Flexible Source Research Articles

Bi-level sitting and sizing of flexi-renewable virtual power plants in the active distribution networks

This paper presents a bi-level optimization problem to obtain the optimal location and size of the flexi-renewable virtual power plants (FRVPPs) in active distribution networks (ADNs). The upper-level formulation of the problem minimizes a normalized objective function (a dimensionless function), which is a normalized summation of the expected annual energy cost and expected annual energy loss of the ADN, subjects to linearized AC optimal power flow (LAC-OPF) equations. Also, the lower-level problem minimizes the annual investment and expected operating costs of flexible and renewable sources constrained to the planning and operation model of these sources in the FRVPP framework. The suggested scheme incorporates the unscented transformation (UT) method to model the uncertainties of load, energy price, and renewable power generation. Then, the Karush-Kuhn-Tucker (KKT) approach converts the proposed bi-level problem into a single-level optimization formulation to achieve the optimal solution using conventional mathematical solvers. Finally, the proposed scheme is applied to a standard test system. Simulation results confirm the capabilities and superiority of the proposed strategy in improving the technical and economic status of the ADN while obtaining the optimal location and size of renewable and flexible sources in the FRVPP framework from an economic aspect.

Book-Shaped All-in-One Piezo-Triboelectric Energy Harvester Module with Enhanced Current Characteristics As an Eco-Friendly Energy Source

A book-shaped all-in-one energy harvester module with a piezo-triboelectric hybrid structure as a next-generation eco-friendly energy source was manufactured based on flexible piezoceramic nanofibers with enhanced current characteristics obtained by controlling the added amount of carbon black (CB). To prepare flexible piezoceramic nanofibers with favorable current properties, 0.78Bi0.5Na0.5TiO3−0.22SrTiO3 (BNT-ST) piezoelectric ceramics were composited with CB, a highly conductive material, and then electrospun with a poly(vinylidene fluorideco–trifluoroethylene) polymer. The prepared CB/BNT-ST nanofibers were modularized into piezoelectric energy harvester modules (PEHMs) with interdigitated electrodes, yielding an improved output performance with a high voltage of 10.1 V and high current of 2.02 nA. A book-shaped triboelectric energy harvester module (TEHM) was manufactured with polydimethylsiloxane on one side and the CB/BNT-ST nanofibers on the other side, affording an improved output performance with a high voltage of 391 V and high current of 130 μA. A book-shaped all-in-one hybrid energy harvester module (HEHM) was then manufactured by fitting PEHMs at both ends of the book-shaped TEHMs. As a result of optimizing the output performance by connecting HEHM multiple layers, a high voltage and current of 1043 V and 579 μA were observed, respectively, and charging of a 1.0 μF capacitor was completed in 25 s. Furthermore, in simulated energy harvesting experiments using the all-in-one HEHM, LED light bulbs were clearly illuminated in real time, and an electronic calculator was operated without charging. This work suggests the application potential of the all-in-one HEHM as the next generation of eco-friendly flexible energy sources.

Photodynamic therapy with light emitting fabrics: a review.

Photodynamic therapy is a powerful tool in the localized and selective treatment of dermatologic diseases, such as actinic keratosis, acne vulgaris, Bowen's disease and basal cell carcinoma. The success of photodynamic therapy is mainly attributed to the development of flexible light sources for homogenous and reproducible illumination during clinical studies. The essential requirement for this therapy includes, a suitable photosensitizer, presence of oxygen and a light of specific wavelength and intensity. The use of light emitting fabric comprising of optical fibers provides an exciting and an efficient way to transfer light directly to the skin uniformly on the infected body parts. As the optical fibers can transmit light from 400 to 1200nm it is possible to combine light emitting fabric with laser sources for medical applications. This review focusses on the challenges and recent developments in the use of light emitting fabric for photodynamic therapy in clinical studies and its future perspectives.

Investigation of SARS-CoV-2 inactivation using UV-C LEDs in public environments via ray-tracing simulation

This paper proposes an investigating SARS-CoV-2 inactivation on surfaces with UV-C LED irradiation using our in-house-developed ray-tracing simulator. The results are benchmarked with experiments and Zemax OpticStudio commercial software simulation to demonstrate our simulator's easy accessibility and high reliability. The tool can input the radiant profile of the flexible LED source and accurately yield the irradiance distribution emitted from an LED-based system in 3D environments. The UV-C operating space can be divided into the safe, buffer, and germicidal zones for setting up a UV-C LED system. Based on the published measurement data, the level of SARS-CoV-2 inactivation has been defined as a function of UV-C irradiation. A realistic case of public space, i.e., a food court in Singapore, has been numerically investigated to demonstrate the relative impact of environmental UV-C attenuation on the SARS-CoV-2 inactivation. We optimise a specific UV-C LED germicidal system and its corresponding exposure time according to the simulation results. These ray-tracing-based simulations provide a useful guideline for safe deployment and efficient design for germicidal UV-C LED technology.

Design and optimal energy management of community microgrids with flexible renewable energy sources

Energy communities is a new, but already successful prosumer model of the local energy systems' construction. It is based on distributed energy sources and the electricity consumers’ flexibility who are the members of the community. In search of the most effective ways to interact within themselves and with the external energy system, local energy communities become platforms for exciting experiments in the field of new energy practices including local markets for flexibility, building cooperative microgrids, achieving energy autonomy, and many others. This work aims to present a unified approach to building and optimally managing the community microgrids with an internal market, given the social, environmental, and economic benefits of a particular location of such a community. A new modeling framework is introduced, based on bilevel programming and reinforcement learning, for structuring and solving the internal local market of a community microgrids, composed of entities that may exchange energy and services among themselves. The overall framework is formulated in the form of a bilevel model, where the lower level problem clears the market, while the upper level problem plays the role of the community microgrid operator (Community EMS). We strengthen the traditional bilevel problem statement by the local energy management system (Local EMS) introduction based on Monte-Carlo tree search algorithm. Our approach makes it possible to enable interaction of the local control systems for microgrids with the community microgrid operator as part bilevel programming problem solution. Numerical results obtained on the real test case of the microgrid community for the settlements located in the Transbaikal National Park (Russia), which include various renewable energy sources (wind, solar power, biomass gasifiers) and storage devices, show reduction of the LCOE index from 20% to 40% and improving the quality of electricity supply to the analyzed settlements.

The Strategy of Achieving Flexibility in Materials and Configuration of Flexible Lithium‐Ion Batteries

In recent years, with the development of flexible intelligent wearable devices, flexible batteries have attracted widespread attention in energy storage systems. To satisfy the power supply as well as the integrity of flexibility for the flexible intelligent wearable devices, the development of batteries with both excellent electrochemical performance and wearable flexibility has attracted a lot attention. This review is focused on the discussion of how to realize battery flexibility from the perspective of flexible lithium‐ion batteries as one of the most ideal and promising flexible power sources. Also, the development of flexible lithium‐ion batteries in recent years and the methods to achieve the flexibility are reviewed from the aspects of battery materials and electrode structures, to provide new ideas for research about flexible lithium‐ion battery with a high energy density in the future.

Electrothermal Tristability Causes Sudden Burn‐In Phenomena in Organic LEDs (Adv. Funct. Mater. 47/2021)

Electrothermal Tristability Thin and flexible large-area light sources open up a universe of new applications in lighting technology. In article number 2106716, Axel Fischer and co-workers present how electrothermal self-heating phenomena in area light sources scale with panel size. They find an unprecedented inherent tristability that jeopardizes stable device operation and promotes abrupt failure.

Researches on the yellow emission properties of 2 at.%Dy: Gd0.1Y0·9AlO3 crystal

Dy3+-actived Gd0.1Y0·9AlO3 (abbr. as Dy: GdYAP) crystal was grown successfully by using Czocharlski (CZ) method and yellow emission performances were characterized to study the influence of Gd3+ ions on the absorption or emission spectra, which are non-optically active in the visible and infrared ranges. Minor changes have been observed in the absorption peaks of the crystal near 450 nm but the yellow emission peaks are still located near 572 nm. The largest emission cross-section σem was obtained to be 5.62 × 10−21 cm2 (E//b) and the fluorescence lifetime τr (Dy3+: 4F9/2) of Dy: GdYAP crystal was fitted to be 0.316 ms. As compared with 2 at.% Dy: YAP crystal, the lifetimes τr of the lower energy level (Dy3+: 6H13/2) has decreased in the Dy: GdYAP crystal. Particularly, the yellow emission has enhanced greatly in Dy: GdYAP crystal excited by 275 nm through the sensitization of Dy3+ by Gd3+, making it potential to realize yellow lasers with available UV pump source. The mixed crystal doped with rare-earth ions provide more options for exploring different laser characteristics and more flexible pump sources.

Alkaline sodium polyacrylate-starch hydrogels with tolerance to cold conditions for stretchable zinc-air batteries

With the advancement of wearable electronic devices, it is critical to create a flexible power source that is high performing, cost effective, and safe. The flexible zinc-air battery as a promising candidate has been widely concerned, while most hydrogel electrolytes lose their stretchability in a strong alkaline environment. Herein, a sodium polyacrylate-starch double-network hydrogel is prepared by simple solution copolymerization and swelling techniques. Not only does the hydrogel exhibit exceptional mechanical strength, toughness, and ionic conductivity, but it also exhibits an exceptional freezing-tolerance capability. The stretchable zinc-air battery with sandwich construction has a high energy efficiency of 68%, a high energy density of 67.5 mW cm −2 , and a high degree of dependability in stretched modes. Additionally, the battery performs well mechanically and electrochemically at a cold environment (−20 °C). The batteries can be incorporated into a range of energy-consuming gadgets, suggesting that they are very practicable as wearable power sources. • a hydrogel electrolyte based on sodium polyacrylate and starch was prepared. • Air cathode and Zn anode were designed based on stainless-steel knitted fabric. • The stretchable zinc-air battery operated both under room and cold conditions.

Co/Zn bimetal organic framework elliptical nanosheets on flexible conductive fabric for energy harvesting and environmental monitoring via triboelectricity

Flexible and portable power sources are imperative chunks of wearable electronic devices. Fabric-based triboelectric nanogenerators (TENGs) have become most promising energy sources for wearable electronic devices as they can generate electrical energy from biomechanical movements with great flexibility. In this study, a highly flexible Co/Zn bimetal organic framework based TENG (BMOF TENG) is fabricated. Facilely prepared Co/Zn BMOF nanosheets are coated on flexible conductive fabric (BMOF/FCF) and utilized as the tribo-positive material against PTFE/Al based tribo-negative material for the fabrication of the BMOF TENG. The content of Zn is varied from 0% to 50% to achieve superior electrical output and observed that the 15% of Zn is appropriate for superior electrical output. The open circuit voltage, the short circuit current, and the charge density of the BMOF TENG are increased from 11 V to 47 V, from 1.06 µA to 7 µA, and from 4 nC/cm 2 to ~17 nC/cm 2 , respectively when the Zn content is increased from 0% to 15%. Thus, the optimized content of Zn in Co/Zn BMOF helped to enhance the electrical output of the BMOF TENG by nearly 450%. The output power of the BMOF TENG is found to be 1.1 mW/m 2 at a load resistance of 2 MΩ. As the phenomenon of gas sensing is largely associated to the surface of the material, the advantage of unique surface features of the BMOF/FCF is utilized in sensing hazardous gases. The device has shown variations in its electrical output in the presence of air and targeted gas and the good selectivity towards ammonia at room temperature. Ultimately, the BMOF TENG proposed in this study can convert mechanical energy into electrical energy and can be employed as an ammonia sensor in environmental monitoring and food quality assessment. • For the first time, Co/Zn bimetal organic framework (BMOF) nanosheet coated fabric is used for TENG. • At the optimized content of Zn (15%) in Co/Zn BMOF, the BMOF TENG is generated enhanced electrical output. • Fabric based flexible BMOF TENG is successfully employed as a room temperature ammonia sensor. • The unique surface morphology of BMOF has helped to evince good sensing behavior of the device. • Proposed BMOF TENG is able to serve as an energy harvesting as well as environmental monitoring device.

High current output direct-current triboelectric nanogenerator based on organic semiconductor heterojunction

The high demand on direct current (DC) power source generated through triboelectric effect drives the research on semiconductor-based triboelectric nanogenerators (TENGs), which have lower internal resistance. With high flexibility, organic semiconductor-based DC TENGs are more intriguing. In this work, we use organic semiconductor Poly (3,4-ethylene dioxythiophene): poly(styrene sulfonate) (PEDOT: PSS) as a friction layer to make organic semiconductor-based TENGs. By experimentally analyzing the work functions of PEDOT: PSS, Al alloy, Si, ITO, Cu, and graphene, the DC devices with PEDOT: PSS/Al alloy triboelectric layers exhibit impressive performance. Our PEDOT: PSS/Al alloy DC TENGs achieves open-circuit voltage about 1 V, and short-circuit current up to 309 μA. The internal resistance of the DC TENG is tested to be about 2×104 Ω, and the power density reaches 11.67 mW/m2. Effects of the load pressure, sliding speed, and size of the devices are systematically studied in this work. The charging probability of our DC TENGs as power sources and human body motion detecting capability as force sensors are all experimentally tested, indicating further potential applications of our PEDOT: PSS/Al alloy DC TENGs as flexible energy sources and motion detector.

Free trajectory cone beam computed tomography reconstruction method for synchronous scanning of geometric calibration phantom and imaging object

In order to suppress the geometrical artifacts caused by random jitter in ray source scanning, and to achieve flexible ray source scanning trajectory and meet the requirements of task-driven scanning imaging, a method of free trajectory cone-beam computed tomography (CBCT) reconstruction is proposed in this paper. This method proposed a geometric calibration method of two-dimensional plane. Based on this method, the geometric calibration phantom and the imaging object could be simultaneously imaged. Then, the geometric parameters could be obtained by online calibration method, and then combined with the geometric parameters, the alternating direction multiplier method (ADMM) was used for image iterative reconstruction. Experimental results showed that this method obtained high quality reconstruction image with high contrast and clear feature edge. The root mean square errors (RMSE) of the simulation results were rather small, and the structural similarity (SSIM) values were all above 0.99. The experimental results showed that it had lower image information entropy (IE) and higher contrast noise ratio (CNR). This method provides some practical value for CBCT to realize trajectory freedom and obtain high quality reconstructed image.

Deep Stackelberg heuristic dynamic programming for frequency regulation of interconnected power systems considering flexible energy sources

The flexible energy sources (FESs) could refuse to execute the generation commands (GCs) if the benefits fell short of their expectations when applying traditional automatic generation control methods, this problem leads to frequency instability and the waste of scheduling resources. Accordingly, a deep Stackelberg heuristic dynamic programming (DSHDP) is proposed for the frequency regulation and power dispatch of smart generation control (SGC). Firstly, the heuristic deep dynamic programming, whose networks are replaced by three deep neural networks, can be trained offline by historical data to fit the optimal performance index. Then, the GCs can be optimized through an online updating strategy for stabilizing the frequency of interconnected power systems. To maximize the benefits of FESs further, an improved SGC framework based on the Stackelberg game is built to let FESs play games with conventional power plants in a fair environment. Finally, the optimal GCs can be distributed by the Nash equilibrium to obtain higher profits than traditional methods, and the control accuracy is increased indirectly. Two cases, i.e., IEEE two-area power system and six-area power system based on China Southern Power Grid (CSPG), are provided to verify the superiority of the DSHDP. The results indicate that the excellent flexibility and stability of the proposed algorithm in complex power systems containing renewable energy and FESs. Totally, the frequency deviation obtained by DSHDP is reduced by up to 59.38%, while the total profit of FESs rises by up to 67.47% when compared with the other seven representative algorithms.

Simultaneous Long-Term Planning of Flexible Electric Vehicle Photovoltaic Charging Stations in Terms of Load Response and Technical and Economic Indicators

Photovoltaic charging stations (PVCSs) are one of the most important pieces of charging equipment for electric vehicles (EVs). Recently, the process of designing solar charging stations as flexible sources has been growing and developing. This paper presents a relatively complete design of a solar charging station as a flexible economic resource in a 10-year planning horizon based on a genetic algorithm in two scenarios. PVCSs are not considered in the first scenario. This scenario is only to confirm the results, and the proposed method is proposed. However, in the second scenario, the effects of PVCSs and the demand response strategy (DR) on this development are considered. Copula probability distribution functions are used to create appropriate scenarios for vehicles during different planning years. The proposed energy management system shows a stable performance in terms of the annual load growth index and electricity price of each level of demand over the time horizon along with minimizing power losses and costs required, which makes PVCS efficiency higher and gives them a suitable structure and stability. The modeling results in terms of uncertainties in the system indicate that the use of load management along with PVCS design and flexible electric vehicle charge control strategies improves power quality parameters and optimizes system cost over a period of 10 years. Compared to the obtained results with the traditional case, it is observed that long-term planning in terms of DR and PVCSs and the technical specifications of the network have been improved. As a result of this proposed long-term planning, PVCSs are more flexible.

Large-area 280 nm LED flexible sterilization light source with improved thermal performance

This study focuses on the LED flexible sterilization light source at 280 nm wavelength, and the adjustment of the thickness and area dimensions of the heat dissipation substrate to explore the thermal behavior. The empirical results indicated the priority order for factors affecting the heat dissipation of the substrate to be k > A > t. At the same time, a large-area, flexible, deep-ultraviolet light-emitting diode (DUV LED) was successfully obtained with an area of 5 × 5 cm2 and a 3 cm bending diameter. This sterilization light source was used to carry out the sterilization inactivation test with Escherichia coli. The sterilization rate reached 95% in 60 s. The good sterilization rate and flexibility of the sterilization light source will improve the sterilization performance of the applied product.

Highly efficient flexible perovskite solar cells with vacuum-assisted low-temperature annealed SnO2 electron transport layer

The demand for lightweight, flexible, and high-performance portable power sources urgently requires high-efficiency and stable flexible solar cells. In the case of perovskite solar cells (PSCs), most of the common electron transport layer (ETL) needs to be annealed for improving the optoelectronic properties, while conventional flexible substrates could barely stand the high temperature. Herein, a vacuum-assisted annealing SnO2 ETL at low temperature (100 °C) is utilized in flexible PSCs and achieved high efficiency of 20.14%. Meanwhile, the open-circuit voltage (Voc) increases from 1.07 V to 1.14 V. The flexible PSCs also show robust bending stability with 86.8% of the initial efficiency is retained after 1000 bending cycles at a bending radius of 5 mm. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and contact angle measurements show that the density of oxygen vacancies, the surface roughness of the SnO2 layer, and film hydrophobicity are significantly increased, respectively. These improvements could be due to the oxygen-deficient environment in a vacuum chamber, and the rapid evaporation of solvents. The proposed vacuum-assisted low-temperature annealing method not only improves the efficiency of flexible PSCs but is also compatible and promising in the large-scale commercialization of flexible PSCs.

Abrasion and Fracture Self‐Healable Triboelectric Nanogenerator with Ultrahigh Stretchability and Long‐Term Durability

AbstractSince triboelectrification results from materials in physical contact, the durability of triboelectric nanogenerators (TENGs) must be improved. However, it still poses challenges to continuously repair surface abrasion even when self‐healable materials are introduced. In this study, an ultrastretchable TENG (US‐TENG) that simultaneously heal the fracture and abrasion at room temperature is fabricated. By incorporating hydrogen bonds and dynamic metal‐ligand coordination into polydimethylsiloxane chains, the synthesized elastomers possess ultrahigh stretchability (10 000%) and remarkable self‐healing property (100% efficiency) at room temperature. Working in contact‐separation mode, the electrical outputs with 2 × 2 cm2 area can reach 140 V, 40 nC, 1.5 µA, respectively. Besides, the US‐TENG shows a stretchability of 1800% with high electrical outputs. Even if it is stretched to break or scratched to wear out, it can recover its electrical outputs in 20 min and 2 h at room temperature, respectively. Finally, the application of the US‐TENG as flexible power sources and self‐powered pressure sensors is demonstrated. This designed strategy with ultrahigh stretchability and excellent self‐healing properties can meet the wide applications of flexible and wearable electronics for long‐term use.

Polyimide‐Based Flexible Plasma Sheet and Surface Ionization Waves Propagation

AbstractSurface discharges on flexible substrates are attracting attention for their unique capability to generate large‐scale non‐thermal plasma and potential adaptability to complex objects in many fields, like biomedical inactivation and material processing. Two fundamental issues are manufacture of stable flexible plasma sources and mechanism of multiple surface ionization waves (SIWs) propagation on curved gas‐solid interfaces. A polyimide‐based flexible plasma sheet is realized through printed circuit board with a non‐exposed electrode structure for discharge and the propagation properties of SIWs along its surface are investigated by experiments and simulations. Results show that SIWs start near the high‐voltage electrodes, and develop to the ground electrodes in a symmetrical petal pattern shaped by the potential gradient. The counter‐propagating SIWs merge above the ground electrodes, as the electrons’ distribution converts from filament channel to a diffuse spatial distribution. Furthermore, bending the flexible sheet can change the charge density above the surface of polyimide, thus affects the space electron number density and electron temperature, but does not influence the overall appearance of SIWs propagation. This work will not only help to understand the surface process of ionization waves, but also benefit further researches on the application of flexible‐material‐based plasma source.

54 cm2 Large-Area Flexible Organic Solar Modules with Efficiency Above 13.

Development of large-area flexible organic solar cells (OSCs) is highly desirable for their practical applications. However, the efficiency of the large-area flexible OSCs severely lags behind small-area devices. Here, efficient large-area flexible single cells with power conversion efficiency (PCE) of 13.1% and 12.6% for areas of 6 and 10 cm2 , and flexible modules with a PCE of 13.2% (54 cm2 ) based on poly(ethylene terephthalate)/Ag grid/silver nanowires (AgNWs):zinc-chelated polyethylenimine (PEI-Zn) composite electrodes are reported. The solution-processed flexible transparent electrode of AgNWs:PEI-Zn shows low surface roughness and good optoelectronic and mechanical properties. PEI-Zn is conductive and optically transparent. It can adhere to and wrap the AgNWs under electrostatic interaction between the negatively charged surface (AgNWs) and positively charged protonated amine groups (in PEI-Zn). It wraps the AgNWs networks and fills the void space to achieve a smooth surface. The flexible electrode is validated in both flexible OSCs and flexible quantum-dots light-emitting diodes (QLEDs). Small-area flexible OSCs show a PCE of 16.1%, and flexible QLEDs show an external quantum efficiency of 13.3%. In the end, a flexible module is demonstrated to charge a mobile phone as a flexible power source (shown in Video S1, Supporting Information).

Impact of source variability on flexibility for demand response

This paper assesses the quality of the services provided for demand response by analysing the results of experimental work activating flexible sources in buildings, while evaluating the impacts on occupant comfort and extending the dataset through aggregation, to quantify the uncertainty for multiple systems. Power and energy flexibility is an integral part of the solution to address the challenge of grid balancing with increased renewable generation integration. However, the variability of the provided flexibility, as measured by the stability and consistency of load reduction or increase, may vary widely. To address this, the concept of quality of flexibility is introduced and analysed through the results of experiments conducted at a case study building to activate three sources of flexibility: heat pumps, Air Handling Unit fans and battery storage. The results show that fan data exhibits low uncertainty, suitable for ancillary services, whereas heat pumps’ volatility is large. Standard error for heat pumps was within the quality threshold of 10 %, appropriate for energy services. Aggregation of multiple systems through the creation of a semi-synthetic dataset decreased the uncertainty for hourly energy services to as low as 2 %. For all cases, the impact on occupant comfort was not found to be significant.