• Energy Research
• 2021-2021close
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In this study, the important role of radiating gas effect to obtain higher thermal performance in a planar double-pass solar gas heater (DP-SGH) is discussed. Two inclined passages are deployed in ...

Abstract A new composite heat transfer fluid consisting of tetralin and fullerene has been proposed for photovoltaic thermal hybrid solar harvesting. It features a unique absorption spectrum that is capable of sharply cutting off solar energy irradiated in the range of wavelength from 300 to 650 nm, making it a perfect candidate for simultaneous harvesting of both photovoltaic and thermal components of solar energy. The proposed composite revealed outstanding stability and facile synthesize root, which are the two main obstacles for applicability of nanofluids. It was shown experimentally that the additives of fullerene to tetralin do not alter significantly it’s thermophysical properties apart from viscosity that increases moderately. Besides, tetralin/fullerene solutions show similar thermohydraulics performance to that of pure tetralin in laminar flow regime or insignificantly lower in transient and turbulent flow regimes. A new figure of merit was proposed to analyze the thermohydraulics performance that consider not only exergy losses due to the kinetic energy dissipation, but also exergy losses associated with a finite temperature difference in the heat exchanger. As a result, the proposed figure of merit indicates the decrease of the heat transfer performance of tetralin/fullerene solutions that directly proportional to fullerene concentration. The performed simulation suggests that the total energy efficiency of flat-plate photovoltaic/thermal solar collector goes up to 60.4 % estimated according regulation (EU) No. 811/2013. Finally, life cycle analysis revealed further improvement root in view of environmental impact.

Abstract Self-rectifying impulse turbines are a popular alternative to the Wells turbine for oscillating-water-column wave energy converters. Self-rectifying impulse turbines have two sets of guide-vanes placed symmetrically on each side of the rotor, instead of a single set as in unidirectional turbines. The efficiency of self-rectifying turbines with fixed guide-vanes is severely affected by the significant aerodynamic losses due to the inherent misalignment between the outflow from the rotor and the downstream guide-vane system. The paper presents a new design method for high-deflection guide-vane systems arranged into multiple, rather than single, rows. The design method aims to increase the turbine efficiency by reducing the losses caused by aerodynamic outflow stalling at the exit guide-vane system while ensuring the required inlet guide-vane system inflow deflection. The new design method was validated by testing and comparing detailed experimental results for a pair of single-row guide-vane stators, with conventional camber line and thickness distribution vane sections, and a five-row guide-vane stator, with constant thickness circular-arc profiles, on each side of the rotor. A Reynolds number effect correction methodology is presented to estimate the performance of a full-scale self-rectifying turbine from model testing results.

Abstract Different photovoltaic technologies have achieved notable improvements in efficiency in recent years, allowing photovoltaic cells to convert a higher percentage of incident solar radiation into electrical energy. However, the search for new, more efficient technologies as well as the improvement of existing ones, remains the aim of researchers and manufacturers. New materials have been considered, requiring the development of more accurate mathematical models to simulate their behavior. This study focusses on the validation of a modified multidimension diode model to determine a suitable model for different photovoltaic technologies. This model includes m-diodes connected in series and u-strings of diodes in parallel, providing a reconfigurable diode network, which allows the determination of the optimal number of diodes in the equivalent electrical circuit based on manufacturer or experimental data. The guaranteed convergence particle swarm optimization algorithm was used to estimate the photovoltaic parameters of the modified multidimension diode model. The validation was carried out with six different photovoltaic technologies, namely polycrystalline silicon, monocrystalline silicon, amorphous silicon, copper indium selenide, heterojunction with intrinsic thin-layer, and cadmium sulfide/cadmium telluride. The results revealed that the modified multidimension diode model accurately reflects the behavior of different photovoltaic technologies with high performance, providing a good compromise between accuracy and computational cost. Specifically, the modified multidimension diode model, when compared to the single-diode model (most commonly used in literature), achieved up to 14% more accuracy for the photovoltaic technologies considered under this study. Furthermore, the mathematical models identified as most suitable for the photovoltaic technologies under study are suggested as references for future works.

Trust is a fundamental ingredient of prosperous democracies. In Europe, trust in existing elected democratic institutions is fading while authoritarian nationalist movements grow. Experiences of neglect, ignorance, and inferiority are one explanation for this. This paper explores the link between the experiences of households in a state of energy poverty and their trust in institutions and social networks. Using qualitative data from ten different European countries, we show that a lack of trust in both public and private institutions is widespread among energy-poor households. Our interviewees show distrust in various dimensions. In their contacts with institutions, they report experiences of powerlessness, bad and unfair treatment, and feelings of inferiority. While some interviewees do trust single individuals within institutions, others trust only their own social networks and some have no trust in anyone. We further show how trust in networks or (people in) institutions can strengthen the coping capacities of energy-poor households while a lack of trust even cuts people off from the support they could attain and thus deepens their state of energy poverty. energy poverty, trust, vulnerability, institutions 1-12 140

E-Motions wave energy converter is a promising device capable of harnessing energy from wave/wind induced roll oscillations onto a generic floating platform, whose development was initiated with an experimental proof of-concept study that, despite demonstrating the potentialities of the device, also highlighted the need for further developments, aimed at improving its performance and efficiency. This justified a new phase of numerical modelling, where E-Motions was reproduced within the ANSYS (R) AQWATM environment, a potential theory based numerical model widely used in the field of wave energy converter development. The model was setup (first stage) and calibrated (second stage) with experimental data from a proof-of-concept study, carried out on a 1:40 geometric scale, with a good agreement being obtained for the hydrostatic properties (difference below 5%) and hydrodynamic roll response (minimum average error of 2.83 degrees). From a follow-up third stage, focused on comparing eight different hull solutions with similar natural roll periods, it was determined that the half-sphere and trapezoidal prism geometries produced the highest power outputs for the studied conditions (maximum average outputs of nearly 5 kW/m and 8 kW/m, respectively). These two designs were then adapted to a 1:20 geometric scale alongside an updated version of the half-cylinder, which served as a "control" case, and subjected to a final stage of numerical modelling centered on assessing the Power Take-Off's influence (namely through variable damping and mass) in their performance. Outcomes from this stage denote the necessity of a careful selection of Power Take-Off mass/damping combinations, as a disproportionate relationship could lead to scenarios where the conversion system would stall on one of the superstructure's sides, moving within a very limited range of the available sliding amplitude. Maximum average power output values reach nearly 24 kW, 30 kW and 18 kW for the half-cylinder, half-sphere and trapezoidal prism, respectively, with a follow-up experimental study being planned for the near future, in order to evaluate the validity of these results.

Passive monitoring techniques have been used for peak temperature measurements during irradiation tests by exploiting the melting point of well-characterized materials. Recent efforts to expand the capabilities of such peak temperature detection instrumentation include the development and testing of additively manufactured (AM) melt wires. In an effort to demonstrate and benchmark the performance and reliability of AM melt wires, we conducted a study to compare prototypical standard melt wires to an AM melt wire capsule, composed of printed aluminum, zinc, and tin melt wires. The lowest melting-point material used was Sn, with a melting point of approximately 230 °C, Zn melts at approximately 420 °C, and the high melting-point material was aluminum, with an approximate melting point of 660 °C. Through differential scanning calorimetry and furnace testing we show that the performance of our AM melt wire capsule was consistent with that of the standard melt-wire capsule, highlighting a path towards miniaturized peak-temperature sensors for in-pile sensor applications.