Дисертації: "CONVERSION OF ENERGY"

1

Lundin, Staffan. "Marine Current Energy Conversion." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-280763.

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Marine currents, i.e. water currents in oceans and rivers, constitute a large renewable energy resource. This thesis presents research done on the subject of marine current energy conversion in a broad sense. A review of the tidal energy resource in Norway is presented, with the conclusion that tidal currents ought to be an interesting option for Norway in terms of renewable energy. The design of marine current energy conversion devices is studied. It is argued that turbine and generator cannot be seen as separate entities but must be designed and optimised as a unit for a given conversion site. The influence of support structure for the turbine blades on the efficiency of the turbine is studied, leading to the conclusion that it may be better to optimise a turbine for a lower flow speed than the maximum speed at the site. The construction and development of a marine current energy experimental station in the River Dalälven at Söderfors is reported. Measurements of the turbine's power coefficient indicate that it is possible to build efficient turbines for low flow speeds. Experiments at the site are used for investigations into different load control methods and for validation of a numerical model of the energy conversion system and the model's ability to predict system behaviour in response to step changes in operational tip speed ratio. A method for wake measurements is evaluated and found to be useful within certain limits. Simple models for turbine runaway behaviour are derived, of which one is shown by comparison with experimental results to predict the behaviour well.

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2

Silva, Ubiravan Geraldo de Oliveira e. [UNESP]. "Análise energética em refino de petróleo." Universidade Estadual Paulista (UNESP), 2010. http://hdl.handle.net/11449/99282.

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Made available in DSpace on 2014-06-11T19:29:53Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-07-29Bitstream added on 2014-06-13T20:00:00Z : No. of bitstreams: 1 silva_ugo_me_guara.pdf: 1310169 bytes, checksum: 03b83347690591e428c0b581f7931124 (MD5)
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
No trabalho apresentado foi realizada uma análise de eficiência energética levando em conta variáveis tais como a pressão, a temperatura, o estado físico dos componentes e a atividade de cada elemento que compõe a unidade de craqueamento em refino de petróleo. Tal análise foi realizada baseando-se na Primeira e Segunda leis da Termodinâmica. Destacou-se na análise do FCC a geração e a perda de energia com os gases, levando em conta a concentração molar de cada gás na entrada e na saída do FCC. No riser foram levadas em conta as transformações ocorridas e sua cinética com o propósito de fazer uma análise de gasto de energia no processo de formação inicial dos produtos do FCC; com isso, determinaram-se as quantidades de calor que foram utilizados no processo principal de formação. Foram realizadas análises sobre os fluxos de massas no vaso separador com a abordagem de um suposto fluxo interno, que seria a diferença entre as energias adquiridas com o vapor de retificação com os fluxos de carbono arrastados e com energia vinda do riser, e o fluxo de saída também para o processo de retificação no stripper. Verificou-se a energia gerada pelo regenerador e sua distribuição, que é feita com o aquecimento do catalisador na linha de transmissão do stripper e das perdas de energia com a troca do catalisador gasto e pela massa de catalisador que entra no riser. A energia perdida durante o processo foi associada à energia perdida na integralidade e em cada unidade. Verificou-se que uma parcela do calor gerado no processo é absorvida por gases inertes necessários ou integrados a gases reagentes; além disso, observou-se a formação de novos gases e compostos químicos que geram certas quantidades de energia, e que estão e são importantes na contabilização de toda energia que é gerada. Em tal análise levou-se em conta a energia de formação dos gases e a...
In the present study it was performed an analysis of energy efficiency taking into account variables such as pressure, temperature, physical state of the components and activities of each element that makes up a cracker in petroleum refining. The First and Second Law of Thermodynamics were used for the present analysis. It was highlighted in the analysis of the FCC the generation and loss of energy with the gases, taking into account the molar concentration of each gas at the inlet and outlet of the FCC. In the riser it was taken into account the transformations and their kinetics in order to make an analysis of energy use in the process of initial formation of the products of the FCC; with these results, it was determined the amounts of heat that were used in the main proceedings training. It was analyzed the flow of masses in the separator vessel with the approach of a supposed internal flow, which would be the difference between the energy gained steam with the rectification of carbon fluxes and dragged with energy coming from the riser, and the outflow also for the grinding process in stripper. There was the energy generated by the regenerator and its distribution, which is made by heating the catalyst in the transmission line striper and loss of energy with the exchange of spent catalyst and the mass of catalyst entering the riser. The energy lost during the process was associated with the energy that disappeared in the whole and in each unit. It was found that a portion of the heat generated is absorbed by inert gases necessary or integrated reactive gases; in addition, it was observed the formation of new gases and chemicals that generate amounts of energy, and are important in accounting for all energy that is generated. In this analysis it was taken into account the energy of formation of exhaust gases and the opportunities of products formation in the conditions ... (Complete abstract click electronic access below)

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3

Thorburn, Karin. "Electric Energy Conversion Systems : Wave Energy and Hydropower." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7081.

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4

Balouchi, Farouk. "Footfall energy harvesting : footfall energy harvesting conversion mechanisms." Thesis, University of Hull, 2013. http://hydra.hull.ac.uk/resources/hull:8433.

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Ubiquitous computing and pervasive networks are prevailing to impact almost every part of our daily lives. Convergence of technologies has allowed electronic devices to become untethered. Cutting of the power-cord and communications link has provided many benefits, mobility and convenience being the most advantageous, however, an important but lagging technology in this vision is the power source. The trend in power density of batteries has not tracked the advancements in electronic systems development. This has provided opportunity for a bridging technology which uses a more integrated approach with the power source to emerge, where a device has an onboard self sustaining energy supply. This approach promises to close the gap between the increased miniaturisation of electronics systems and the physically constrained battery technology by tapping into the ambient energy available in the surrounding location of an application. Energy harvesting allows some of the costly maintenance and environmentally damaging issues of battery powered systems to be reduced. This work considers the characteristics and energy requirements of wireless sensor and actuator networks. It outlines a range of sources from which the energy can be extracted and then considers the conversion methods which could be employed in such schemes. This research looks at the methods and techniques for harvesting/scavenging energy from ambient sources, in particular from the motion of human traffic on raised flooring and stairwells for the purpose of powering wireless sensor and actuator networks. Mechanisms for the conversion of mechanical energy to electrical energy are evaluated for their benefits in footfall harvesting, from which, two conversion mechanisms are chosen for prototyping. The thesis presents two stair-mounted generator designs. Conversion that extends the intermittent pulses of energy in footfall is shown to be the beneficial. A flyback generator is designed which converts the linear motion of footfall to rotational torque is presented. Secondly, a cantilever design which converts the linear motion to vibration is shown. Both designs are mathematically modelled and the behaviour validated with experimental results & analysis. Power, energy and efficiency characteristics for both mechanisms are compared. Cost of manufacture and reliability are also discussed.

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5

Zhao, Yixin. "Developing Nanomaterials for Energy Conversion." Cleveland, Ohio : Case Western Reserve University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1270172686.

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6

Laestander, Joakim, and Simon Laestander. "OTEC - Ocean Thermal Energy Conversion." Thesis, KTH, Energiteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-98974.

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OTEC is a technology where power is produced by utilizing the temperature difference in the oceans between surface water and water from the deep. It is considered that a temperature difference of 20K is required – a temperature difference found close to the equator.This report investigates if OTEC can produce enough electricity to provide 100 000 people, living on a generic island of 10 km2 somewhere alongside the equator in the pacific ocean, with their electricity needs. In this project a literature review has been made to establish a basic knowledge of OTEC and later a mathematical model has been programmed and simulated. Finally the results of the simulation has been examined and discussed.Two different cycles has been simulated alongside each other with the goal to establish which one of these two cycles that were best suited the island. To facilitate computing some assumptions and simplifications were made.The closed cycle (CC) was the most effective but the open cycle (OC) had several positive synergies that the closed cycle didn’t have. The costs of a facility of both cycles were based on older studies in the field and the conclusion was that the open cycle was the cheaper one. Facilities of both cycles can effectively meet the islands energy needs but if OC is chosen before CC more facilities has to be built due to the OC has lower energy output.Further work and development is necessary before OTEC seriously can challenge todays fossil fuel based energy systems, or until the oil starts to get too expensive. Today OTEC technology demands large investments but if the positive environmental effects and the fact that the island releases itself from import of energy are taken into account there are incentives to invest in OTEC already.
OTEC är en teknik där kraft utvinns från havsvatten genom att utnyttja temperaturdifferensen mellan ytvatten och vatten från djupet. Denna teknik kräver dock generellt en temperaturdifferens på minst 20K. En sådan temperaturskillnad är geografiskt begränsad till den tropiska zonen runt ekvatorn.I rapporten undersöks om OTEC kan användas till att förse 100 000 människor, boende på en 10 stor generisk ö i just den tropiska zonen, med dess elbehov. I detta projekt har det gjorts en litteraturstudie för att etablera en kunskapsbas och sedan gjorts en matematisk modell i programmet EES och slutligen har resultaten från modellen granskats och diskuterats. I modellen jämfördes två olika cykler och målet var att bestämma vilken av dessa som var det bästa alternativet för ön. För att underlätta beräkningarna gjordes vissa antaganden och förenklingar.Den slutna cykeln var mest effektiv men den öppna cykeln (OC) hade positiva synergieffekter som den sluta cykeln (CC) saknade. Kostnaden för en anläggning baserades på äldre studier och enligt dessa var den öppna cykeln billigare än den slutna. Anläggningar av de båda cyklerna kan tillgodose den fiktiva öns energibehov, det behöver dock byggas fler anläggningar om OC väljs framför CC.Det kommer krävas ytterligare arbete med att utveckla tekniken innan OTEC på allvar kan utmana dagens fossilbränslebaserade energisystem – eller att oljan helt enkelt blir för dyr. Idag är OTEC för dyrt för att kunna motiveras rent ekonomiskt, men om även miljövinsterna beaktas, samt att ön befriar sig från importer och därigenom får större kontroll över sitt eget energisystem, finns goda incitament att investera i OTEC redan idag.

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7

Chin, Timothy Edward. "Electrochemical to mechanical energy conversion." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/63015.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Electrode materials for rechargeable lithium ion batteries are well-known to undergo significant dimensional changes during lithium-ion insertion and extraction. In the battery community, this has often been looked upon negatively as a degradation mechanism. However, the crystallographic strains are large enough to warrant investigation for use as actuators. Lithium battery electrode materials lend themselves to two separate types of actuators. On one hand, intercalation oxides and graphite provide moderate strains, on the order of a few percent, with moderate bandwidth (frequency). Lithium intercalation of graphite can achieve actuation energy densities of 6700 kJ m-3 with strains up to 6.7%. Intercalation oxides provide strains on the order of a couple percent, but allow for increased bandwidth. Using a conventional stacked electrode design, a cell consisting of lithium iron phosphate (LiFePO4) and carbon achieved 1.2% strain with a mechanical power output of 1000 W m 3 . Metals, on the other hand, provide colossal strains (hundreds of percent) upon lithium alloying, but do not cycle well. Instead, a self-amplifying device was designed to provide continuous, prolonged, one-way actuation over longer time scales. This was still able to achieve an energy density of 1700 kJ n 3, significantly greater than other actuation technologies such as shape-memory alloys and conducting polymers, with displacements approaching 10 mm from a 1 mm thick disc. Further, by using lithium metal as the counterelectrode in an electrochemical couple, these actuation devices can be selfpowered: mechanical energy and electrical energy can be extracted simultaneously.
by Timothy Edward Chin.
Ph.D.

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8

Clark, Joanna Helen. "Inorganic materials for energy conversion." Thesis, University of Liverpool, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.569768.

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In an effort to design systems that harvest solar light and convert this into chemical energy, the primary aim of the work presented in this thesis was to develop complex metal oxide materials that were active photocatalysts under visible light. The existing methods for visible light incorporation into photocatalytically active materials are reviewed. Of these, metal to metal charge transfer (MMCT) between bimetallic surface- grafted assemblies was taken as particular inspiration. It was hypothesised that MMCT between metal centres within a bulk complex metal oxide could be similarly applied to yield photocatalytic ally active charge carriers. This approach takes advantage of the stability of bulk systems and the ability to tune the compositions of complex oxide materials. Moreover, it was proposed that MMCT between metal centres located on crystallographically distinct sites of a bulk material would aid charge separation and migration throughout the extended lattice. The optical properties of the RE2 Ti207 (RE = Y, La, Ce, Pr) and Ba2XTizM3015 (X = La, Ce, Pr, Nd, Bi; M = Nb, Ta) series, which include some novel cerium(III) titanates, revealed systematic changes in the electronic structures of these materials. These were rationalised with respect to the energy of Ln 4f states. The proposed electronic structures present the partial achievement of the bulk MMCT hypothesis, with optical transitions from occupied Ce 4f midgap states to the unoccupied primarily Ti 3d conduction band. These Ce3+ /rr" charge transfer materials were inactive photocatalysts, attributed to the presence the Ce 4f-based midgap states that facilitate charge recombination. The double perovskite CaCu3T40IZ, with A-site Cu2+ and B-site Ti4+ cations and whose dielectric properties have been studied extensively in the past, is an ideal candidate for the two site MMCT strategy. Here, the optical and photocatalytic properties, rationalised with the aid of DFT calculations, present the partial achievement of the bulk MMCT hypothesis. Sol-gel derived Pt-CaCu3 Ti4012 is an active photocatalyst toward the visible light photo-oxidation of model pollutants methyl orange (MO) and 4-chlorophenol (4CP). Optical spectra and product analysis show that these reactions proceed via more selective routes than the typical reaction over TiOz P25 under DV light. Interestingly, the products of 4CP photo-oxidation were shown to be dependent on the wavelength of incident light. Cu-doping of BizTiz07 was found to stabilise the pyrochlore structure with respect to the Aurivillius phase Bi4 Ti3012 and to impart significant visible light absorption. Sol-gel derived Pt-BiI.6Cuo.4 Tiz07 photo-oxidised MO under visible light via conventional band gap excitation, as determined by quantum efficiency measurements. In contrast, sol-gel derived Pt-B4 Ti3012 photo-oxidised MO via the excitation of adsorbed MO, and was also active toward 4CP photo-oxidation under visible light. The excitation method, mechanisms and product distributions have been investigated for each of the photo-oxidation reactions presented in this thesis. In particular, the photo- oxidation of MO over some Pt-modified metal oxides has been shown to proceed via excitation of adsorbed MO and not of the semiconductor. Additionally, the mechanism and products of these processes are far more selective than the related DV reactions over TiOz P25, and have been shown to depend to some extent on the semiconductor support.

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9

Qiu, Xiaofeng. "NANOSTRUCTURED MATERIALS FOR ENERGY CONVERSION." Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1207243913.

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10

Riboni, F. "PHOTOCATALYTIC REACTIONS FOR ENERGY CONVERSION." Doctoral thesis, Università degli Studi di Milano, 2014. http://hdl.handle.net/2434/244319.

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General upward trends in fossil fuel consumption and CO2 emissions, along with the accepted belief that global chemistry substantially influences climate, require that scientific research provides efficient remedies and/or alternatives to the present scenario. Photocatalysis is often proposed as one of the most promising technique to achieve these purposes. This PhD thesis is mainly focused on the investigation of TiO2-based systems for the photocatalytic oxidation of formic acid in aqueous suspension, as well as for H2 production by methanol photo steam reforming in the gas phase. Two different approaches were adopted to minimize the drawbacks usually characterizing TiO2 photocatalysts: i) TiO2-WO3 mixed oxide photocatalysts were prepared with the aim of reducing the recombination rate of photopromoted electron/hole pairs. The superior photocatalytic performance of the mixed oxide system was mainly attributed to the positive effect induced by W in efficiently trapping the photopromoted electron from the conduction band of TiO2, ensuring extended charge carriers separation. Even better results were obtained upon the surface modification with Pt nanoparticles which, by virtue of the metal high work function, further enhanced e-/h+ separation. ii) surface modification of TiO2 with Au nanoparticles, possessing a Localized Surface Plasmon Resonance (LSPR) at λ = 530 nm was proved to be an efficient way to promote TiO2 photoactivity under visible light irradiation. By selecting three titania samples (i.e., a stoichiometric, nearly non defective TiO2, a N-doped TiO2 and a oxygen vacancy-rich TiO2), evidence of two different plasmonic photoactivity mechanisms was provided, with the so-called hot electron transfer promoting plasmonic photoactivity in the stoichiometric TiO2 and Plasmon Resonance Energy Transfer accounting for the observed plasmonic visible light photoactivity of doped samples. Being the abatement of CO2 through (photo)electrochemical reduction very challenging (E0(CO2/CO2-* = -2.14 V)), an alternative way has been studied: pyridinyl radicals (1-PyH*), photogenerated by irradiating a pyridine (Py) solution, were found to efficiently react with CO2 yielding a carbamic species (HPy-1-COOH), triggered by a stepwise mechanism where electron transfer from 1-PyH* precedes proton transfer. Formate (HCOO-) was also obtained, demonstrating that photoexcited pyridine does catalyze the 2e—reduction of CO2. Finally, Fenton oxidation of gaseous isoprene on the surface of aqueous Fe2+ droplets, yielding carboxylic acids, polyols and carbonyl compounds, detected in situ through ElectroSpray Ionization Mass Spectrometry, accounted for alternative routes for the conversion of organic gases into secondary organic aerosol, occurring under tropospheric conditions, and may be incorporated into present atmospheric chemistry models.

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11

Chandrasekaran, Rajeswari. "Modeling of electrochemical energy storage and energy conversion devices." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37292.

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With increasing interest in energy storage and conversion devices for automobile applications, the necessity to understand and predict life behavior of rechargeable batteries, PEM fuel cells and super capacitors is paramount. These electrochemical devices are most beneficial when used in hybrid configurations rather than as individual components because no single device can meet both range and power requirements to effectively replace internal combustion engines for automobile applications. A system model helps us to understand the interactions between components and enables us to determine the response of the system as a whole. However, system models that are available predict just the performance and neglect degradation. In the first part of the thesis, a framework is provided to account for the durability phenomena that are prevalent in fuel cells and batteries in a hybrid system. Toward this end, the methodology for development of surrogate models is provided, and Pt catalyst dissolution in PEMFCs is used as an example to demonstrate the approach. Surrogate models are more easily integrated into higher level system models than the detailed physics-based models. As an illustration, the effects of changes in control strategies and power management approaches in mitigating platinum instability in fuel cells are reported. A system model that includes a fuel cell stack, a storage battery, power-sharing algorithm, and dc/dc converter has been developed; and preliminary results have been presented. These results show that platinum stability can be improved with only a small impact on system efficiency. Thus, this research will elucidate the importance of degradation issues in system design and optimization as opposed to just initial performance metrics. In the second part of the thesis, modeling of silicon negative electrodes for lithium ion batteries is done at both particle level and cell level. The dependence of the open-circuit potential curve on the state of charge in lithium insertion electrodes is usually measured at equilibrium conditions. Firstly, for modeling of lithium-silicon electrodes at room temperature, the use of a pseudo-thermodynamic potential vs. composition curve based on metastable amorphous phase transitions with path dependence is proposed. Volume changes during lithium insertion/de-insertion in single silicon electrode particle under potentiodynamic control are modeled and compared with experimental data to provide justification for the same. This work stresses the need for experiments for accurate determination of transfer coefficients and the exchange current density before reasoning kinetic hysteresis for the potential gap in Li-Si system. The silicon electrode particle model enables one to analyze the influence of diffusion in the solid phase, particle size, and kinetic parameters without interference from other components in a practical porous electrode. Concentration profiles within the silicon electrode particle under galvanostatic control are investigated. Sluggish kinetics is established from cyclic voltammograms at different scan rates. Need for accurate determination of exchange current density for lithium insertion in silicon nanoparticles is discussed. This model and knowledge thereof can be used in cell-sandwich model for the design of practical lithium ion cells with composite silicon negative electrodes. Secondly, galvanostatic charge and discharge of a silicon composite electrode/separator/ lithium foil is modeled using porous electrode theory and concentrated solution theory. Porosity changes arising due to large volume changes in the silicon electrode with lithium insertion and de-insertion are included and analyzed. The concept of reservoir is introduced for lithium ion cells to accommodate the displaced electrolyte. Influence of initial porosity and thickness of the electrode on utilization at different rates is quantitatively discussed. Knowledge from these studies will guide design of better silicon negative electrodes to be used in dual lithium insertion cells for practical applications.

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12

Silva, Ubiravan Geraldo de Oliveira e. "Análise energética em refino de petróleo /." Guaratinguetá : [s.n.], 2010. http://hdl.handle.net/11449/99282.

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Resumo: No trabalho apresentado foi realizada uma análise de eficiência energética levando em conta variáveis tais como a pressão, a temperatura, o estado físico dos componentes e a atividade de cada elemento que compõe a unidade de craqueamento em refino de petróleo. Tal análise foi realizada baseando-se na Primeira e Segunda leis da Termodinâmica. Destacou-se na análise do FCC a geração e a perda de energia com os gases, levando em conta a concentração molar de cada gás na entrada e na saída do FCC. No riser foram levadas em conta as transformações ocorridas e sua cinética com o propósito de fazer uma análise de gasto de energia no processo de formação inicial dos produtos do FCC; com isso, determinaram-se as quantidades de calor que foram utilizados no processo principal de formação. Foram realizadas análises sobre os fluxos de massas no vaso separador com a abordagem de um suposto fluxo interno, que seria a diferença entre as energias adquiridas com o vapor de retificação com os fluxos de carbono arrastados e com energia vinda do riser, e o fluxo de saída também para o processo de retificação no stripper. Verificou-se a energia gerada pelo regenerador e sua distribuição, que é feita com o aquecimento do catalisador na linha de transmissão do stripper e das perdas de energia com a troca do catalisador gasto e pela massa de catalisador que entra no riser. A energia perdida durante o processo foi associada à energia perdida na integralidade e em cada unidade. Verificou-se que uma parcela do calor gerado no processo é absorvida por gases inertes necessários ou integrados a gases reagentes; além disso, observou-se a formação de novos gases e compostos químicos que geram certas quantidades de energia, e que estão e são importantes na contabilização de toda energia que é gerada. Em tal análise levou-se em conta a energia de formação dos gases e a ... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: In the present study it was performed an analysis of energy efficiency taking into account variables such as pressure, temperature, physical state of the components and activities of each element that makes up a cracker in petroleum refining. The First and Second Law of Thermodynamics were used for the present analysis. It was highlighted in the analysis of the FCC the generation and loss of energy with the gases, taking into account the molar concentration of each gas at the inlet and outlet of the FCC. In the riser it was taken into account the transformations and their kinetics in order to make an analysis of energy use in the process of initial formation of the products of the FCC; with these results, it was determined the amounts of heat that were used in the main proceedings training. It was analyzed the flow of masses in the separator vessel with the approach of a supposed internal flow, which would be the difference between the energy gained steam with the rectification of carbon fluxes and dragged with energy coming from the riser, and the outflow also for the grinding process in stripper. There was the energy generated by the regenerator and its distribution, which is made by heating the catalyst in the transmission line striper and loss of energy with the exchange of spent catalyst and the mass of catalyst entering the riser. The energy lost during the process was associated with the energy that disappeared in the whole and in each unit. It was found that a portion of the heat generated is absorbed by inert gases necessary or integrated reactive gases; in addition, it was observed the formation of new gases and chemicals that generate amounts of energy, and are important in accounting for all energy that is generated. In this analysis it was taken into account the energy of formation of exhaust gases and the opportunities of products formation in the conditions ... (Complete abstract click electronic access below)
Orientador: José Antonio Perrella Balestieri
Coorientador: Rubens Alves Dias
Banca: Luiz Roberto Carrocci
Banca: Luciano Fernando dos Santos Rossi
Mestre

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13

Ahmed, Shehab. "Compact harsh environment energy conversion systems." [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1289.

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14

Boström, Cecilia. "Electrical Systems for Wave Energy Conversion." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-140116.

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Wave energy is a renewable energy source with a large potential to contribute to the world's electricity production. There exist several technologies on how to convert the energy in the ocean waves into electric energy. The wave energy converter (WEC) presented in this thesis is based on a linear synchronous generator. The generator is placed on the seabed and driven by a point absorbing buoy on the ocean surface. Instead of having one large unit, several smaller units are interconnected to increase the total installed power. To convert and interconnect the power from the generators, marine substations are used. The marine substations are placed on the seabed and convert the fluctuating AC from the generators into an AC suitable for grid connection. The work presented in the thesis focuses on the first steps in the electric energy conversion, converting the voltage out from the generators into DC, which have an impact on the WEC's ability to absorb and produce power. The purpose has been to investigate how the generator will operate when it is subjected to different load cases and to obtain guidelines on how future systems could be improved. Offshore experiments and simulations have been done on full scale generators connected to four different loads, i.e. one linear resistive load and three different non-linear loads representing different cases for grid connected WECs. The results show that the power can be controlled and optimized by choosing a suitable system for the WEC. It is not obvious which kind of system is the most preferable, since there are many different parameters that have an impact on the system performance, such as the size of the buoy, how the generator is designed, the number of WECs, the highest allowed complexity of the system, costs and so on. Therefore, the design of the electrical system should preferably be carried out in parallel with the design of the WEC in order to achieve an efficient system.

Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 727

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15

Giddings, S. L. "Heterogeneous reactions in solar energy conversion." Thesis, Swansea University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637056.

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Photochemical systems for the splitting of water into hydrogen and oxygen represent an attractive route for the conversion of solar energy into a chemical fuel. However, the success of such systems depends on the identification of suitable redox catalysts for the oxidation and reduction processes. While colloidal platinum has proved to be an efficient catalyst for the reduction of water, the development of stable and effective catalysts for water oxidation has been less successful. The work described in this thesis involves the study of ruthenium dioxide hydrate (RuO₂.xH₂)O as a heterogeneous catalyst for the oxidation of water to oxygen. Although this material has already been widely used as an oxygen catalyst, there have been many doubts as to its ability to act in this capacity. In Chapter Three an attempt is made to resolve this controversy via an investigation of the stability and catalytic activity of RuO₂.xH₂O when exposed to various oxidising agents. The results indicate that the catalytic activity and corrosion stability of an RuO₂.xH₂O sample is related to its degree of hydration. In Chapter Four an investigation is described into the effect of heat-treatment of RuO₂.xH₂O at different temperatures on its physical and chemical properties. From these results it appears that any sample of RuO₂xH₂O may be transformed into a stable, reproducible oxygen catalyst by simply heat-treating it at 140-150^oC in air for ca. 5 hours. The latter conditions represent an optimum for catalytic activity where anodic corrosion is absent. This 'thermally-activated' RuO₂.xH₂O is shown to compare favourably with alternative oxygen catalysts. Chapters Five and Six involve a kinetic study of the RuO₂.xH₂O-catalysed oxidation of water by Ce(IV) ions in an attempt to elucidate the mechanism of catalysis of the oxide powder. The study is based on an electrochemical model in which the RuO₂.xH₂O particles are considered as microelectrodes. The initial charging of the RuO₂.xH₂O prior to water oxidation is discussed in Chapter Five and in Chapter Six the effect of an increase in the redox potential of the Ce⁴⁺/Ce³⁺ couple by changing the acid medium is investigated.

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16

Hassan, Ibrahim. "Solar energy conversion by photoelectrochemical processes." Thesis, University of Bath, 2011. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542078.

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17

Muralidharan, Shylesh. "Assessment of ocean thermal energy conversion." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/76927.

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Thesis (S.M. in Engineering and Management)--Massachusetts Institute of Technology, Engineering Systems Division, System Design and Management Program, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 103-109).
Ocean thermal energy conversion (OTEC) is a promising renewable energy technology to generate electricity and has other applications such as production of freshwater, seawater air-conditioning, marine culture and chilled-soil agriculture. Previous studies on the technology have focused on promoting it to generate electricity and produce energy-intensive products such as ammonia and hydrogen. Though the technology has been understood in the past couple of decades through academic studies and limited demonstration projects, the uncertainty around the financial viability of a large-scale plant and the lack of an operational demonstration project have delayed large investments in the technology. This study brings together a broad overview of the technology, market locations, technical and economic assessment of the technology, environmental impact of the technology and a comparison of the levelized costs of energy of this technology with competing ones. It also provides an analysis and discussion on application of this technology in water scarce regions of the world, emphasized with a case study of the economic feasibility of this technology for the Bahamas. It was found that current technology exists to build OTEC plants except for some components such as the cold water pipe which presents an engineering challenge when scaled for large-scale power output. The technology is capital intensive and unviable at small scale of power output but can become viable when approached as a sustainable integrated solution to co-generate electricity and freshwater, especially for island nations in the OTEC resource zones with supply constraints on both these commodities. To succeed, this technology requires the support of appropriate government regulation and innovative financing models to mitigate risks associated with the huge upfront investment costs. If the viability of this technology can be improved by integrating the production of by-products, OTEC can be an important means of producing more electricity, freshwater and food for the planet's increasing population.
by Shylesh Muralidharan.
S.M.in Engineering and Management

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18

Mur, Miranda José Oscar 1972. "Electrostatic vibration-to-electric energy conversion." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/16609.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.
Includes bibliographical references (p. 193-197).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Ultra-Low-Power electronics can perform useful functions with power levels as low as 170 nW. This makes them amenable to powering from ambient sources such as vibration. In this case, they can become autonomous. Motivated by this application, this thesis provides the necessary tools to analyze, design and fabricate MEMS devices capable of electrostatic vibration-to-electric energy conversion at the microwatt level. The fundamental means of en- ergy conversion is a variable capacitor that is excited through a generating energy conversion cycle with every vibration cycle of the converter. This thesis presents a road map on how to design MEMS electrostatic vibration-to- electric energy converters. A proposed converter is designed to illustrate the design process, and is based on vibration levels typical of rotating machinery, which are around 2% of the acceleration of gravity from 1-5 kHz. The converter consists of a square centimeter with a 195 mg proof mass which travels ±200 pm. This mass and travel can couple to a sinusoidal acceleration source of 0.02g at 2.5 kHz, typical of rotating machinery, so as to capture 24 nJ per cycle. This moving proof mass is designed to provide a variable capacitor ranging from 1 pF to 80 pF. Adding a capacitor of 88 pF in parallel with this device will result in a capacitance change from 168 pF to 89 pF that is required to extract 24 nJ using a charge-constrained cycle.
(cont.) This device can be attached to power electronics that implement a charge-constrained cycle and deliver 0.5 nJ back to the reservoir for a total power output of 1.3 [mu]/W at 2.5 kHz. The efficiency of the electrical conversion is 2%. Including packaging, the power per volume would be 0.87 [mu]W/cm3 and the power per mass would be 1.3 [mu]W/g. System improvements are also identified such as those that address the principal sources of loss. For example, decreasing the output capacitance of the MOSFET switches from 10 pF to 1 pF, while keeping the energy conversion cycle the same, results in an energy output of 13 nJ out of 24 nJ, for an efficiency of 54% and a power output of 33 [mu]W. This argues strongly for the use of integrated circuits in which the output capacitance of the MOSFET switches can be reduced for this application.
José Oscar Mur Miranda.
Ph.D.

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19

SCILLETTA, CLAUDIA. "Carbon nanotubes for solar energy conversion." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2009. http://hdl.handle.net/2108/1039.

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E’ stato dimostrato che la nanotecnologia ed i nanomateriali possono offrire valide soluzioni per migliorare l’efficienza di conversione sfruttando gli effetti indotti a scala mesoscopica. In questo ambito di ricerche, l’attività sui nano tubi di carbonio CNT come elementi costituenti di dispositivi di conversione dell’energia solare è in grande sviluppo. Il lavoro presentato in questa tesi è stato dedicato all’investigazione dei meccanismi fisici alla base della foto-risposta dei nanotubi di carbonio a multi parete (MWCNT) quando vengono utilizzati in celle elettrochimiche e in dispositivi a stato solido. Larga parte dell’attività è consistita nello sviluppo di strategie per la crescita controllata dei MWCNT. MWCNTs sono stati sintetizzati mediante CVD termico variando i parametri di crescita sperimentali. Utilizzando tecniche di caratterizzazione morfologica e strutturale, è stato possibile fissare i parametri di sintesi appropriati per ottenere strutture di MWCNT controllate su specifici substrati. Esperimenti di generazione di corrente fotochimica da parte dei MWCNT cresciuti su substrati SiO2/Si sono stati effettuati così come misure di fotoconduttività a stato solido. Tali esperimenti hanno confermato la capacità dei MWCNT di generare una corrente elettronica sotto illuminazione, nonostante la loro stretta similarità con la grafite metallica. Spettri EELS mostrano una spalla ad energie comprese tra 2 - 4 eV, sotto il tipico plasmone π -π* della grafite altamente orientata. Questa può essere associata, in analogia con i nano tubi a singola parete SWNT, alla presenza di singolarità di Van Hove nella densità degli stati elettronici. Tali transizioni permettono la generazione sotto illuminazione di un eccitone. L’elettrolita all’interno della cella chimica e/o la presenza di giunzioni Schottky tra MWCNT differenti separano le cariche. I risultati di fotoconducibilità a stato solido sono stati confrontati con quelli ottenuti negli esperimenti fotochimici, e quelli riportati in letteratura. Sulla base di calcoli teorici della DOS di nanotubi multi pareti (4WCNT), è possibile affermare che i MWCNT possono creare delle giunzioni locali p-n e/o Schottky con il substrato di silicio, dando luogo ad una estesa regione di svuotamento. Questo implica una modifica delle caratteristiche degli spettri di foto corrente attesi per i MWCNT. MWCNT sono stati decorati con nanoparticelle di rame e la loro foto risposta è stata studiata e confrontata con quella dei soli nano tubi. L’efficienza quantica dei sistemi ibridi aumenta su tutto lo spettro e due modelli sono proposti per spiegare questo risultato. Infine una prima misura sulle prestazioni di un dispositivo MWCNTs/SiO2/Si come cella fotovoltaica è stata effettuata mediante un simulatore solare. La caratteristica I-V sotto illuminazione non è la ben nota curva aspettata per le celle PV, ma mostra come dispositivi a stato solido basati sui MWCNT possano operare come generatore di potenza attivo sotto illuminazione solare.
It has been demonstrated that nanotechnology and nanomaterials could offer valid solutions to improve the conversion efficiency by exploiting effects induced at mesoscopic scales. In this research field, the activity on carbon nanotubes CNTs as building blocks for solar energy conversion devices is developing. The work presented in this thesis has been devoted to investigate the physical mechanisms underlying the photoresponse generation of multiwall carbon nanotubes (MWCNTs) when exploited in electrochemical cells and solid-state devices. A large part of the activity has consisted of the development of suitable strategies for the controlled growth of MWCNTs. MWCNTs have been synthesised by thermal CVD varying the experimental growth parameters. By using morphological and structural characterization techniques, it has been possible to fix the proper synthesis parameters to obtain controlled MWCNTs structures on specific substrates. Experiments of photochemical current generation by MWCNTs grown on SiO2/Si substrates have been performed as well as solid-state photoconductivity measurements. They have confirmed the capability of MWCNTs to generate a current of electrons under light irradiation, despite their close similarity to metallic graphite. EELS spectra show a shoulder at energies 2-4 eV, below the typical plasmon π -π* peak for HOPG. That can be associated, similarly to SWCNTs, to the presence of van Hove singularities in electronic density of states. These transitions allow the generation upon illumination of an exciton. The electrolyte inside the chemical cell and/or the presence of localized Schottky junctions between different MWCNTs separates the charges. The solid-state photoconductivity results have been compared with those obtained in photochemical experiments, and with other described in literature. On the basis of theoretical calculations of DOS for a specific four-wall carbon nanotube (4WCNT), it is possible to affirm that MWCNTs are able to locally create p-n and/or Schottky junctions with the silicon substrate underneath, giving rise to an extended depletion layer. This implies a modification of the feature in the expected photocurrent spectrum of MWCNTs. MWCNTs have been decorated by Cu nanoparticles and their photoresponse has been studied and compared with that of bare nanotubes. The quantum efficiency of the hybrid system increases over the entire spectrum and two models have been proposed to explain these results. Finally, a first measurement of the performance of a MWCNTs/SiO2/Si device as PV cell has been performed by using a solar simulator. The I-V characteristic under illumination is not the expected well-shaped curve of a PV cell, but it demonstrates that the MWCNT solid-state device can operate as an active power supply element under solar illumination.

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20

Zuo, Yong. "Nanostructured Metal Sulfides for Electrochemical Energy Conversion." Doctoral thesis, Universitat de Barcelona, 2020. http://hdl.handle.net/10803/670925.

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Storing the fluctuating renewable energy into synthetic fuels or in batteries is meaningful due to the emerging energy crisis. In this thesis, four nanostructured catalysts based on two kinds of metal sulfides, namely Cu2S and SnS2, were produced and optimized to improve their performance towards three key electrochemical energy conversion processes, namely electrochemical oxygen evolution, photoelectrochemical water splitting and lithium-ion batteries. Chapter 1 presented a general introduction to explain the motivation of the thesis topic. In chapter 2, a metallic copper substrate was used as current collector and chemical template to produce Cu2S nanorod arrays for electrochemical oxygen evolution reaction (OER). Suitable characterization tools were applied to investigate the chemical, structural and morphological transformation in OER operation, during which the initial Cu2S nanorod arrays would perform as a “pre-catalyst” that in-situ changed to CuO nanowires. Notably, the Cu2S-derived CuO showed significant improved OER performance compared with that of CuO prepared by directly annealing a Cu(OH)2 precursor, in terms of both activity and stability. Thus obtained electrocatalyst can be ranked among the best Cu-based OER catalysts reported so far. To take advantage of the unlimited solar energy, an ultrathin SnS2 NPL with a suitable band gap around 2.2 eV was produced via a hot-injection solution-based process in chapter 3. The unsatisfied photoelectrochemical (PEC) performance of bare SnS2 motivated me to deposit Pt NPs on its surface as cocatalyst via in-situ reduction of a Pt salt. The resulting SnS2-Pt heterostructures with optimal Pt amount showed significant improvement (six fold) towards PEC water oxidation. Mott-Schottky analysis and PEC impedance spectroscopy (PEIS) were used to analyze in more detail the effect of Pt on the PEC performance. The optimal SnS2-Pt heterostructure presented acceptable performance towards PEC water splitting. However, it still suffered from a moderate stability due to the peel-off of the catalyst layer from the FTO surface. To solve this problem, in chapter 4 we detailed a simple, versatile and scalable amine/thiol- based molecular ink to grow nanostructured SnS2 layers directly on conductive substrates such as FTO, stainless steel and carbon cloth. Such layers on FTO were characterized by excellent photocurrent densities. The same strategy was used to produce SnS2-graphene composites, SnS2-xSex ternary coatings and even phase pure SnSe2 layers. Finally, the potential of this precursor ink to produce gram scale amounts of unsupported SnS2 was also investigated. Apart from the application as a photocatalyst, SnS2 can also be a promising anode material for Li-ion batteries (LIB). In chapter 5, nanostructured SnS2 with different morphologies produced in chapter 3 were tested as LIB anodes firstly to find that thin SnS2 NPLs provided the highest performance. Thereafter, a colloidal synthesis strategy to grow the same SnS2 NPLs within a matrix of porous g-C3N4 (CN) and graphite plates (GPs) was developed and the obtained materials were tested for LIB application. Such hierarchical SnS2/CN/GP composites using SnS2-NPL as active materials, porous CN to provide avenues for electrolyte diffusion and ease the volumetric expansion of SnS2, and GP as “highways” for charge transport displayed excellent rate capabilities (536.5 mAh g-1 at 2.0 A g-1) and an outstanding stability (~99.7 % retention after 400 cycles), which were partially associated with a high pseudocapacitance contribution (88.8 % at 1.0 mV s-1). The excellent electrochemical properties of these nanocomposites were ascribed to the synergy created between the three components. Overall, four nanostructured catalysts based on Cu2S and SnS2 were prepared, and proper optimizations/treatments were defined to improve their catalytic performance. The results shown in this thesis demonstrate the promising application of non-toxic, low cost metal sulfides in electrochemical energy conversion technologies.
En esta tesis, se produjeron y optimizaron cuatro catalizadores nanoestructurados basados en Cu2S y SnS2 para mejorar su rendimiento hacia la conversión de energía electroquímica. El Capítulo 1 presentó una introducción general para explicar la motivación del tema de tesis. En el capítulo 2, las matrices de las nanovarillas de Cu2S se sintetizaron in situ sobre un sustrato de cobre metálico para la reacción electroquímica de evolución de oxígeno (OER). Se aplicaron herramientas de caracterización adecuadas para investigar la transformación en la operación OER, durante la cual las matrices iniciales de las nanovarillas Cu2S in situ cambió a nanohilos de CuO. En particular, el CuO derivado de Cu2S mostró un rendimiento de OER significativamente mejor cuando comparado al de CuO preparado mediante el recocido. En el capítulo 3, se detalló un proceso basado en una solución de inyección en caliente para producir nanoplacas ultrafinas SnS2 (NPL). Posteriormente, se cultivóPt en su superficie mediante la reducción in situ de una sal de Pt. Posteriormente se probó el rendimiento fotoelectroquímico (PEC) de los fotoanodes hacia la oxidación del agua. Los fotoanodes de SnS2-Pt optimizados proporcionaron densidades de fotocorriente significativamente más altas que el SnS2 desnudo (seis veces). Se analizó el efecto de Pt. En el capítulo 4, se informó una tinta molecular simple para cultivar capas de SnS2 nanoestructuradas directamente sobre sustratos conductores. Tales capas nanoestructuradas en FTO se caracterizaron por excelentes densidades de fotocorriente. Se utilize la misma estrategia para producir compuestos de grafeno-SnS2, recubrimientos ternarios SnS2-xSex, capas de SnSe2 de fase pura e incluso polvo de SnS2 a gran escala. En el capítulo 5, el SnS2 nanoestructurado con diferentes morfologías se probaron como ánodos LIB en primer lugar para encontrar que los NPL de SnS2 delgados proporcionaban el mayor rendimiento. Posteriormente, se desarrolló una estrategia de síntesis coloidal para cultivar los mismos NPL de SnS2 dentro de una matriz de g-C3N4 (CN) poroso y placas de grafito (GP) y se probaron para la aplicación LIB. Tales compuestos jerárquicos SnS2/CN/GP mostraron excelentes propiedades electroquímicas, lo que se atribuye a la sinergia creada entre los tres componentes como se investigó.

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21

Neves, Marcus Godolphim de Castro [UNESP]. "Estudo da viabilidade de implantação de plantas para conversão de energia térmica do oceano (OTEC) no Brasil." Universidade Estadual Paulista (UNESP), 2015. http://hdl.handle.net/11449/124434.

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Made available in DSpace on 2015-07-13T12:10:16Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-02-27. Added 1 bitstream(s) on 2015-07-13T12:25:31Z : No. of bitstreams: 1 000836695.pdf: 1571978 bytes, checksum: 4e307c80099ecf2308070178e4aa39ab (MD5)
Atualmente, a busca por novas fontes de energias renováveis tem sido o motivo de pesquisas e investimentos, sendo que a possibilidade de exploração da energia dos oceanos pode ser uma interessante alternativa. Um desses processos é baseado na extração da energia térmica solar acumulada na superfície dos oceanos. Parte dessa energia pode ser transformada em eletricidade e em vários outros subprodutos por meio de um processo conhecido como Conversão da Energia Térmica dos Oceanos (OTEC), que utiliza a água fria obtida a partir de uma profundidade de 1.000 m. As usinas OTEC podem operar em sistemas térmicos aberto, fechado ou híbrido, sendo que, para operar de forma adequada, o local de instalação da usina OTEC deve ter águas com temperatura média da superfície maior que 24 °C. O Brasil possui várias regiões que atendem esta condição sendo, portanto, um dos países com boa capacidade de instalação de usina OTEC para ajudar a suprir sua demanda energética. Este trabalho apresenta o estudo de viabilidade termodinâmica, termoeconômica e econômica de instalação de uma usina OTEC no Brasil por meio de simulações numéricas de seis casos de ciclos fechados, sendo cinco deles com um estágio (três com coletores solares e dois sem); e um caso com dois estágios, sem coletor solar. Os resultados mostraram que a planta com dois estágios não se mostrou viável. No entanto, observou-se que uma usina com ciclo fechado, com um estágio, é capaz de produzir de 13 a 19 MW, dependendo do caso, com custo entre R$ 0,55 (com coletor) e R$ 0,65 (sem coletor) por kW. Esse valor é inferior ao custo da energia produzida por motores estacionários a Diesel, de modo que essa tecnologia pode ser uma alternativa viável e sustentável para substituição dessa forma de geração de eletricidade no nordeste do Brasil, sendo também capaz de produzir água dessalinizada e sal
The search for new sources of clean renewable energy has been the subject of current research and investment, and the possible exploration of oceanic processes may be an interesting alternative. One of these processes is based on extraction of the solar thermal energy accumulated in the ocean upper layer. A fraction of this energy can be converted into electricity and various byproducts by means of a conversion process known simply as Ocean Thermal Energy Conversion (OTEC), which uses the cold water gotten from a depth of 1,000 m. OTEC plants operate in three distinct thermal cycles: open, closed and hybrid. To operate in an adequate form, the local of installation of an OTEC plant must have the sea's average surface temperature greater than 24 oC. Brazil has several offshore regions with these conditions, being one of the countries with good capacity to install OTEC plants to help to supply the electrical and energy demands. This work presents the study of thermodymanic, thermoeconomic and economic feasibility to install an OTEC plant in Brazil through numerical simulation of six cases of closed thermal cycles of an OTEC plant, being five of them with one stage (three with and two without solar boosters); one case with two stages and none solar booster. The results have shown that the two-stage plant has not been feseable. However, the one-stage closed cycle plants are able to produce between 13 to 19 MW, depending on the case considered, with cost between R$ 0,55 (with solar booster) and R$ 0,65 (without solar booster) per kW. These values is lower than the energy cost produced by Diesel stationary engines, so that this technology may be a feseable and sustainable alternative to replace this kind of power generation in Brazilian Northeast region, being able to produce fresh water and salt too

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22

Neves, Marcus Godolphim de Castro. "Estudo da viabilidade de implantação de plantas para conversão de energia térmica do oceano (OTEC) no Brasil /." Ilha Solteira, 2015. http://hdl.handle.net/11449/124434.

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Orientador: Ricardo Alan Verdú Ramos
Co-orientador: Cassio Roberto de Macedo Maia
Banca: Emanuel Rocha Woiski
Banca: Mauro Conti Pereira
Resumo: Atualmente, a busca por novas fontes de energias renováveis tem sido o motivo de pesquisas e investimentos, sendo que a possibilidade de exploração da energia dos oceanos pode ser uma interessante alternativa. Um desses processos é baseado na extração da energia térmica solar acumulada na superfície dos oceanos. Parte dessa energia pode ser transformada em eletricidade e em vários outros subprodutos por meio de um processo conhecido como Conversão da Energia Térmica dos Oceanos (OTEC), que utiliza a água fria obtida a partir de uma profundidade de 1.000 m. As usinas OTEC podem operar em sistemas térmicos aberto, fechado ou híbrido, sendo que, para operar de forma adequada, o local de instalação da usina OTEC deve ter águas com temperatura média da superfície maior que 24 °C. O Brasil possui várias regiões que atendem esta condição sendo, portanto, um dos países com boa capacidade de instalação de usina OTEC para ajudar a suprir sua demanda energética. Este trabalho apresenta o estudo de viabilidade termodinâmica, termoeconômica e econômica de instalação de uma usina OTEC no Brasil por meio de simulações numéricas de seis casos de ciclos fechados, sendo cinco deles com um estágio (três com coletores solares e dois sem); e um caso com dois estágios, sem coletor solar. Os resultados mostraram que a planta com dois estágios não se mostrou viável. No entanto, observou-se que uma usina com ciclo fechado, com um estágio, é capaz de produzir de 13 a 19 MW, dependendo do caso, com custo entre R$ 0,55 (com coletor) e R$ 0,65 (sem coletor) por kW. Esse valor é inferior ao custo da energia produzida por motores estacionários a Diesel, de modo que essa tecnologia pode ser uma alternativa viável e sustentável para substituição dessa forma de geração de eletricidade no nordeste do Brasil, sendo também capaz de produzir água dessalinizada e sal
Abstract: The search for new sources of clean renewable energy has been the subject of current research and investment, and the possible exploration of oceanic processes may be an interesting alternative. One of these processes is based on extraction of the solar thermal energy accumulated in the ocean upper layer. A fraction of this energy can be converted into electricity and various byproducts by means of a conversion process known simply as Ocean Thermal Energy Conversion (OTEC), which uses the cold water gotten from a depth of 1,000 m. OTEC plants operate in three distinct thermal cycles: open, closed and hybrid. To operate in an adequate form, the local of installation of an OTEC plant must have the sea's average surface temperature greater than 24 oC. Brazil has several offshore regions with these conditions, being one of the countries with good capacity to install OTEC plants to help to supply the electrical and energy demands. This work presents the study of thermodymanic, thermoeconomic and economic feasibility to install an OTEC plant in Brazil through numerical simulation of six cases of closed thermal cycles of an OTEC plant, being five of them with one stage (three with and two without solar boosters); one case with two stages and none solar booster. The results have shown that the two-stage plant has not been feseable. However, the one-stage closed cycle plants are able to produce between 13 to 19 MW, depending on the case considered, with cost between R$ 0,55 (with solar booster) and R$ 0,65 (without solar booster) per kW. These values is lower than the energy cost produced by Diesel stationary engines, so that this technology may be a feseable and sustainable alternative to replace this kind of power generation in Brazilian Northeast region, being able to produce fresh water and salt too
Mestre

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23

Yuen, Katarina. "System Aspects of Marine Current Energy Conversion." Licentiate thesis, Uppsala University, Electricity, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-113339.

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Free-flowing water currents such as tides and unregulated water courses could contribute to world electricity production given the emergence of robust technical solutions for extracting the energy. At Uppsala University, a concept for converting water currents to electricity using a vertical axis turbine with fixed blade pitch and a direct drive permanentmagnet generator is studied. A system approach is desired, and in this thesis, a first analysis of two system components, the generator and the turbine, is presented. This thesis also deals with some issues concerning the design and construction of a low speed generator for this application. An experimental generator for verification of simulations has been designed and constructed. For the electromagnetic design, a FEM simulation tool has been used. The construction work has given valuable practical experience concerning for example handling permanent magnets and winding the generator with cable. Simulations and measurements of the experimental generator have been carried out for different speeds and loads. The generator can operate at the speeds and loads corresponding to maximum power capture for different turbines for water current velocities between approximately 0.5 and 2.5 m/s. At higher water current velocities the turbines may need to be run at a tip speed ratio that gives a lower power capture in order to limit the electrical currents in the generator, cavitation of the blades, or mechanical loads. Comparisons of measurements and simulations show an agreement. The FEM simulation tool can be used to simulate and design electrical machines with a low electrical frequency, i.e. 2–16 Hz.

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24

Grabbe, Mårten. "Marine Current Energy Conversion : Resource and Technology." Licentiate thesis, Uppsala University, Electricity, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-113365.

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25

Nyhlén, Erik. "Control of marine current energy conversion system." Thesis, Uppsala University, Electricity, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-129988.

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This thesis involves the development of a system for control of a marine current energy conversion system. The control system is developed on the principles of load control, i.e. it aims to control the rotational speed of the turbine by controlling the power extracted from the generator. The system operates by feedback of the generator DC-voltage and current as well as the speed of the water current passing through the turbine. An IGBT-transistor controlled by an AVR-microcontroller executes control of the generator and hence the turbine. A digitally implemented PID-controller serves as the fundamental automatic control regime. The control system can be operated from a PC-application connected to the microcontroller through a serial wire connection. From the graphical user interface ofthe PC-application the system operator can set the system control parameters and monitor the state of the generator and turbine. The control system can be set to keep the turbine operating at a desired tip speed ratio, rotational speed or generator voltage. Further, for purposes of indoor testing of the control system a separate system, a motor control system, was developed as a part of this thesis work. The purpose of the motor control system is to enable simulating the behavior of a turbine with a motor driving the generator instead of an actual turbine. The motor control system operates by control of an ACS800 variable frequency drive that is connected to the motor. The motor control system allows its operator to feed in data describing the variations in water speed over time as well as data describing how the simulated turbine's power coefficient depends on its tip speed ratio. From this data the motor control system continuously calculates the torque that should be put on the generator axis by the motor. Results from test runs of the system show that the performance of the system is good. The system responds quickly to changes in the control parameters. Also the system manages to keep the specified control parameter quite well even during rapid changes in the water speed.

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26

Ekeström, Anton. "Sustainable energy conversion in ruralareas in Cuba." Thesis, KTH, Energiteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-99019.

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This study focuses on the village of Los Tumbos. It is located in a mountainous area of Cuba, farfrom the closest electric grid. The village consists of a few public buildings and around 80households. The public buildings and ten of the households are located in a small center that liesclose to a river. The villagers today use a few solar cells in order to electrify some importantpublic buildings and there is also an old hydropower plant which does not work at present. Theaccess to wind and biomass is very low, which makes the use of techniques involving theseunsuitable for electricity production. The options that will be used to electrify the dispersedhouseholds are solar cells. Combined with battery storage these works well, constantly able todeliver the electricity demand. They can also be used separately without connection the eachother, which eliminate the need to create a local grid. For the center of the village the locationclose to the river implies that the use of hydropower is a suitable option in order to power itsbuildings. Solar water heaters can also be used in order to give access to hot water and furtherincrease the life standards of the villagers.The model calculates the electricity demand in the village and estimates the sizes of theproduction facilities needed to meet the demand on the grid. In the model the load curves bothfor the dispersed households and the center of the village will be calculated. By using these resultsthe number of batteries and solar cell modules for the dispersed households can be calculated.For the center of the village the possible output from the hydropower plant can be calculated andthe number of collectors needed in the solar water heater system could also be estimated.From the model three different load curves were examined showing the peak-demand and thedaily average energy consumption for the demand levels. For each of the different levels the sizeof the energy conversion facilities were estimated showing the number of solar cells, batteries andsolar water heater collectors needed for the different levels. Any unambiguous result about asuitable demand level and by that the number of solar cells, collectors and batteries for LosTumbos cannot be selected without a complementary study of the economics available. This issince the economics is a very important factor in the decision. The output from the hydropowerplant is not dependent on the demand levels and it is capable of delivering a maximal power of2616 W and an average daily electrical consumption of 62,8 kWh per day. This result is verydependent on water flow and the available head and since the records were bad it needs to bereevaluated using records of the water flow from a longer time period, and an onsitemeasurement of the water head.

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27

Yuen, Katarina. "System Perspectives on Hydro-Kinetic Energy Conversion." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-181555.

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Free-flowing water currents such as tides and unregulated water courses could contribute to world electricity production given the emergence of robust technical solutions for extracting the energy. At Uppsala University, a concept for converting the energy in water currents to electricity using a vertical axis turbine with fixed blade-pitch and a direct-drive permanent magnet generator is studied. Technological equipment for extracting energy from water currents can be studied at desktop to some extent, but physical realizations, first in a laboratory setting, and later in a natural aquatic setting, are necessary. For this reason, a laboratory generator has been constructed and evaluated, and an experimental setup comprising turbine, generator and control system has been constructed. The turbine and generator are to be deployed in the Dalälven River in Söderfors, and operated from an on-land control station. The author has worked with constructing and evaluating the low-speed laboratory generator, participated in the design and construction of the Söderfors generator, and designed and constructed the control system for Söderfors. The generator design incorporates a low rotational speed, permanent magnets, and many poles, in order to adapt the generator to the nature of water currents. Simulations and experimental data for the laboratory prototype have been compared and show that the simulation tool used is adequate for design studies of this type of generator. The generator has also been shown to be able to operate with the intended turbine design and range of water velocities. The control system to be used in Söderfors has been tested in a laboratory environment. Simulations of the control system show that it should be able to operate the turbine and generator at the desired rotational speeds in water velocities up to about 1.8 m/s. Simulations of the system have also shown that maximizing system power output may not correspond with maximizing turbine power.

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28

Zhu, Qirong. "Modular polyoxometalate architectures for solar energy conversion." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066437.

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Les travaux présentés s'inscrivent dans les thèmes de l'électronique moléculaire et de la conversion photovoltaïque. Nous étudierons plus précisément les interactions électroniques à l'interface entre l'électrode anodique et une fine couche de polyoxométallates, POM. Nous dédirons le premier chapitre à une structure de POM qui sera étudiée en détail. Nous démontrerons que dans des conditions de concentration, recuit thermique appropriées la couche atteint un haut degré d'organisation la rendant conductrice. Après une analyse XPS/UPS fine nous montrons que les mécanismes de conduction prennent place sur la couche externe du POM dans les oxygènes lacunaires. De plus ces lacunes d'oxygène génèrent des états autorisés dans le gap interdit sous le niveau de Fermi. Une deuxième étape du travail consistera a étudié les effets des contreions sur la structure électronique précédemment décrite. Dans ce chapitre démontrons que les contreions, souvent décrits comme des espèces spectatrices, influence grandement le comportement électronique d'une espèce de POM. Puis nous étudierons l'impact de la nature du métal constituant le polyoxométallate. Enfin nous ferons dans un dernier chapitre une synthèse des résultats obtenus qui nous permettrons de conclure au regard des hypothèses formulées en présentant des tests de validation photovoltaïques
In this work, the main objective were to understand the electronic processes of polyoxometalates solid films at an indium tin oxide interface. A well-organized polyoxometalate film was deposited onto ITO and with an appropriate annealing process a highly ordered conductive surface was observed. The anisotropic morphology has been proved to be able to optimize electrical/electronic properties and further improve hole transport in organic photovoltaic devices by inserting as anode interfacial layer. We demonstrated the conductivity took place at the outer shell of the polyoxometalate due to oxygen vacancies which generate very localized gap state. We pursue the study by investigating the counter-ions (K+, Li+ and H+) effect on the identical polyoxoanion [P2W18O62]6-. We show it can not only influence the film aggregation mechanism, but allow tuning the density of gap states. The substitution of tungsten, especially by molybdenum, result in a more favorable energy level alignment from ITO and P3HT, i.e. desirable position and higher density of gap states. In a last we integrated the polyoxometalate in organic solar cells to prove the previous demonstration

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29

Basta, Marek. "Low energy photovoltaic conversion in MIND structures." Thesis, Strasbourg, 2013. http://www.theses.fr/2013STRAD019/document.

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Dispositifs photovoltaïques d'aujourd'hui convertissent l'énergie solaire en électricité de manière propre, renouvelable et inépuisable et représentent un remplacement possible pour les combustibles fossiles. Toutefois, afin de rivaliser avec les sources d'énergie classiques une augmentation significative de l'efficacité de conversion est inévitable. Dans ce travail, nous nous concentrons sur des aspects pouvant propulser le rendement de conversion au-dessus des limites de cellules présentes. La première partie de l'étude est consacrée à de nouvelles idées théoriques considérés comme le photovoltaïque de 3ème génération, alors que le plus d'intérêt est maintenu à étudier les avantages possibles de la multiplication d'électrons faible seuil. Dans la deuxième partie de l'étude, nous développons un modèle qui permet un traitement précis des propriétés optiques et de transport des structures de silicium avec des interfaces enterrées. Les analyses théoriques et expérimentales approfondies des structures existantes MIND sont ensuite effectuées. En étudiant le flux exacte et la distribution d'énergie à l'intérieur de plusieurs structures dans le cadre de leur géométrie, nous estimons les rendements quantiques possibles et les comparer avec les résultats expérimentaux. Grâce aux moyens de simulations numériques couplées avec caractérisation expérimentale, nous extrayons l'efficacité de la collecte de porteur de cellules étudiées. De nouveaux effets sont observés, une telle augmentation possible de l'efficacité de la collecte au-dessus de l'unité. Une analyse plus approfondie des résultats expérimentaux couplés avec l'étude numérique suit quelques explications classiques et non classiques de l'augmentation de l'efficacité de la collecte ou l'augmentation résultante de l'efficacité quantique. Avec la plupart des explications classiques exclu, nous concluons que l'explication la plus probable, mais non définitive de cet effet peut être interprété comme le résultat d'une multiplication des porteurs faible seuil
Photovoltaic devices of today convert solar energy into electricity in a clean, renewable and inexhaustible way and represent a possible replacement for the fossil fuels. However, in order to compete with classical energy sources a significant increase in the conversion efficiency is inevitable. In this work, we concentrate on the aspects able to raise the conversion efficiency above the limitations of present cells. The first part of the study is devoted to new theoretical ideas considered as 3rd generation photovoltaics, while the most interest is kept at studying the possible benefits of electron multiplication at low-energies. In the second part of the study, we develop a model that allows a precise treatment of optical and transport properties of silicon structures with buried interfaces. Extensive theoretical and experimental analyses of existing MIND structures are then conducted. By studying the exact flux and power distribution inside several structures in conjunction with their geometry, we estimate the possible quantum efficiencies and compare them with experimental results. Through the means of numerical simulations coupled with experimental characterization, we extract the carrier collection efficiency of studied cells. New effects are being observed, such a possible increase in collection efficiency above unity. A deeper analysis of the experimental results coupled with the numerical study analyzes several classical and non-classical explanations of the increase in collection efficiency or the resulting increase in the quantum efficiency. With most of the classical explanations ruled out, we conclude that the most probable, but not definitiveexplanation of this effect can be interpreted as the result of a low-energy carrier multiplication

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30

Warner, John M. "Wave energy conversion in a random sea." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ31537.pdf.

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31

Thomas, Karin. "Low Speed Energy Conversion from Marine Currents." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8400.

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32

Grabbe, Mårten. "Hydro-Kinetic Energy Conversion : Resource and Technology." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-195942.

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The kinetic energy present in tidal currents and other water courses has long been appreciated as a vast resource of renewable energy. The work presented in this doctoral thesis is devoted to both the characteristics of the hydro-kinetic resource and the technology for energy conversion. An assessment of the tidal energy resource in Norwegian waters has been carried out based on available data in pilot books. More than 100 sites have been identified as interesting with a total estimated theoretical resource—i.e. the kinetic energy in the undisturbed flow—in the range of 17 TWh. A second study was performed to analyse the velocity distributions presented by tidal currents, regulated rivers and unregulated rivers. The focus is on the possible degree of utilization (or capacity factor), the fraction of converted energy and the ratio of maximum to rated velocity, all of which are believed to be important characteristics of the resource affecting the economic viability of a hydro-kinetic energy converter. The concept for hydro-kinetic energy conversion studied in this thesis comprises a vertical axis turbine coupled to a directly driven permanent magnet generator. One such cable wound laboratory generator has been constructed and an experimental setup for deployment in the river Dalälven has been finalized as part of this thesis work. It has been shown, through simulations and experiments, that the generator design at hand can meet the system requirements in the expected range of operation. Experience from winding the prototype generators suggests that improvements of the stator slot geometry can be implemented and, according to simulations, decrease the stator weight by 11% and decrease the load angle by 17%. The decrease in load angle opens the possibility to reduce the amount of permanent magnetic material in the design.

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33

Lin, Ziyin. "Functionalized graphene for energy storage and conversion." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51871.

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Graphene has great potential for energy storage and conversion applications due to its outstanding electrical conductivity, large surface area and chemical stability. However, the pristine graphene offers unsatisfactory performance as a result of several intrinsic limitations such as aggregation and inertness. The functionalization of graphene is considered as a powerful way to modify the physical and chemical properties of graphene, and improve the material performance, which unfortunately still being preliminary and need further knowledge on controllable functionalization methods and the structure-property relationships. This thesis aims to provide in-depth understanding on these aspects. We firstly explored oxygen-functionalized graphene for supercapacitor electrodes. A mild solvothermal method was developed for graphene preparation from the reduction of graphene oxide; the solvent-dependent reduction kinetics is an interesting finding in this method that could be attributed to the solvent-graphene oxide interactions. Using the solvothermal method, oxygen-functionalized graphene with controlled density of oxygen functional groups was prepared by tuning the reduction time. The oxygen-containing groups, primarily phenols and quinones, reduce the graphene aggregation, improve the wetting properties and introduce the pseudocapacitance. Consequently, excellent supercapacitive performance was achieved. Nitrogen-doped graphene was synthesized by the pyrolysis of graphene oxide with nitrogen-containing molecules and used as an electrocatalyst for oxygen reduction reactions. We achieved the structural control of the nitrogen-doped graphene, mainly the content of graphitic nitrogen, by manipulating the pyrolysis temperature and the structure of nitrogen-containing molecules; these experiments help understand the evolution of the bonding configurations of nitrogen dopants during pyrolysis. Superior catalytic activity of the prepared nitrogen-doped graphene was found, due to the enriched content of graphitic nitrogen that is most active for the oxygen reduction reaction. Moreover, we demonstrated a facile strategy of producing superhydrophobic octadecylamine-functionalized graphite oxide films. The long hydrocarbon chain in octadecylamine reduces the surface energy of the graphene oxide film, resulting in a high water contact angle and low hysteresis. The reaction mechanism and the effect of hydrocarbon chain length were systematically investigated. In addition to the researches on graphene-based materials, some results on advanced carbon nanomaterials and polymer composites for electronic packaging will also be discussed as appendix to the thesis. These include carbon nanotube-based capacitive deionizer and gas sensor, and hexagonal boron nitride-epoxy composites for high thermal conductivity underfill.

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34

Michas, Marios. "Control of turbine-based energy conversion systems." Thesis, Cardiff University, 2018. http://orca.cf.ac.uk/117586/.

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This thesis investigated the modelling and control of wind and hydrokinetic turbine-based energy conversion systems. Wind turbines are a mature technology and the technical challenges are associated with their connection to the grid. However, hydrokinetic energy conversion systems are fairly new and their design is usually based on knowledge transferred from the wind industry. Variable-speed wind turbines are either fully or partially decoupled from the frequency of the grid. Therefore, as conventional plants are decommissioned, wind turbines have to comply with requirements issued by the transmission system operator of each country. To investigate this, vector control schemes of a doubly fed induction generator (DFIG) and of a fully rated converter (FRC)-based wind turbine were modelled using MATLAB/Simulink. Simulations showed that in case of a fault at the point of connection to the grid there is a larger impact on the torque of a DFIG than a FRC-based wind turbine. In addition, the FRC-based wind turbines can increase their output to contribute to the restoration of the grid frequency. Technical knowledge from the design, control and the modelling of variable-speed wind turbines was used for the design of an electrical subsystem for a hydrokinetic energy conversion system for man-made waterways. An FRC-based configuration based on a dc-dc converter was used for the control of the laboratory prototype of a hydrokinetic energy conversion system and the derivation of its characteristic power curves. Very high efficiencies of the system were observed due to the restricted flow conditions. Similarly to wind turbines, the variable-speed operation of the hydrokinetic energy conversion system enabled its maximum power point tracking (MPPT). A gradient-based method was analysed and a ‘perturb and observe’ algorithm-based control scheme was used for the maximum power extraction. The technical challenges are associated with the selection of the sampling time of the algorithm according to the inertia of the system and the convergence speed coefficient according to the voltage constant of the generator. The laboratory prototype and the projected full-scale system were modelled and simulated. Simulation and experimental results show good agreement on achieving the MPPT of the hydrokinetic energy conversion system. These findings are very important for the future design of heuristic MPPT control schemes for hydrokinetic energy conversion systems.

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ALMEIDA, SILVIO CARLOS ANIBAL DE. "DIRECT CONVERSION OF THERMAL ENERGY INTO ELECTRICAL." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1987. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=33281@1.

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COMISSÃO NACIONAL DE ENERGIA NUCLEAR
O presente trabalho descreve o desenvolvimento de um gerador termoelétrico cujos termoelementos são obtidos a partir de um composto de dissiliceto de ferro (FeSi2). A originalidade do trabalho reside na simplificação do processo de obtenção do termoelemento e na utilização de matérias-primas com grau de pureza industrial, em contraposição aos processos usuais que utilizam materiais de custo elevado, com alto grau da pureza e sofisticados processos de fabricação. O composto é obtido pelo processo de fusão num forno de indução à vácuo. A forma geométrica do termoelemento é assegurada pelo processo de sinterização. Um processo de recozimento garante a formação da fase Beta, assegurando a existência das propriedades termoelétricas. O coeficiente de Seebeck mostrou-se dependente do tempo de recozimento. Para os materiais desenvolvidos, o termoelemento tipo P apresentou um coeficiente de Seebeck de 250 MV/K e o material tipo N, um coeficiente de 75 MV/K, valores estes que qualificam o material para construção de geradores termoelétricos. Estima-se que o custo de fabricação do material desenvolvido reduziu de oito para dois dólares o custo de fabricação de materiais termoelétricos por watt de eletricidade gerado. Experiências preliminares utilizando a técnica de serigrafia para fabricação de termoelementos parecem confirmar a possibilidade de uma redução ainda maior do custo de fabricação.
This work describes the development of a thermoelectric generator whose thermoelements are made of a new thermoelectric material, FeSi2, an iron disilicide alloy. The originality of this work relies on the simplicity of the process by which the termoelements are obtained and also on the possibility to use a raw material with industrial purity grade, as opposed to conventional techniques which use costly materials, with a high degree of purity, and sofisticated process of fabrication. The alloy is obtained by a process of fusion in a vacuum induction type furnace. The geometric shape of the thermoelement is obtained by a process of sinterization. An annealing process garantees the formation of the Beta phase, thus assuring the existence of thermoelectric propertyes. The Seebeck coefficient proved to be dependent on the time duration of the annealing. As for the material developed, the P Type material presented an average Seebeck coefficient of 250 MV/K and the N type material, a coefficient of 75 MV/K, these figures qualify the materials for construction of thermoelectric generators. It is estimated that the manufacturing cost of the material developed reduced the cost of thermoelectric materials per watt of electricity generated from eight to two dollars. Preliminary experiments using the silk-scream technique in manufacturing of thermoelements seems to promise an even greater reducting in the manufacturing costs.

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36

Altalhi, Amal A. "Energy conversion and storage via photoelectrochemical methods." Thesis, University of Hull, 2013. http://hydra.hull.ac.uk/resources/hull:16512.

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Photoelectro analytical chemistry provides an elegant technique by which to explore, amongst others, various industrial and environmental applications. To this end, four areas of photoelectroanalytical chemistry are investigated in order to develop industrially - and environmentally - relevant galvanic and photogalvanic cells, together with exploring the electro-generation of an industrially important molecule and diffusion factors they may affect this generation. The first study is investigated a long-range charge transfer, using tert-butylferrocene (tBuFc) as model hydrophobic system. It is found that the apparent one-dimensional diffusion coefficient depends on the tBuFc loading. It is suggested that an efficient relay mechanism for electron transfer is through the partitioning of the oxidised form between the two subphases, with inter-pseudophase reaction. However, the second study investigated the normal lyotropic liquid crystals (in the lamellar or hexagonal phases) as a route to afford a structured, three-dimensional, quasi-biphasic framework within which electron transfer cascades may take place using cyclic voltammetry. It is shown that these can take place through reagent partitioning between the hydrophobic and hydrophilic subphases, and it is illustrated how the structure and its orientation, the nature of the ionic doping of the framework, and the hydrophobicity of the redox analyte may give rise to changes in the observed voltammetric waveshape. For the case of an artitifical mimic of the first few stages of Photosystem I, it is demonstrated that photo-induced electron transfer is likewise affected by the orientation, and develop a system of photon efficiency of ~0.1%. Thirdly, a novel attempt at power production was attempted with the construction and optimisation of a photogalvanic cell system. A literature review was conducted and a system proposed utilizing 10-methylphenothiazine (NMP) as a light harvester and zinc as a sacrificial electrode with tetrabutylammonium chloride (TBAP) as a supporting electrolyte and chloroform as a mediator. The study aimed to create a cell that could be produced using industrial run-off or other waste water supplies. A series of cells was produced with varying concentrations of both zinc and NMP solutions and the power conversions studied by producing a voltage-current plot for each system. A system that exhibited 9.02% conversion efficiency keep, future studies were conducted to show whether the zinc species effected the power conversion or if silver would act in a similar way. A mechanism was proposed for the power production process and so studies using 2, 4-Dichlorophenol (DCP) rather than chloroform we conducted; it was believed that the dissociation step for DCP was step wise rather than concerted. Lower power production was seen in these cells as predicted by the reaction mechanism. Tris - (4-bromophenyl) - amine (TBA), an alternative light harvester to NMP, was used to see if altering the active chemical agent resulted in efficiency change. Finally , A photogalvanic cell that employs 2,4-dichlorophenol as a fuel source, an N-substituted phenothiazine as light harvester, and sacrificial zinc anode is presented, and shown to afford a ca. 4% light-to-electrical power conversion efficiency in violet light.

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37

Jo, Won Jun. "Solar energy conversion via photovoltaics and photocatalysis." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111409.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Due to the forthcoming shortage of natural resources, the demand for more efficient and ecofriendly chemical processes for the conversion of energy and matter, especially with respect to carbon management, is growing rapidly. Therefore, a search for high-performance solar energy conversion systems to end the current carbon economy era is of paramount importance in both academic and industrial sectors. In this regard, we have studied organic photovoltaics and solar water splitting by using oCVD (Oxidative Chemical Vapor Deposition) polymers and doping-treated bismuth vanadate (BiVO 4), respectively. oCVD is a solvent-free conformal vacuum-based technique to enable thin-film fabrication of insoluble polymers at moderate vacuum (~ 0.1 Torr) and low temperature (25 150 °C). Moreover, oCVD carries the well-cited processing benefits of vacuum processing, such as parallel and sequential deposition, well-defined thickness control, large-area uniformity, and inline integration with other standard vacuum processes (e.g., vacuum thermal evaporation). Based on the above-mentioned technical advantages from oCVD, polyselenophene and poly(3,4- dimethoxythiophene) have been successfully applied to organic photovoltaics. Cost-effective solar hydrogen production requires catalytic materials that have earth-abundant element composition, suitable photoelectrochemical properties, and broad technological applicability. To create this versatile catalytic material, controlling the catalyst's atomic structure is of primary importance since their functionalities (e.g., electronic band structure, catalytic activity, chemical stability, etc.) are governed by its atomic structure. According to the strategy, BiVO 4's atomic structure has been engineered via phosphorus, indium and molybdenum doping. The improved photocatalytic behavior of doping-treated BiVO4 has been studied within experimental and computational domains.
by Won Jun Jo.
Ph. D.

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38

Ansovini, Davide. "Catalysis for sustainable energy conversion and storage." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/413468/.

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Climate change, pollution, unprecedented population growth, geopolitical tensions and rapid technological development are intrinsically connected to the nature, level and availability of global energy, which shapes present and future aspects of human society. Particularly, in a society where global energetic demand is continuously rising and the awareness of the negative impact of fossil fuels on the environment is becoming widespread, the exploitation of renewable sources for the generation of sustainable energy is highly needed. In this regard one key requirement for an effective deployment and expansion of renewable energy in the global energy market is represented by its ability to conveniently convert and store the energy derived from intermittent sources, in order to guarantee a constant supply to the electric grid. The technologies for the energy conversion and storage present various degrees of maturity, each one having specific advantages and disadvantages depending on the type of application and energetic source. This thesis aims to give a tiny contribution to the complex problem of energy conversion and storage, through the design, characterisation and testing of electrocatalytic materials for water electrolysis, photoelectrochemical water splitting and direct methanol fuel cell. It is expected that the first two processes will play an important role in the future as convenient technologies for the conversion of solar and wind power into chemical energy in the form of hydrogen. The third process is regarded as promising way to convert the renewable chemical energy in the form of methanol into electrical energy. At the core of the research lies the design and development of electrocatalysts, which are directly responsible for lowering the reaction overpotentials and ultimately increasing the overall efficiency of the processes. As such, in this thesis three materials were synthesised using straightforward methodologies and evaluated as electrocatalysts for the alkaline hydrogen evolution, the photoelectrochemical oxygen evolution and the alkaline methanol oxidation. Their performances were directly linked to the morphological and structural properties which in turn significantly affected the nature of active sites. For the first work reported in Chapter 3, a material based on a mixed cobalt nickel sulphide nanoparticles supported onto Ni foam showed high activity toward the hydrogen evolution reaction, with a required small overpotentials of 163 mV at a current density of 10 mA/cm2 in 1.0 M KOH electrolyte. This value compares well with the best existing hydrogen evolution reaction electrocatalysts based on non-noble elements. Moreover the catalyst showed good durability which was tested under chronoamperometric conditions, maintaining an optimal performance for 72 hours. The origin of such high activity was attributed to the existence of an optimal nickel-cobalt sulphide ratio at the surface of the electrode, which was obtained by selecting the appropriate temperature and time of thermal annealing of the material. This optimal presence of the biphasic nickel-cobalt sulphide nanoparticles led to high electrochemically active surface area and small charge transfer resistance, as evidenced by the extensive characterisation analysis carried out on these materials. For the second work reported in Chapter 4, a WO3/Co3O4 photoanode was successfully synthesised via a facile sol-gel method and tested for the photoelectrochemical oxygen evolution. It was found that the degree of crystallinity of the cocatalyst influenced heavily the photoelectrochemical activity towards the oxygen evolution. In particular, a poorly crystalline structure of Co3O4 led to an improvement of up to 40% in photocurrent generation compared to the bare WO3. Interestingly, the highly crystalline Co3O4 significantly suppressed the photocurrent generation, as a result of the creation of an unfavourable band alignment, with a dramatic increase in the charge recombination at the interface. Finally, for the third and last work reported in Chapter 5, ultra-small Pt nanoparticles embedded on a 3D structure composed of CeO2, NiO and Ni foam was synthesised and tested as electrocatalyst for the alkaline methanol oxidation reaction. The generated catalyst showed extremely high activity for the alkaline methanol oxidation, with mass and geometric current density values of 1160 mA/mgPt and 202 mA/cm2, whose values are among the highest ever reported for Pt-based materials. It was demonstrated that the unique morphological architecture and existence of a synergistic effect between Pt and adjacent CeO2 nanoparticles contributed decisively to the observed high performance. Particularly the presence of defective and poorly crystalline CeO2 nanoparticles was beneficial to the efficient oxidative removal of the CO from the Pt active sites which resulted in a higher durability of the electrocatalyst. Moreover, the concomitant presence of the superficial Ni(OH)2 was thought to contribute to the supply of OH species to the Pt, which act as reactants for the CO removal. The most active electrocatalyst was subjected to stability test, retaining 40 % of the initial geometric current density after 6 hours, and quite surprisingly the activity could be totally restored through straightforward CV scans in 1.0 M NaOH electrolyte.

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39

Afzal, Muhammad. "Nanocomposite Materials for New Energy Conversion Device." Thesis, KTH, Materialvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-122675.

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This thesis gives an approach how to develop newperovskite and nanocomposite cathode material for low temperature solid oxidefuel cells on the basis of nanocomposite approach to lower the operatingtemperature of SOFC. BaxCa1-xCoyFe1-yO3-δ(BCCF) and BSCF perovskite or nanocomposite oxides have been synthesized andinvestigated as catalytically potential cathode materials for low temperaturesolid oxide fuel cells (LTSOFC). Some single component materials have been alsosynthesized for new energy conversion device or EFFC. These nanocomposite andperovskite electrical conductors were synthesized by wet chemical, sol gel,co-precipitation and solid state reaction methods. Comparison with that ofcommercial Ba0.5Sr0.5Co0.8Fe0.2O3-δ(BSCF) cathode material, BCCF and locally prepared BSCF exhibit higher electricalconductivities as compared to that of commercial BSCF at same setup andconditions. In particular, novel Ba0.3Ca0.7Co0.8Fe0.2O3-δhas shown the maximum conductivity of 143 S/cm in air and local BSCF withconductivity of 313 S/cm in air at 550°C were measured by DC 4 probe method. Anadditional positive aspect of BCCF is that it is cost effective and works atroom temperature but with small output which will lead SOFC to operate atextremely low temperatures. XRD patterns of the samples reveal perovskite andnanocomposite structures of the said materials. Microstructure studies give thehomogeneous structure and morphology of the nanoparticles by using HighResolution Scanning Electron Microscopy (SEM). Cell resistance has beendetermined by Electrochemical Impedance Spectroscopy (EIS). Devised materialshave shown very good mechanical strength and stability proving their importancein advanced fuel cell technology. Power density of devices from 126 to 192 mWcm-2hasbeen achieved.

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40

Bardagot, Olivier. "N-type organic semiconductors for energy conversion." Thesis, Université Grenoble Alpes (ComUE), 2019. https://thares.univ-grenoble-alpes.fr/2019GREAV027.pdf.

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A l’heure où les impacts du changement climatique sont devenus indéniables, le développement des énergies décarbonées s’impose. Potentiellement bas coût comparées aux technologies établies, les technologies organiques émergentes offrent une alternative éco-efficiente pour l’exploitation de l’énergie solaire et de l’énergie thermique (< 473 K). Dans le premier chapitre, les avantages et inconvénients des différentes technologies actuellement développées sont discutés. Les dispositifs photovoltaïques, tout comme thermoélectriques, requièrent deux types de matériaux conduisant respectivement les trous (type p) et les électrons (type n). Malgré des avancées remarquables, le développement de semi-conducteurs de type n constitue un levier d’amélioration majeur pour les technologies organiques. Dans ce contexte, ce travail doctoral présente la conception, la synthèse, la caractérisation et la mise en œuvre au sein de dispositifs, de polymères et petites molécules pi-conjugués de type n.Basées sur trois unités électro acceptrices – l’isoindigo (ISI), le naphtalène diimide (NDI) et le benzodifurandione-oligo(p-phénylènevinylène) fluoré (FBDOPV) – la conception et la synthèse de copolymères alternés sont présentées dans le deuxième chapitre. Ces polymères démontrent de hautes affinités électroniques comprises entre 3,5 eV et 4,1 eV. Les études de modélisations DFT et de diffraction de rayons X en couches minces ont permis d’identifier les principaux facteurs structuraux à l’origine des hautes mobilités en électron obtenues en transistor organique à effet de champ allant jusqu’à 0,26 cm2.V-1.s-1.Pour une application thermoélectrique, le dopage moléculaire de ces semi conducteurs organiques est requis et fait l’objet du troisième chapitre. Les conditions nécessaires à la thermo- et photo activation du dopant N-DMBI ont été identifiées. En particulier, la dégradation du dopant activé en présence d’oxygène a été mise en évidence par diffraction de rayons X sur monocristaux. Les polymères et deux petites molécules à base d’ISI et NDI ont été dopés avec succès. Les mécanismes de dopage et les conductivités obtenues sont discutés au cas par cas à l’aide d’expériences spectroscopiques UV Visible-Proche-Infrarouge et Résonance Paramagnétique Electronique. Des conductivités de l’ordre de 10-4 S.cm-1 sont obtenues sans apport énergétique ni avant ni après dépôt. Des conductivités encourageantes de l’ordre de 10-3 S.cm-1 pour une petit molécule à base de NDI et de 10-2 S.cm-1 pour un polymère à base de FBDOPV ont été atteintes. La stabilité et la réversibilité des conductivités des couches minces exposées à l’air ont été examinées et corrélées au niveau LUMO des matériaux. Le contrôle minutieux des conditions de dépôts et de dopage ont permis l’obtention d’un facteur de puissance de l’ordre de 0,3 µW.m 1.K-2 associé à une conductivité thermique de 0,53 W.m-1.K-1. Des figures de mérite d’environ 2.10-4 à 303 K et 5.10-4 à 388 K ont été mesurées, lesquelles représentent les premières valeurs reportées à ce jour pour un semi-conducteur organique dopé n sur un même dispositif.Ces matériaux permettent également le remplacement des dérivés fullerènes en dispositif photovoltaïque comme présenté dans le dernier chapitre. Ils démontrent notamment de forte propriétés d’absorption, étendue jusqu’au domaine proche infrarouge pour l’un des polymères. Un rendement de conversion de 1,3% a été obtenu en cellule solaire à hétérojonction en volume « tout-polymère » avant optimisation. Suivant une conception moléculaire de type donneur-espaceur-accepteur, deux dérivés d’ITIC ont été conçus et caractérisées. La modification de substituants alkyles sur l’espaceur permet d’obtenir des propriétés d’absorptions et d’organisations améliorées comparé à ITIC. De hautes tensions de circuit-ouvert allant jusqu’à 1,10 V et des rendements de 4,2% ont été obtenus avec ces accepteurs non-fullerènes
At a time when the impacts of climate change have become undeniable, the development of low-carbon energies is crucial. Potentially low cost compared to established technologies, emerging organic technologies offer an eco-efficient alternative for harvesting solar and thermal (< 473 K) energies. In the first chapter, the advantages and drawbacks of the different technologies currently being developed are discussed. Photovoltaic devices, like thermoelectric devices, require two types of materials conducting holes (p type) and electrons (n-type) respectively. Despite remarkable advances, the development of n-type semiconductors represents a major lever for improving organic technologies. In this context, this doctoral work presents the design, synthesis, characterization and device developments of innovative pi-conjugated n-type polymers and small molecules.Based on three electron-accepting units – isoindigo (ISI), naphthalene diimide (NDI) and fluorinated benzodifurandione-oligo(p-phenylenevinylene) (FBDOPV) – the design and synthesis of alternated copolymers are presented in the second chapter. These polymers exhibit high electron affinities ranging from 3.5 eV to 4.1 eV. DFT modelling and thin-film X-ray diffraction studies allowed to identify the main structural aspects leading to electron mobility as high as 0.26 cm2.V 1.s 1 achieved in organic field effect transistors.For thermoelectricity, molecular doping of these organic semiconductors is required. It is the subject of the third chapter. The necessary conditions for thermo- and photo-activation of N DMBI dopant have been identified. In particular, the degradation of the activated dopant in the presence of oxygen has been demonstrated by single crystal X-ray diffraction. Each polymer and two small molecules based on ISI and NDI cores have successfully being doped. The doping mechanisms and conductivities obtained are discussed on a case by case basis using UV-Visible-Near-Infrared and Electron Paramagnetic Resonance spectroscopies. In particular, conductivities in the range of 10-4 S.cm-1 were obtained without external energy supply neither before nor after deposition. Encouraging conductivities in the range of 10-3 S.cm 1 for a small molecule based on NDI and 10-2 S.cm 1 for a polymer based on FBDOPV have been achieved. The stability and reversibility of thin film conductivities when exposed to air were investigated and correlated to the LUMO level of the materials. The thorough control of deposition and doping conditions have afforded to achieve a power factor of about 0.3 µW.m-1.K-2 associated to a thermal conductivity of 0.53 W.m 1.K 1. Figure of merits of approximately 2.10-4 at 303 K and 5.10-4 at 388 K have been obtained, which represent the first values reported to date for an n-doped organic semiconductor measured on a single device.These materials also allow the replacement of fullerene derivatives in photovoltaic devices as presented in the last chapter. In particular, they demonstrate strong absorption properties, extended to the near infrared domain for one of the polymers. A conversion efficiency of 1.3% was obtained in all polymer bulk-heterojunction solar cell before optimization. Following the donor-spacer-acceptor approach, two ITIC derivatives have been designed and characterized. The modification of alkyl substituents on the spacer provides improved absorption and molecular packing properties compared to ITIC. High open-circuit voltages up to 1.10 V and conversion efficiencies of 4.2% have been achieved with these non-fullerene acceptors

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41

Hosomizu, Kohei. "Photoactive molecular assemblies for solar energy conversion." 京都大学 (Kyoto University), 2008. http://hdl.handle.net/2433/136306.

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42

Zou, Yu. "Supported Composite Electrocatalysts for Energy Conversion Applications." Thesis, Griffith University, 2022. http://hdl.handle.net/10072/417198.

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Increasing energy demand and environmental awareness have promoted the development of efficient and environment-friendly hydrogen technologies. Water electrolysis (2𝐻2𝑂→2𝐻2+𝑂2) is a promising way to store renewable electricity generated by solar or wind energy into chemical fuel in the form of H2. Water electrolysis is comprised of a hydrogen evolution reaction (HER) on the cathode and an oxygen evolution reaction (OER) on the anode. For both HER and OER, highly catalytic active electrocatalysts are required to lower the overpotentials and to speed up the sluggish kinetics. To date, noble metal catalysts are still the most efficient electrocatalysts for these two reactions, but their high cost and low abundance on Earth limit the scalable application of water electrolysis. Therefore, investigation of alternative catalysts with low cost and high electrocatalytic activity is urgently needed. This thesis focuses on alkaline electrocatalytic HER, as well as related reactions such as OER, and hydrazine oxidation(HzOR)-assistant HER. In terms of material design, the components are introduced to improve conductivity and mass transfer, as well as boost the intrinsic catalytic activity. Moreover, the mechanism was investigated through exploring the link between structure and performance, as well using density functional theory (DFT) calculations. The first two experimental chapters employed a two-dimensional (2D) material, MXene, as support. In Chapter 2, ruthenium single atoms were incorporated onto ultrathin Ti3C2Tx MXene nanosheets to unlock its electrocatalytic activity. The RuSA@Ti3C2Tx presented a 1 A cm−2 HER current density with an over potential of 425.7 mV, outperforming the commercial Pt/C benchmark. Operando Raman test under HER potential showed the different protonation level between RuSA@Ti3C2Tx and Ti3C2Tx, suggesting the different hydrogen absorption energy of the oxygen terminal on the Ti3C2Tx basal plane. Finally, the theoretical calculations confirmed that the RuSA not only facilitates water dissociation, but also modulates the hydrogen After increasing the Ru content and conducting electroreduction, RuTi alloy nanoclusters were constructed on the surface of Ti3C2Tx. Surprisingly, the RuTi@Ti3C2Tx showed better performance in HER, and excellent hydrazine oxidation reaction (HzOR) performance. The overpotential to attain a current density of 10 mA cm−2 for HER was only 14 mV, lower than that of the commercial Pt/C. The HzOR catalytic activity also outperformed most reported work. In addition, the overall hydrazine spitting was conducted in an H-type electrolytic cell, demonstrating superior thermodynamic advantage and good stability. Defect-abundant active carbon (AC-DCD) as support was prepared by the hydrothermal reaction with dicyanamide. Then, the Ru nanoparticles were grown on the surface. Compared to the catalyst with pristine AC as support prepared under same conditions, Ru600@AC-DCD presented a larger electrochemical special area with strain-abundant Ru nanoparticles. Ru600@AC-DCD delivered excellent HER performance in alkaline media, and good catalytic properties in acidic and neutral media. Finally, another novel metal@carbon composite, Ni nanoparticles encapsulated in graphite carbon layers, was synthesized by directly annealing the Ni-imidazole framework precursors at 350 °C in H2/Ar. By tuning the annealing time under H2/Ar flow, Ni nanoparticles with different crystalline phases were synthesized. These Ni@C samples are di-function electrocatalysts for HER and OER in alkaline condition. The mixed-phase catalyst mix2-Ni@C delivered the highest activity to catalyze HER, while the pure hcp phase catalyst hcp-Ni@C showed best OER activity. This work provided a practical method to prepare low-cost difunctional electrocatalysts for overall water electrolysis. In summary, the thesis innovatively contributes to the knowledge in material science and water electrolysis in the aspects of: (i) designing novel supported composite electrocatalysts with high catalytic activity for HER, OER, and HzOR; (ii) monitoring the changing of surface terminal by operando Raman spectroscopy to verify the HER mechanism; (iii) development of metal nanostructures, like RuTi alloy, hcp phase Ni and mixed-phase Ni, via facile methods, and investigation of their unique properties; and (iv) application of large current HER and exploration of the kinetics under different potentials.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
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43

Baniasadi, Mahsa <1986&gt. "Thermal Processes for Biomass to Energy Conversion." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7493/1/Mahsa_Baniasadi-Thesis.pdf.

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Production of energy from biomassis an attractive alternative to conventional fossil fuels. Use of solid organic wastes to produce biofuel is seen as a promising route from the sustainability point of view. Pyrolysis is one of the possible thermochemical methods to convert solid biomasses to valuable liquid and gas products. In this study, the slow pyrolysis process of poultry litter was investigated using different experimental and analytical techniques. A fixed bed reactor was used for the simulation of the slow pyrolysis process up to a constant temperature (400-800°C) under nitrogen flow. Yields of the different product fractions were determined. Several analytic methods were used to characterise the products. On-line FTIR techniques were used to detect the most significant compounds in the evolved gas. GC-MS results allowed the identification of the most important categories of compounds in the liquid condensate. HCNS composition of the products was revealed by elemental analysis and the fate of nitrogen and sulphur, present in relevant amounts in the original substrate, was studied. The energy transfer from the original biomass substrate to the different product fractions was also investigated. However, the bio-oil obtained from pyrolysis can be used as biofuel only after an upgrading step. A suitable method for upgrading bio-oil is catalytic cracking of the pyrolysis products, which converts high molecular weight compounds of the bio-oil into lower-weight molecules. Therefore, in the following step of the present study in-situ catalytic pyrolysis of poultry litter was studied by zeolites (zsm-5) catalyst. In order to study the effect of influential factors (temperature and catalyst to biomass ratio) on the obtained products, experimental design techniques were used. Overall, the results achieved shed some light on the potential use of the slow pyrolysis process for sanitation and waste-to-energy valorization of poultry litter.

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44

Boni, Alessandro <1987&gt. "Electrochemistry of Nanocomposite Materials for Energy Conversion." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7510/1/boni_alessandro_tesi.pdf.

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Energy is the most relevant technological issue that the world experiences today, and the development of efficient technologies able to store and convert energy in different forms is urgently needed. The storage of electrical energy is of major importance and electrochemical processes are particularly suited for the demanding task of an efficient inter-conversion. A potential strategy is to store electricity into the chemical bonds of electrogenerated fuels, like hydrogen and/or energy-dense hydrocarbons. This conversion can be accomplished by water splitting and CO2 electrolysis. In this context, are herein presented three different electrochemical approaches towards water and CO2 reduction. In Chapter 1 is reported a novel class of nanostructured electrocatalysts, MWCNTs@Pd/TiO2, able to efficiently reduce water at neutral pH. Multi-walled carbon nanotubes, Pd nanoparticles and titanium dioxide are mutually integrated within the nanocomposites, whose electrocatalytic properties are thoroughly investigated and optimized. By electrochemical methods it is rationalized the effect of each building block on the overall activity, which originate from the synergic cooperation of the three units. In Chapter 2 is presented an electrochemical study of MWCNTs@CeO2, a noble-metal free electrocatalyst with a similar architecture to MWCNTs@Pd/TiO2. The electroreduction of CO2 has often the drawbacks of a poor selectivity and high energy losses for the high overpotential required to drive the reaction. However, detailed studies of MWCNTs@CeO2 highlights the possibility to convert CO2 to formic acid at very low overpotential and with a high selectivity. A reaction mechanism that involves the participation of surface hydride species and the CeO2 shell is proposed. Finally, in Chapter 3 is presented a photo-electrochemical approach to hydrogen production. Solar energy is converted to hydrogen via water reduction on the surface of a catalyst-free, oxide-protected solar cell. The large solar-to-hydrogen activity of the photocathode assembly has been explained by a combination of experimental and theoretical studies.

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45

Guerrero, Felipe Martinez. "Development of a wave energy basin to maximize wave energy conversion." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/20241.

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46

Sagaidak, Iryna. "Bi-functional materials combining energy storage and energy conversion from sunlight." Thesis, Amiens, 2019. http://www.theses.fr/2019AMIE0025.

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La nature intermittente de l'énergie solaire est souvent résolue par un couplage entre le PV et une batterie. Notre approche plus fondamentale vise à développer des matériaux capables de combiner ces deux fonctions à l'échelle moléculaire. Des nanocristaux de TiO2 de 5 nm ont été synthétisés dans notre groupe, ce qui a permis une réaction quantitative de photorecharge sous illumination standard. Nous présentons ici une étude originale portant sur l'évolution des propriétés optoélectroniques et de la dynamique du transfert de charge dans une électrode de TiO2 à l'aide d'expériences spectroscopiques in operando effectuées pendant le fonctionnement de la batterie. L'augmentation de la valeur de la bande interdite et de l'absorbance a été observée lors de l'insertion du lithium dans TiO2. Un décalage négatif en énergie de la bande de conduction indique un potentiel plus oxydant des trous photogénérés dans le Li0.6TiO2 par rapport au TiO2 initial. En analysant les processus de recombinaison dans Li0.6TiO2, nous avons établi une compétition entre les processus ultra-rapides (gamme ps) de recombinaison directe et de transfert de charge vers Ti3+ dans Li0.6TiO2, ce qui limite potentiellement le rendement de la réaction de photorécharge. Cette étude a été étendue à d'autres matériaux d'insertion généralement utilisés dans les batteries lithium-ion (Li4Ti5O12, LiCoO2, LiFePO4, MoO3, etc.). Les positions de bord de bande, la bande interdite, le type de porteurs de charge et leur concentration ont été mesurées et rassemblées dans une base de données. Basé sur ces résultats, la possibilité de photorécharge induite par la lumière a été évaluée et les premiers résultats discutés
The problem of intermittent nature of solar energy is often addressed by the traditional coupling of the PV and battery units. Our more fundamental approach targets the development of materials able to combine solar energy conversion and storage at the molecular level. The 5 nm anatase TiO2 nanocrystals were synthesized in our group affording a quantitative photorecharge reaction by a sole contribution of illumination. Here, we present a study of the evolution of the optoelectronic properties and dynamics of charge transfer in TiO2 electrode using in situ / in operando experiments performed during the battery functioning (UV-visible, Mott-Schottky, fluorescence spectroscopy). The increase of the bandgap value and the rise of absorbance are observed upon lithium insertion into TiO2. A negative shift of the conduction band indicates a more oxidizing potential of the photogenerated holes in Li0.6TiO2 compared to TiO2. By analysis of the recombination processes in TiO2 upon lithium insertion, we established a competition of the ultra-fast (ps range) processes of direct recombination and charge transfer towards Ti3+ in Li0.6TiO2, potentially limiting the yield of the photorecharge reaction. This study was extended to other insertion materials typically used in lithium-ion batteries (Li4Ti5O12, LiCoO2, LiFePO4, MoO3, etc.). The measured band edge positions, band gap, charge carrier type and concentration were gathered into a database, based on which the fundamental evaluation of the possibility of the light-induced photorecharge was conducted. The first results of the photoelectrochemical study of chosen materials are also discussed

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47

Oh, Sang Joon. "Electromagnetics of inertial energy storage systems with fast electromechanical energy conversion /." Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.

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48

Conceição, Ricardo Filipe Carrão da. "Soiling in solar energy conversion technologies: assessment and mitigation." Doctoral thesis, Universidade de Évora, 2019. http://hdl.handle.net/10174/25527.

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Soiling, the process of particle deposition onto surfaces, has been studied since the 40’s. Initially, it was studied as a physical process, including types of adhesion forces, and later its effect on performance of solar energy conversion technologies was analyzed, such as in photovoltaics and concentrated solar power. This thesis approaches the problem from a cause-effect point of view and how it can be mitigated. Soiling is characterized, mineral and chemically, using a Scanning Electron Microscope. Polycristalline photovoltaic modules deposition rates are retrieved and related to environmental parameters, as well as, to long-range Saharan desert dust transport, a non-local phenomenon. Attention is also given to Spring, where atmospheric pollen concentration enhances soiling. The effect of soiling on the photovoltaic optimum tilt angle, for fixed and multiple angles, is studied along with a simple economic analysis. Cleaning schedules, for a desired system efficiency, are calculated based on annual soiling. Mirror soiling, related to concentrated solar power technologies, is also analyzed. Soiling rates are calculated and interlinked with environmental parameters such as air temperature, relative humidity, particulate mater concentration and vertical wind speed. From a collaboration with the Institut de Recherche en Energie Solaire et Energies Nouvelles, Morocco, an insightful study is made comparing soiling effect between Portugal and Morocco. A passive cleaning method, impregnated anti-soiling coating, is tested. Comparison between coated and uncoated mirrors is done to evaluate its performance and conclude if it stands as a possible tool to reduce water consumption in cleaning solar harvesting technologies; Resumo: Sujidade em Tecnologias de Conversão de Energia Solar: Avaliação e Mitigação A sujidade, o processo de deposição de partículas em superfícies, tem sido estudada desde os anos 40. Inicialmente, começou a ser estudada como um processo fisico, incluindo tipos de forças de adesão, e mais tarde o seu efeito no desempenho de tecnologias de conversão de energia solar, como na tecnologia fotovoltaica e e de concentração. Esta tese aborda este problema de um ponto de vista causa-efeito e como pode ser mitigado. A sujidade é caracterizada, mineral e químicamente, usando um Microscópio Eletrónico de Varrimento. As taxas de deposição em módulos fotovoltaicos policristalinos são calculadas e relacionadas com parametros ambientais, tal como com o transporte de longo alcance de areia do deserto do Sahara, um fenómeno não local. Também é dada atenção à Primavera, onde a concentração de pólen na atmosfera aumenta a sujidade. O efeito da sujidade no ângulo de inclinação fotovoltaico óptimo, para ângulos fixos e múltiplos, é estudado juntamente com analises económicas. Calendários de limpeza, para uma eficiência de sistema desejada, são calculados com base em dados anuais de deposição de particulas. A sujidade em espelhos, relacionada com as tecnologias de energia solar concentrada, é também analisada. As taxas de deposição são calculadas e relacionadas com parâmetros ambientais, tais como temperatura do ar, humidade relativa, concentração de particulas e velocidade vertical do vento. A partir de uma colaboração com o Institut de Recherche en Energie Solaire et Energies Nouvelles, Marrocos, fez-se um estudo esclarecedor, comparando o efeito da sujidade entre Portugal e Marrocos. Um método passivo de limpeza, revestimentos impregnados anti-sujidade, é testado. A comparação entre espelhos revestidos e não revestidos é realizada para avaliar o seu desempenho e concluir se é um método importante para alcançar uma redução no consumo de água na limpeza de tecnologias de energia solar.

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49

Carter, Jesse James. "Analysis of a direct energy conversion system using medium energy helium ions." Texas A&M University, 2005. http://hdl.handle.net/1969.1/3790.

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A scaled direct energy conversion device was built to convert kinetic energy of singly ionized helium ions into an electric potential by the process of direct conversion. The experiments in this paper aimed to achieve higher potentials and higher efficiencies than ever before. The predicted maximum potential that could be produced by the 150 kV accelerator at the Texas A&M Ion Beam Lab was 150 kV, which was achieved with 92% collection efficiency. Also, an investigation into factors affecting collection efficiency was made. It was concluded that charge was being lost due to charge exchange occurring near the surface of the target which caused positive target atoms to be ejected from the face and accelerated away. Introducing a wire mesh near the face of the target with an electric potential, positive or negative, which aimed to control secondary ion emissions, did not have an effect on the collection efficiency of the system. Also, it was found that the gas pressure inside the chamber did not have an effect on the collection efficiency. The goal of achieving higher electric potentials and higher efficiencies than previous direct conversion work was met.

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50

Wang, Huizhi, and 王慧至. "Electrochemical conversion of aluminum energy: energy efficiency, co-production concept and systemcharacteristics." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B4697040X.

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