Performance Degradation Rate Research Articles

A Study on Disposal Diagnosis Algorithm of PV Modules Considering Performance Degradation Rate

A Study on Disposal Diagnosis Algorithm of PV Modules Considering Performance Degradation Rate

Filtration performance of novel microfibrous media embedded with nanofiber flocs for aerosol particle removal

Ingestion and accumulation of sea salt and other impurities is a major challenge for high speed vessels, turbine engines, and other air breathing systems. The performance and reliability of filters are anticipated to be improved significantly after the rate of performance degradation is reduced via enhanced filtration media and well-designed filtration approaches. This study proposes to apply anionic surfactant to disperse the nanofibers thoroughly and employ cationic surfactant to flocculate the dispersed nanofibers into numerous small groups of nanofiber flocs. Using the wet-lay procedure in the lab, the novel porous microfiber media was then fabricated with small groups of nanofiber flocs together with activated carbon and polyester fibers. The unique nanofiber filter media was then evaluated for filtration performance using face velocity, pressure drop, and filtration efficiency parameters. Due to nanoflocced fiber inclusion, an anomalous region in the filtration efficiency versus pressure drop regime was observed where wall slip occurring at the nanostructured surface provided an unusually high level of filtration efficiency near the most penetrating particle size (MPPS) region of 0.1–0.4 μm with a concomitant reduction in the normally encountered levels of pressure drop. This anomalous increase in the filtration efficiency versus pressure drop is a novel phenomenon and it is highly beneficial to aerosol filtration. The enhanced filtration reveals that the quality factor near the MPPS region increases significantly due to the inclusion of nanofiber flocs. The unique porous filtration media is expected to increase the dirt holding capacity and prolong the lifecycle of the turbine air filter systems.

Estimating Recoverable Performance Degradation Rates and Optimizing Maintenance Scheduling

Many of the components on a gas turbine are subject to fouling and degradation over time due to debris buildup. For example, axial compressors are susceptible to degradation as a result of debris buildup on compressor blades. Similarly, air-cooled lube oil heat exchangers incur degradation as a result of debris buildup in the cooling air passageways. In this paper, we develop a method for estimating the degradation rate of a given gas turbine component that experiences recoverable degradation due to normal operation over time. We then establish an economic maintenance scheduling model, which utilizes the derived rate and user input economic factors to provide a locally optimal maintenance schedule with minimized operator costs. The rate estimation method makes use of statistical methods combined with historical data to give an algorithm with which a performance loss rate can be extracted from noisy data measurements. The economic maintenance schedule is then derived by minimizing the cost model in user specified intervals and the final schedule results as a combination of the locally optimized schedules. The goal of the combination of algorithms is to maximize component output and efficiency, while minimizing maintenance costs. The rate estimation method is validated by simulation where the underlying noisy data measurements come from a known probability distribution. Then, an example schedule optimization is provided to validate the economic optimization model and show the efficacy of the combined methods.

High growth-rate atomic layer deposition process of cerium oxide thin film for solid oxide fuel cell

Cerium oxide (CeO2) shows superior surface exchange, and therefore is widely used for the cathode interlayer coating material to reduce the activation loss in low temperature solid oxide fuel cell (LT-SOFC). Here, we report on the application of the high growth-rate atomic layer deposition (ALD) process of CeO2 thin films as cathodic interlayers for LT-SOFCs. We demonstrate that the maximum power density of the SOFC with pure CeO2 interlayer increases by 45% compared to the one without interlayer at 450 °C. More importantly, the performance degradation rate of the ALD CeO2 interlayered cell improves by 25 times compared to the cell without interlayer during 24 h operation at 450 °C.

Improved Long Term Performance Stability of Sr-Fe-O Infiltrated LSM/YSZ Solid Oxide Fuel Cells under High Steam and High Temperature

The LSM/YSZ cathode of commercial available anode supported button cells were infiltrated with a solution containing salts with strontium and iron cations in a 1:2 ratio. Both the uninfiltrated baseline cells and the infiltrated cells were evaluated for their performance and long-term stability in the humidified air and at high current density and high temperature. In comparison with baseline cell that experience severe performance degradation, Sr-Fe-O-infiltrated cells exhibited much higher performance and most importantly it significantly lowered performance degradation rate. This study demonstrated that appropriate nanomaterial infiltration can improve the cell performance and simultaneously mitigate performance degradation of solid oxide fuel cells. Nanostructure characterization using TEM revealed that LSM/YSZ baseline cell operated under steam was mainly caused by the formation of secondary phase nanoparticles and associated cracks along LSM/YSZ interfaces that are adjacent to the electrolyte. By contrast, Sr-Fe-O infiltration mitigated the formation of secondary phase particles and the associated nano-cracks in LSM/YSZ interface. Furthermore, Sr-Fe-O infiltration induced the formation of electrocatalyst of both Mn-Fe-O and Fe-doped LSM nano-particles on the surface of LSM and YSZ backbone, that could introduce additional new triple phase boundaries for adding the electrochemical reaction sites. In the meanwhile, there is continuous cation inter-diffusion between infiltrate and backbone and such cation exchange render the electronic conductor LSM backbone becoming Fe-doped LSM that is a mixed electronic conductor for further improving the cell performance.

Impact of the NAND Flash Power Supply on Solid State Drives Reliability and Performance

The NAND flash memory technology is the fundamental building block of storage systems like solid state drives. Their reliability drastically impacts the design choices of the error recovery flows exploited to improve drive’s performance, which progressively degrades as the number of bit errors to be corrected increases. Among the many causes producing errors, it is found that the NAND flash power supply plays a non-negligible role. In this paper, we will show how the drive’s performance degradation rate measured by the sustainable bandwidth, read latency, and quality of service metrics, heavily depends on the power supply. The results will show that by using a lower power supply in endeavor to reduce the energy consumption of the drive will yield a significant bandwidth (up to 44.4 kIOPS), latency (up to $504~\boldsymbol {\mu }\text{s}$ ), and quality-of-service (up to 1.5 ms) detriment. Counterintuitively, we will show that the overall energy consumption per byte will increase (up to 4.5 times) in specific working conditions of the drive.

Microstructure optimization for high-performance PrBa0.5Sr0.5Co1.5Fe0.5O5+δ-La2NiO4+δ core-shell cathode of solid oxide fuel cells

Four PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF)-La2NiO4+δ (LN) core-shell cathodes, designated as PL-0, PL-1, PL-3 and PL-5, are prepared by infiltrating LN solution into PBSCF scaffold, and they are investigated in terms of the effect of LN thickness on their electrochemical performance. PL-3 with a continuous LN coating of a moderate average thickness (∼9 nm) demonstrates the lowest initial polarization resistance (0.51 Ω cm2) and highest power density (0.71 W cm−2) among all the cathodes. Polarized at 400 mA cm−2 and 700 °C for up to 40 h, the polarization resistance of all the prepared cathodes increases to approach a stable level after early stage decrease due to current activation, and PL-3 exhibits a slower average rate of performance degradation (25%). The electrochemical performance improvement is mainly attributed to that LN has a relatively high oxygen surface exchange coefficient and continuous LN coating depresses Sr segregation at PBSCF/LN interface.

Performance analysis of a micro CHP system based on high temperature PEM fuel cells subjected to degradation

Micro Combined Heat and Power (microCHP) systems based on High Temperature Polymer Electrolyte Membrane (HTPEM) fuel cells is a promising technology allowing to produce electricity and heat with very high efficiency and low emissions also for small power systems. Polybenzimidazole (PBI) based HTPEM fuel cells, thanks to their high CO tolerance, allow the use of fuels other than pure hydrogen by means of a simplified fuel processing unit. However, their relatively low performance and performance degradation rate are still issues to be overcome in order to allow commercialization. In this work, an energy simulation model developed by the authors in a previous research work, has been improved taking into account the degradation of the fuel cell stack in order to assess the performance of the system over long period of operation. The fuel cells performance degradation over time has been implemented on the basis of experimental data obtained by the authors and on data found in literature. The performance of the system has been studied in different configurations that include the introduction of a lithium battery storage in addition to the fuel cell stack.System parameters, such as electrical and thermal energy production, import/export of electricity and primary energy savings have been calculated and compared for different system configurations. Results show that battery integration can improve system performance and that the effect of fuel cell degradation reduces the electricity production. The effect on overall efficiency can be mitigated if heat is recovered.

Evaluation of HT-PEM Fuel Cells via Load Cycling at High Current Densities

Polymer electrolyte membrane (PEM) fuel cells have a wide range of applications: stationary, transportation and portable communication [1]. Irrespective of type or operating temperature, for all fuel cells persist the same requirements like long term stability and reproducibility. To assemble an entire fuel cell stack, the utilized membrane electrode assemblies (MEA) should not only be the same type, they are also required to exhibit similar performances and power outputs. Vision of the German project QUALIFIX, funded by the Ministry of Economic Affairs and Energy (SC: 03Et6046A), is the development of consistent conditions for improved batch production to analyze and monitor quality of fuel cells, systems and components. With help of defined quality standards, the lifetime of fuel cell systems should be improved and cost-intensive losses can be minimized at an early production stage. Within QUALIFIX, the reproducibility of MEAs has been screened by evaluating several small batch series. One operation strategy, which has been used for this investigation, is load cycling between high current densities of 0.6 and 1.0 A/cm² and under equal test conditions. High temperature (HT) PEM MEAs with PBI-membranes of four different providers have been tested and their results will be presented in this work. All MEAs passed identical break-in procedures and activation phase under 0.3 A/cm². These start time intervals lasted 48 hours for each MEA respectively followed by initial characterization including polarization curves, impedance spectroscopy, cyclic and linear sweep voltammetry. Afterwards the load cycling operation started with 16 min of 1.0 A/cm² followed by 4 min of 0.6 A/cm². At the end of tests (EoT), after 500 h of operation, a second complete characterization has been performed. The characterizations have been replenished by ante- and post-mortem analysis via micro-computed tomography (µ-CT) and by product water and MEA analysis to provide phosphoric acid concentration changes. In Figure 1 the voltage changes for four MEAs from different suppliers are displayed as function of time. Indeed, all four MEAs are from the same type but their performances differ strongly; only MEA B and D show a good and similar performance but unequal degradation rates. All degradation rates are listed in Table 1. Table 1: Degradation rates at 0.3 A/cm² of load cycling tests after 500 h of operation. MEA Degradation Rate [µV/h] A -37 B +36 C -94 D -6 In addition, another MEA of the batches of MEA B and D have been adducted for inner-batch evaluations and comparisons. For both MEA-types (two different providers), the degradation rates vary within the batches of identical assemblies and under same operation conditions of load cycling at high current densities. Hence the production of MEAs with reproducible performances seem to be still of major concern. The in-situ electrochemical and ex-situ post- and ante-mortem evaluation (e.g. MEA acid content and µ-CT investigations) of all tested MEAs will be presented and compared. Figure 1: Voltage changes as function of time under load cycling conditions, (0.6 A/cm²: 4 min, 1.0 A/cm²: 16 min, 160 °C) under H2 and air supply (λH2=1.5; λair=2.0), MEAs of 4 different suppliers.

Power Electronics for Extending Lifetime and Robustness of Fuel Cell Systems

The papers in this special section focus on the fuel cell systems with particular emphasis on extended the lifetime and robustness of these systems. The fuel cell is an electrochemical device that converts the chemical energy stored in a fuel directly into electrical energy, with only heat and water as by-products. Hence, it is one of the cleanest technologies for producing electric power. However, the durability of fuel cells is a main concern for the massive deployment of fuel cell technology for transportation and stationary power generation applications. The fuel cell power generation system consists of a fuel cell stack and the balance of plant consisting of auxiliary units such as air compressor, cooling circuit, power converter, etc. The fuel cell’s lifetime is closely related to its electrode/electrolyte material aging and degradation during its operation. Over time and with use, the degradation of fuel cell performance cannot be avoided; however, with well-designed balance of plant and control system, the rate of performance degradation can be minimized, and the robustness of the fuel cell systems can be improved.

Time-Dependent Energy and Resource Management in Mobility-Aware D2D-Empowered 5G Systems

The 5G mobile networks are expected to offer higher degrees of radio access heterogeneity across a wide range of technologies (LTE, WiFi, mmWave, etc.), which operate in both licensed and unlicensed spectrum providing dissimilar data rates and coverage. In light of the stringent requirements in terms of resource and energy efficiency, the performance optimization of such heterogeneous 5G systems becomes an involved task that demands abundant information on the states of users to solve a complex, large-scale optimization problem. However, the unpredictable mobility of communicating entities, including dual mobility of D2D partners, may lead to a rapid deviation from the initial, optimized system state and thus requires frequent re-optimizations of the entire network. In this article, we aim to deliver a comprehensive tutorial on the implications of system- wide energy and resource management with the emphasis on its time-dependent behavior. Proposing a novel network-centric 5G optimization framework, we employ insights from the random walk and Markov chain theories, and also confirm our findings with an extensive system-level simulation campaign. These results reveal an exponential performance degradation rate that primarily depends on the average user speeds. Together with reporting the divergence exponents for different 5G system configurations, we also provide practical insights into how to exploit them in order to non-incrementally improve the thro

Performance Analysis of a Grid-Connected Upgraded Metallurgical Grade Silicon Photovoltaic System

Because of their low cost, photovoltaic (PV) cells made from upgraded metallurgical grade silicon (UMG-Si) are a promising alternative to conventional solar grade silicon-based PV cells. This study investigates the outdoor performance of a 1.26 kW grid-connected UMG-Si PV system over five years, reporting the energy yields and performance ratio and estimating the long-term performance degradation rate. To make this investigation more meaningful, the performance of a mono-Si PV system installed at the same place and studied during the same period of time is presented for reference. Furthermore, this study systematizes and rationalizes the necessity of a data selection and filtering process to improve the accuracy of degradation rate estimation. The impact of plane-of-array irradiation threshold for data filtering on performance ratio and degradation rate is also studied. The UMG-Si PV system’s monthly performance ratio after data filtering ranged from 84% to 93% over the observation period. The annual degradation rate was 0.44% derived from time series of monthly performance ratio using the classical decomposition method. A comparison of performance ratio and degradation rate to conventional crystalline silicon-based PV systems suggests that performance of the UMG-Si PV system is comparable to that of conventional systems.

Suspension plasma spraying of La0.6Sr0.4Co0.2Fe0.8O3−δ cathodes: Influence of carbon black pore former on performance and degradation

Suspension plasma spray deposition is utilized to fabricate solid oxide fuel cell cathodes with minimal material decomposition. Adding carbon black as a pore former to the feedstock suspension results in smoother and more porous coatings, but over the range of carbon black concentrations studied, has little impact on the overall symmetrical cell performance. The cathode made with a suspension containing 25 wt% carbon has the highest deposition efficiency and a polarization resistance of 0.062 Ωcm2 at 744 °C. This cathode is tested for 500 h, and it is observed that adding an SDC interlayer between the YSZ electrolyte and the cathode(s) and/or coating the metal substrate with lanthanum chromite decrease the rate of performance degradation.

Condensation Prevention Performance Assessment Taking Into Account Thermal Insulation Performance Degradation Due to Aging for Apartment Housing

Purpose: The current study analyzed trends in thermal insulation performance with aging, and condensation characteristics caused by the former. Method: Thermal insulation and condensation prevention performance of an architecture were assessed using Temperature Difference Ration Inside, or TDRi. Subjects of this quantitative analysis in thermal insulation performance change due to aging included recently constructed apartments and aged apartments older than 40 years. Time series comparison and analysis were conducted to observed changes in the thermal insulation performance and condensation characteristics. Result: Analysis showed that wall insulation performance degraded with aging regardless of fortified insulating material usage or insulating material type, which caused increased danger of condensation. In addition, when fortified insulating material was installed on the connection between the walls, insulation performance degradation was lower compared to cases in which fortified materials were not used. In all cases from 1 to 10, the rate of thermal insulation performance degradation increased after 20 years of aging.

ChemInform Abstract: Low‐Temperature Solid‐Oxide Fuel Cells

AbstractReview: 50 refs.

Metallographic autopsies of full-scale ITER prototype cable-in-conduit conductors after full testing in SULTAN: 1. The mechanical role of copper strands in a CICC

Cables made with Nb3Sn-based superconductor strands will provide the 13 T maximum peak magnetic field of the ITER central solenoid (CS) coils and they must survive up to 60 000 electromagnetic cycles. Accordingly, prototype designs of CS cable-in-conduit-conductors (CICC) were electromagnetically tested over multiple magnetic field cycles and warm-up-cool-down scenarios in the SULTAN facility at CRPP. We report here a post-mortem metallographic analysis of two CS CICC prototypes which exhibited some rate of irreversible performance degradation during cycling. The standard ITER CS CICC cable design uses a combination of superconducting and Cu strands, and because the Lorentz force on the strand is proportional to the transport current in the strand, removing the copper strands (while increasing the Cu:SC ratio of the superconducting strands) was proposed as one way of reducing the strand load. In this study we compare the two alternative CICCs, with and without Cu strands, keeping in mind that the degradation after the SULTAN test was lower for the CICC without Cu strands. The post-mortem metallographic evaluation revealed that the overall strand transverse movement was 20% lower in the CICC without Cu strands and that the tensile filament fractures found were less, both indications of an overall reduction in high tensile strain regions. It was interesting to see that the Cu strands in the mixed cable design (with higher degradation) helped reduce the contact stresses on the high pressure side of the CICC, but in either case, the strain reduction mechanisms were not enough to suppress cyclic degradation. Advantages and disadvantages of each conductor design are discussed here aimed to understand the sources of the degradation.

9000 Hours Operation of a 25 Solid Oxide Cells Stack in Steam Electrolysis Mode

The operation of 25 solid oxide cells stacks in steam electrolysis mode over 9000 hours is reported. The stack has been operated at current densities of 0.57 and 0.72 A/cm2, using a 50% steam conversion, in the 750-780°C temperature range. Performance degradation rates of 2.30%/ kh are reported, with some non-homogeneity in the stack repeat units behavior observed. Stack repeat units located at the bottom of the stack feature degradation rates below 2%/kh. The possibility to use the operating temperature as a buffer to counter the performance degradation is highlighted. The stack performance was not affected by incidents that occurred during the test.

Proton Irradiation Effects on the Performance of III-V-Based, Unipolar Barrier Infrared Detectors

An examination of the collective results from recent experiments quantifying the performance degradation rates of III-V-based, unipolar barrier infrared detectors with various designs and materials, cutoff wavelengths and operating conditions due to 63 MeV proton irradiation is presented. Empirical relationships were established between the radiation damage factors for dark current density, lateral optical collection length, and quantum efficiency and the inverse product of the detectors' cutoff wavelength and operating temperature. Fitting the dark current density damage factor's empirical relationship reflected these detectors' tendency to remain diffusion-limited during irradiation, which was previously established using Arrhenius-analysis of the post-irradiation, temperature-dependent dark current measurements on each. Collectively, the results affirmed the performance degradation stemmed from a reduction of the minority carrier recombination lifetime via generation of additional defects by proton-induced displacement damage. For comparing detector's radiation-tolerance, the results indicated that damage factors alone were not ideal, but their empirical relationships would serve as heuristics in this role.

Ageing studies of a PEM Fuel Cell stack developed for reformate fuel operation in μCHP units: Development of an accelerated degradation procedure

Proton Exchange Membrane Fuel Cells (PEMFC) durability of stationary systems should be improved for large scales development and commercialization. The aim of this work is to improve degradation understanding in order to propose operating strategies enhancing lifetime and to design specific accelerated tests experiments for micro-CHP application and reformate operation. This paper is focused on results obtained on performance and membrane electrodes assemblies (MEAs) degradation during ageing tests of PEM fuel cells stacks.Durability tests conducted on short stacks over hundreds of hours (up to 900 h) showed how the fuel composition, particularly carbon monoxide content, and the load cycles profiles are impacting on performance degradation rates. The analyses of each cell by electrochemical diagnostics show the modifications of MEAs properties caused by the degradation occurring in both cathode and anode catalyst layers. Results allowed proposing major accelerating features and subsequent relevant accelerated tests, enhancing particularly the ruthenium dissolution identified as the specific limiting mechanism.

Performance Impact Associated with Ni-Based SOFCs Fueled with Higher Hydrocarbon-Doped Coal Syngas

Energy generation strategies demonstrating high efficiency and fuel flexibility are desirable in the contemporary energy market. When integrated with a gasification process, a solid oxide fuel cell (SOFC) can produce electricity at efficiencies exceeding 50 pct by consuming fuels such as coal, biomass, municipal solid waste, or other opportunity wastes. The synthesis gas derived from such fuel may contain trace species (including arsenic, lead, cadmium, mercury, phosphorus, sulfur, and tars) and low concentration organic species that adversely affect the SOFC performance. This work demonstrates the impact of exposure of the hydrocarbons ethylene, benzene, and naphthalene at various concentrations. The cell performance degradation rate is determined for tests exceeding 500 hours at 1073 K (800 °C). Cell performance is evaluated during operation with electrochemical impedance spectroscopy, and exposed samples are post-operationally analyzed by scanning electron microscopy/energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The short-term performance is modeled to predict performances to the desired 40,000-hours operational lifetime for SOFCs. Possible hydrocarbon interactions with the nickel anode are postulated, and acceptable hydrocarbon exposure limits are discussed.