Aplicação de um ciclo orgânico de Rankine à indústria Naval

Trabalho Final de Mestrado para obtenção de grau de Mestre em Engenharia Mecânica

Otimização estocástica para a exploração de centrais de concentração solar considerando incerteza e risco

Dissertação para obtenção do grau de Mestre em Engenharia Eletrotécnica

Fonte comutada de baixa tensão para utilização em supercondensadores como fonte primária de energia

Dissertação para obtenção do grau de Mestre em Engenharia Electrotécnica Ramo Energia

Stochastic Framework for Strategic Decision-making of Load-serving Entities for Day-ahead Market

The deregulation of electricity markets has diversified the range of financial transaction modes between independent system operator (ISO), generation companies (GENCO) and load-serving entities (LSE) as the main interacting players of a day-ahead market (DAM). LSEs sell electricity to end-users and retail customers. The LSE that owns distributed generation (DG) or energy storage units can supply part of its serving loads when the nodal price of electricity rises. This opportunity stimulates them to have storage or generation facilities at the buses with higher locational marginal prices (LMP). The short-term advantage of this model is reducing the risk of financial losses for LSEs in DAMs and its long-term benefit for the LSEs and the whole system is market power mitigation by virtually increasing the price elasticity of demand. This model also enables the LSEs to manage the financial risks with a stochastic programming framework.

Melhoria da eficiência energética nos ascensores: a recuperação de energia

A presente tese descreve diferentes soluções que permitem a reutilização da energia recuperada em ascensores eléctricos de roda de aderência dotados de conversores electrónicos de frequência e dessa forma contribuir para a melhoria da eficiência energética nos ascensores. Nos ascensores, a energia potencial é constantemente transferida enquanto a cabina está em movimento. Se a cabina se estiver a movimentar em sentido descendente com plena carga, ou em sentido ascendente, mas vazia, o motor estará em modo gerador. Quando a cabina se movimenta em sentido descendente, e o peso na cabina é superior ao peso do contrapeso, então o binário do motor encontra-se em sentido contrário à velocidade, isto é, o motor está a travar, havendo lugar à recuperação de energia. Igualmente, se a cabina subir vazia, também se poderá recuperar energia eléctrica. A energia acumulada em forma de energia potencial nas pessoas e no contrapeso pode ser recuperada, dado que o motor estará a funcionar como um gerador. De modo a estudar a viabilidade técnica e económica das diferentes soluções foram realizadas medições a uma amostra representativa de ascensores eléctricos de roda de aderência. Esta amostra é constituída por 39 ascensores que estão instalados em diferentes tipos de edifícios e que pertencem a diferentes categorias de utilização, de acordo com a norma VDI 4707:2009. Para cada ascensor foi medida a energia consumida e a energia gerada para uma manobra completa – a descida e a subida da cabina sem carga. A partir das medições, e com base na norma VDI 4707:2009 foram calculados os valores anualizados de energia eléctrica consumidos e produzidos por cada ascensor. A partir das 5 hipóteses identificadas para a utilização da energia recuperada (carregamento de bateria para alimentação dos circuitos em stand-by; carregamento de supercondensador para alimentação dos circuitos em stand-by; carregamento de supercondensador para alimentar o barramento DC; reinjecção da energia no barramento DC de um conjunto de ascensores em grupo; reinjecção da energia na rede eléctrica do edifício onde o ascensor está instalado) foi realizada a avaliação técnica e a avaliação económico-financeira para cada um dos ascensores. Por último, foi desenvolvido um simulador que permite definir a solução de recuperação de energia que seja técnica e economicamente mais viável, para um dado ascensor eléctrico de roda de aderência instalado, mediante a introdução dos parâmetros técnicos do ascensor em avaliação.

Impacto da Introdução de Baterias de armazenamento de Energia em Smart Grids

De forma a não comprometer o conforto ou a qualidade de vida, nos dias de hoje, é obrigatório que a energia elétrica esteja presente. Sendo indispensável, torna-se necessário assegurar que a sua distribuição seja feita da forma mais qualitativa possível. Uma resposta rápida e eficaz a possíveis falhas que ocorram na rede, irá garantir a tal qualidade de serviço desejada. Para isso, a automatização dos processos é uma grande evolução e objetivo de concretização do setor elétrico. Neste contexto surge o conceito de Smart Grid, que tem como principal objetivo a combinação entre o setor elétrico e a evolução da tecnologia. A par desta característica, estes tipos de redes vêm também trazer evoluções no âmbito ambiental, pois a produção de energia elétrica é feita, maioritariamente, por fontes de energia renovável. Este projeto incide na análise das vantagens técnicas e económicas da inclusão de equipamentos que detêm capacidades de armazenamento de energia, as Baterias de Armazenamento de Energia (BAE), neste tipo de redes. Para tal, procedeu-se à utilização do método do Despacho Económico, que tem como principal objetivo a determinação dos níveis de produção de todas as unidades geradoras do sistema, satisfazendo a carga, ao mais baixo custo de produção. Com este método, foram criados vários cenários de estudo com vista a validar todo o propósito deste projeto. Nesta dissertação, é também realizado um estudo de viabilidade económica destes equipamentos de armazenamento de energia.

Studies On The Electrical Properties Of Some Crystalline Organic Compounds And Conducting Polymers

Solid electrolytes for applications like chemical sensing, energy storage, and conversion have been actively investigated and developed since the early sixties. Although of immense potential, solid state protonic conductors have been ignored in comparison with the great interest that has been shown to other ionic conductors like lithium and silver ion conductors. The non-availability of good, stable protonic conductors could be partly the reason for this situation. Although organic solids are better known for their electrical insulating character, ionic conductors of organic origin constitute a recent addition to the class of ionic conductors. However, detailed studies (N1 such conductors are scarce. Also the last decade has witnessed an unprecedented boom in research on organic "conducting polymers". These newly devised materials show conductivity spanning from insulator to metallic regimes, which can be manipulated by appropriate chemical treatment. They find applications in devices ranging from rechargeable batteries to "smart windows". This thesis mainly deals with the synthesis and investigations on the electrical properties of (i) certain organbc protonic conductors derived from ethylenediamine and (ii) substituted polyanilines

Theoretical Design and Synthesis of Donor-Acceptor Conjugated Polymers for Photovoltaic and NLO Applications

Polymers with conjugated π-electron backbone display unusual electronic properties such as low energy optical transition, low ionization potentials, and high electron affinities. The properties that make these materials attractive include a wide range of electrical conductivity, mechanical flexibility and thermal stability. Some of the potential applications of these conjugated polymers are in sensors, solar cells, field effect transistors, field emission and electrochromic displays, supercapacitors and energy storage. With recent advances in the stability of conjugated polymer materials, and improved control of properties, a growing number of applications are currently being explored. Some of the important applications of conducting polymers include: they are used in electrostatic materials, conducting adhesives, shielding against electromagnetic interference (EMI), artificial nerves, aircraft structures, diodes, and transistors.

Modelling and simulation of a photovoltaic fuel cell hybrid system

A stand-alone power system is an autonomous system that supplies electricity to the user load without being connected to the electric grid. This kind of decentralized system is frequently located in remote and inaccessible areas. It is essential for about one third of the world population which are living in developed or isolated regions and have no access to an electricity utility grid. The most people live in remote and rural areas, with low population density, lacking even the basic infrastructure. The utility grid extension to these locations is not a cost effective option and sometimes technically not feasible. The purpose of this thesis is the modelling and simulation of a stand-alone hybrid power system, referred to as “hydrogen Photovoltaic-Fuel Cell (PVFC) hybrid system”. It couples a photovoltaic generator (PV), an alkaline water electrolyser, a storage gas tank, a proton exchange membrane fuel cell (PEMFC), and power conditioning units (PCU) to give different system topologies. The system is intended to be an environmentally friendly solution since it tries maximising the use of a renewable energy source. Electricity is produced by a PV generator to meet the requirements of a user load. Whenever there is enough solar radiation, the user load can be powered totally by the PV electricity. During periods of low solar radiation, auxiliary electricity is required. An alkaline high pressure water electrolyser is powered by the excess energy from the PV generator to produce hydrogen and oxygen at a pressure of maximum 30bar. Gases are stored without compression for short- (hourly or daily) and long- (seasonal) term. A proton exchange membrane (PEM) fuel cell is used to keep the system’s reliability at the same level as for the conventional system while decreasing the environmental impact of the whole system. The PEM fuel cell consumes gases which are produced by an electrolyser to meet the user load demand when the PV generator energy is deficient, so that it works as an auxiliary generator. Power conditioning units are appropriate for the conversion and dispatch the energy between the components of the system. No batteries are used in this system since they represent the weakest when used in PV systems due to their need for sophisticated control and their short lifetime. The model library, ISET Alternative Power Library (ISET-APL), is designed by the Institute of Solar Energy supply Technology (ISET) and used for the simulation of the hybrid system. The physical, analytical and/or empirical equations of each component are programmed and implemented separately in this library for the simulation software program Simplorer by C++ language. The model parameters are derived from manufacturer’s performance data sheets or measurements obtained from literature. The identification and validation of the major hydrogen PVFC hybrid system component models are evaluated according to the measured data of the components, from the manufacturer’s data sheet or from actual system operation. Then, the overall system is simulated, at intervals of one hour each, by using solar radiation as the primary energy input and hydrogen as energy storage for one year operation. A comparison between different topologies, such as DC or AC coupled systems, is carried out on the basis of energy point of view at two locations with different geographical latitudes, in Kassel/Germany (Europe) and in Cairo/Egypt (North Africa). The main conclusion in this work is that the simulation method of the system study under different conditions could successfully be used to give good visualization and comparison between those topologies for the overall performance of the system. The operational performance of the system is not only depending on component efficiency but also on system design and consumption behaviour. The worst case of this system is the low efficiency of the storage subsystem made of the electrolyser, the gas storage tank, and the fuel cell as it is around 25-34% at Cairo and 29-37% at Kassel. Therefore, the research for this system should be concentrated in the subsystem components development especially the fuel cell.

Erneuerbare Energien im Verbund mit Hochleistungs-Bleiakkumulatoren zur Bereitstellung von Spitzenleistung - am Beispiel von Windkraftwerken im 20 kV-Versorgungsnetz der CEGEDEL / Luxemburg -

Die wachsende Weltbevölkerung bedingt einen höheren Energiebedarf, dies jedoch unter der Beachtung der nachhaltigen Entwicklung. Die derzeitige zentrale Versorgung mit elektrischer Energie wird durch wenige Erzeugungsanlagen auf der Basis von fossilen Primärenergieträgern und Kernenergie bestimmt, die die räumlich verteilten Verbraucher zuverlässig und wirtschaftlich über ein strukturiertes Versorgungssystem beliefert. In den Elektrizitätsversorgungsnetzen sind keine nennenswerten Speicherkapazitäten vorhanden, deshalb muss die von den Verbrauchern angeforderte Energie resp. Leistung jederzeit von den Kraftwerken gedeckt werden. Bedingt durch die Liberalisierung der Energiemärkte und die geforderte Verringerung der Energieabhängigkeit Luxemburgs, unterliegt die Versorgung einem Wandel hin zu mehr Energieeffizienz und erhöhter Nutzung der dargebotsabhängigen Energiequellen. Die Speicherung der aus der Windkraft erzeugten elektrischen Energie, wird in den Hochleistungs-Bleiakkumulatoren, errichtet im ländlichen Raum in der Nähe der Windkraftwerke, eingespeichert. Die zeitversetzte Einspeisung dieser gespeicherten elektrischen Energie in Form von veredelter elektrischer Leistung während den Lastspitzen in das 20 kV-Versorgungsnetz der CEGEDEL stellt die Innovation in der luxemburgischen Elektrizitätsversorgung dar. Die Betrachtungen beschränken sich somit auf die regionale, relativ kleinräumige Einbindung der Windkraft in die elektrische Energieversorgung des Großherzogtums Luxemburg. Die Integration der Windkraft im Regionalbereich wird in den Vordergrund der Untersuchung gerückt. Überregionale Ausgleichseffekte durch Hochspannungsleitungen der 230/400 kV-Systeme werden außer Acht gelassen. Durch die verbrauchernahe Bereitstellung von elektrischer Spitzenleistung vermindern sich ebenfalls die Übertragungskosten aus den entfernten Spitzenlastkraftwerken, der Ausbau von Kraftwerkskapazitäten kann in die Zukunft verschoben werden. Die Emission von Treibhausgasen in thermischen Kraftwerken wird zum Teil reduziert. Die Berechnungen der Wirtschaftlichkeit von Hybridanlagen, zusammengesetzt aus den Windkraftwerken und den Hochleistungs-Bleiakkumulatoren bringen weitere Informationen zum Einsatz dieser dezentralen Speichern, als Partner der nachhaltigen Energieversorgung im ländlichen Raum. Die untersuchte Einspeisung von erneuerbarer Spitzenleistung lässt sich auch in die Entwicklungsländer übertragen, welche nicht über zentrale Kraftwerkskapazitäten und Verteilungsnetze verfügen.

Thermal Noise Behavior of the Bridge Circuit

This paper considers a connection between the deterministic and noisy behavior of nonlinear networks. Specifically, a particular bridge circuit is examined which has two possibly nonlinear energy storage elements. By proper choice of the constitutive relations for the network elements, the deterministic terminal behavior reduces to that of a single linear resistor. This reduction of the deterministic terminal behavior, in which a natural frequency of a linear circuit does not appear in the driving-point impedance, has been shown in classical circuit theory books (e.g. [1, 2]). The paper shows that, in addition to the reduction of the deterministic behavior, the thermal noise at the terminals of the network, arising from the usual Nyquist-Johnson noise model associated with each resistor in the network, is also exactly that of a single linear resistor. While this result for the linear time-invariant (LTI) case is a direct consequence of a well-known result for RLC circuits, the nonlinear result is novel. We show that the terminal noise current is precisely that predicted by the Nyquist-Johnson model for R if the driving voltage is zero or constant, but not if the driving voltage is time-dependent or the inductor and capacitor are time-varying

Wind turbine blade pitch control system

The present invention provides an improvement for a wind turbine (20) having at least one blade (21) mounted on a hub (22) for controlled rotation about a blade axis (yb-yb) to vary the pitch of the blade relative to an airstream. The hub is mounted on a nacelle (23) for rotation about a hub axis (xh-xh). The wind turbine includes a main pitch control system for selectively controlling the pitch of the blade, and/or a safety pitch control system for overriding the main blade pitch control system and for causing the blade to move toward a feathered position in the event of an overspeed or fault condition. The improvement includes: an energy storage device (26) mounted on the nacelle and associated with the blade; a pitch-axis controller (25) mounted on the nacelle and associated with the blade and with the energy storage device; an electro-mechanical actuator (28) mounted on the hub and associated with the blade; and at least one slip ring (29) operatively arranged to transmit power and/or data signals between the pitch-axis controller and the electro-mechanical actuator; whereby the mass on the rotating hub may be reduced.

Performance of phase change material boards under natural convection

The high thermal storage capacity of phase change material (PCM) can reduce energy consumption in buildings through energy storage and release when combined with renewable energy sources, night cooling, etc. PCM boards can be used to absorb heat gains during daytime and release heat at night. In this paper, the thermal performance of an environmental chamber fitted with phase change material boards has been investigated. During a full-cycle experiment, i.e. charging–releasing cycle, the PCM boards on a wall can reduce the interior wall surface temperature during the charging process, whereas the PCM wall surface temperature is higher than that of the other walls during the heat releasing process. It is found that the heat flux density of the PCM wall in the melting zone is almost twice as large as that of ordinary wall. Also, the heat-insulation performance of a PCM wall is better than that of an ordinary wall during the charging process, while during the heat discharging process, the PCM wall releases more heat energy. The convective heat transfer coefficient of PCM wall surface calculated using equations for a normal wall material produces an underestimation of this coefficient. The high convective heat transfer coefficient for a PCM wall is due to the increased energy exchange between the wall and indoor air.

Observed changes in top-of-the-atmosphere radiation and upper-ocean heating consistent within uncertainty

Global climate change results from a small yet persistent imbalance between the amount of sunlight absorbed by Earth and the thermal radiation emitted back to space. An apparent inconsistency has been diagnosed between interannual variations in the net radiation imbalance inferred from satellite measurements and upper-ocean heating rate from in situ measurements, and this inconsistency has been interpreted as ‘missing energy’ in the system. Here we present a revised analysis of net radiation at the top of the atmosphere from satellite data, and we estimate ocean heat content, based on three independent sources. We find that the difference between the heat balance at the top of the atmosphere and upper-ocean heat content change is not statistically significant when accounting for observational uncertainties in ocean measurements, given transitions in instrumentation and sampling. Furthermore, variability in Earth’s energy imbalance relating to El Niño-Southern Oscillation is found to be consistent within observational uncertainties among the satellite measurements, a reanalysis model simulation and one of the ocean heat content records. We combine satellite data with ocean measurements to depths of 1,800 m, and show that between January 2001 and December 2010, Earth has been steadily accumulating energy at a rate of 0.50±0.43 Wm−2 (uncertainties at the 90% confidence level). We conclude that energy storage is continuing to increase in the sub-surface ocean.

Electricity use in the commercial kitchen

Academic and industrial literature concerning the energy consumption of commercial kitchens is scarce. Electricity consumption data were collected from distribution board current transformers in a sample of fourteen UK public house restaurants. This was set up to identify patterns of appliance use as well as to assess the total energy consumption of these establishments. The electricity consumption in the selected commercial kitchens was significantly higher than current literature estimates. On average, 63% of the premises electricity consumption was attributed to the catering activity. Key appliances that contributed to the samples average electricity consumption were identified as refrigeration (70 kwh, 41%), fryers (11 kwh, 13%), combi-ovens (35 kwh, 12%) bain maries (27 kwh, 9%) and grills (37kwh, 12%). Behavioral factors and poor maintenance were identified as major contributors to excessive electricity usage with potential savings of 70% and 45% respectively. Initiatives are required to influence operator behavior, such as the expansion of mandatory energy labeling, improved feedback information and the use of behavior change campaigns. Strict maintenance protocols and more appropriate sizing of refrigeration would be of great benefit to energy reduction.