Renewable Energy Global Innovations features: Controlling Heat Release from a Close-Packed Bisazobenzene–Reduced-Graphene-Oxide Assembly Film for High-Energy Solid-State Photothermal Fuels

Significance Statement

Photo-induced isomerization of organic compounds has shown an excellent approach for utilizing solar energy. In this category, azobenzene can undergo a photo-induced change from low energy trans-isomer to high-energy cis-isomer through the absorption of photons at a particular wavelength. The resulting cis-isomer can reverse back trans-isomer owing to its low thermodynamic stability of when exposed to external stimulus, for example, heat and light.

The reversible photo isomerization attributes makes Azo-based element to be a crucial building block for photo-thermal fuels in view of its capacity to store light energy in chemical bonds and release it later as heat energy. However, the implementation of the photochromic azo compounds as photo-thermal fuels is greatly hindered by their low exothermicity as well as low activation barrier to thermal reversion. For this reason, most research works have been based on ways to enhance isomerization enthalpy and half-life through the design of several substituents.

Multi-branched Azo molecules have exhibited potential for application in photo-thermal fuels thanks to their intermolecular interactions. The isomerization is limited by large steric hindrance, which in turn increases the half-life. The intermolecular hydrogen bonds lead to an increase in isomerization enthalpy counting on the decreased energy of the trans-isomer. For this reason, tuning the steric configuration of the multi-branched Azo molecules is fundamental in the occurrence of a number of molecular interactions.

Researchers led by Professor Wei Feng at the Tianjin University in China presented a template assembly of bisazobenzene that was grafted covalently onto reduced graphene oxide. The two Azo assemblages with varying branched structures were synthesized to analyze the impact of the molecular interactions on the photo-thermal attributes. Their research work is published in ChemSusChem.

The authors prepared the reduced graphene oxide-bisazobenzene solution where it was then irradiated with Ultraviolet light in order to induce trans-to-cis isomerization. This was continuously done until the photo-stationary was noted. The absorbed energy was stored in metastable cis-isomer of the azo benzene on the reduced graphene oxide.

The resulting graphene oxide-bisazobenzene films were then irradiated with the same UV light until a photo stationary state was realized. Long duration irradiation was implemented to initiate trans-to-cis isomerization of azobenzene in the film owing to steric hindrance.

The research team successively prepared uniform photo-thermal fuel implementing a close packed graphic oxide-bisazobenzene. The grafting density was set at 1/23. Reduced Graphene oxide-bisazobenzene-2 posted high energy density of approximately 131Whkg^-1, a power density of 2517Wkg^-1. The compound also posted a long half-life of about 37days with good cyclic performance for about 50 cycles reference to inter- and intramolecular hydrogen bonding and steric performance.

The low isomerization in the solid-state graphene-based bisAzobenzene films led to energy density decrease of about 25% from what was reported for powder sample reference to steric hindrance. The authors also investigated a closed cycle of UV radiation, storage and heat release of the resulting photo-thermal. Graphene oxide based Azobenzene films were able to release and accumulate heat to realize a maximum temperature difference of 15°C. However, the films were observed to retain a temperature difference of more than 10° for about 30 minutes when the temperature difference on the environment was over 100° C.

From the results of their study it was concluded that molecular engineering for high-energy storage as well as an optimized microstructure for high degree isomerization are necessary for high-performance photo thermal fuels. The ability to tune heat release in the solid-state assembly bears a groundbreaking mechanism for developing photo thermal fuels into functional gadgets.

About The Author

Wei Feng received his PhD in 2000 from the Xi’an Jiaotong University of China after studying optic-electric properties and device applications of novel conducting polymers, and then worked at the Osaka University and the Tsinghua University as a JSPS fellow and postdoctoral researcher, respectively. In 2004, he became a full professor at Tianjin University, where he works on functional nanocarbon materials.

About The Author

Yiyu Feng obtained his PhD of materials science from Tianjin University in 2009. He is currently a full research professor at Tianjin University. His scientific interest is focused on designing and developing high-strength and high density hierarchical carbon materials & hybrid for multifunction.

Reference

Xiaoze Zhao, Yiyu Feng, Chengqun Qin, Weixiang Yang, Qianyu Si, and Wei Feng. Controlling Heat Release from a Close-Packed Bisazobenzene–Reduced-Graphene-Oxide Assembly Film for High-Energy Solid-State Photothermal Fuels. ChemSusChem 2017, 10, 1395 – 1404.

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Renewable Energy Global Innovations features: Comparisons among Bat algorithms with various objective functions on grouping photovoltaic power patterns

Significance Statement

Power generation from photovoltaic systems has been the focus of many research studies. The main aim has been to tackle environmental and financial issues of typical power resources. Unstable fossil fuel prices and a considerable portion of environmental pollutions and greenhouse emissions are major concerns when it comes to industrialized countries. Ability to produce electricity for a long time with minimal maintenance and reduction in capital costs are factors to be considered while integrating photovoltaic systems into the electrical grid.

Unfortunately, output power of photovoltaic system is dependent on ambient temperature and irradiation level. In addition, fluctuations in the output power could be experienced owing to shadowing or power quality interference. Therefore, it is important to study the effect of these output power fluctuations before photovoltaic systems installation. To achieve this, simulation implementing historical data and extensive analysis should be done.

Handling this data is computationally expensive and time consuming. Therefore, developing solutions that can ease the burden of extensive studies and simulations relating to integrating photovoltaic systems into the electrical grid is of outmost importance. Clustering methods can be used to group photovoltaic power patterns with similar properties. Thus, a representative power pattern for every group can be integrated in the simulations.

Amr Munshi and Yasser Mohamed from the University of Alberta presented the outcomes of an in-depth analysis of Bat clustering algorithms based on a number of objective functions in a bid to establish the grouping mechanism of photovoltaic power patterns. Their main objective was to enhance the clustering formation of the former clustering algorithm, Bat J. Their research work is published in Solar Energy.

The authors performed and in-depth analysis of the performance of Bat clustering algorithms dictated by a number of integrated objective functions to validate the clustering of photovoltaic power pattern process. They then compared the performance of the K-means and Bat J clustering algorithms with the new Bat clustering on the clustering process of photovoltaic power patterns data.

The researchers also illustrated the original Bat clustering algorithm methods to undertake photovoltaic power patterns grouping. They adopted the principle component analysis in a bid to reduce the dimensionality of the photovoltaic power patterns data.

Bat clustering algorithms were comparable or surpassed K-means in the validity index, compactness and separation values. The within-cluster-sum-of-squares validity index values of Bat were observed to have improved as opposed to K-means by approximately 14.10% and 14.71% over the knee-points for the first and second datasets, respectively. The authors observed that Bat within-cluster-sum-of-squares posted the best outcomes and was capable of enhancing Bat J algorithm that exhibited the best cluster data.

Nevertheless, this corresponded to more complexity since the number of parameters ought to have been priori calibrated. The preferable combination presenting the optimum number of clusters was observed to be Bat within-cluster-sum-of-squares clustering and within-cluster-sum-of-squares validity index. They presented considerably high separated and compact clusters.

Lower within-cluster-sum-of-squares values at a selected partition presented the most preferable combination of separation and compactness. Therefore, Munshi and Mohamed study on the Bat within-cluster-sum-of-squares could offer well-defined photovoltaic power pattern clusters as well as cluster representatives that can be used in photovoltaic output power analyses.

About The Author

Amr A. Munshi received the B.Sc. degree in computer engineering from Umm Al-Qura University, Makkah, Saudi Arabia, in 2008, and the M.Sc. degree in computer engineering from the University of Alberta, Edmonton, AB, Canada, in 2014, where he is currently pursuing the Ph.D. degree in computer engineering. His research interests include machine learning, data mining and big data analytics. Mr. Munshi is a Member of the Golden Key International Honor Society. He is currently an Editor of the Alberta Academic Review Journal.

Reference

Amr A. Munshi and Yasser A.-R.I. Mohamed. Comparisons among Bat algorithms with various objective functions on grouping photovoltaic power patterns. Solar Energy, volume 144 (2017), pages 254–266.

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Renewable Energy Global Innovations features: Thermodynamic analysis of siphon flash evaporation desalination system using ocean thermal energy

Significance Statement

Ocean thermal energy can be described as the thermal potential energy produced by the temperature difference between the warm surface and the cold deep seawaters. Reference to the large ocean area, ocean thermal energy reserves are huge. Ocean thermal energy is considered green in the sense that its production is without pollution. Nevertheless, this renewable energy sources suffers from low temperature difference between the deep seawater and the surface, which is generally in the range of 15-25K. The source also suffers the weakness of low specific heat that is approximately 4J/(gK), while seawater heat of vaporization is approximately 2400J/g.

To enhance the efficiency of the ocean thermal energy, it has been found profound to use the ocean thermal energy for seawater desalination directly. Using it directly can help skip the numerous conversion steps for converting ocean thermal energy to electricity and then converting the resulting electrical energy to chemical energy. Considering the scarcity of fresh water, it becomes paramount to produce fresh water using ocean thermal energy. However, in a previous system, energy consumption on seawater transportation was observed to be very high and this led to poor economic tradeoff of the systems.

In addition, the effect of a number of parameters on the performance of this system was not assessed. Above all, placing the evaporator and the condenser into a single unit caused the system to be very large, and the system’s exergy efficiency should be determined. Therefore, Zhejiang University researchers Zhi-jiang Jin, Hao Ye, Jin-yuan Qian and in collaboration with Hao Wang at Air Liquide Hangzhou Co., Ltd. And Hao Li at Nuclear Power Institute of China explained the working principle of siphon flash evaporation desalination system and analyzed the exergy efficiency of the entire system. They created a simulation model in ASPEN PLUS and analyzed the effects of a number of factors on the functioning of the system through the model. Their work is published in Energy Conversion and Management.

The vapor produced in the flash evaporator is normally absorbed into the condenser chamber reference to the pressure difference between the condenser and the evaporator. The vapor is condensed into freshwater by the cold deep ocean water. Owing to a particular degree of vacuum difference between the evaporator and the condenser, then the vapor can be absorbed into the condenser continuously.

However, the initial vacuum degree of the condenser shell side must be the same as the evaporator. There are two main functions of the ocean thermal energy; one is to generate and maintain the vacuum difference between the flash evaporator and the condenser. This will ensure that the surface water is vaporized continuously and absorbed into the condenser without extra energy consumption. The second function is that the cold deep seawater is used as a condensing agent for condensing the vaporized water into fresh water.

Under design conditions, the authors realized that the exergy efficiency of the entire system turned out very well at 7.81%. This value was higher than the typical utilization of the ocean thermal energy. The exergy efficiency of the flash evaporator was observed to reduce with a rise in the surface seawater temperature, but the condenser efficiency remained unchanged.

The flow rate of the deep seawater decreased with a rise of temperature change of the deep seawater. However, the flow rate of the surface water decreased with the increase in change in temperature of the surface water. The surface water flow rate also influenced the pressure difference between the condenser and the evaporator. Non-condensable gases in the water might have caused this. Therefore, taking into account the influence of non-condensable gases in the actual production is paramount.

About The Author

Zhi-jiang Jin, Ph.D., Professor

Institute of Process Equipment, Zhejiang University, China

Prof. Jin is the Deputy Director of Institute of Process Equipment, Zhejiang University, the Deputy Director of Energy Assessment Center, Zhejiang University. He is also a member of Pressure Vessel Branch Pipeline Committee, China Mechanical Engineering Society, and the Technical Committee of Chinese Safety and Pressure Relief Device Standardization. His research areas are focus on high efficient process equipment design and pressure pipeline safety technology.

About The Author

Jin-yuan Qian, Ph.D

Department of Energy Sciences, Lund University, Sweden

Dr. Qian received the B.Sc. and Ph.D. degrees both in Chemical Process Equipment from Zhejiang University, China in 2011 and 2016, respectively. He was a joint Ph.D. student at TU Bergakademie Freiberg, Germany, from 2013~2014. Currently, he is a postdoc fellow at Department of Energy Sciences, Lund University, Sweden. His research interests include Thermofluids, Micro/Nano Heat Transfer, Flow Control, Hydraulics, Computational Fluid Dynamics et al.

Reference

Zhi-jiang Jin, Hao Ye, Hao Wang, Hao Li, Jin-yuan Qian. Thermodynamic analysis of siphon flash evaporation desalination system using ocean thermal energy. Energy Conversion and Management, volume 136 (2017), pages 66–77.

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Renewable Energy Global Innovations features: Improvement of Cyclability of Li-Ion Batteries Using C-Coated Si Nanopowder Electrode Fabricated from Si Swarf with Limitation of Delithiation Capacity

Significance Statement

Silicon is among the most promising building blocks for negative electrode active materials used in the fabrication of lithium ion batteries. It has been identified that silicon has a theoretical capacity of approximately 3578 mAh/g and this is much more than 372 mAh/g for graphite currently applied in standard lithium ion batteries. Silicon powder prepared by expensive approaches including laser ablation as well as plasma-enhanced chemical vapor deposition has been evaluated to mitigate the stress of silicon caused by the change in size in the course of delithiation and lithiation.

Despite the outstanding attributes of silicon, silicon nanopowder still suffers several problems to use as lithium ion battery electrode active materials. Silicon nanopowder experiences volume expansion of about four times during lithiation, and considerable shrinkage during delithiation. This results in the formation of cracks in the nanopowder. Electrical isolation of the silicon nanopowder is another problem, which leads to an increase in internal resistance, low columbic efficiency and poor cyclability.

In a bid to suppress the volume change of the silicon powder, the lithiation capacity has been limited at 1500 mAh/g and 1200 mAh/g after considerable delithiation. Nevertheless, the impact of limitation of the delithiation capacity after deep lithiation on cyclability has not been studied.

Researchers led by Professor Taketoshi Matsumoto from Osaka University fabricated lithium ion battery half cells using silicon nanopowder generated from silicon swarf and investigated the impact of delithiation and lithiation capacity after deep lithiation at 0.01V on the performance of the cell. They found that the limitation of the delithiation capacity at 1500mAh/g improved the cyclability. Their work is published in Journal of The Electrochemical Society.

Silicon swarf was annealed in hydrogen atmosphere at 1000°C and later at 1000°C in ethylene environment to coat the silicon nanopowder with a 10nm carbon layer. The carbon coated silicon nanopowder was then mixed with polymer binders. The authors coated copper foil with the resulting slurry and the sample was dried where it was then packed as working electrode in a coin cell with a lithium foil counter electrode. The coin cell was also equipped with a polyethylene separator and an electrolyte.

The authors then cycled the cells in the cell voltage range of 0.01-1.5V in the course of 300 cycles using a battery charge-discharge unit. They set delithiation and lithiation current densities at 180mA/g for the first 5 cycles and 1800mA/g for the next 295 subsequent cycles.

The authors observed that limitation of delithiation capacity at 1500mAh/g resulted in the best cyclability. This capacity remained constant at 1500mAh/g until the 290^th cycle, where it reduced slightly to 1480mAh/g at the 300^th cycle. The overvoltage for delithiation-limited case was observed to be lower than that for lithiation-limited case. The low overvoltage as well as excellent cyclability was referenced to suppression of electrical isolation of silicon nanopowder owing to limited shrinkage of the silicon powder in the high lithium concentration zone.

Limitation of lithiation capacity at 1500mAh/g caused the delithiation capacity to remain at 1470mAh/g until the 137^th cycle and then decreased to 860mAh/g at the 300^th cycle. Electrical isolation, high overvoltage, and peeling-off of the silicon nanopowder resulted from low inter-particle contact reference to large size change of the silicon powder.

About The Author

Dr. Taketoshi Matsumoto is an Associate Professor in The Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan.  His research is focused on energy related nano-materials and devices.  He has been engaged in research on Li ion batteries, luminous materials, solar cells, ultra-low power thin film transistors and MOS transistors, permanent memories, fuel cells, hydrogen storages and catalysts.

He received his Ph.D. (2001) and M.S. (1998) in Electronic Chemistry from Tokyo Institute of Technology, Japan, and B.S. (1996) in Chemistry from Keio University, Japan.  He was a research fellow of the Japan Society for the Promotion of Science, a Postdoctoral Research Associate in University of Southern California, US, a Lecturer in University of Tsukuba, Japan, a Research Associate in Institute for Molecular Science, Japan, and an Assistant Professor in Osaka University, Japan.

Reference

Katsuya Kimura, Taketoshi Matsumoto, Hirotomo Nishihara, Takatoshi Kasukabe, Takashi Kyotani, and Hikaru Kobayashi. Improvement of Cyclability of Li-Ion Batteries Using C-Coated Si Nanopowder Electrode Fabricated from Si Swarf with Limitation of Delithiation Capacity. Journal of the Electrochemical Society, 164 (6) A995-A1001 (2017).

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Renewable Energy Global Innovations features: Landscape control of nitrous oxide emissions during the transition from conservation reserve program to perennial grasses for bioenergy

Significance Statement

Renewable fuels are an integral part of the liquid fuels portfolio of the United States and in fulfilling the stipulations of the federal threshold of 80 billion liters of ethanol produced from cellulosic sources by 2022. This will necessitate planting approximately 21 million hectares with cellulosic crops such as switchgrass, a perennial grass native to the United States. Land currently enrolled in the Conservation Reserve Program (CRP) – about 12 million hectares – might be suitable for energy crops. Some of this area is seasonally wet, environmentally sensitive, and with limitation for annual cropping. Converting these CRP lands to energy crops may increase the emissions of nitrous oxide, a potent greenhouse gas, particularly when converting lands that are seasonally wet due to soil or topographic attributes. Low carbon footprint is critical to accrue the benefit of energy crops. For such crops to qualify as renewable, their greenhouse gas emissions must be at most 50% of those from fossil fuels. Therefore, nitrous oxide emissions must be kept low in the feedstock production phase. Controlling nitrous oxide emissions from these energy crops requires an in-depth understanding of the interactive effects of landscape properties, crops growth rates, nutrient, and hydrology.

The research conducted by Debasish Saha and colleagues at The Pennsylvania State University identifies the potential of growing sustainable energy crops on these CRP landscapes without increasing greenhouse gas emissions. The researchers measured nitrous oxide emissions from plots converted from CRP to switchgrass and Miscanthus in central Pennsylvania. The physiography of the experimental site, representative of the Appalachian Ridge and Valley region with cropped uplands and wet bottomland that are occasionally under CRP. The emissions from the plots of energy crops were compared to the emissions from adjacent, unconverted CRP land under different landscape positions with varying soil and hydrologic properties. The researchers also established an autonomous network of 144 soil moisture sensors installed at three soil depths in 48 monitoring points in the landscape to continuously measure soil moisture, an important factor for nitrous oxide emissions. The monitoring period extended from May to September of 2013 growing season, which includes a summer storm that saturated the soil – the perfect conditions to expect nitrous oxide emissions. Their research work is published in GCB Bioenergy.

Nitrous oxide is produced by soil microbes when soil mineral nitrogen from organic/inorganic fertilizer and other sources exceeds plant demand and coincides with wet soil conditions usually after a storm or snowmelt event. “The transition phase from CRP to energy crops is critical for nitrous oxide emissions as soil disturbance may increase nitrogen availability in excess of demand when plants are small and the root system is not extensive,” said Saha.

The authors realized that nitrous oxide emissions from energy crops increased above the CRP control baseline only in the wetter footslope positions. “While near-stream footslope soils with prolonged subsoil wetness had higher nitrous oxide emissions from energy crops than CRP, a large portion of the landscape had comparable emissions to those of CRP. The footslope positions of the landscape occupy at most a third of the lower part of the watershed. For this reason, about two-thirds of the set-aside conservation area (CRP) could be used for energy crops production.” Saha further added, “It is expected that large emissions from the footslope can eventually be curtailed as the grasses get established.”

Saha said “Apart from carbon benefits of energy crops, growing energy crops in these seasonally wet CRP lands usually on steep areas of the landscape can offer additional ecosystem services. Energy crops in these landscapes can function as riparian buffers to provide water-quality benefits by curtailing nutrient as well as sediment loads to surface and groundwater. Owing to vigorous biomass production by these grasses and little disturbance of the perennial rooting systems, these crops can store carbon in the soil because of their extensive below-ground carbon allocation.”

The outcomes of their study revealed that managing the conversion from CRP to energy crops while maintaining low nitrous oxide emissions could be optimized by designing a sufficient transition process that curtails co-occurrence of high mineral nitrogen and wet soils.

This research was funded by U.S. Department of Transportation Sungrant, the USDA, and the Richard King Mellon Foundation. Other research team members include Armen Kemanian, associate professor of production systems and modeling and Felipe Montes, research associate in Plant Science, Penn State; Jason Kaye, professor of soil biogeochemistry in Ecosystem Science and Management, Penn State; Paul Adler, research agronomist with the Pasture Systems and Watershed Management Research Unit, USDA-Agricultural Research Service; and Benjamin Rau, former USDA-Agricultural Research Service soil scientist, now a research ecologist with the USDA, Forest Service.

About The Author

Dr. Debasish Saha obtained his BSc in Agricultural Sciences with specialization in Agricultural Chemistry and Soil Science in 2008 from Bidhan Chandra Krishi Viswavidyalaya, West Bengal, India. As a Junior Research Fellow of Indian Council of Agricultural Research (ICAR-JRF), he received his MSc degree in Soil Science from Punjab Agricultural University, Ludhiana, India in 2010. In 2015, he received his Ph.D. in Soil Science and Biogeochemistry under the supervision of Dr. Armen Kemanian at the Pennsylvania State University. His dissertation research investigated nitrous oxide (N₂O) emissions, a potent greenhouse gas, during the transition from Conservation Reserve Program grassland to perennial energy crops switchgrass and Miscanthus for renewable biomass energy production.

He is currently (2015-2017) appointed as a post-doc at the Department of Plant Science at the Pennsylvania State University. His post-doc research is focused on the core theme of enhancing the sustainability of organic cropping systems by mitigating N₂O emissions from soils. His research combines chamber-based N₂O monitoring, N₂O isotopomers, and microbial molecular techniques to quantify soil microbial processes contributing to N₂O production in interaction with tillage, cover crop, and manure management practices in a Reduced-Tillage Organic System Experiments.

For more information: Google Scholar ,  ResearchGate.  

Reference

Debasish Saha, Benjamin M. Rau, Jason P. Kaye, Felipe Montes, Paul R. Adler, and Armen R. Kemanian. Landscape control of nitrous oxide emissions during the transition from conservation reserve program to perennial grasses for bioenergy. GCB Bioenergy (2017) 9, 783–795.

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Renewable Energy Global Innovations features: Thinness- and Shape-Controlled Growth for Ultrathin Single-Crystalline Perovskite Wafers for Mass Production of Superior Photoelectronic Devices

Significance Statement

The commercialization of organic-inorganic hybrid perovskite light-absorber material has been hampered by factors such as environmental stability, substandard interface and defects. Focus has shifted to the single-crystalline perovskite which is believed to be defect free, has better stability, longer carrier lifetime and diffusion length, wider optical absorption spectrum, and lower trap-state-density.

Professor Shengzhong (Frank) Liu and colleagues have successfully used a dynamic flow microreactor system to grow geometry-controlled ultrathin single crystalline perovskite wafers of different ranges of thicknesses. Their work is published in Advanced Materials, 2016, 28, 9204-9209; Adv. Opt. Mater. 2016, 4 (11), 1829-1837; Sci. China Chem. 2017, DOI:10.1007/s11426-017-9081-3.

The authors employed a dynamic-flow reaction system. They used 2 spacers to separate and align 2 thin glass slides so as to limit the crystal growth to a slit channel. A peristaltic pump was used to achieve dynamic flow of the precursor solution.

The research team fabricated single crystalline wafers of approximately 150, 330, 670, and 1440 mm in thickness, which showed that the crystal growth was confined within the microreactor.

The authors observed no obvious grain boundaries and cracks from the scanning electron microscopy examination, indicating that the wafer is of  high single-crystalline quality throughout. The mapping analysis and line scan results of the scanning electron microscopy energy-dispersive x-ray spectroscopy show an even distribution as well as consistency in atomic ratio of carbon, nitrogen, lead, and iodine constituents of the produced wafer.

When the single crystalline perovskite wafer is compared with the microcrystalline thin films in UV-Vis-NIR spectrophotometry, the authors observed that the former displayed a significant red-shifted light absorption edge at 900 nm as compared with 800 nmfor the latter, a significant advantage for PV and optoelectronic applications.

From the thermogravimetric analysis, the single crystalline wafer is similar to bulk single crystals in thermal decomposition,  exhibiting stability at higher temperatures over the microcrystalline films.

The authors designed a hole only device to analyze the trap density of the single crystalline wafer by testing, at different biases, the evolution of space-charge-limited current. The trap density of both the single crystalline wafer and the large single crystals was found to be similar. The Hall effect is also similar for both the single crystalline wafer and the single large crystals.

To simulate an optoelectronic device, the team designed 100 photodetectors on the perovskite wafer, which demonstrated the feasibility of integrated circuits being mass produced on these wafers. At different bias voltages and illumination, the authors observed that at a 2V bias the photocurrent in the wafer was approximately 700 µA, while this was limited to only 2 µA for the microcrystalline thin films which is approximately 350 times smaller. The single crystalline wafer detector showed significant response  at 880 nm while the microcrystalline thin film device shows no response at all, which confirmed that the former has a broader optical absorption than the latter.

Reference

Yucheng Liu, Yunxia Zhang, Zhou Yang, Dong Yang, Xiaodong Ren, Liuqing Pang, and Shengzhong(Frank) Liu. Thinness- and Shape-Controlled Growth for Ultrathin Single-Crystalline Perovskite Wafers for Mass Production of Superior Photoelectronic Devices. Advanced Materials, 2016, 28, 9204-9209.

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Renewable Energy Global Innovations features: Probabilistic small signal stability analysis with large-scale integration of wind power considering dependence

Significance Statement

Reference to an increase in the wind power generation, power system stability and reliability has been affected by the wind farms. The attributes of winds farms have been observed to be different from the normal power plants, such as thermal or nuclear and hydraulic. Intermittency characterizes wind power and consequently introduces many uncertainties in the electric power systems. Therefore, for optimal operation of the power systems integrated with more sources of uncertainties, it is important to incorporate probabilistic models in the management systems.

Probabilistic methodologies proposed in most studies are perfect for the analyses of uncertainties, in order to account for the uncertainty arising from the generation of wind power. The methodologies are also important in modelling the uncertainty from the loads. More research works have focused on how conventional power systems made of synchronous generators respond to wind power integration, and how their electromechanical modes of oscillation are affected.

The results of the effect of various levels of wind power integration to a system’s small signal stability reveal that the small signal stability is affected negatively when the wind power penetration is increased. On the other hand, similar analyses reveal that wind power integration has both negative and positive effects on the system’s small signal stability.

Keyou Wang and his colleague from Shanghai Jiao Tong University presented a critical and timely review of the methodologies used in the probabilistic small signal stability analysis and dependence modelling. They also presented in their work, a comparative analysis of these methodologies and preferences of the methodologies under various wind power integration scenarios. The report is now published in Renewable and Sustainable Energy Reviews.

Wind turbines do not participate directly in the electromechanical oscillations in power systems; however, they affect the small signal stability by altering the power dispatch to synchronous generators as well as transmission networks. An evaluation of how sources of uncertainties affect a system’s small signal stability is fundamental for optimal operation.

A variety of methodologies has been proposed to account for the uncertainties, and can be classified into three categories: numerical, analytical, and approximate methods, which are represented by the Monto Carlo simulation, cumulant-based method, and point of estimation method, respectively.

Point of estimation and cumulant-based methods have been identified to be better due many advantages. However, the cumulant-based method demands less deterministic simulations as compared to point of estimation method.

The authors realized that accounting for the dependence between the various uncertainty sources was necessary in a bid to determine dependency structures that bear the actual state of the system, and consequently, after carrying out the small signal stability analysis, the outcomes would bear the actual response of the system to small perturbations taking into account dependence and uncertainty.

Out of all the dependence modeling methodologies considered, the pair-copula was identified as the most accurate but time consuming. It was suitable for power systems with small-scale wind power sources integration, and linear correlation coefficients as well as normal copula models were less accurate but were more efficient in large-scale power plants with large-scale wind power sources integration. Therefore, the choice of dependence modeling methods would largely depend on the scale of wind power integration, efficiency and accuracy needed.

About The Author

Jin Xu (S’16) received his B.S. degree in electrical engineering from Sichuan University, Chengdu, China, in 2013. He is currently pursuing the Ph.D. degree at Department of Electrical Engineering School of Electronic information and Electrical Engineering, Shanghai Jiao Tong University, Shanghai, China.

His research interests include power system dynamic modelling and stability analysis, electromagnetic modelling and simulation.

About The Author

Peter Kairu Kanyingi was born in 1986. He received his undergraduate degree in Energy Engineering from Kenyatta University in the year 2011. In the year 2016, he received his MSc degree from Shanghai Jiao Tong University with a Major in Power Systems and its Automation. From Sep 2016 to March 2017 he was with the Department of Renewable Energy at Jaramogi Oginga Odinga University as a part time lecturer. Currently he is a lecturer in the Department of Energy Technology at Kenyatta University, Nairobi Kenya.

His major research interests include power system stability, probabilistic modeling of power systems, modeling of complex dependence and uncertainty existing in renewable energy sources, analysis of the impact of wind and solar power integration into existing power systems, smart grid, HVDC and power system design, modeling and simulation.

About The Author

Keyou Wang (S’05–M’09) received the B.S. and M.S. degrees in electrical engineering from Shanghai Jiao Tong University, Shanghai, China, in 2001 and 2004, respectively, and the Ph.D. degree from the Missouri University of Science and Technology (formerly University of Missouri-Rolla), Rolla, MO, USA, in 2008.

He is currently an Associate Professor and the Deputy Department Head of Electrical Engineering with Shanghai Jiao Tong University. His research interests include power system dynamics and stability, renewable energy integration, and converter dominated power system. He serves as an Associated Editor of IET Generation Transmission & Distribution.

About The Author

Guojie Li (M’09-SM’12) received his B.E. and M.E. degrees in Electrical Engineering from Tsinghua Univ., Beijing, China in 1989 and 1993, respectively. He also received PhD degree in the School of EEE, Nanyang Technological University Singapore in 1999.

He was an associate professor in the Dept. of Electrical Engineering, Tsinghua Univ., Beijing, China. He is now a professor in the Dept. of Electrical Engineering, Shanghai Jiao Tong Univ., Shanghai, China. His current research interests include ac/dc power system analysis and control, wind and PV power control and integration, and DAB control.

About The Author

Bei Han received M.S degree in electrical engineering from Shanghai Jiao Tong University and received Ph.D degree in electrical engineering from Politecnico di Torino. Currently, she is an Assistant Professor of Shanghai Jiao Tong University. Her research interests are complex distribution system modeling with multi-microgrids and DER uncertainties.

About The Author

Xiuchen Jiang was born in Shandong, China. He received the B.E. degree in high voltage and insulation technology from Shanghai Jiao Tong University, Shanghai, China, in 1987, the M.S. degree in high voltage and insulation technology from Tsinghua University, Beijing, China, in 1992, and the Ph.D. degree in electric power system and automation from Shanghai Jiao Tong University in 2001.

Currently, he is a Professor in the Department of Electrical Engineering, Shanghai Jiao Tong University. His research interests are electrical equipment online monitoring as well as condition-based maintenance and automation.

Reference

Jin Xu, Peter Kairu Kanyingi, Keyou Wang, Guojie Li, Bei Han, and Xiuchen Jiang. Probabilistic small signal stability analysis with large-scale integration of wind power considering dependence. Renewable and Sustainable Energy Reviews, volume 69 (2017), pages 1258–1270.

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