Renewable Energy Global Innovations featured article: Application of a three-dimensional aeroelastic model to study the wind-induced response of bridge stay cables in unsteady wind conditions [/author] Read more research excellence studies on: Renewable Energy Global Innovations (http://ift.tt/21cCPA4)
Renewable Energy Global Innovations featured article: Future European biogas: Animal manure, straw and grass potentials for a sustainable European biogas production [/author] Read more research excellence studies on: Renewable Energy Global Innovations (http://ift.tt/21cCPA4)
Renewable Energy Global Innovations featured article: Low-Voltage Thermoelectric Energy Harvesting System for Wireless Sensor Nodes [/author] Read more research excellence studies on: Renewable Energy Global Innovations (http://ift.tt/21cCPA4)
Renewable Energy Global Innovations featured article: The way to panchromatic copper(I)-based dyesensitized solar cells: co-sensitization with the organic dye SQ2 [/author] Read more research excellence studies on: Renewable Energy Global Innovations (http://ift.tt/21cCPA4)
Presently, many countries are still persistently using fossil fuels despite the high environmental pollution risk they pose. Currently, the effects of excessive emission of the oxides of carbon, nitrogen and sulphur are evident through acid rain and global warming. To counteract this, the world is turning to biofuels mainly due to the lower carbon dioxide emissions. Biodiesel, consisting of a mixture of fatty acid methyl esters, is mainly obtained by transesterification of triglycerides found in vegetable oils and animal fats. Due to its economic feasibility, homogeneous alkaline transesterification is widely used in the biodiesel production industry. However, this technique becomes inapplicable when the raw material has a high free fatty acids content, as it results in the consumption of the catalyst, yield reduction and soap production.
Soapstock, a low cost and highly acid raw material, mainly obtained as a residue from chemical processes used in the refining of vegetable oils, seems to be a promising and sustainable material for biodiesel production. Conversely, due to its high free fatty acids content, an alternative production route is required to convert such fatty acids in methyl esters. The use of chemical and biological heterogeneous catalysts in such process seems promising. Even though, the use of acid oil from soapstock for biofuels production, and more specifically the applicability of bio-catalysts for its esterification, are still poorly studied.
A research study, led by Joana Maia Dias at LEPABE-Laboratory for Process Engineering, Environment, Biotechnology and Energy (Faculty of Engineering, University of Porto) in Portugal, evaluated the enzymatic esterification of an acid oil from soapstocks obtained in vegetable oil refining using a commercial lipase in batch reactors under specific conditions. Her team established as main objectives to characterize the acid waste oil aiming enzymatic esterification and evaluate the need for pretreatment, study the effect of enzyme concentration during esterification using selected reaction conditions and perform complementary studies for assessing the effect of other key variables. This research work is now published in the Renewable Energy journal.
The researchers started their empirical work by conducting a pretreatment on the acid oil to reduce its mineral acidity before enzymatic esterification could be undertaken. They then undertook the esterification reactions under batch conditions where vigorous magnetic stirring was maintained. The methyl ester content in the final product was determined by gas chromatography.
They observed that the amount and type of alcohol utilized had minor influence in the reaction conversion and that the fractionated addition of methanol had only expressive effect for lower catalyst concentrations, with final conversions being still unsatisfactory. They noted that the best conditions were 4 wt.% of enzyme, 35 °C, 24 h, and 1:1.5 molar ratio of acid:alcohol, which afforded an 80% reduction of acidity.
Herein, enzymatic esterification of acid oil of soapstock from vegetable oil refining has successfully been demonstrated. It has been seen that the enzyme concentration deeply influences the reaction at the range of conditions studied. More so, the enzymes allow not only the esterification of the fatty acids but also the transesterification of various glycerides present, thereby obtaining a final product having a good concentration of methyl esters, which is highly valued in the biofuels industry. This technique is very adaptable and will enable the future production of biodiesel in a more sustainable manner.
Mariana Cruz, Sílvia Cardinal Pinho, Ricardo Mota, Manuel Fonseca Almeida, Joana Maia Dias. Enzymatic esterification of acid oil from soapstocks obtained in vegetable oil refining: Effect of enzyme concentration. Renewable Energy (2017) 1-7
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The use of n-type dye sensitized solar cells for the conversion of solar photons into electrical energy is now a mature field of research with the conversion efficiency extending beyond 11% to approximately 14%. This has been made possible by the implementation of ruthenium-based, zinc(II), and organic porphyrin-based dyes. Unfortunately, the low earth abundance and high cost of ruthenium-based sensitizers have continued to limit their application despite them taking the lead among inorganic compounds. However, copper-based dyes are sustainable and appear to be promising alternatives to ruthenium.
In order to achieve high performance of dye-sensitized solar cells, the absorbance of the incident rays, injection of electrons into the semiconductor, and the interconnection between the electrolyte and the dye must be optimal. When the absorption range of the dye overlaps with the spectrum of the incident rays, there is a possibility of attaining higher conversion efficiencies. It has been observed that the most efficient copper-based dyes attain >3% photoconversion efficiency, which is relative to the values in the range of 7.12-7.63% for the benchmark ruthenium dyes.
Contrary to the panchromatic absorption of ruthenium dye N719 as well as related dyes, the metal-to-ligand charge transfer band of copper(I) sensitizers is typically in the range of 430 to 570 nm. However, this range can be extended by broadening the π-system of the copper-bound ligands. This would result in higher short-circuit current density values, but would not necessarily lead to enhanced global efficiency.
Frederik Malzner, Markus Willgert, Edwin Constable and Catherine Housecroft at the University of Basel in Switzerland successfully reported the first co-sensitization of a copper(I)-based dye-sensitized solar cell with a complementary organic dye in a bid to realize improved dye-sensitized solar cell photo-conversion efficiency. Their research work is published in Journal of Materials Chemistry A.
The authors described the first example of co-sensitization in dye-sensitized solar cells implementing copper(I)-based sensitizer as well as a commercially available dye. The authors combined the heteroleptic copper(I) dye with a commercially available squaraine derivative. They then matched the external quantum efficiency maxima from the two dyes in complementary parts of the visible spectrum.
Through this combination, the authors realized the highest photo-conversion efficiency of 65.6% so far reported for a copper-based dye-sensitized solar cell. This is the confirmation of the potential implementation of earth-sustainable copper as a sensitizer in dye-sensitized solar cells.
The Swiss research team found that the sequences in which the photo-anodes of the n-type dye-sensitized solar cells were exposed to the heteroleptic copper(I) dye and the squaraine derivative, as well as the time the electrodes were exposed to the dyes, immensely affected the overall performance of the solar cells. The aggregation of the squaraine molecules on the surface of the electrode was necessary for realizing panchromatic light harvesting for the co-sensitized dye-sensitized solar cells. However, excess aggregation would have been detrimental. The outcomes of the external quantum efficiency measurements done with varying wavelength-range filters were consistent with the two dyes operating separately.
Frederik J. Malzner, Markus Willgert, Edwin C. Constable and Catherine E. Housecroft. The way to panchromatic copper(I)-based dyesensitized solar cells: co-sensitization with the organic dye SQ2. Journal of Materials Chemistry A, volume 5 (2017), pages 13717–13729.
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High production cost and low efficiency are the key roadblocks to realizing advances in solar technology. At present, solar photovoltaics can only account for less than 2% of today’s global electricity. More so, a complex inhibition is encountered when attempts to increase the power conversion efficiency of a single-junction solar cell are made. As a result, inquest into the formation of multiple-junctions in a cell is receiving considerable attention. In recent advancements, organometal halide perovskite-based solar cells have emerged as promising top cell candidates due to their suitable electrical and optical properties. To achieve highly efficient tandem devices, the realization of a high efficiency semi-transparent perovskite solar cell is still an essential challenge. Moreover, the development of a suitable deposition process that does not deteriorate the low-cost advantage and maintains the high performance of the perovskite solar cells will be of great importance.
A team of researchers led by Doh-Kwon Lee at the Photo-electronic Hybrids Research Center, Korea Institute of Science and Technology designed semi-transparent inverted planar perovskite solar cells for monolithic tandem construction with an electrodeposited copper-indium-selenide solar cell. Their aspirations were to attempt and realize a high-efficiency monolithic thin film tandem device. In order to achieve this, they hoped to eliminate the severe degradation of the perovskite/PCBM layers during the sputtering process of the transparent conducting oxide, using a thin zinc oxide-nanoparticle introduced onto the electron-extracting PCBM layer by a simple solution process without a post-annealing step. Their research work is now published in the journal, Journal of Materials Chemistry A.
The procedure undertaken involved selecting a sputter aluminum-doped zinc oxide layer as the top transparent conducting oxide while employing a thin zinc oxide-nanoparticles layer prepared by a simple solution process as a buffer layer to protect the underlying PCBM and/or perovskite layers from possible damage during the sputter deposition of the aluminum-doped zinc oxide electrode. To demonstrate the feasibility of all-solution processed, monolithic two-terminal tandems, an electrodeposited copper-indium-selenide thin-film solar cell with a power conversion efficiency of ca. 10% was used as a bottom cell. An intrinsic zinc oxide/ aluminum-doped zinc oxide double layer was applied as a transparent recombination layer at the junction between the sub-cells by tuning its thickness. As a result, monolithically integrated, two-terminal copper-indium-selenide/perovskite tandem solar cells with a higher power conversion efficiency than the constituent single-junction devices were realized.
The research team observed that the thin zinc oxide-nanoparticles layer with an optimal thickness facilitates the electron transfer from PCBM to the silver back contact in opaque devices while also helping to protect the underlying layers from plasma-induced damage in semi-transparent devices. As a result, semi-transparent perovskite solar cell devices with an inverted architecture having a sputtered aluminum-doped zinc oxide top electrode are realized with power conversion efficiencies over 10%.
Within a semi-transparent perovskite solar cells in the p–i–n architecture, in which a solution processed zinc oxide-nanoparticles layer was introduced as an effective charge selective layer between the PCBM and transparent conducting oxide layers, has been demonstrated. It has been seen that due to the sputter-buffering ability of the zinc oxide-nanoparticles layer, an aluminum-doped zinc oxide top transparent conducting oxide layer could be deposited without causing severe plasma damage to the underlying perovskite/PCBM layers. The technique presented in their paper is important in that it allows current matching between the sub-cells, optimization of the recombination layer for good transmission of low-energy photons and low interfacial resistance and the development of a fabrication strategy that is viable for industrial use. All in all, the results obtained shed light on the possibility of all-solution-processed, highly efficient tandem solar cells.
PCBM – phenyl-C61-butyric acid methyl ester
Yoon Hee Jang, Jang Mi Lee, Jung Woo Seo, Inho Kim, Doh-Kwon Lee. Monolithic tandem solar cells comprising electrodeposited CuInSe2 and perovskite solar cells with a nanoparticulate ZnO buffer layer. J. Mater. Chem. A, 2017, 5, 19439–19446
Globally, research and development of electrical energy storage is rapidly gaining popularity amongst scholars. These can be attributed to the fact that it plays a crucial role in the areas of: renewable energy power generation, smart grid, off-peak electricity utilization, distributed energy system, micro-grid and energy internet. At present, several power storage techniques exist. Amongst these techniques, compressed air energy storage system is the most promising technique given its highly desired advantages that include: low initial, operational and maintenance costs, environmental friendliness, deployable at large scale, high efficiency and long lifetime. Conversely, conventional compressed air energy storage systems are subject to limitations such as: dependency on fossil fuels and large chambers, reduced efficiency and minimal energy density, thereby, their development and large scale application is limited. To counteract these issues, researchers have sought to introduce the supercritical compressed air energy storage system.
In a recent paper published in the journal, Applied Energy, Haisheng Chen and colleagues from Institute of Engineering Thermophysics at Chinese Academy of Sciences set out to present an analytical solution for a novel compressed air energy storage system – supercritical compressed air energy storage system. Their goal was to explore the influence of key parameters on system efficiency since it is known that the coupling relationships of system processes and parameters cannot be explored thoroughly with numerical approaches.
The research team commenced their empirical work by obtaining and calculating the exergy destruction for each part of the model. A method of sectional treatment of the system and Taylor expansion ignoring higher order terms was also carried out so as to obtain the variation of system efficiency with key parameters through the analytical solution as well as the reasons for such variation. Eventually, a sensitivity analysis and an exergy analysis were undertaken for supercritical compressed air energy storage system.
The authors mainly observed that the system efficiency varies linearly with isentropic efficiencies of compressor and expander, temperature difference of intercooler and reheater, pressure loss of intercooler and reheater. More so, they noted that the analytical solution was universal for compressed air energy storage system systems with similar layout to the supercritical compressed air energy storage system due to the deduced method of sectional treatment.
Concise analytical model of the supercritical compressed air energy storage system has been established in their study. A comparison of the existing compressed air energy storage system with our novel supercritical compressed air energy storage system has also been presented. It has been mainly noted that our novel system possesses great development potential with important advantages such as: eliminating reliance on fossil fuel and large chambers, increased energy storage density and high system efficiency. The outcomes of this study are impressive and can be used as reference for designing and optimizing of the supercritical compressed air energy storage system and other similar compressed air energy storage systems.
Currently, the world’s first 10MW advanced CAES plant has been built in Bijie, China by the research team, and the plant is shown in Fig.1.The test data of the plant will provide support to verify the analytical solution of this work.
Huan Guo, Yujie Xu, Haisheng Chen, Cong Guo, Wei Qin. Thermodynamic analytical solution and exergy analysis for supercritical compressed air energy storage system. Applied Energy volume 199 (2017) pages 96–106.
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