Search results for "efficien"
showing 10 items of 3014 documents
Efficient Hot Electron Transfer in Quantum Dot-Sensitized Mesoporous Oxides at Room Temperature
2018
Hot carrier cooling processes represent one of the major efficiency losses in solar energy conversion. Losses associated with cooling can in principle be circumvented if hot carrier extraction toward selective contacts is faster than hot carrier cooling in the absorber (in so-called hot carrier solar cells). Previous work has demonstrated the possibility of hot electron extraction in quantum dot (QD)-sensitized systems, in particular, at low temperatures. Here we demonstrate a room-temperature hot electron transfer (HET) with up to unity quantum efficiency in strongly coupled PbS quantum dot-sensitized mesoporous SnO2. We show that the HET efficiency is determined by a kinetic competition b…
Excitonic States in Semiconducting Two-dimensional Perovskites
2018
Hybrid organic/inorganic perovskites have emerged as efficient semiconductor materials for applications in photovoltaic solar cells with conversion efficiency above 20 \%. Recent experiments have synthesized ultra-thin two-dimensional (2D) organic perovskites with optical properties similar to those of 2D materials like monolayer MoS$_2$: large exciton binding energy and excitonic effects at room temperature. In addition, 2D perovskites are synthesized with a simple fabrication process with potential low-cost and large-scale manufacture. Up to now, state-of-the-art simulations of the excitonic states have been limited to the study of bulk organic perovskites. A large number of atoms in the …
Linear versus Three-Arm Star Polybutadiene: Effects of Polymer Architecture on the Thermodynamic Solution Behavior
2012
The interaction of linear and of three-arm star polybutadiene (PB) with THF was studied in the temperature range between 25 and 55 °C. Information for dilute solution rests on light scattering experiments; Flory–Huggins interaction parameter χ stem from vapor pressure measurements as a function of φ, the volume fraction of polymer. Despite the minute divergence in the architecture, the second osmotic virial coefficients of the two PBs differ noticeably. The present work demonstrates that these disparities become much more pronounced as φ increases and that they depend strongly on temperature. These findings are interpreted on the basis of an approach accounting for the effects of chain conn…
Temperature Coefficients of Compensated Silicon Solar Cells – Influence of Ingot Position and Blend-in-ratio
2015
Published version of an article in the journal: Energy Procedia. Also available on Science Direct: http://dx.doi.org/10.1016/j.egypro.2015.07.004 Solar-grade silicon made from a metallurgical route presents boron and phosphorus compensation. Earlier work has shown that cells made from such material produce more energy than reference polysilicon modules when the temperature and irradiance is high. In the present study, solar cells from two different ingots with different blend-in-ratios were made from wafers at varying ingot heights in order to investigate how the temperature coefficients vary with compensation level and ingot height. The results suggest that solar modules made with solar ce…
Temperature profiles of field-aged multicrystalline silicon photovoltaic modules affected by microcracks
2021
In this work, the temperature sensitivities of field-aged multicrystalline silicon PV modules affected by microcracks are investigated. It is found that the temperature coefficient of efficiency of all modules has increased more than 10 times over the 20 years period, mainly due to a degradation in the temperature coefficients of fill factor. Temperature coefficient of efficiency of PV modules affected by microcracks changed from -0.44 %/ °C to -1.51 %/°C under solar irradiance conditions at 1010 - 1030 W/m2. Inconsistent values for the Evans–Floschuetz efficiency ratio versus temperature plots for the microcrack affected modules were also observed.
Experimental characterization of a novel configuration of thermoelectric refrigerator with integrated finned heat pipes
2021
Abstract Thermoelectric refrigerating systems (TER) are environment-friendly technologies. They have several advantages such as low maintenance costs, are less cumbersome and long lifetime. However, these systems have low coefficient of performance and are limited in achieving low temperature levels. This study investigates a new configuration of TE refrigerator employing a novel arrangement of heat sinks with integrated flat and finned heat pipes. A mathematical model is firstly developed to predict transient temperatures and cooling limit time. An experimental characterization is then performed and it includes optimization of energy consumption, cooling time, temperature levels and TE ref…
Chain Connectivity and Conformational Variability of Polymers: Clues to an Adequate Thermodynamic Description of Their Solutions, 1
2003
This is the first of two parts investigating the Flory-Huggins interaction parameter, χ, as a function of composition and chain length. Part 1 encompasses experimental and theorical work. The former comprise the synthesis of poly(dimethylsiloxane)s with different molar mass and the measurements of their second second osmotic virial coefficients, A 2 , in solvents of diverse quality as a function of M via light scattering and osmotic pressures. The theorical analysis is performed by subdividing the dilution process into two clearly separable steps. It yields the following expression for χ ο , the χ value in range of pair interaction : χ ο = α - ζ λ. The parameter α measures the effect of con…
Regeneration units for thermolytic salts applications in water & power production: State of the art, experimental and modelling assessment
2021
Abstract Thermolytic solutions are often proposed as high salinity or “draw” stream to generate a chemical potential driving force in Salinity Gradient Power (SGP) and Forward Osmosis (FO) technologies. Depleted “draw” solutions exiting the process can be regenerated by a thermal process powered at very-low grade heat, which is able to decompose the salt into gaseous ammonia and carbon dioxide, which can be stripped and then reabsorbed in the draw solution, restoring its initial concentration. In this work, two different experimental prototypes for the regeneration of ammonium bicarbonate aqueous solution were designed, built and tested. The effect of several operating parameters on the reg…
Determination of limiting current density and current efficiency in electrodialysis units
2018
Abstract A crucial parameter for the design and operation of electrodialysis (ED) units is the limiting current density (LCD). This is often identified with the diffusion-limited current density, which corresponds to the complete solute depletion in the layer adjacent to the membrane. Current-voltage curves obtained from measurements with electrodes in contact with the solution (i.e. without membranes) are consistent with this interpretation and exhibit a horizontal plateau identifying LCD. However, real ED systems show more complex behaviours, with a reduced-slope tract instead of a plateau and a third region in which the current increases more markedly (overlimiting current). The phenomen…
User-oriented evaluation of mechanical single-channel axial pipettes.
2013
Hand tools should be designed so that they are comfortable to use, fit the hand and are user-oriented. Six different manual, single-channel axial pipettes were evaluated for such objective outcomes as muscular activity, wrist postures and efficiency, as well as for subjective outcomes concerning self-assessed features of pipette usability and musculoskeletal strain. Ten experienced laboratory employees volunteered for the study. The results showed that light and short pipettes with better tool comfort resulted in reduced muscular activity and perceived musculoskeletal strain when they were compared with a long and heavy pipette. There were no differences in the efficiency between the differ…