovery CASD, Tempe, AZ 85287 USA.
    Muller, Jiri
    Inst Energiteknikk, Kjeller, Norway.
    Orchard, Katherine L.
    Univ Cambridge, Dept Chem, Cambridge, England.
    Rosser, Timothy E.
    Univ Cambridge, Dept Chem, Cambridge, England.
    Saadi, Fadl H.
    CALTECH, Div Engn & Appl Sci, Pasadena, CA 91125 USA.
    Schuttauf, Jan-Willem
    Swiss Ctr Elect & Microtechnol CSEM, PV Ctr, Neuchatel, Switzerland.
    Seger, Brian
    Tech Univ Denmark DTU, Dept Phys, Lyngby, Denmark.
    Sheehan, Stafford W.
    Catalyt Innovat, Fall River, MA 02723 USA.
    Smith, Wilson A.
    Delft Univ Technol, MECS, Dept Chem Engn, Maasweg 9, NL-2629 HZ Delft, Netherlands.
    Spurgeon, Joshua
    Univ Louisville, Conn Ctr Renewable Energy Res, Louisville, KY 40292 USA.
    Tang, Maureen H.
    Drexel Univ, Chem & Biol Engn, Philadelphia, PA 19104 USA.
    van de Krol, Roel
    Helmholtz Zentrum Berlin Mat & Energie GmbH, Inst Solar Fuels, Berlin, Germany.
    Vesborg, Peter C. K.
    Tech Univ Denmark DTU, Dept Phys, Lyngby, Denmark.
    Westerik, Pieter
    Univ Twente, MESA Inst Nanotechnol, Mesoscale Chem Syst Grp, Enschede, Netherlands.
    Pathways to electrochemical solar-hydrogen technologies2018In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 11, no 10, p. 2768-2783Article, review/survey (Refereed)
    Abstract [en]

    Solar-powered electrochemical production of hydrogen through water electrolysis is an active and important research endeavor. However, technologies and roadmaps for implementation of this process do not exist. In this perspective paper, we describe potential pathways for solar-hydrogen technologies into the marketplace in the form of photoelectrochemical or photovoltaic-driven electrolysis devices and systems. We detail technical approaches for device and system architectures, economic drivers, societal perceptions, political impacts, technological challenges, and research opportunities. Implementation scenarios are broken down into short-term and long-term markets, and a specific technology roadmap is defined. In the short term, the only plausible economical option will be photovoltaic-driven electrolysis systems for niche applications. In the long term, electrochemical solar-hydrogen technologies could be deployed more broadly in energy markets but will require advances in the technology, significant cost reductions, and/ or policy changes. Ultimately, a transition to a society that significantly relies on solar-hydrogen technologies will benefit from continued creativity and influence from the scientific community.

  • 10.
    Aydin, Murat
    et al.
    Bochum Univ Appl Sci, Int Geothermal Ctr, D-44801 Bochum, Germany;Istanbul Tech Univ, Energy Inst, TR-34469 Istanbul, Turkey.
    Onur, Mustafa
    Univ Tulsa, McDougall Sch Petr Engn, Tulsa, OK 74104 USA.
    Sisman, Altug
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Istanbul Tech Univ, Energy Inst, TR-34469 Istanbul, Turkey.
    A new method for analysis of constant-temperature thermal response tests2019In: Geothermics, ISSN 0375-6505, E-ISSN 1879-3576, Vol. 78, p. 1-8Article in journal (Refereed)
    Abstract [en]

    In this study, a new analysis method is proposed for estimating thermal conductivity of a ground by using the constant-temperature thermal response test data. The new method is based on an analytical solution of heat transfer rate per unit borehole length by using the Laplace transformation for constant-temperature thermal response tests. Its advantage is that it allows one to estimate thermal conductivity directly from the slope of the logarithmic time dependency of inverse unit-heat-transfer rate value without making an estimation of volumetric heat capacity. The method has been verified by using a numerical model and applied to different experimental data based on different test temperatures and compared with the classical thermal response test method. The results show that the proposed method reliably and effectively estimates thermal conductivity of ground.

  • 11.
    Aydin, Murat
    et al.
    Istanbul Technical University, Energy Institute.
    Sisman, Altug
    Istanbul Technical University, Energy Institute.
    Experimental and computational investigation of multi U-tube boreholes2015In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 145, p. 163-171Article in journal (Refereed)
    Abstract [en]

    In ground source heat pump (GSHP) applications, borehole drilling cost constitutes an important part ofthe investment cost and it can be reduced by improving borehole performance. In vertical GSHP applications,usually double-U tube configurations are used to improve the heat transfer rate per unit length of aborehole, (unit HTR value). To determine the optimal number of U-tubes which maximizes the commercialand engineering benefits of multi U-tube applications, cost and performance analyses of multi U-tubeboreholes are crucial. In this study, a triple U-tube is used in a borehole of 50 m depth. Time variation ofunit HTR value of the borehole is experimentally measured when single, double and triple U-tubes are inoperation separately. Furthermore a computational model is calibrated by fitting the computationalresults to the experimental ones, and effects of using four and five U-tubes in a borehole are computationallyinvestigated. The relations between number of U tubes and time variation of unit HTR value ofa borehole as well as investment cost are analyzed. Long term borehole performance predictions aremade and compared for multi U-tube applications. Both experimental and computational results showedthat performance improvements are remarkable for 2U-tube and 3U-tube configurations while it isnearly insignificant for 4U and 5U ones. If the investment cost per thermal power is considered, 2U-tubeconfiguration is the optimal one if the prices of polyethylene pipes are relatively high, like in Turkey.When the cost of pipes decreases, then 3U-tube or even 4U–tube configuration can be the cheapestsolution.

  • 12.
    Ayob, Mohd Nasir
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Malaysia Perlis, Sch Mechatron Engn, Arau 02600, Perlis, Malaysia.
    Castellucci, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Small-Scale Renewable Energy Converters for Battery Charging2018In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 6, no 1, article id 26Article in journal (Refereed)
    Abstract [en]

    This paper presents two wave energy concepts for small-scale electricity generation. In the presented case, these concepts are installed on the buoy of a heaving, point-absorbing wave energy converter (WEC) for large scale electricity production. In the studied WEC, developed by Uppsala University, small-scale electricity generation in the buoy is needed to power a tidal compensating system designed to increase the performance of the WEC in areas with high tides. The two considered and modeled concepts are an oscillating water column (OWC) and a heaving point absorber. The results indicate that the OWC is too small for the task and does not produce enough energy. On the other hand, the results show that a hybrid system composed of a small heaving point absorber combined with a solar energy system would be able to provide a requested minimum power of around 37.7W on average year around. The WEC and solar panel complement each other, as the WEC produces enough energy by itself during wintertime (but not in the summer), while the solar panel produces enough energy in the summer (but not in the winter).

  • 13.
    Babac, Gulru
    et al.
    Istanbul Technical University, Energy Institute.
    Sisman, Altug
    Istanbul Technical University, Energy Institute.
    Cimen, Tolga
    Istanbul Technical University, Energy Institute.
    Two-dimensional thermal analysis of liquid hydrogen tank insulation2009In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 34, p. 6357-6363Article in journal (Refereed)
    Abstract [en]

    Liquid hydrogen (LH2) storage has the advantage of high volumetric energy density, whileboil-off losses constitute a major disadvantage. To minimize the losses, complicatedinsulation techniques are necessary. In general, Multi Layer Insulation (MLI) and a Vapor-Cooled Shield (VCS) are used together in LH2 tanks. In the design of an LH2 tank with VCS,the main goal is to find the optimum location for the VCS in order to minimize heatleakage. In this study, a 2D thermal model is developed by considering the temperaturedependencies of the thermal conductivity and heat capacity of hydrogen gas. The developedmodel is used to analyze the effects of model considerations on heat leakagepredictions. Furthermore, heat leakage in insulation of LH2 tanks with single and doubleVCS is analyzed for an automobile application, and the optimum locations of the VCS forminimization of heat leakage are determined for both cases.

  • 14.
    Bao, Haiyan
    et al.
    Changsha Univ Sci & Technol, Sch Hydraul Engn, Changsha.; Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan.
    Yang, Jiandong
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan.
    Zhao, Guilian
    PowerChina Chengdu Engn Corp Ltd, Chengdu.
    Zeng, Wei
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Hubei, Peoples R China..
    Liu, Yanna
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan.
    Yang, Weijia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan.
    Condition of setting surge tanks in hydropower plants - A review2018In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 81, p. 2059-2070Article, review/survey (Refereed)
    Abstract [en]

    Hydropower plays an important role in the safe, stable and efficient operation of power systems, especially with current trends toward renewable energy systems. The total global potential of gross, technical, economic, and exploitable hydropower are still enormous in the future, and the developments of new hydropower stations (HPSs) are of great importance. For constructions of new HPSs, the condition of setting surge tanks (CSST) is crucial for various perspectives, e.g. safety, stability and economy of HPSs. In this review, the CSST are summarized and analyzed from the three aspects: regulation assurance, operation stability, and the regulation quality, with an aim of providing a reference and guidance for research and engineering applications regarding surge tanks. Upstream and downstream surge tanks in conventional HPSs and pumped storage power stations are all included. Moreover, a comprehensive comparison of CSST under different conditions is conducted. One of the main focuses of this review is on Chinese studies, for introducing many meaningful results written in Chinese to more readers all over the world.

  • 15.
    Basirat, Farzad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Sharma, Prabhakar
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Fagerlund, Fritjof
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Experimental and modeling investigation of CO2 flow and transport in a coupled domain of porous media and free flow2015In: International Journal of Greenhouse Gas Control, ISSN 1750-5836, E-ISSN 1878-0148, Vol. 42, p. 461-470Article in journal (Refereed)
    Abstract [en]

    A solid understanding of the transport mechanisms of gaseous CO2 near the land surface is necessary for developing reliable monitoring techniques and predictive models for possible CO2 leakage from deep underground storage. The objective of this work has been to develop an experimental method along with a simulation model for gaseous CO2 flow and transport in a system including both the porous media and the free air space above it. The experimental system consisted of a two-dimensional bench scale rectangular sandbox containing homogenous sand with an open space of still air above it. Gaseous CO2 was injected in different modes and the CO2 breakthrough was measured on specified ports in the system by using CO2 concentration sensors. A numerical model combining the gas flow in the porous medium and the free flow region was developed and used to model the experimental data. In this quest, the Discontinuous One-Domain approach was selected for modeling transport between the free flow and porous regions. The observed and simulated CO2 breakthrough curves both in the dried sand and in the free flow matched very well in the case of uniform injection and satisfactorily even in the case of point injection. Consequently, it seems that the model reasonably matches the observed data in the cases where the boundary condition is well defined. In summary, our results show that the developed experimental setup provides capability to study gaseous CO2 flow and transport in a coupled porous medium - free flow system and that our modeling approach is able to predict the flow and transport in this system with good accuracy.

  • 16.
    Bastholm, Caroline
    et al.
    Högskolan Dalarna, Energiteknik.
    Fiedler, Frank
    Högskolan Dalarna, Energiteknik.
    Techno-economic study of the impact of blackouts on the viability of connecting an off-grid PV-diesel hybrid system in Tanzania to the national power grid2018In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 171, no 1, p. 647-658Article in journal (Refereed)
    Abstract [en]

    National electrification plans for many countries with a low level of electrification promote the implementation of centralized and decentralized electrification in parallel. This paper explores different ways of utilizing an established off-grid PV-diesel hybrid system when the national grid becomes available. This is a rather unique starting point within the otherwise well-explored area of rural electrification. With particular focus on the impact of blackouts in the national grid, we evaluate the economic viability of some alternatives: to continue to use the off-grid micro-grid, to connect the existing micro-grid with or without battery backup to the national grid, or to use the national grid only. Our simulation results in HOMER demonstrate that with a grid without blackouts, there are few benefits to maintain the existing system. Low grid-connection fees, low tariffs and low revenues from selling excess electricity to the grid contribute to this result despite the fact that the system does not carry any investment costs. With a grid with blackouts, it is beneficial to maintain the system. The extent of blackouts and the load on the system determine which system configuration is most feasible. The results make clear the importance of taking blackouts in the national grid into consideration when possible system configurations are being evaluated. This is rarely quantified in studies comparing different electrification alternatives, but deserves more attention.

  • 17.
    Baudoin, Antoine
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooling Strategies for Wave Power Conversion Systems2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The Division for Electricity of Uppsala University is developing a wave power concept. The energy of the ocean waves is harvested with wave energy converters, consisting of one buoy and one linear generator. The units are connected in a submerged substation. The mechanical design is kept as simple as possible to ensure reliability.

    The submerged substation includes power electronics and different types of electrical power components. Due to the high cost of maintenance operations at sea, the reliability of electrical systems for offshore renewable energy is a major issue in the pursuit of making the electricity production economically viable. Therefore, proper thermal management is essential to avoid the components being damaged by excessive temperature increases.

    The chosen cooling strategy is fully passive, and includes no fans. It has been applied in the second substation prototype with curved heatsinks mounted on the inner wall of the pressurized vessel. This strategy has been evaluated with a thermal model for the completed substation. First of all, 3D-CFD models were implemented for selected components of the electrical conversion system. The results from these submodels were used to build a lumped parameter model at the system level.

    The comprehensive thermal study of the substation indicates that the rated power in the present configuration is around 170 kW. The critical components were identified. The transformers and the inverters are the limiting components for high DC-voltage and low DC-voltage respectively. The DC-voltage—an important parameter in the control strategy for the WEC—was shown to have the most significant effect on the temperature limitation.

    As power diodes are the first step of conversion, they are subject to large power fluctuations. Therefore, we studied thermal cycling for these components. The results indicated that the junction undergoes repeated temperature cycles, where the amplitude increased with the square root of the absorbed power.

    Finally, an array of generic heat sources was optimized. We designed an experimental setup to investigate conjugate natural convection on a vertical plate with flush-mounted heat sources. The influence of the heaters distribution was evaluated for different dissipated powers. Measurements were used for validation of a CFD model. We proposed optimal distributions for up to 36 heat sources. The cooling capacity was maximized while the used area was minimized.

    List of papers
    1. Optimized distribution of a large number of heat sources cooled by conjugate turbulent natural convection
    Open this publication in new window or tab >>Optimized distribution of a large number of heat sources cooled by conjugate turbulent natural convection
    (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606Article in journal (Refereed) Submitted
    National Category
    Energy Engineering
    Identifiers
    urn:nbn:se:uu:diva-307944 (URN)
    Available from: 2016-11-24 Created: 2016-11-23 Last updated: 2017-11-29
    2. Temperature and velocity measurements in a buoyant flow induced by a heat source array on a vertical plate
    Open this publication in new window or tab >>Temperature and velocity measurements in a buoyant flow induced by a heat source array on a vertical plate
    2017 (English)In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 88, p. 234-245Article in journal (Refereed) Published
    Abstract [en]

    Heat source arrays are common in engineering applications. Natural convection is a reliable and silent cooling strategy. Therefore, an array of flush-mounted heat sources has been studied under conjugate conduction and natural convection condition. This studies was performed for a system with relatively large dimensions, typical for power electronics, and a modified Rayleigh number up to 2 . 10(10) A modular set of heaters was designed to vary the distribution of heat sources on the plate and investigate the influence of the spacing. Velocity and temperature were measured in the convective flow with particle image velocimetry and micro-thermocouple. The velocity field was analyzed with proper orthogonal decomposition. The first instabilities of the convective flows were described. The results gave abetter understanding of the heat transfers in these configurations and are valuable for model validation.

    National Category
    Energy Engineering Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:uu:diva-307943 (URN)10.1016/j.expthermflusci.2017.06.002 (DOI)000409285600023 ()
    Funder
    SweGRIDS - Swedish Centre for Smart Grids and Energy StorageStandUp
    Available from: 2016-11-24 Created: 2016-11-23 Last updated: 2017-12-01Bibliographically approved
    3. Experimental Optimization of Passive Cooling of a Heat Source Array Flush-Mounted on a Vertical Plate
    Open this publication in new window or tab >>Experimental Optimization of Passive Cooling of a Heat Source Array Flush-Mounted on a Vertical Plate
    2016 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 9, no 11, article id 912Article in journal (Refereed) Published
    Abstract [en]

    Heat sources, such as power electronics for offshore power, could be cooled passively—mainly by conduction and natural convection. The obvious advantage of this strategy is its high reliability. However, it must be implemented in an efficient manner (i.e., the area needs to be kept low to limit the construction costs). In this study, the placement of multiple heat sources mounted on a vertical plate was studied experimentally for optimization purposes. We chose a regular distribution, as this is likely to be the preferred choice in the construction process. We found that optimal spacing can be determined for a targeted source density by tuning the vertical and horizontal spacing between the heat sources. The optimal aspect ratio was estimated to be around two.

    Keywords
    discrete heat sources, source array, natural convection, optimization
    National Category
    Energy Engineering
    Identifiers
    urn:nbn:se:uu:diva-307831 (URN)10.3390/en9110912 (DOI)000388580000054 ()
    Funder
    SweGRIDS - Swedish Centre for Smart Grids and Energy StorageStandUp
    Available from: 2016-11-22 Created: 2016-11-22 Last updated: 2017-11-29Bibliographically approved
    4. Assessment of Thermal Cycling in a Rectifier For WavePower Generation
    Open this publication in new window or tab >>Assessment of Thermal Cycling in a Rectifier For WavePower Generation
    2016 (English)Conference paper, Published paper (Refereed)
    Abstract [en]

    Natural convection allows for passive cooling which isused in many engineering applications. Placing dissipatingcomponents on a common vertical heatsink can be opti-mized to give the best possible cooling capacity. In thisstudy, a numerical model for three-dimensional conjugatedconvective and conductive heat transfer was used to evalu-ate the distribution of up to 36 ush-mounted rectangularheaters. The temperature proles and the heat uxes werecompared with experimental data for validation. The dis-sipated power was set as an input parameter and the op-timal distribution was selected as the one with the lowesttemperature elevation. Two dierent heuristicsa geo-metric parameter and an articial neural networkwereproposed and evaluated as alternatives to heavy CFD cal-culations.

    National Category
    Energy Engineering
    Identifiers
    urn:nbn:se:uu:diva-307945 (URN)
    Conference
    IET Renewable Power Generation
    Available from: 2016-11-23 Created: 2016-11-23 Last updated: 2016-11-25
    5. Thermal Rating of a Submerged Substation for Wave Power
    Open this publication in new window or tab >>Thermal Rating of a Submerged Substation for Wave Power
    2016 (English)In: IEEE Transactions on Sustainable Energy, ISSN 1949-3029, E-ISSN 1949-3037, Vol. 7, no 1, p. 436-445Article in journal (Refereed) Published
    Abstract [en]

    The costs of offshore maintenance operations put high reliability-requirements on offshore equipment for ocean energy, especially on submerged ones. Thermal management is thus essential in the design of the prototypes of a marine substation, developed at Uppsala University, for grid interface of wave power parks. The cooling system itself should be efficient as well as reliable. Therefore, the feasibility of a completely passive cooling strategy was evaluated. The studied substation includes various power components, which dissipate heat and are installed in one pressurized vessel. Thermal cross-coupling was investigated with 3-D submodels and a thermal network model. An electric circuit was coupled to determine the rated power of the substation. The results depend mainly on the dc-voltage, the seawater temperature, and the thermal contact between the components and the hull.

    Keywords
    Computational fluid dynamics;Computational modeling;Heat transfer;Heating;Integrated circuit modeling;Substations;Wave power;Computational fluid dynamic (CFD);natural convection;ocean energy;passive cooling;power electronics;thermal management;wave power
    National Category
    Engineering and Technology Ocean and River Engineering
    Identifiers
    urn:nbn:se:uu:diva-267226 (URN)10.1109/TSTE.2015.2425045 (DOI)000367340700044 ()
    Funder
    SweGRIDS - Swedish Centre for Smart Grids and Energy StorageStandUpSwedish Energy Agency
    Available from: 2015-11-19 Created: 2015-11-19 Last updated: 2017-12-01Bibliographically approved
    6. Thermal modelling of a passively cooled inverter for wave power
    Open this publication in new window or tab >>Thermal modelling of a passively cooled inverter for wave power
    2015 (English)In: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 9, no 4, p. 389-395Article in journal (Refereed) Published
    Abstract [en]

    Owing to very costly maintenance operations, the reliability of electrical systems for offshore renewable energy is a major issue to make electricity production economical. Therefore proper thermal management is essential in order to avoid the components from being damaged by excessive temperature increase. Both analytic and computational fluid dynamics (CFD) models were implemented to assess the temperature increase in the inverter installed in a submerged substation and during working conditions. It was shown that this inverter could transmit a total power of up to about 35 kW. This limit is dependent on a certain distance between the modules and a perfect thermal contact with the hull. The influence of several of such parameters as well as the efficiency of passive cooling were studied.

    Keywords
    wave power plants, invertors, substations, cooling, thermal modelling, passively cooled inverter, wave power, CFD models, submerged substation, thermal contact, passive cooling
    National Category
    Environmental Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-252981 (URN)10.1049/iet-rpg.2014.0112 (DOI)000352809300011 ()
    Available from: 2015-05-19 Created: 2015-05-18 Last updated: 2017-12-04Bibliographically approved
    7. Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden: A Status Update
    Open this publication in new window or tab >>Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden: A Status Update
    Show others...
    2015 (English)Conference paper, Published paper (Refereed)
    Abstract [en]

    This paper provides a summarized status update ofthe Lysekil wave power project. The Lysekil project is coordinatedby the Div. of Electricity, Uppsala University since 2002, with theobjective to develop full-scale wave power converters (WEC). Theconcept is based on a linear synchronous generator (anchored tothe seabed) driven by a heaving point absorber. This WEC has nogearbox or other mechanical or hydraulic conversion systems,resulting in a simpler and robust power plant. Since 2006, 12 suchWECs have been build and tested at the research site located atthe west coast of Sweden. The last update includes a new andextended project permit, deployment of a new marine substation,tests of several concepts of heaving buoys, grid connection,improved measuring station, improved modelling of wave powerfarms, implementation of remote operated vehicles forunderwater cable connection, and comprehensive environmentalmonitoring studies.

    Keywords
    Wave energy, point absorber, experiments, arrays, generators, ROVs
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering Ocean and River Engineering
    Identifiers
    urn:nbn:se:uu:diva-265218 (URN)
    Conference
    Proceedings of the 11th European Wave and Tidal Energy Conference. Nantes, France, September 2015
    Available from: 2015-10-26 Created: 2015-10-26 Last updated: 2019-08-19Bibliographically approved
    8. Measurement System For Wave Energy Converter - Design And Implementation
    Open this publication in new window or tab >>Measurement System For Wave Energy Converter - Design And Implementation
    2014 (English)In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 9A: Ocean Renewable Energy, AMER SOC MECHANICAL ENGINEERS , 2014Conference paper, Published paper (Refereed)
    Abstract [en]

    A Wave Energy Converter (WEC) measurement system has been constructed and installed with the purpose to measure, log and evaluate the WEC's performance during operation at sea. The WEC is to be deployed at Uppsala University's wave power research site in Lysekil on the west coast of Sweden. In designing such a system the key research objectives has been (1) to study the risk of overheating due to high currents in the stator windings, (2) to evaluate how the WEC's outer structure withstands drag and bending forces from the buoy line and (3) to construct a detection system which indicates if water leaks into the generator. The measurement system was designed to collect data essential to study these key objectives. Transducers were used to measure: buoy line force, translator position, phase currents, bending and tensile strain on the generator hull, water level inside generator and the temperature at multiple places inside the generator. The measurement system has been installed and calibrated in the WEC. Furthermore, the design has been evaluated in lab experiments in order to verify the function and accuracy of the different measurements. This paper presents the underlying research objectives for developing the WEC generator measurement system, together with a description of the technical implementation.

    Place, publisher, year, edition, pages
    AMER SOC MECHANICAL ENGINEERS, 2014
    National Category
    Energy Systems Ocean and River Engineering
    Identifiers
    urn:nbn:se:uu:diva-272118 (URN)000363499000005 ()978-0-7918-4553-0 (ISBN)
    Conference
    33Rd International Conference On Ocean, Offshore And Arctic Engineering
    Note

    Första författaren har bytt efternamn till Ulvgård

    Available from: 2016-01-12 Created: 2016-01-12 Last updated: 2017-09-28
    9. Status Update of the Wave Energy Research at Uppsala University
    Open this publication in new window or tab >>Status Update of the Wave Energy Research at Uppsala University
    Show others...
    2013 (English)Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Aalborg, Denmark: , 2013
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-212701 (URN)
    Conference
    10th European Wave and Tidal Conference (EWTEC)
    Available from: 2013-12-13 Created: 2013-12-13 Last updated: 2017-12-07
    10. Temperature Study in a Marine Substation for Wave Power
    Open this publication in new window or tab >>Temperature Study in a Marine Substation for Wave Power
    Show others...
    2012 (English)In: International Journal of Mechanic Systems Engineering, ISSN 2225-7403, Vol. 2, no 4, p. 126-131Article in journal (Refereed) Published
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-190091 (URN)
    Available from: 2013-01-07 Created: 2013-01-07 Last updated: 2017-01-18Bibliographically approved
    11. Marine substation design for grid-connection of a research wave power plant on the Swedish West coast
    Open this publication in new window or tab >>Marine substation design for grid-connection of a research wave power plant on the Swedish West coast
    2013 (English)Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Aalborg, Denmark: , 2013
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-212687 (URN)
    Conference
    10th European Wave and Tidal Conference (EWTEC)
    Available from: 2013-12-13 Created: 2013-12-13 Last updated: 2016-11-24
    12. Lysekil Research Site, Sweden: A status update
    Open this publication in new window or tab >>Lysekil Research Site, Sweden: A status update
    Show others...
    2011 (English)In: 9th European Wave and Tidal Energy Conference, Southampton, UK, 2011, 2011Conference paper, Published paper (Refereed)
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-160039 (URN)
    Conference
    9th European Wave and Tidal Energy Conference, Southampton, UK, 5-9 September 2011
    Available from: 2011-10-13 Created: 2011-10-13 Last updated: 2017-01-25
  • 18.
    Baudoin, Antoine
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Saury, Didier
    Assessment of Thermal Cycling in a Rectifier For WavePower Generation2016Conference paper (Refereed)
    Abstract [en]

    Natural convection allows for passive cooling which isused in many engineering applications. Placing dissipatingcomponents on a common vertical heatsink can be opti-mized to give the best possible cooling capacity. In thisstudy, a numerical model for three-dimensional conjugatedconvective and conductive heat transfer was used to evalu-ate the distribution of up to 36 ush-mounted rectangularheaters. The temperature proles and the heat uxes werecompared with experimental data for validation. The dis-sipated power was set as an input parameter and the op-timal distribution was selected as the one with the lowesttemperature elevation. Two dierent heuristicsa geo-metric parameter and an articial neural networkwereproposed and evaluated as alternatives to heavy CFD cal-culations.

  • 19.
    Baudoin, Antoine
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Saury, Didier
    Univ Poitiers, ENSMA, CNRS, Inst PPRIME, BP 40109, F-86961 Futuroscope, France.
    Temperature and velocity measurements in a buoyant flow induced by a heat source array on a vertical plate2017In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 88, p. 234-245Article in journal (Refereed)
    Abstract [en]

    Heat source arrays are common in engineering applications. Natural convection is a reliable and silent cooling strategy. Therefore, an array of flush-mounted heat sources has been studied under conjugate conduction and natural convection condition. This studies was performed for a system with relatively large dimensions, typical for power electronics, and a modified Rayleigh number up to 2 . 10(10) A modular set of heaters was designed to vary the distribution of heat sources on the plate and investigate the influence of the spacing. Velocity and temperature were measured in the convective flow with particle image velocimetry and micro-thermocouple. The velocity field was analyzed with proper orthogonal decomposition. The first instabilities of the convective flows were described. The results gave abetter understanding of the heat transfers in these configurations and are valuable for model validation.

  • 20.
    Baudoin, Antoine
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Saury, Didier
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Optimized distribution of a large number of heat sources cooled by conjugate turbulent natural convectionIn: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606Article in journal (Refereed)
  • 21.
    Baudoin, Antoine
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Saury, Didier
    Univ Poitiers, ENSMA, CNRS, Inst PPRIME, BP 40109, F-86961 Futuroscope, Chassencuil, France.
    Zhu, Bo
    Univ Poitiers, ENSMA, CNRS, Inst PPRIME, BP 40109, F-86961 Futuroscope, Chassencuil, France.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Experimental Optimization of Passive Cooling of a Heat Source Array Flush-Mounted on a Vertical Plate2016In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 9, no 11, article id 912Article in journal (Refereed)
    Abstract [en]

    Heat sources, such as power electronics for offshore power, could be cooled passively—mainly by conduction and natural convection. The obvious advantage of this strategy is its high reliability. However, it must be implemented in an efficient manner (i.e., the area needs to be kept low to limit the construction costs). In this study, the placement of multiple heat sources mounted on a vertical plate was studied experimentally for optimization purposes. We chose a regular distribution, as this is likely to be the preferred choice in the construction process. We found that optimal spacing can be determined for a targeted source density by tuning the vertical and horizontal spacing between the heat sources. The optimal aspect ratio was estimated to be around two.

  • 22.
    Bee, Elena
    et al.
    Univ Trento, Dept Civil Environm & Mech Engn, Trento, Italy.
    Prada, Alessandro
    Univ Trento, Dept Civil Environm & Mech Engn, Trento, Italy.
    Baggio, Paolo
    Univ Trento, Dept Civil Environm & Mech Engn, Trento, Italy.
    Psimopoulos, Emmanouil
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences. Dalarna Univ, Energy Technol, Borlange, Sweden.
    Air-source heat pump and photovoltaic systems for residential heating and cooling: Potential of self-consumption in different European climates2019In: Building Simulation, ISSN 1996-3599, E-ISSN 1996-8744, Vol. 12, no 3, p. 453-463Article in journal (Refereed)
    Abstract [en]

    Renewable sources will play a key role in meeting the EU targets for 2030. The combined use of an aerothermal source through a heat pump and a solar source with a photovoltaic (PV) system is one feasible and promising technology for the heating and cooling of residential spaces. In this study, a detailed model of a single-family house with an air-source heat pump and a PV system is developed with the TRNSYS simulation software. Yearly simulations are run for two types of buildings and nine European climates, for both heating and cooling (where needed), in order to have an overview of the system behaviour, which is deeply influenced by the climate. The storage system (electrical and thermal) is also investigated, by means of multiple simulation scenarios, with and without the battery and with different water storage sizes. The numerical results provide an overview of the performance of the considered heating and cooling system, as well as the balance of the electrical energy exchange between the grid, the building, and the PV array.

  • 23.
    Benesperi, Iacopo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Uppsala Univ, Dept Chem, Angstrom Lab, S-75120 Uppsala, Sweden.
    Michaels, Hannes
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Freitag, Marina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    The researcher's guide to solid-state dye-sensitized solar cells2018In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 6, no 44, p. 11903-11942Article, review/survey (Refereed)
    Abstract [en]

    In order to sustainably support its ever-increasing energy demand, the human society will have to harvest renewable energy wherever and whenever possible. When converting light to electricity, silicon solar cells are the technology of choice to harvest direct sunlight due to their high performance and continuously dropping price. For diffused light and indoor applications, however, silicon is not the material of choice. To power the next gizmo in your smart home, dye-sensitized solar cells (DSCs) are a viable alternative. Made from inexpensive, earth-abundant, and non-toxic materials, DSCs perform best at low light intensity. So far, issues such as leakage of the liquid electrolyte and its corrosive nature have limited the commercialization of this technology. To overcome these limitations, solid-state DSCs (ssDSCs) - in which the liquid electrolyte is replaced by a solid material - have been developed. For many years their efficiencies have been poor, preventing them from being widely employed. In the past six years, however, research efforts have led them to rival with their liquid counterparts. Here, we will review recent advancements in the field of ssDSCs. Every device component will be acknowledged, from metal oxides and new dyes to novel hole transporters, dopants, counter-electrodes and device architectures. After reviewing materials, long-term stability of devices will be addressed, finally giving an insight into the future that awaits this exciting technology.

  • 24.
    Berggren, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Study of auxiliary power systemsfor offshore wind turbines: an extended analysis of a diesel gen-setsolution2013Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Until today the offshore wind power has grown in a steady pace and many new wind farms are being constructed around the globe. An important factor that is investigated today in the industry are the security of power supply to the equipment needed for controlling the offshore system during emergency situations. When a offshore wind farm is disconnected from the external grid and an emergency case occur the wind turbine generators lose their ability to transfer power and they are forced to be taken out of operation. As there are a number of loads in the wind turbines (navigation lights, sensor- and communication-apparatus, ventilation- and heating equipment etc.) they have a load demand which must be supplied in emergency mode. The German Transmission System operator (TSO) TenneT GmbH has set a requirement that the wind turbines is to be supplied by an auxiliary power supply (APS) in 12 hours and therefore there is need for a long-term auxiliary power supply system. This master thesis was assigned to investigate the most feasible APS-system. From the study of a number of different APS's one concept was chosen. This was the diesel gen-set solution placed on an offshore substation at sea. The system was modeled in the software DIgSILENT PowerFactory where a load flow analysis validated the calculated data and a study of the impact of  transients in the system was performed.

  • 25.
    Björk, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Analys av stationsreglering vid Forsmarks kärnkraftverk: koppling mot eldynamiska simuleringsverktyg och modeller2016Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master thesis is done within the Energy Systems Engineering program at Uppsala University and performed for Forsmarks Kraftgrupp, Vattenfall. The nuclear power plant at Forsmark consists of three BWR units and is an important component in the Swedish power system. The nuclear power units are individually connected to the 400 kV transmission grid to export their production, but also to supply the units with auxiliary power when needed. As a backup the units are also connected to the 70 kV grid and each have several sub grids supported by backup diesel engines and batteries.This is to guarantee that the nuclear power units always have electrical power to support their vital auxiliary systems.

    To evaluate the function of the separate local power grids of Forsmark’s nuclear units and their interaction with the offsite grid, the simulation software Simpow have been used. With Simpow, the function of controllers, pumps and motors, vital for the plants safety, can be analyzed for different operation conditions and plant changes. Today the Electrical Power Analysis and Plant Engineering Group are in the process of changing from Simpow to new simulation software, PowerFactory. During this process the question of how to best implement the plant controller have been raised. The plant controller controls the thermal power, pressure and water level of the reactor, all contributing to the dynamics of the units power supply during operation. An implementation of the plant controller exist in Simpow for the plant’s older units Forsmark 1 and 2, but for the newest unit Forsmark 3 there is only a standard model of a steam turbine with governor implemented.

    In this thesis the effect of the plant controller systems are investigated to serve as a basis for implementation of the plants dynamics in the modelling of Forsmark 3 in PowerFactory.

  • 26.
    Björklund, Markus
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Utveckling av beräkningsmodell för värmepumpstillsats i avfuktarsystem2018Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    One way to make a dehumidifier system more energy efficient is to attach a heat pump onto the dehumidifier. In this master thesis, a MATLAB-based computational model is developed to simulate the heat pump application. The aim for this model is to optimize various configurations of the heat pump, and to be used as a tool in theproduct development process. The computational model should also verify the measurements that have been made on the prototype for the heat pump application. The heat pump application is mathematically described by a set of equations. Together with a set of unknown model parameters, this creates an equation system. Theequation system is then solved numerically with Newton's method in multiple variables. The validation of the calculation model shows relatively small model errors between simulated and measured data. The exception is the model error of the condensing temperature of the refrigerant, where the model error is more than twice as big as the error in other simulated temperatures. This may be due to extrapolating of curve fitted data in order to calculate the total efficiency of the compressor. Another method to calculate the total efficiency of the compressor should therefore be considered in order to reduce the model error of the condensing temperature of the refrigerant. Simulations of the model also show that choosing the refrigerant R134a over R1234yf increases the heat pump coefficient of performance (COP) by an average of 12 %. The results have also shown that heat exchangers with 3 tube rows instead of 2 gives the heat pump an increased COP. This result could be utilized tocompensate for the reduced COP when R1234yf is the refrigerant of choice.

  • 27. Bladh, Johan
    et al.
    Sundqvist, Per
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Torsional stability of hydropower units under influence of subsynchronous oscillations2013In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 28, no 4, p. 3826-3833Article in journal (Refereed)
    Abstract [en]

    Hydropower units are known to be comparatively insensitive to subsynchronous power oscillations. During a startup test of an electrical island in the Nordic power system, a series capacitor tripped due to a subsynchronous oscillation within the normal frequency range of hydropower unit torsional modes. Since no thermal units were connected, it is motivated to question the traditional view. In this paper, the small-signal and transient torsional mode stability of hydropower units is assessed through time-domain simulations. The model is based on the first IEEE benchmark model for subsynchronous resonance which has been tuned to fit one of the blackstart test system units for which detailed measurements are available. The stability conditions are investigated for several load conditions and machine configurations. It is found that the damping in the startup test system is sufficient to prevent growing oscillations. A fault however could expose the machines to high transient torques.

  • 28.
    Blücher, Jakob
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Koncepttest av Mikroskalig Vattenkraft: Kraftelektronik och varvtalsstyrning2017Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This project describes the design and assembly of the power electronic and control system for variable speed control of a micro scale hydro power station in Sweden. The turbine is a new type of integrated turbine-generator unit, called Turbo, designed by prof. Urban Lundin at Uppsala University. Power electronic components was dimensioned, purchased and assembled.

    The projects purpose is to create an installation for testing and evaluation of Turbo and the main goal was to determine Turbos optimal rotational speed.

    A commercial 20 kW solar power inverter from Fronius was used and it was controlled using LabVIEW and communicating through the serial protocol Modbus. To control the rotational speed of the generator a PI-regulator with negative feedback was used and controlled from LabVIEW. Test results shows a functioning system where the inverter is to slow to work in an optimal way. This is likely due to the fact that solar power inverters doesn't have to regulate as fast as inverters designed for hydro- and windpower.

    When testing the integrated turbine generator on site it didn't rotate and final tests could therefore not be completed. This might be because of a bearing that is not properly designed and further research on the area must therefore be completed before determining the optimal rotational speed.

  • 29.
    Boquist, Pär
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    OFFSHORE WIND POWER INVESTMENT MODEL USING A REFERENCECLASS FORECASTING APPROACH TO ESTIMATE THE REQUIRED COSTCONTINGENCY BUDGET2015Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Forecasting capital expenditures in early stages of an offshore wind power project is aproblematic process. The process can be affected by optimism bias and strategicmisrepresentation which may result in cost overruns. This thesis is a response to issuesregarding cost overruns in offshore wind power projects. The aim of this thesis is tocreate a cost forecasting method which can estimate the necessary capital budget in awind power project.

    The author presents a two-step model which both applies the inside view and outsideview. The inside view contains equations related to investment and installation costs.The outside view applies reference class forecasting in order to adjust the necessary costcontingency budget. The combined model will therefore forecast capital expenditures fora specific site and adjust the cost calculations with regard to previous similar projects.

    The results illustrate that the model is well correlated with normalized cost estimationsin other projects. A hypothetical 150MW offshore wind farm is estimated to costbetween 2.9 million €/MW and 3.5 million €/MW depending on the location of the windfarm.

  • 30.
    Boström, Cecilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Operation analysis of a wave energy converter under different load conditions2011In: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 5, no 3, p. 245-250Article in journal (Refereed)
    Abstract [en]

    This study analyses the electrical behaviour of a direct-driven linear generator under different load conditions. The studied generator is used in a wave energy converter (WEC) that converts the energy in ocean waves into electric energy. To enable a grid connection of a WEC, the voltage must be converted, and thereby, the generator will be subjected to a non-linear damping. Depending on how the conversion system is designed, the damping will be different. In the case studied, the voltage is first rectified, and on the dc-side of the rectifier the voltage is kept constant by controlling the power through a converter. In order to study the electrical behaviour of the generator in this operation mode, a simulation model was made in MATLAB Simulink. The model of the generator was verified with experimental data from an offshore operating WEC. The result of the study shows that the model of the generator agrees with the real generator and can be used for analysing the electrical behaviour of the WEC. Moreover, the results show that the operation with a non-linear load will be different compared to a linear load case.

  • 31.
    Bright, Jamie M
    et al.
    Fenner School of Environment and Society, Australian National University, Canberra, Australia .
    Gueymard, Christian A
    Solar Consulting Services, Colebrook, NH, USA.
    Killinger, Sven
    Fraunhofer Institute for Solar Energy Systems ISE, 79100 Freiburg, Germany .
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sun, Xixi
    Department of Mathematics and System Sciences, Beihang University, Beijing, China .
    Wang, Peng
    Department of Mathematics and System Sciences, Beihang University, Beijing, China;Beijing Advanced Innovation Center for Big Data, Beihang University, Beijing, China .
    Engerer, Nicholas A
    Fenner School of Environment and Society, Australian National University, Canberra, Australia .
    Climatic and Global Validation of Daily MODIS Precipitable Water Data at AERONET Sites for Clear-sky Irradiance Modelling2018In: Proceedings of the ISES EuroSun 2018 Conference: 12th International Conference on Solar Energy for Buildings and Industry, International Solar Energy Society, 2018, p. 1490-1501Conference paper (Refereed)
    Abstract [en]

    Precipitable water (PW) is an influential variable in regards to clear-sky radiation modelling and solar resource assessment. Thus, the accuracy of solar energy estimates depends on the accuracy of PW measurements. Gridded satellite information is commonly used for solar modelling because of its benefit of a broad geographical coverage, thus a global validation of commonly utilised PW products is imperative. Here, all Level-3 Moderate Resolution Imaging Spectroradiometer (MODIS) daily PW products from the Aqua and Terra satellites (at 1° × 1° spatial resolution) from 01/2000 to 02/2018 are compared and validated against all of NASA’s ground-sensing Aerosol Robotic NETwork (AERONET) V3 Level-2 PW daily averages from sites that have at least one year of observa- tions during 2000–2018 (452 sites representing 675,158 observations). Furthermore, sub-categorisation by Kö- ppen-Geiger climate regions enables climate specific validation to ascertain any distinct climatic influence. The results demonstrate significant climatological influences that impact the derived PW products. It is found that the Terra PW is more accurate than the Aqua PW, and that blending these two products yields a higher accuracy of daily PW estimates. The MODIS PW product also suffers from overestimation at larger magnitudes (>3 cm). The absolute errors do not reduce linearly with the PW magnitude, so that relative errors are far worse in areas of low PW, such as the polar climate. The equatorial climate, with the highest PW records, behaves best. Finally, a simple sensitivity test using the REST2 clear-sky radiation model shows that the global PW RMSE (0.511 cm) of the combined MODIS data would result in a 1.5-2.5% under- or overestimate on direct normal irradiance (DNI) de- pending on latitude relative to using the AERONET mean PW of 1.8971 cm. It is thus concluded that the daily MODIS PW product is not ideal for clear-sky radiation modelling, at least whenever accurate DNI predictions are necessary on a global scale.

  • 32.
    Bright, Jamie M.
    et al.
    Australian Natl Univ, Fenner Sch Environm & Soc, Canberra, ACT 2601, Australia.
    Killinger, Sven
    Australian Natl Univ, Fenner Sch Environm & Soc, Canberra, ACT 2601, Australia.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Australian Natl Univ, Fenner Sch Environm & Soc, Canberra, ACT 2601, Australia.
    Engerer, Nicholas A.
    Australian Natl Univ, Fenner Sch Environm & Soc, Canberra, ACT 2601, Australia.
    Improved satellite-derived PV power nowcasting using real-time power data from reference PV systems2018In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 168, p. 118-139Article in journal (Refereed)
    Abstract [en]

    Rapid growth in the global penetration of solar photovoltaic (PV) systems means electricity network operators and electricity generators alike are increasingly concerned with the short-term solar forecasting (nowcasting) of solar irradiance. This paper proposes a methodology that considers a varying number of available reference PV systems for supporting satellite-derived PV power real-time nowcasting. We evaluate conventional satellite-only and upscaling-only PV fleet estimate methodologies and compare them to two newly developed correction and hybrid cases. When using only a single reference PV system to estimate the aggregated power of 48 independent target PV systems for the location of Canberra, Australia; we show that the newly proposed correction or hybrid cases improve the performance of the satellite-derived PV power estimate medians in terms of MBE, rMBE, RMSE and rRMSE from 0.031 W/W-p, 7.46%, 0.079 W/W-p and 23.4%, down to 0.006 W/W-p,-0.711%, 0.068 W/W-p and 20.0%, representing relative improvements of 80.6%, 90.5%, 13.9% and 14.5%, respectively. Similarly, when using 30 reference PV systems, we report median improvements from 0.036 W/W-p, 8.25%, 0.083 W/W-p and 24.8%, down to 0.01 W/W-p, 1.41%, 0.049 W/W-p and 11.4%, representing relative improvements of 72.2%, 82.9%, 41.0% and 54.0%, respectively. We discuss the fundamental challenges facing the use of reference PV systems, satellite-derived power estimates, combining the two data sources, and the knowledge required to address these issues. We ultimately conclude that combining satellite-based PV power estimates with data from reference PV systems is always more beneficial than either on their own.

  • 33.
    Bright, Jamie M
    et al.
    Australian National University.
    Killinger, Sven
    Fraunhofer ISE, Freiburg (Germany).
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Engerer, Nicholas A
    Australian National University, Canberra (Australia).
    Integration of distributed solar forecasting with distribution network operations in Australia2017In: Proc. of the ISES Solar World Congress 2017, 2017Conference paper (Other academic)
    Abstract [en]

    Advances in solar integration technologies such as high-resolution solar forecasting and photovoltaic (PV) modelling are making it possible to remove some of the uncertainty facing electrical network operators and service providers with behind-the-meter (BtM) solar PV. However, a key challenge facing energy markets and networks is the integration ofthese technologies with their operations in a manner that is both useful and secure. The current lack of visibility of the aggregated power output from BtM solar PV within areas of the electrical distribution grid results in a dependency on reactive grid management; the future of effective management is to facilitate proactive strategies. Little published information is available on the usefulness ofsolar forecasting data at the distribution network level as well as best practice for the integration of such forecasts with their operations. This paper is intended to inform readers ofa large Australian Renewable Energy Agency (ARENA) fundedsolar forecasting research project at the Australian National University (ANU) in collaboration with new solar forecasting company Solcast. The overall aim is to offer distribution networks service providers (DNSPs) and other interested parties (e.g. researchers) with historic, real-time and forecasted BtM solar PV power outputs at multiple levels of the electricity grid infrastructure. To date, 11 of the 15 Australian DNSPs are partnered with the project and have started to use the solar forecasting information. Furthermore, at least one international inverter manufacturer has engaged in a partnership for real-time visibility of BtM solar PV systems. The first key take home message is that the project can deliver real-time solar estimates (currently at 30-min mean resolution) for anywhere around the world, along with a 7 day forecast; note that post-coded/substation specific information is only available where a DNSP has provided the relevant metadata. The second is that research collaborations are welcomed in order to work together to the overall goal of increasing the global penetration of solar PV in the world’s energy mix. The structure of this paper is as follows. The scene is set for BtM solar PV installations in Australia beforeintroducing the problems faced by DNSPs with regards to PV interaction with the electricity grid. A brief overview of the solar forecasting methodology is provided as well as the nature of the ARENA-funded ANU project collaboration with Solcast. The current status of the project is detailed before showing examples of the project in action. Lastly, the future outlook of the project is made stating the nature of contemporary and ambitious goals.

  • 34.
    Broström, Tor
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Arts, Department of Art History.
    Legnér, Mattias
    Gotland University, School of Culture, Energy and Environment. Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Arts, Department of Art History.
    Inneklimat i kyrkor förr och nu2014In: Från Gutabygd 2014, Visby: Gotlands Hembygdsförbunds förlag , 2014, p. 117-138Chapter in book (Other (popular science, discussion, etc.))
  • 35.
    Broström, Tor
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Arts, Department of Art History, Conservation.
    van Schijndel, Jos
    Building Physics and Services, Department of the Built Environment, Technische Universiteit Eindhoven, .
    Wessberg, Magnus
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Arts, Department of Art History, Conservation.
    Klenz Larsen, Poul
    National museum of Denmark, Copenhagen, Denmark..
    Energy efficient climate control in historic buildings2014In: Climate for culture: Built culturalheritage in times of climate change / [ed] Johanna Leissner, Urban Kaiser, Ralf Kilian, Leipzig: Fraunhofer MOEZ , 2014, p. 29-32Chapter in book (Other academic)
  • 36. Butros, Peter
    Simulations of Rotating Brushless AC Excitation System with Controlled Thyristor Bridge Rectifier for Hydropower Generators2011Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis aims to simulate and find out more about the electrical dynamics of a six-phase exciter for hydropower generators. Because ordinary electric circuit-based simulation software only simulate three-phase electrical systems, a FEM-based software is used for the electrical dynamics simulations of the six-phase system. The objective is to analyse the pulsation behaviour of the rectified electrical output on the six-phase system and compare it to the three-phase system. The three-phase system is also simulated with filters with the aim of decreasing the amplitude of the pulsations on the electrical output.

    It is expected that an upgraded system from a three-phase system to a six-phase system should double the pulsation frequency on the rectified electrical output. However, the result shows that the rectified electrical output of the six-phase system consists of pulsations with unexpected frequencies. The simulated RL-filter on the three-phase system shows only insignificantly small changes on the rectified electrical pulsation amplitude.

  • 37. Butros, Peter
    Simulations of Rotating Brushless AC Excitation System with Controlled Thyristor Bridge Rectifier for Hydropower Generators2011Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis aims to simulate and find out more about the electrical dynamics of asix-phase exciter for hydropower generators. Because ordinary electric circuit-basedsimulation software only simulate three-phase electrical systems, a FEM-basedsoftware is used for the electrical dynamics simulations of the six-phase system. Theobjective is to analyse the pulsation behaviour of the rectified electrical output on thesix-phase system and compare it to the three-phase system. The three-phase systemis also simulated with filters with the aim of decreasing the amplitude of the pulsationson the electrical output.It is expected that an upgraded system from a three-phase system to a six-phasesystem should double the pulsation frequency on the rectified electrical output.However, the result shows that the rectified electrical output of the six-phase systemconsists of pulsations with unexpected frequencies. The simulated RL-filter on thethree-phase system shows only insignificantly small changes on the rectified electricalpulsation amplitude.

  • 38.
    Bäckbro, Hannes
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A study of potential approaches to simulate power output as well as identifying anomalous operation of wind turbines2014Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    From an economical perspective, ice accretion on wind turbines located in cold climates can cause severe and costly production losses. To reduce the cost caused by such factors, it is important to early detect anomalous operation. This requires the knowledge of expected operation for all possible states of operation. The purpose of this M.Sc. thesis was first of all to investigate the feasibility to define a model able to simulate expected power output regardless time of the year. A second purpose was to investigate possible approaches for the identification of wind turbines deviating from expected operation. Regarding the first purpose, two different models were developed to investigate the possibility to simulate expected power output. A deterministic model based on the characteristic power curve and a non-deterministic regression tree model based on machine learning algorithms. As regards the second model, two control charts were implemented and their ability to identify abnormal operation was evaluated. The development and evaluation of the models as well as the control charts were performed in Matlab R2013b.

  • 39.
    Castellucci, Valeria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kamf, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Nearshore Tests of the Tidal Compensation System for Point-Absorbing Wave Energy Converters2015In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 8, no 4, p. 3272-3291Article in journal (Refereed)
    Abstract [en]

    The power production of the linear generator wave energy converter developed at Uppsala University is affected by variations of mean sea level. The reason is that these variations change the distance between the point absorber located on the surface and the linear generator located on the seabed. This shifts the average position of the translator with respect to the center of the stator, thereby reducing the generator output power. A device mounted on the point absorber that compensates for tides of small range by regulating the length of the connection line between the buoy at the surface and the linear generator has been constructed and tested. This paper describes the electro-mechanical, measurement, communication and control systems installed on the buoy and shows the results obtained before its connection to the generator. The adjustment of the line was achieved through a linear actuator, which shortens the line during low tides and vice versa. The motor that drives the mechanical device was activated remotely via SMS. The measurement system that was mounted on the buoy consisted of current and voltage sensors, accelerometers, strain gauges and inductive and laser sensors. The data collected were transferred via Internet to a Dropbox server. As described within the paper, after the calibration of the sensors, the buoy was assembled and tested in the waters of Lysekil harbor, a few kilometers from the Uppsala University research site. Moreover, the performance of the sensors, the motion of the mechanical device, the power consumption, the current control strategy and the communication system are discussed.

  • 40.
    Chatzigiannakou, Maria Angeliki
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ulvgård, Liselotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dolguntseva, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Offshore Deployments of Wave Energy Converters by Uppsala University2017In: Article in journal (Refereed)
  • 41.
    Christians, Gabriel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Prognostisering av Fjärrvärmebehov: -En jämförelse av fastigheter med olikastor varmvattenanvändning2017Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis aims to investigate the differences in diurnal and annual use of districtheating for two kind of heat users with different amount of warm water usage. Thefirst user is a hotel including spa facilities that uses a large amount of warm water, thesecond user is an office building that has a very low usage of warm water.The aim is to develop and validate methods for forecasting district heat use onvarious timescales. The average daily temperature for each month is shown to benormally distributed and average temperatures are therefore suitable for long-termforecasting. It is also shown that there is a clear linear relationship between lowerout-door temperature and higher use of district heating power. The thesis shows thatthe hotel will have a different power signature for their district heating compared tothe office that use a relative low amount of warm water.Short term forecasts, with a horizon of 10 days, are made for both the hotel andoffice building. As a result of the forecasts it is shown that the it is easier todetermine when the peak district heating power outtake will occur for the buildingwith a high amount of domestic hot water usage. However, forecasts for total diurnalheat use are equally accurate for the investigated buildings

  • 42.
    Claesson, Emma
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Analys av sorptiv kylning i industri- och kontorsbyggnader2013Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Energy efficiency is important both to reduce costs and to reduce greenhouse gas emissions in the atmosphere. Reducing costs will also help maintain business competitiveness.

    Scania in Södertälje is a company where the optimization of energy use is an ongoing and continual process. One area with potential to make energy and cost savings is the effectiveness of the ventilation systems in offices and industrial premises at Scania. During the summer months an increased demand for cooling occurs, leading to increased ventilation and a peak in district cooling system usage. Sorptive cooling is a technology where the supplied air is cooled by applying external heat. This technique involves a reduction in electricity consumption compared to electrically-powered cooling machines and does not affect the district cooling system usage. It was therefore of interest to investigate if sorptive cooling would be an energy efficient and viable solution for Scania in the future.

    This investigation shows that sorptive cooling requires more power than a conventional ventilation system. Despite the fact that Scania has access to free heat during the summer months, the study shows that sorptive cooling would not be economically viable to install in the industrial premises, where no cooling systems currently exist. However, compared to an electrically-powered cooling machine, sorptive cooling is anyway more energy efficient. The conclusion is that sorptive cooling is a viable solution for the offices, but not for the industrial premises at Scania in Södertälje

  • 43.
    Constanda, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Control Rod Effect at Partial SCRAM: Upgrade of Plant Model for Forsmark 2 in BISON After Power Uprate2015Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This study aims to improve the modeling of partial SCRAM in the BISON plant model for the Forsmark 2 nuclear reactor after power uprate. Validation of the BISON model against tests performed from March to May in 2013 have shown that this is one of the areas in which there is room for improvement. After partial SCRAM is performed, the model underestimates the reactor power, recirculation flow and steam flow when compared to the measurement data.

    In BISON the partial SCRAM is modeled using a relative control rod effect vector (ASC vector). The aim is to replace the old values in this vector to improve the model. The new model was shown to give an improved result for the reactor power, recirculation flow and steam flow. The study gives recommendations on how to apply the new model and what values of the relative control rod effect vector that can be used in the future.

  • 44.
    da Silva Soares, José Pedro
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    WIND ENERGY UTILIZATION IN ARCTIC CLIMATE – RACMO 2.3 GREENLAND CLIMATE RUNS PROJECT2016Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The potential for wind power development in Greenland is evaluated based on the analysis of 58 years of data (1957-2015) from RACMO 2.3 (Regional Atmospheric Climate Model). In order to create a wind power development tool, mesoscale maps based on RACMO 2.3 model were created containing the following characteristics: mean wind speeds (at 10 m), averaged maximum wind speed (with and without gusts at 10 m), temperature, humidity, geopotential, ice sheet mask and land sheet mask. A relevant aspect for this thesis is the mean wind speed. Over Greenland, the lower mean wind speeds range from 2-3 m/s on the tundra areas near the coast. This is influenced by high temperature inversion over the arctic tundra which disintegrates the predominant katabatic flow leading to lower wind speeds. On the other hand, the highest mean wind speeds range from 6 to 10 m/s and are observed in the northeastern region, due to cyclonic activity over the Greenland Sea. Maps of both the mean wind speed and averaged maximum wind speed are combined in order to achieve the highest mean wind speed value while at the same time avoiding maximum wind speeds higher than the cut-off value of the selected turbine model. This map combination is synchronized with pre-determined construction constraints, resulting in the suggestion of three different sites (sites 4, 5 and 6) as potential targets for wind power development. Multi-level data is sorted for different heights (10, 35, 70, 100 and 120 m) to perform a micro-scale analysis exercise for the three different site suggestions. A Vestas V90 3MW with an 80 meter hub height is selected as the standard turbine model to be deployed at the three recommended positions and for use in further simulations using WindSim. Annual Energy Production (AEP) for these three turbines in the recommended locations is calculated based on the interpolation from the climatology data at 70 m which is closest to the turbines’ hub heights. The AEP results are compared and show that site suggestion 4 presents the best potential for wind power development, surpassing by 79% and 23% the production results from sites 5 and 6, respectively. Based on the study developed, it is concluded that the in terms of wind resource assessment the potential for wind power development in Greenland exists. However the selection of possible deployment sites should be carefully done and real measurements must be performed.

  • 45. Dahlbäck, Niklas
    et al.
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Examples of Benefits from Efficiency Evaluation Using Comparative Tests2014In: 10th International Conference on Hydraulic Efficiency Measurements 2014-09-16 - 19, Itajubá, Brazil, 2014Conference paper (Refereed)
    Abstract [en]

    Traditionally, most field efficiency measurements are made to verify guarantees for a new project, which have led to that this issue is well covered by standardization guidelines. There are however several other situations where information from field efficiency measurements contributes with value. Depending on issue and site characteristics, there are several feasible options, that are not described in current standards of primary methods.

    A comparative test is here defined as a test where efficiency is evaluated at the same flow conditions but with modified or changed turbine or water conduits. At an efficiency evaluation of a comparative test, many systematic uncertainties will cancel, and the overall evaluation of uncertainty will be at a very useful level. 

    This paper presents experiences of the hydropower producer Vattenfall, from several efficiency tests, where different types of comparative tests settings have been used.

  • 46.
    Davidsson, Simon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Natural Resources and Sustainable Development.
    Höök, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Natural Resources and Sustainable Development.
    Material requirements and availability for multi-terawatt deployment of photovoltaics2017In: Energy Policy, ISSN 0301-4215, E-ISSN 1873-6777, Vol. 108, p. 574-582Article in journal (Refereed)
    Abstract [en]

    This study investigates growth rates and material flows required to reach and sustain multi-terawatt installed capacity of photovoltaics (PV). The dynamics of material flows over time are captured, taking account for the life expectancy of PV technology. Requirements of solar grade silicon and silver for crystalline silicon (c-Si) technology, as well as indium, gallium, selenium, tellurium, and cadmium for currently commercial thin film (TF) technology are explored, accounting for different technology choices and potential improvements in material intensities. Future availability of these materials from primary resources, as well as secondary resources from end-of-life recycling, is also analyzed. Rapid deployment of c-Si technologies would require a major expansion of solar grade silicon production, and significant quantities of silver. Availability of materials such as indium and tellurium could become problematic for major implementation of TF technology, unless production can be scaled up significantly, or material intensities radically decreased. Availability of secondary resources from end-of-life recycling have little impact on material availability during the growth phase, but could be important for sustaining a low-carbon energy system over longer time perspectives. Material availability could cause problems for rapid PV growth, but does not necessarily limit total PV deployment, especially if material intensities are decreased.

  • 47.
    Deglaire, Paul
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engblom, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Ågren, Olov
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Analytical solutions for a single blade in vertical axis turbine motion in two dimensions2009In: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 28, p. 506-520Article in journal (Refereed)
  • 48.
    Dehghan, Babak
    et al.
    Istanbul Technical University, Energy Institute.
    Sisman, Altug
    Istanbul Technical University, Energy Institute.
    Aydin, Murat
    Istanbul Technical University, Energy Institute.
    Parametric investigation of helical ground heat exchangers for heat pump applications2016In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 127, p. 999-1007Article in journal (Refereed)
    Abstract [en]

    The installation cost and performance of ground source heat pump (GSHP) systems can greatly be affectedby application parameters of ground heat exchangers (GHEs). These parameters affecting the helical GHE’sperformance are their spacing, major diameter and pitch length. In large scale GSHP applications, morethan one GHE is needed. Therefore determining the distance between GHEs (spacing) becomes as animportant issue. In this work, the effect of distance between vertical helical GHEs on the heat transferrate (HTR) is studied. Performance of helical GHE is determined for different spacing and the properdistance is examined. Furthermore, the influences of the pitch length (Lp) as well as major diameter (D)of GHE on HTR value are numerically studied in COMSOL environment. The available experimental dataare used to validate the numerical results. Computational results show that they are in good agreementwith the experimental one. The proper distance between GHEs is suggested as 7 m and more. Furthermorethe results of the simulations prove that 100% changes in Lpand D can affect the performance of GHE onlyin order of 10% although the excavation cost increase more than 10%. The results provide useful guidancefor optimum design of vertical helical GHE for GSHP systems.

  • 49.
    Dyachuk, Eduard
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Simulating Pitching Blade With Free Vortex Model Coupled With Dynamic Stall Model for Conditions of Straight Bladed Vertical Axis Turbines2015In: Journal of solar energy engineering, ISSN 0199-6231, E-ISSN 1528-8986, Vol. 137, no 4, article id 041008Article in journal (Refereed)
    Abstract [en]

    This study is on the straight bladed vertical axis turbines (VATs), which can be utilized for both wind and marine current energy. VATs have the potential of lower installation and maintenance cost. However, complex unsteady fluid mechanics of these turbines imposes significant challenges to the simulation tools. Dynamic stall is one of the phenomena associated with the unsteady conditions, and it is in the focus of the study. The dynamic stall effects are very important for VATs, since they are usually passively controlled through the dynamic stall. A free vortex model is used to calculated unsteady attached flow, while the separated flow is handled by the dynamic stall model. This is compared to the model based solely on the Leishman-Beddoes algorithm. The results are assessed against the measured data on pitching airfoils. A comparison of force coefficients between the simulations and experiments is done at the conditions similar to the conditions of H-rotor type VATs.

  • 50.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    A concentrated effort2019In: NATURE ENERGY, ISSN 2058-7546, Vol. 4, no 5, p. 354-355Article in journal (Other academic)
    Abstract [en]

    While recent gains in the efficiency of photoelectrochemical devices for hydrogen production are encouraging, high efficiency is rarely combined with high power output, which is important for large-scale viability. Towards this goal, researchers now demonstrate a promising thermally integrated device driven by concentrated solar irradiation.

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