Improvement of multicrystalline silicon solar cells by a low temperature anneal after emitter diffusion

The influence of an annealing step at about 500 °C after emitter diffusion of multicrystalline solar cells is investigated. Neighboring wafers from a silicon ingot were processed using different annealing durations and temperatures. The efficiency of the cells was measured and detailed light beam induced current measurements were performed. These show that mainly areas with high contents of precipitates near the crucible walls are affected by the anneal. An efficiency increase from 14.5 to 15.4% by a 2 h anneal at 500 °C was observed. The effect seems to be more likely external than internal gettering. Copyright © 2010 John Wiley & Sons, Ltd.     

Comprehensive comparison of FACTS devices for exclusive loadability enhancement

A complete comparison of a number of well‐known flexible alternating current transmission system (FACTS) devices for static voltage stability enhancement is presented. Various performance measures including power–voltage (P–V) curves, voltage profiles, and power losses are compared under normal and contingency conditions. The importance of proper modeling of FACTS devices, including the DC side, is emphasized because, at their limits, most of these devices behave like a fixed capacitor or inductor. A simple placement technique of series FACTS devices and unified power flow controller (UPFC) is proposed considering exclusive loading margin enhancement. A new idea of loading margin increase per cost is proposed to find the appropriate FACTS devices for investment. The paper provides a guide for utilities to have an appropriate choice of FACTS device for enhancing static voltage stability and loading margin by comparing technical merits and demerits of each of these devices in terms of system performance. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Combination of visible reflectance and acoustic response to improve non-destructive assessment of maturity and indirect prediction of internal quality of red-fleshed pomelo

Maturity and the internal quality of red-fleshed pomelo in terms of the sugar–acid ratio were studied by assessing whole fruit properties using acoustic response and local properties based on the visible reflectance of the fruit surface. Pomelo fruit samples were harvested at different maturity stages. Maturity classification and prediction models were built using discriminant analysis and partial least squares regression, respectively. Better classification was achieved by the model incorporating both surface visible reflectance and the resonant frequency compared with the model based on only surface visible reflectance. Similarly, the sugar–acid ratio was better predicted by the model using both acoustic response and surface visible reflectance. The accuracy of prediction was maintained when the data from two harvest seasons were combined to build the model for prediction.     

Dimethyl ether synthesis from methanol over diatomite catalyst modified using nitric acid treatment

Dimethyl ether synthesis from methanol over diatomite catalysts modified using nitric acid was investigated. The catalytic performance of diatomite was tested in a fixed-bed reactor under atmospheric pressure and within the temperature range of 250–350°C. It was discovered that high acidity of the catalyst yielded a higher methanol conversion rate. Moreover, it was revealed that the acidity of the catalyst surface was controlled by Al^(IV) ions whereas basicity of the catalyst surface was determined by Al^(V) and Al^(VI) ions. From this finding, the authors were able to propose the mechanism of DME synthesis from methanol over treated diatomite.     

Characterization of platinum–iron catalysts supported on MCM-41 synthesized with rice husk silica and their performance for phenol hydroxylation

Mesoporous material RH-MCM-41 was synthesized with rice husk silica by a hydrothermal method. It was used as a support for bimetallic platinum−iron catalysts Pt–Fe/RH-MCM-41 for phenol hydroxylation. The catalysts were prepared by co-impregnation with Pt and Fe at amounts of 0.5 and 5.0 wt.%, respectively. The RH-MCM-41 structure in the catalysts was studied with x-ray diffraction, and their surface areas were determined by nitrogen adsorption. The oxidation number of Fe supported on RH-MCM-41 was + 3, as determined by x-ray absorption near edge structure (XANES) analysis. Transmission electron microscopy (TEM) images of all the catalysts displayed well-ordered structures, and metal nanoparticles were observed in some catalysts. All the catalysts were active for phenol hydroxylation using H₂O₂ as the oxidant at phenol : H₂O₂ mole ratios of 2 : 1, 2 : 2, 2 : 3 and 2 : 4. The first three ratios produced only catechol and hydroquinone, whereas the 2 : 4 ratio also produced benzoquinone. The 2 : 3 ratio gave the highest phenol conversion of 47% at 70 °C. The catalyst prepared by co-impregnation with Pt and Fe was more active than that prepared using a physical mixture of Pt/RH-MCM-41 and Fe/RH-MCM-41.     

Methanol dehydration to dimethyl ether over strong-acid-modified diatomite catalysts

Dimethyl ether synthesis via methanol dehydration over strong-acid-modified (with sulfuric, hydrochloric and nitric acid) diatomite (DM) catalysts was conducted in a fixed-bed reactor with elevated temperature reaction from 250 to 350°C. The modified DM catalysts were characterized by using X-ray diffraction, scanning electron microscopy, fourier transform infrared spectroscopy, fourier transform Raman spectroscopy, temperature-programmed desorption of ammonia, temperature-programmed of carbon dioxide, thermal gravimetric analysis, and solid-state 27Aluminum magic angle spinning/nuclear magnetic resonance spectroscopy. It was found that sulfuric-acid-modified DM catalyst yielded the highest DME selectivity (~99%). It was also revealed that methanol conversion depended on Al ions. The methanol conversion increased with Al^(IV) but decreased with Al^(V) and Al^(VI).