ES - Comunicações em actas de encontros científicos internacionais
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- Sistema solar para aquecimento ambiente e aquecimento de piscinas: uma solução promissora para climas do Sul da EuropaPublication . Carvalho, Maria João; Neves, AnaA avaliação do sistema apresentado neste trabalho foi focada em sistemas que podem fornecer água quente, aquecimento ambiente e aquecimento de piscinas, e que são projectados para climas do Sul da Europa, especialmente para habitações uni-familiares. Pelas características climáticas do Sul da Europa, o aquecimento ambiente é apenas necessário para um curto período do ano, sendo para esta avaliação considerado um período de seis meses para aquecimento ambiente e um período de seis meses para aquecimento de piscinas. Estes sistemas são actualmente utilizados por um mercado reduzido de pessoas, que estão a construir as suas casas como habitações uni-familiares e que desejam também usufruir das condições climáticas dos seus países, para o uso da energia solar. É comum que a integração de uma piscina seja também projectada e construída. A avaliação apresentada foi realizada considerando como sistema de referência um sistema do tipo “kit” com uma área de colector de 4m 2 e um depósito de 300 l. O sistema em avaliação oferece um serviço extra aquecimento ambiente e de piscinas e é constituído por um campo de colectores e por um depósito combinado, capaz de fornecer águas quentes sanitárias e aquecimento ambiente no período de Inverno e também aquecimento de piscinas no período de Verão. A avaliação realizada mostra que nos climas do Sul da Europa este sistema irá fornecer um serviço extra em comparação com os sistemas solares térmicos tradicionais, podendo também ser economicamente interessante.
- Avaliação de desempenho de protótipo de secador solar passivo para tratamento de efluente de processo de dessalinização por destilação multi-efeitoPublication . Mendes, J. Farinha; Horta, Pedro; Collares-Pereira, M.; Korovessis, N.O projecto AQUASOL-Enhanced Zero Discharge Seawater Desalination using Hybrid Solar Technology (EVK1-CT2001-00102) teve como principais objectivos a melhoria do desempenho económico e a minimização dos impactes ambientais associados a um processo de dessalinização por Destilação Multi-Efeito (MED)(Blanco et al, 2002). No âmbito do projecto, decorre o estudo de um secador solar passivo utilizado no tratamento do efluente produzido no processo de dessalinização, salmoura, através da sua concentração e/ou através da produção directa de sal a partir do efluente. Nesta etapa adicional do processo de dessalinização foi considerada não só a maior concentração do efluente relativamente à concentração da água marinha utilizada no processo MED, mas também a sua possível integração numa salina tradicional, com o potencial de substituir etapas intermédias da evaporação com vantagem face ao processo convencional de produção de sal marinho. Após um estudo das especificidades da produção de sal em Salinas tradicionais e do processo de evaporação de uma camada de salmoura, a construção e avaliação de cinco configurações distintas de um protótipo preliminar de secador solar passivo, permitiu o desenho final de um secador para a recuperação de sal a partir do efluente do processo MED (Collares Pereira et al, 2004), construido numa salina industrial na ilha de Lesvos (Grécia) (Collares Pereira et al, 2005). Neste artigo serão apresentados os primeiros resultados de operação do protótipo, bem como uma avaliação inicial do seu desempenho.
- Modelação de sistemas solares térmicos de pequena dimensão (sistemas tipo kit) e identificação de parâmetros característicos para determinação do comportamento térmico a longo prazoPublication . Carvalho, Maria João; Neves, AnaOs Sistemas Solares Térmicos de pequena dimensão (sistemas do tipo kit) são ensaiados de acordo com as normas de ensaio EN 12976-2 e ISO 9459-5 para determinação do comportamento térmico, considerando uma metodologia de ensaio dinâmico. Neste artigo é apresentado um modelo fisíco que descreve o balanço térmico para um sistema solar. O modelo descrito assenta num depósito unidimensional e tem como variável de entrada a energia fornecida pelo colector e como variável de saída a energia fornecida para consumo. Considera-se que existe estratificação no interior do depósito, recorrendo a um modelo de segmentos isotérmicos de dimensão variável. Com o modelo desenvolvido e com os dados de ensaio é possível identificar os parâmetros característicos do sistema. A identificação dos parâmetros é conseguida por um processo iterativo de optimização utilizando o método de Levenberg-Marquardt. O cálculo do Comportamento térmico a longo prazo (LTPP - Long Term Performance Prediction), do sistema, é efectuado considerando o modelo estabelecido para o balanço térmico e os parâmetros identificados.
- Experimental study of a double-diffusive system: application to solar pondsPublication . Tavares, Célia; Coelho, João M. P.; Alves, D. Castro; Abreu, Manuel A.; Joyce, A; Fernandes, E. C.A salt gradient solar pond is an artificial device used to collect and store solar thermal energy. A non-convective zone, in the middle of the solar pond, reduces thermal losses and allows a significant rise of temperature in the saltier lower zone where the solar thermal energy is stored. The non-convective zone, also named gradient zone, is characterized by a salinity gradient that increase the density with depth promoting the stability of this layer. The absorption of solar radiation in the pond creates a destabilizing temperature gradient in the non-convective zone that contradicts the density gradient. The different molecular diffusivities of heat and salt and the opposing effects on the vertical density distribution of the two gradients can lead to double-diffusive convection phenomena. In this context, a double-diffusive system has been studied experimentally in laboratory by heating a stratified salt layer from below. The instabilities caused by the destabilizing temperature gradients lead to the formation of convective zones separated from purely diffusive zone by thin interfaces. The main goals of this work are the study of the evolution of the double-diffusive layer and the analysis of the behaviour of the diffusive interface near conditions for which instabilities appear.
- On the sustainable development of solar thermal obligations in buildings in the framework of the Portuguese casePublication . Prates, Manuel João Lopes; Costa, J. Cruz; Mendes, J. Farinha; Carvalho, Maria JoãoThis paper starts remembering the steps given in Portugal to prepare the introduction of a solar thermal obligation. Next, it presents a description of the present legislation related to the Solar Thermal Obligation (STO) and to other incentive measures for growth of the solar thermal market in Portugal. The main problems with implementation of the new regulation are analysed and systematized. Based on the acquired knowledge, further actions are presented to guarantee the success of Solar Thermal Obligation, namely proposals for updating the obligation in conformity with best practice for solar thermal installations and taking into account the new realities upcoming from the actual solar thermal
- Solar climate of Azores: results of monitoring at Faial and Terceira islandsPublication . Aguiar, Ricardo; Silva, António R.; Coelho, RicardoThe North Atlantic archipelago of Azores (Portugal) consists of nine islands, located about 1,500 km from mainland Europe. Currently the Azores has about 243,000 inhabitants, which depend heavily on imported fossil fuel for their energy supply. This is a concern for the regional Government and its Agency for Energy and Environment, ARENA, which naturally support energy efficiency and use of renewable energies. The Azores are rich in several renewable resources, and have even pioneered Portuguese exploitation of wind, wave, and high enthalpy geothermal energy for electricity generation. However, so far solar energy has not been a priority in the renewable energy panorama, probably because the Azores climate has been considered too cloudy. Nevertheless, this is true only in comparison with the Portuguese mainland, as the radiation levels are probably similar or even better than those of Northern Europe. In this context ARENA is developing efforts for increasing the use of solar systems. A collaboration, partly financed by an INTERREG III B Project of the European Community, has been established with INETI, the Portuguese Public Laboratory for the area of Energy, to improve the solar climatology of the Azores. This climatology is indeed quite incomplete. It consists mainly on daily measurements for two sites only at the S. Miguel and Terceira islands. Some sunshine records are available from Campbell-Stokes heliographs. Satellite data exists but their quality is uncertain due to the small size of the islands and the shallow view angle.
- Novel solar absorber surfaces with organic pigmentsPublication . Nunes, Clarisse; Brites, Maria João; Mendes, J. Farinha; Prates, Manuel João Lopes; Alexandre, J.; Ferreira, M.; Martins, A. J.; Teixeira, V.; Carneiro, V.; Carvalho, Maria JoãoThis paper presents results of application of natural and synthetic organic pigments in selective solar absorber coatings. Some of these photo excite pigments were tested like solar radiation absorber pigments in paint coatings and others as a form to increase the absorption of solar radiation in titanium oxide monolayer selective coatings produced by reactive magnetron sputtering. Morphologic aspects and optical properties are discussed as a function of deposition parameters and of formulation parameters. The main goal is to prepare solar absorber surfaces as a tandem of TiOx thin films, organic pigment using a conductive substrate or of paint with organic and/or inorganic pigments and conductive substrate, all reaching great photo thermal conversion efficiency, high durability and low costs to the ending product and stability at medium range temperatures (120-150ºC). The best optical properties for titanium oxide sputtered films were 88% for solar absorption, with 7% of emissivity for deposition parameters of: pulsed frequency 200kHz, reverse time of 0.4μs, discharge current of 0.7A, argon flow rate of 50ml/min and oxygen flow rate changing from 0 to 2.5ml/min. The results obtained with paints were not satisfactory. The best couple values for solar absorption and emissivity were respectively 94%, and 74%
- Solar thermal collector yield: experimental validation of calculations based on steady-state and quasi-dynamic test methodologiesPublication . Horta, Pedro; Carvalho, Maria João; Fischer, S.The characterization of collector efficiency is the fundamental tool for long term calculation of collector yield. It is, thus, one of the most important inputs in software tools aiming the design of solar thermal systems. Presently two test methodologies are available for characterization of the efficiency of glazed collectors: i) steady state test and ii) quasi-dynamic test, methodologies based in different model approaches to a solar collector, providing different collector efficiency curve parameters and, consequently, imposing different power calculation algorithms. Moreover, Horta et al (2008) demonstrated that the use of the collector efficiency curve derived from steady state test method is not enough for a thorough characterization of the long term performance of a collector. The present work takes into account the introduction of the above referred test methodologies in the European Test Standard for Solar Thermal Collectors, and aims at clarifying how each test results should be used in long term thermal performance calculations. The paper presents a synthesis of the different efficiency parameters provided by each test methodology and corresponding algorithms, applicable in the calculation of delivered power. Application of these algorithms to two days of measured data allows for a comparison of the results obtained with these different methodologies. For validation purposes, results of tests performed on a CPC type collector with a concentration ratio C=1.72 are used. Measurement sequences are used to validate the calculation of power delivered by the collector using both algorithms based on steady-state methodology (with and without correction) and quasi-dynamic methodology.
- Thermal energy production by a dual solar poundPublication . Lima, Maria Margarida de Lemos Canedo Giestas; Joyce, A; Milhazes, Jorge P.; Loureiro, DavidA Salt Gradient Solar Pond (SGSP) is a salt water basin that collects and stores solar energy. These devices rely on the existence of a non-convective zone (NCZ) that functions as a transparent thermal insulation zone, created by a salt gradient. Salinity and temperature gradients in this zone can give rise to double diffusive problems that can decrease the insulation properties of this zone. The stability of this zone is thus crucial in a SGSP. Stability control, analysis of energy extraction, device efficiency and maintenance strategies are determinant for the correct performance of the SGSP. The implementation of these strategies can be expensive and not sufficient to prevent instability problems. This paper intends to give a contribution to the maintenance problem presenting a new concept of a SGSP utilisation: The Dual Solar Pond (DSP)
- High-technology elements for thin-film photovoltaic applications :a demand-supply outlook on the basis of current energy and PV market growths scenariosPublication . Reiser, Fiona K. M.; Rodrigues, Carlos; Rosa, DiogoOn the basis of current energy and photovoltaic market outlooks and scenarios, the total growth rate potential of thin-film photovoltaic (PV) techniques have been analysed and calculated. For the European Photovoltaic Industry Association (EPIA) Advanced Scenario [1] total thin-film PV annual production values of 2.4 GWp for 2010, 25 GWp for 2020 and 132 GWp for 2030, were calculated. These values were used to estimate individual annual production for each thin-film technology in order to predict the future thin-film PV material needs for indium, selenium, tellurium, germanium and gallium. Considering global reserve and refinery data, this work also provides estimations on the current static depletion time of these elements. Such estimations are of course an approximation but emphasise that some of the considered elements are highly constrained when assuming steady production rates. This is particularly the case for indium, for which we calculated a static depletion time of 22 years. Selenium and tellurium could be also in danger of running out soon if their consumption increases. This implies that additional efforts are needed in the exploration and evaluation of mineral deposits which can supply these scarce elements such as the deposits of the Iberian Pyrite Belt.