Long-term Performance Degradation Research Articles

Durability and Long-Term Performance Prediction of Carbon Fiber Reinforced Polymer Laminates.

The feasibility of strengthening deteriorated or under-capacity concrete structures with external carbon-fiber-reinforced polymer (CFRP) laminates has been widely validated in the literature. However, there is a lack of knowledge on the in situ long-term performance and age-related environmental degradation of the mechanical properties of the laminates. The current study involved the immersion of coupons from a common new CFRP laminate in heated water at 23, 45, and 60 °C for 224 days. The coupons were then tested for residual tensile properties, such as tensile capacity and elastic modulus, using ASTM D3039 (2017) specifications. The CFRP tensile capacity and elastic modulus decreased by a maximum of 33% and 26%, respectively, for 224 days of exposure. Based on the test data, an age-based long-term prediction model with excellent reliability for CFRP laminate tensile capacity was developed. The model was then calibrated with test results from old CFRP coupons collected from an existing CFRP laminate retrofitted concrete bridge. The calibrated model output was then compared with the environmental reduction factor from ACI 440.2R-17 and a few other common sources. It was found that the ACI specified a reduction factor of 0.75, which does not consider the CFRP age and overestimates the design tensile strength of the CFRP laminate by approximately 13%, which may compromise the structural safety of retrofitted bridges. The reduction factors from the other guidelines varied between 0.51 and 0.85.

(Digital Presentation) Interface Engineering of Transition Metal-Selenide Heterostructures for Application in Electrochemical Water-Splitting

Transition metal selenides (TMS) have sparked great interest in energy storage and catalysis because they are direct bandgap materials, have a highly layered structure, high redox activity, abundant active sites at the edges, short diffusion paths, and large surface area1. However, low electrical conductivity and structural instability result in long-term performance degradation. The development of high-performance water electrolyzers and metal-air batteries requires the design and construction of efficient TMS electrocatalysts. In order to boost electrochemical activity, increasing emphasis has been devoted to interface engineering of TMS heterostructures through manipulation of composition, adjustment of crystal facets, and heteroatomic doping2. Interface engineering helps in optimizing reaction intermediates, modulating charge carrier characteristics, and preventing the aggregation of active components. Herein, we designed and studied the interface between hydrothermally synthesized tin selenide (SnSe2) and tungsten selenide (WSe2). The intimate electronic interaction between the bimetallic selenides leads to a rich interface boundary that reduces the surface energy and creates a larger number of active sites involved in both the hydrogen evolution and oxygen evolution reactions3. These heterostructures exhibited a low overpotential of 180 mV at 10 mA cm-2 and good stability of up to 12 hours for the hydrogen evolution reaction, and a low overpotential of 250 mV at 10 mA cm-2 and stability up to 12 hours for the oxygen evolution reaction. This study gives a better insight into the design of TMS heterostructures using interface engineering for high electrocatalytic activity.

(Keynote) Degradation Processes in Solid Oxide Cell Ni-YSZ Electrodes

Solid oxide cells (SOCs) can have a significant impact on climate change over the next decade and beyond, in applications such as balancing renewable grid electricity via electrolytic fuel production, and producing electricity from bio-fuels combined with CO2 product sequestration. However, long-term performance degradation remains a key variable that may limit further implementation of SOCs. This talk focuses on the Ni-YSZ fuel electrode that is widely used but is known to be an important contributor to SOC degradation. Various processes that cause Ni-YSZ degradation are discussed. Results on 3D tomography measurements of accelerated Ni coarsening are described and a quantitative model is developed to predict long-term degradation. Although the results indicate that coarsening effects can be minimized in well-designed Ni-YSZ microstructures, degradation can still occur, especially during high-current-density electrolysis operation. For operation under low H2O/H2 conditions, high electrolysis current density can yield reduction of zirconia to form Ni-Zr compounds, along with substantial microstructural damage. For operation under high H2O/H2conditions, high electrolysis current density can yield Ni migration away from the electrolyte. A phase-field simulation is described that predicts this Ni migration, using actual Ni-YSZ microstructures measured using 3D tomography as the starting point, and compared with experimental observations. The model assumes that Ni transport is driven by a spatial gradient in surface tensions, i.e., a decrease in the Ni/YSZ contact angle with increasing distance from the electrolyte. Recent results on electrolysis and reversibly operated SOCs, making use of Ceria-infiltrated Ni-YSZ to improve stability, are described.

Experimental assessment of long-term performance degradation for a PV power plant operating in a desert maritime climate

Photovoltaic (PV) installations are being intensively deployed and their capacity are approaching to terawatt around the world. In this context, the long-term performance and reliability of PV modules, component and systems are critical metrics for the economic viability of PV power plants. Furthermore, this is linked to the environmental conditions in which the PV plants operate. In this study, the performance degradation of a 302.4 kWp solar PV power plant is investigated over the first five years of operation in the desert maritime climate of Djibouti. The analysis is led on collected data extracted from the PV installation and that have been pre-processed and filtered. For this purpose, several criteria have been introduced to identify anomalies such as grid outages. Then, the power degradation rate was considered using Photovoltaics for Utility Scale Applications (PVUSA) regression analysis and Performance Ratio (PR) analysis based on continuous monitoring data at 1-min intervals. The degradation rates were found to be 1.01 ± 0.38%/year for PR and 0.085 ± 0.68%/year for PVUSA. According that the PVUSA did not detect any degradation, new test conditions that were set by experimental data have been introduced. Finally, the resulting measure allowed a degradation rate of 0.74 ± 0.29%/year to be observed.

Machine-learning-assisted prediction of long-term performance degradation on solid oxide fuel cell cathodes induced by chromium poisoning

We implement the machine-learning-assisted (MLA) method to predict the long-term stability of Solid Oxide Fuel Cell (SOFC) cathodes under the influence of Cr poisoning.

Towards the Validation of a Phase Field Model for Ni Coarsening in Solid Oxide Cells

Ni coarsening in the Ni/yttria-stabilized zirconia (YSZ) fuel electrode of solid oxide cells (SOCs) is a major cause of long-term performance degradation. Phase-field modeling is a powerful tool for studying Ni coarsening in the complex 3D structures of SOC fuel electrodes. In this work, we present a study aimed at validating a phase-field model, comparing simulation results with time-dependent ex-situ tomographic data. Three equilibrium Ni/YSZ contact angles are examined: 97°, 120°, and 150°. Simulated microstructures are characterized through quantities such as the Ni mean radius, triple-phase boundaries, and interface shape distribution. The phase-field model reproduces the improved pore connectivity in the first stage of Ni coarsening observed in the tomography data. This model also indicates that the contact angle plays a key role in the microstructural evolution during Ni coarsening, and the best match to the experiment was obtained with the equilibrium contact angle of 120º, close to a measured value in literature. Finally, the limitations of the model are discussed.

Real-Time Observation of Chemomechanical Breakdown in a Layered Nickel-Rich Oxide Cathode Realized by In Situ Scanning Electron Microscopy

It is well-accepted that massive cracks in Ni-rich cathode secondary particles are the determining factors for long-term performance degradation; however, the corresponding crack generation and the...

Short-term prediction for wind power based on temporal convolutional network

The fluctuation and intermittence of wind power bring great challenges to the operation and control of the distribution network. Accurate short-term prediction for wind power is helpful to avoid the risk caused by the uncertainties of wind powers. To improve the accuracy of short-term prediction for wind power, the temporal convolutional network (TCN) is proposed in this paper. The proposed method solves the problem of long-term dependencies and performance degradation of deep convolutional model in sequence prediction by dilated causal convolutions and residual connections. The simulation results show that the training process of TCN is very stable and it has strong generalization ability. Furthermore, TCN shows higher forecasting accuracy than existing predictors such as the support vector machine, multi-layer perceptron, long short-term memory network, and gated recurrent unit network.

Mechanism and control of the long-term performance evolution of structures

It is well known that structural properties degrade under long-term environmental exposure and loading and that the degradation rate is controlled by inherent physical and chemical degradation mechanisms. The elucidation of the degradation mechanisms and the realization of effective long-term performance degradation control have been a research frontier in the field of civil engineering in recent years. Currently, the major topics that concern this research frontier include revealing the physical and chemical mechanisms of structural performance evolution under long-term environmental exposure and loading and developing structural performance degradation control technologies based on fiber-reinforced materials, for example, fiber-reinforced polymers (FRPs) and fabric-reinforced cementitious matrix (FRCM). In addition, there are novel structural performance control technologies, such as using a shape memory alloy (SMA) and self-healing concrete. This paper presents a brief state-of-the-art review of this topic, and it is expected to provide a reference for subsequent research.

Sources of performance degradation in thin film La0.6Sr0.4FeO3 air electrodes

Origins of long-term oxygen reduction activity degradation at 700 °C in polymeric precursor-derived La0.6Sr0.4FeO3 (LSF) thin film cathodes were investigated. Electrochemical impedance spectroscopy measurements revealed that the LSF thin films pre-calcined at 900 °C (LSF-900) exhibited much faster electrochemical activity loss than did LSF pre-calcined at 700 °C (LSF-700). As similar losses in surface area were determined upon scanning electron microscopy image analyses of samples, microstructure evolution was excluded as a possible reason for the difference in degradation rates. Upon X-ray diffraction analyses and comparison of results with literature, it was suggested that small amounts of Ruddlesden-Popper type (La, Sr)2FeO4 (214) phases were present throughout the 100 hour exposure of both LSF-700 and LSF-900 to 700 °C, thus not affecting the long-term performance degradation rates. X-ray photoelectron spectroscopy analyses revealed that the ratio of surface-bound Sr to the lattice-bound one increased significantly in LSF-900, suggesting electrochemically inactive SrO/Sr(OH)2/SrCO3 rich layer formation and thus contributing to fast activity loss. Overall, it was established that microstructural evolution was not the sole source of degradation in LSF-based cathodes. Since LSF thin films deposited by a solution precursor onto YSZ electrolytes constitute a model structure, the results obtained in the present study can also provide useful information on the degradation of LSF-YSZ composite cathodes prepared by LSF infiltration into YSZ scaffolds.

Comparison of microstructural evolution of fuel electrodes in solid oxide fuel cells and electrolysis cells

Solid oxide cells are electrochemical devices used for the conversion of chemical energy to electrical energy (Solid Oxide Fuel Cells-SOFC) and vice versa (Solid Oxide Electrolysis Cells-SOEC). However, long-term performance degradation impedes the widespread commercialization of the technology. To investigate the effects of operation mode on the degradation of Ni/yttria-stabilized zirconia (YSZ) electrodes, two cells from the same production batch are tested for 1000 h at 800 °C; one as SOFC and the other as SOEC. The cells are fed with the same gas composition at the fuel inlet side (p(H2O)/p(H2) = 0.5/0.5) while the direction of the current (±1 A cm−2) is reversed. It is found that Ni coarsening occurs to a similar extent in both operation modes while Ni depletion is only observed in SOEC mode, in the region close to the electrode/electrolyte interface. Here, the Ni/(Ni + Zr + Y) atomic ratio decreases from ~0.49 before operating the cell to ~ 0.28 and the SOEC shows a pronounced decrease in percolating triple phase boundaries (TPBs). The wettability of Ni on YSZ is studied and hypotheses are presented to correlate the phenomena of Ni coarsening and Ni depletion with the cell operation mode.

Effect of applied current density on the degradation behavior of anode-supported flat-tubular solid oxide fuel cells

The effects of applied current density on the long-term performance degradation behavior of anode-supported flat-tubular type solid oxide fuel cells (SOFCs) are studied. Durability tests on the anode-supported SOFCs are conducted galvanostatically at 800 °C as a function of applied current density (200, 450, 700 and 1000 mAcm-2) for the duration of 1000 h. The performance degradation during the long-term test assessed by a voltage loss over time greatly increases with higher applied current density. The combined impedance spectroscopy and post-test characterization results show that the accelerated degradation at high current density is due to enhanced Ni particles coarsening in the anode, the formation of insulating phase between cathode and electrolyte, and evolution of fine particles in the cathode. Systematic degradation analysis conducted in the present study provides profound insight into the electrochemical performance decay of the anode-supported flat-tubular SOFCs.

Lifetime Prediction of Anode-Supported Solid Oxide Fuel Cell on the Basis of Individual Components Degradation

Long-term stability is an essential requirement for the successful commercialization of solid oxide fuel cell (SOFC) technology. In the present work, the long-term performance degradation of the anode-supported SOFC short stack is analyzed under accelerated operating conditions. The voltage degradation of the short stack was caused by the increase in ohmic and polarization resistance with time. The coarsening of Ni particles in the Ni-cermet anode was found to be the dominant degradation mechanism which decreases the anode performance gradually during the long-term operation. On the cathode side, cation surface segregation and formation of resistive phase between cathode and electrolyte were responsible for the performance degradation. Mathematical correlations were developed for the prediction of performance degradation of SOFC components and integration of single effects degradation can be used to predict the lifetime of the SOFC cell and stack.

Investigation of LSM-YSZ Composite Cathode Performance Degradation with a Multistep Charge Transfer Model

The long-term performance degradation of LSM/YSZ composite cathodes is investigated via calibrated multiphysics simulation with a multistep oxygen reduction reaction (ORR) model and structural coarsening data from a phase field study. Multiphysics simulations, including a multistep ORR mechanism, are first developed for better understanding of the limiting processes in solid oxide fuel cells. The multistep ORR mechanism includes two parallel pathways, surface pathway and bulk pathway, which consist of elementary reaction steps. The multiphysics model is simultaneously calibrated with experimental polarization curves and impedance behavior for various air/fuel supply conditions. To our knowledge, this is the first time that a multistep ORR model is calibrated with such datasets. Next, the calibrated simulations are utilized to simulate a 2D half-cell constructed with measured microstructural data and random heterogeneity. Finally, the long-term performance degradation of the half-cell is predicted by the calibrated multiphysics model coupled with structural coarsening trends simulated using a phase field-based coarsening model. Degradation of both polarization curves and impedance behavior is investigated. Thorough analyses, including changes of contributions from different pathways, the resistance components, and overall reaction order, are performed to provide more insights into cathode performance degradation due to grain coarsening phenomena.

Analysis of the Long-Term Performance Degradation of Crystalline Silicon Photovoltaic Modules in Tropical Climates

The long-term performance degradation of five different types of commercial crystalline silicon (c-Si) photovoltaic (PV) modules (one sample for each type) in the tropics, or more specifically the tropical rainforest climate “Af” by the Koppen climate classification (Singapore), is investigated over a period of seven years, based on outdoor I–V measurements at 10-s intervals. The degradation rates of these c-Si PV modules, based on the temperature-corrected performance ratio, range from –0.03 to –0.47%/year, which satisfy the products’ performance warranty. Further analysis of the short-circuit current ( I sc), open-circuit voltage, and fill factor for these modules shows that the performance degradation is mainly attributed to the I sc loss. The possible causes of the module performance deterioration are also discussed.

Assessment of early degradation and performance loss in five co-located solar photovoltaic module technologies installed in Ghana using performance ratio time-series regression

Abstract Long-term performance degradation in solar photovoltaic modules is generally understood to be linear. Nevertheless, there is increasing acknowledgement of sharper performance decline within the early periods of exposure. Emerging industry trend is geared toward providing multi-staged warranties that provide assurances of both early-period module output and longer-term performance. While studies on performance degradation are increasing in the open literature, there remains significant geographical imbalance. Moreover, many of the studies available are based on discrete measurements, with few resulting from continuous monitoring. This paper presents the outcome of analysis conducted to explore performance degradation of five solar photovoltaic module technologies within the first 14 months of installation in Kumasi Ghana. Based on time-series regression of the performance ratios, early degradation ranged from 8% to 13.8% of initial performance. Technologies studied were amorphous silicon, mono-crystalline silicon, polycrystalline silicon, Copper Indium Sulfide and hybrid Heterojunction with intrinsic Thin-layer (HIT).

Accelerated Aging of Asphalt by UV Photo-Oxidation Considering Moisture and Condensation Effects

AbstractTo understand the long-term performance degradation of asphalt, ultraviolet (UV) photo-oxidation has been used to accelerate the aging process. Three types of asphalt binders extracted from...

The Effect of Upscaling and Performance Degradation on Onshore Wind Turbine Lifetime Extension Decision Making

Ever greater rated wind turbine generators (WTGs) are reaching their end of design life in the near future. In addition, first research approaches quantified the impact of long-term performance degradation of WTGs. As a consequence, this work is aimed at discussing and analysing the impact of upscaling and performance degradation on the economics of wind turbine lifetime extension. Findings reveal that the lifetime extension levelised cost of energy (LCOE2) of an 18 MW wind farm comprising of 0.5 MW rated WTGs are within the order of £23.52 per MWh. Alternatively, if the same wind farm consists of fewer 2 or 3 MW WTGs, the LCOE2 reduces to £16.56 or £15.49 per MWh, respectively. Further, findings reveal that an annual performance degradation of 1.6% (0.2%) increases LCOE2 by 34-41% (3.6-4.3%).

Toward a New Generation of Smart Biomimetic Actuators for Architecture.

Motile plant structures (e.g., leaves, petals, cone scales, and capsules) are functionally highly robust and resilient concept generators for the development of biomimetic actuators for architecture. Here, a concise review of the state-of-the-art of plant movement principles and derived biomimetic devices is provided. Achieving complex and higher-dimensional shape changes and passive-hydraulic actuation at a considerable time scale, as well as mechanical robustness of the motile technical structures, is challenging. For example, almost all currently available bioinspired hydraulic actuators show similar limitations due to the poroelastic time scale. Therefore, a major challenge is increasing the system size to the meter range, with actuation times of minutes or below. This means that response speed and flow rate need significant improvement for the systems, and the long-term performance degradation issue of hygroscopic materials needs to be addressed. A theoretical concept for "escaping" the poroelastic regime is proposed, and the possibilities for enhancing the mechanical properties of passive-hydraulic bilayer actuators are discussed. Furthermore, the promising aspects for further studies to implement tropistic movement behavior are presented, i.e., movement that depends on the direction of the triggering stimulus, which can finally lead to "smart building skins" that autonomously and self-sufficiently react to changing environmental stimuli in a direction-dependent manner.

Ultra-high temperature thermal energy storage. part 1: concepts

Renewable energy sourced from the sun, wind, waves or tides is clean and secure. Unfortunately, the energy that can be extracted from renewables and the demand for it varies both temporally and spatially. Therefore, energy storage is required to match generation with use. To date grid-scale energy storage has been limited by low energy densities, long-term performance degradation, low round-trip efficiencies or limited deployment locations. Although thermal storage has found uses these have been restricted to lower temperatures by thermal losses resulting in low energy densities and uneconomical electricity generation efficiency. In this paper an ultra-high temperature (1800K) storage system is proposed where heat losses are minimised and recovered to make a higher storage temperature attractive, thus unlocking greater energy densities and efficiencies. Radiation dominates heat losses at ultra-high temperatures but can be minimised through the design of the storage medium container. However, even after energy is lost from storage, heat pumps in the store and charge cycles in addition to preheating during the extraction cycle can be used to recover a significant amount of heat. Collectively loss reduction and recovery techniques can lead to a storage system with a performance and utility that exceeds other energy storage methods Here the feasibility of the novel storage technique is demonstrated through thermodynamic and thermal analysis in each of the three key states of operation: charge, store and generation.