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To meet “net zero” emission target for greenhouse gases in the year 2050, it is essential to retrieve most of the produced CO2 from emission intensive activities and store it permanently underground. This study considers integration of a 10 kW solid oxide fuel cell (SOFC) system with vacuum pressure swing adsorption (VPSA). In the integrated system, a small amount of electricity needed for the VPSA directly comes from SOFC system. The oxygen produced by VPSA is used to complete the oxidation of the unconverted fuel from the anodic side of SOFC, and then CO2 is separated automatically after the water condensation. Moreover, in this study, SOFC with VPSA has been optimized for minimizing the energy requirement and number of heat exchangers. Eight heat exchangers have been sized. Finally, the integrated system has waste heat available, to valorise the waste heat of the system, a steam cycle has been integrated for producing around additional electricity, to improve the overall efficiency. Finally, economic analysis has been performed, to understand its market competitiveness.

Solid oxide fuel cell (SOFC) systems show immense potential for efficient biogas utilization, which can significantly reduce carbon emissions by integrating with biogas cleaning units and carbon capture technologies. Despite the significant benefits, the high cost of the integrated system presents a challenge. Therefore, a techno-economic assessment is necessary to evaluate the feasibility of the integrated system and provide guidelines for cost reduction. The ideal capacity for an integrated biogas-fed SOFC power system ranges between 20 kW to 200 kW. Firstly, a comparison of different biogas types and stack technologies is conducted to evaluate the system performance. Secondly, a techno-economic investigation of the feasibility of different system designs is performed by comparing different carbon capture technologies with various biogas cleaning units. The study results can facilitate the optimization of the integrated system's design and operation and pave the way for large-scale implementation of SOFC technology in the energy industry.

This study presents the techno-economic analysis of a 100 kWe Solid Oxide Fuel Cell (SOFC) system for maritime applications fueled by methane, methanol, diesel, ammonia, and hydrogen. Two system configurations are considered for each fuel considering cathode off-gas recirculation (COGR) implementation to improve waste heat recovery both in terms of quantity and quality. The economic benefit of COGR is verified for all fuels, especially for methanol, hydrogen, and diesel, which present Levelized Cost of Exergy (LCOEx) reductions of about 10%, 9%, and 6%, respectively. Ammonia and methanol have the lowest LCOEx of about 0.260 EUR/kWh and 0.270 EUR/kWh, respectively, while hydrogen has the highest LCOEx of about 0.430 EUR/kWh. The sensitivity analyses suggest that fuel purchase cost, stack lifetime, and annual interest rate are the three parameters with the highest influence on the system cost. Overall, ammonia and methanol are the most promising fuels.

Water management of the proton exchange membrane fuel cell (PEMFC) is an important parameter to improve efficiency, especially in cold weather conditions. The generated water of the electrochemical reactions inside PEMFC may stay inside the cell and fill the pores in the gas diffusion layer (GDL), which degrades the cell and reduces the lifetime. The formation of water in PEMFC has a direct relationship with the capillary pressure that can be determined by the GDL's wettability and microstructure. Furthermore, wettability is dependent on the material, which can be changed by the contact angles of the GDL. Using the computational fluid dynamic (CFD) methods, different values of the GDL's contact angle have been examined to observe their corresponding effects on the maximum GDL liquid removal. Higher values of the GDL liquid removal result in better water management. Using the simulation data, an artificial neural network (ANN) model was trained in the current density of 0.4 (A/cm2$$ \mathrm{A}/\mathrm{c}{\mathrm{m}}2 $$) and the voltage of 0.604 (V) to predict the GDL liquid removal in 5700 points and to develop the optimization analysis. Results indicated that the highest GDL liquid removal of 0.225 (kg/m3s$$ \mathrm{kg}/{\mathrm{m}}3\mathrm{s} $$) can be obtained by the GDL's contact angle of 102.63 degrees. Highlights PEMFC three-dimensional simulation model with seven path serpentine flow field. The impacts of GDL contact angle on the maximum GDL liquid removal. Training an ANN model to calculate the maximum GDL liquid removal. At the contact angle of 102.63 degrees, maximum GDL liquid removal is 0.225 [kg/m3s$$ \mathrm{kg}/{\mathrm{m}}3\mathrm{s} $$].

Nickel foam substrates are frequently utilised for renewable energy applications as porous 3D-substrates. Preparation of these substrates usually includes an acid washing step, however the degree to which this step affects the final electrochemical performance after spray coating a catalyst ink is unreported. Herein, we report the effect of acid washing through physicochemical and electrochemical characterisation. The electrochemical performance was determined by repeated measurements of catalyst-coated nickel foam substrates both with and without the initial step of acid washing. Acid washing increased current density by 17.9% for the acid treated, MoS2-coated nickel foam electrode. This increment was affiliated with an electrochemically active surface area which increased by 87.1%, where Tafel analysis indicated that the acid treated, MoS2-coated electrodes facilitates the initial water dissociation step of the hydrogen evolution reaction with greater ease. Similar effects were also discovered for acid treated PtIr(1:3)/C-coated nickel foam substrates, albeit with less pronounced effects. Stability was also improved where the degradation rate was reduced by 18.9% for the acid treated, MoS2-coated electrodes. This proves the utility of acid washing nickel foam electrodes.

This study evaluates two different scenarios of an integrated system to generate electricity for a charging station using proton exchange membrane fuel cell (PEMFC) and solid oxide fuel cell (SOFC). To improve the efficiency, the exhaust heat of these two fuel cells are recovered by two different bottoming power cycles of Kalina Cycle (KC) and Organic Rankine Cycle (ORC). The system is designed for a 100 kW charging station capable to charge five cars simultaneously, assuming a standard car used in daily life with a battery capacity of 36 kWh and a range of 220 km. Thermodynamic analysis of the system is performed in different current densities from 0.5 A/cm(2) to 0.8 A/cm(2). In the first scenario, results indicated that the overall energy efficiency of the system is 58.47% at 0.5 A/cm(2) and 49% at 0.8 A/cm(2), while that of the second scenario is 43.21% at 0.5 A/cm(2) and 35% at 0.8 A/cm(2). To improve the dynamic response of the system, a high capacity battery and a supercapacitor were integrated to the fuel cell system. It was found that a hybrid combination of the battery and supercapacitor improve the performance of the system. (C) 2021 The Author(s). Published by Elsevier Ltd.

The depletion of fossil fuel sources has encouraged the authorities to use renewable resources such as wind energy to generate electricity. A backup/storage system can improve the performance of wind turbines, due to fluctuations in power demand. The novelty of this study is to utilize a hybrid system for a wind farm, using the excess electricity generated by the wind turbines to produce hydrogen in an alkaline electrolyzer (AEL). The hydrogen storage tank stores the produced hydrogen and provides hydrogen to the proton-exchange membrane fuel cell (PEMFC) to generate electricity once the power demand is higher than the electricity generated by the wind turbines. The goal of this study is to use the wind profile of a region in Iran, namely the Cohen region, to analyze the performance of the suggested integrated system on a micro scale. The output results of this study can be used as a case study for construction in the future, based on the exact specification of NTK300 wind turbines. The results indicate that, with the minimum power supply of 30 kW from the wind turbines on a lab scale, the generated power by the PEMFC will be 1008 W, while the maximum generated hydrogen will be 304 mL/h.

Reversible solid oxide cells (rSOC) can convert excess electricity to valuable fuels in electrolysis cell mode (SOEC) and reverse the reaction in fuel cell mode (SOFC). In this work, a five - cell rSOC short stack, integrating fuel electrode (Ni-YSZ) supported solid oxide cells (Ni-YSZ parallel to YSZ vertical bar CGO parallel to LSC-CGO) with an active area of 100 cm(2), is tested for cyclic durability. The fuel electrode gases of H-2/N-2:50/50 and H-2/H2O:20/80 in SOFC and SOEC mode, respectively, are used during the 35 reversible operations. The voltage degradation of the rSOC is 1.64% kh(-1) and 0.65% kh(-1) in SOFC and SOEC mode, respectively, with fuel and steam utilisation of 52%. The post-cycle steady-state SOEC degradation of 0.74% kh(-1) suggests improved lifetime during rSOC conditions. The distribution of relaxation times (DRT) analysis suggests charge transfer through the fuel electrode is responsible for the observed degradation. (C) 2022 The Author(s). Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.

This study investigates the potential application of total harmonic distortion (THD), as a fast online monitoring tool, to identify the early signs of failure modes in solid oxide fuel cells (SOFC). Indeed, the timely detection and identification of faults is crucial for applying mitigation strategies to avoid irreversible damage and increase the system lifetime. Two of the most common faulty conditions are considered in this work, namely fuel and air starvation. This experimental work aims at progressively triggering these errors in a controlled manner, by following different realistic scenarios, and recording THD values on a frequent basis. Several well-established laboratory monitoring tools, like electrochemical impedance spectroscopy (EIS), complemented by the distribution of relaxation times (DRT) are used to analyse and support the interpretation of the THD measurements. A sensitivity analysis on the THD parameters, namely the signal amplitude and the number of harmonics, is carried out to identify the optimal combination of parameters and achieve the best faults detectability. Finally, the impact of the fuel flow direction and the operating temperature are examined. The results of this work are summarised as practical guidelines to better employ the THD technique to identify the early warning signs of reactants’ starvation.

In this review paper, a critical assessment of the main degradation processes in three key components of solid oxide fuel cells and electrolysers (negative and positive electrodes and the interconnect) is undertaken, attempting prioritization of respective degradation effects and recommendation of the best approaches in their experimental ascertainment and numerical modeling. Besides different approaches to quantifying the degradation rate of an operating solid oxide cell (SOC), the latest advancements in microstructural representation (3D imaging and reconstruction) of SOC electrodes are reviewed, applied to the quantification of triple-phase boundary (TPB) lengths and morphology evolution over time. The intrinsic degradation processes in the negative (fuel) electrode and the positive (oxygen) electrode are discussed, covering first the composition and governing mechanisms of the respective electrodes, followed by a comprehensive evaluation of the most important factors of degradation during operation. By this systematic identification of dominant degradation processes, measurement techniques, and modeling approaches, the foundations are laid for the definition of meaningful accelerated stress testing of SOC cells and stacks, which will help the technology achieve the constantly more demanding durability targets in market applications.

The harmful influences of the fossil fuels on the environments have convinced the authorities to set official targets to 100% phase out the sales or registrations of new internal combustion engines (ICEs). As alternatives, batteries and fuel cells are suggested to provide the required power for different applications such as cars, buses, trucks, etc. Although there have been many investigations on the possibility of using integrated fuel cell and battery system as the prime mover for different types of vehicles, limited number of investigations have been developed in the airplane sector. At the current stage, the current suggested integrated system of battery and fuel cell is not able to provide the required power for huge passenger planes, but they can generate the needed electricity to run small size planes (around 100kW to 300 kW), hence the objective of the current study is related to the domain of Unmanned Aerial Vehicles (UAVs). UAVs are designed to fulfill long and high-altitude flight missions. The flight duration and flight altitude have been proved to be improved using the proton exchange membrane fuel cells (PEMFCs) as the prime-mover of the UAVs. However, the low acceleration of the PEMFCs has triggered the idea of combining PEMFCs and Lithium-Ion (Li-ion) battery. Thus, the integrated system can improve the low range of batteries by maintaining high acceleration and fast re-fueling time. Among different types of fuel cells, PEMFCs are established to be the best option for mobility applications, and the well-known Nickel Manganese Cobalt (NMC), and Lithium Titanite Oxide (LTO) Li-Ion batteries are considered as the most efficient types. Among the existing Li-Ion batteries in the market, LTO enjoys from the highest performance, lifespan, and safety by higher costs, whereas NMC provides acceptable performance with low costs and high specific energy. In comparison to the batteries, proton exchange membrane fuel cells (PEMFCs) have faster refueling time and higher ranges, hence the integration of batteries and fuel cells can provide the needs of UAVs. The utilization of PEMFC in an UAV results in the size and weight reduction of the system in addition to improving the flight endurance. Batteries can also ameliorate the acceleration and thrust of the system. So far, it is believed that fuel cells can be suitable for cruise flight while batteries are more appropriate for other flight modes. This study analyzes the possibility of integrating the PEMFC technology to the batteries as an alternative for fossil fuel-based combustion engines for the small sized UAV application. The proposed hybrid system, which is shown in Fig. 1., is designed to provide around 950W power for a UAV with a weight of 14 kg. PEMFC will be used as the selected type of fuel cell while NMC is the considered type of Li-Ion battery. The goal of this study is the characterize the dynamic performance of the current integrated system in an optimized condition. The integrated model of the fuel cell and battery is developed in the MATLAB/Simulink software to be controlled by an energy management system, which provides power to a DC variable power load, representing the different loads of an UAV flight. The load is mainly supplied by the fuel cell, while the battery intervenes in the following cases: As a support when the load is too high for the fuel cell, As a support when the fuel cell takes too long to respond to a load variation, As an additional load when the state of the charge of the battery is low (meaning that the fuel cell recharges the battery). Figure 1

The novelty of this study is to suggest a novel design for electric vehicle charging stations using fuel cell technology. The proposed system benefits from the Organic Rankine Cycle (ORC) to utilize the exhaust energy of the Solid Oxide Fuel Cell (SOFC) stacks in addition to the Lithium-Ion battery to improve the efficiency by partial-load operation of the stacks at night. The study is supported by the thermodynamic analysis to obtain the characteristics of the system in each state point. To analyze the operation of the system during the partial-load operation, the dynamic performance of the system was developed during the day. Furthermore, the environmental impacts of the system were evaluated considering eighteen parameters using a life-cycle assessment (LCA). LCA results also revealed the effects of different fuels and working fluids for the SOFC stacks and ORC, respectively. Results show that the combination of SOFC and ORC units can generate 264.02 kWh with the respective overall energy and exergy efficiencies of 48.96% and 48.51%. The suggested 264.02 kWh contributes to global warming (kg CO2 eq) by 5.17 × 105, 8.36 × 104, 2.5 × 105, 1.98 × 105, and 6.79 × 104 using methane, bio-methanol, natural gas, biogas, and hydrogen as the fuel of the SOFC stacks.

Operando characterization of SOCs generally relies on current–voltage measurements that provide the spatially averaged electrochemical response of the SOC. However, these methods do not fully capture the spatial distribution of the operating conditions (e.g., gas composition, current density). Local information on the operating conditions can be gained by using operando optical characterization methods. In this work, the spatial distribution of the electro-thermal response of an SOC with a 15 cm2 active area operated in fuel cell and electrolysis mode was investigated using lock-in thermography. Lock-in thermography consists of stimulating the solid oxide cell with a sinusoidal current perturbation and analyzing the local thermal response using Fourier transforms. A camera with a silicon-based sensor was used to record the transient temperature field on the oxygen electrode (i.e., the cathode in fuel cell operation) via a specifically designed optical access. The field of view of each pixel was approximately 0.03 mm x 0.03 mm. The Fourier transform generates a compact data set that can be conveniently represented by a phase and amplitude or a real and imaginary image. Using a real–imaginary representation provided a better thermal response contrast than an amplitude–phase representation. The local thermal response was found to be dependent on the direct current bias and the frequency of the current perturbation. The thermal response of the SOC was laterally and longitudinally inhomogeneous, thereby demonstrating the capability of active thermography to characterize the local behavior of an SOC in operando. Lock-in thermography is thus a promising method for defining regions of interest for post-mortem analysis using electron microscopy and helping to link highly localized post-test analysis with spatially averaged operando characterization methods.

The blade tip clearance loss was studied experimentally and numerically for a micro radial fan with a tip diameter of 19.2mm. Its relative blade tip clearance, i.e., the clearance divided by the blade height of 1.82 mm, was adjusted with different shims. The fan characteristics were experimentally determined for an operation at the nominal rotational speed of 168 krpm with hot air (200 °C). The total-to-total pressure rise and efficiency increased from 49 mbar to 68 mbar and from 53% to 64%, respectively, by reducing the relative tip clearance from 7.7% to the design value of 2.2%. Single and full passage computational fluid dynamics simulations correlate well with these experimental findings. The widely-used Pfleiderer loss correlation with an empirical coefficient of 2.8 fits the numerical simulation and the experiments within +2 efficiency points. The high sensitivity to the tip clearance loss is a result of the design specific speed of 0.80, the highly-backward curved blades (17°), and possibly the low Reynolds number (1 × 105). The authors suggest three main measures to mitigate the blade tip clearance losses for small-scale fans: (1) utilization of high-precision surfaced-grooved gas-bearings to lower the blade tip clearance, (2) a mid-loaded blade design, and (3) an unloaded fan leading edge to reduce the blade tip clearance vortex in the fan passage.

With a growing energy demand in a carbon-constrained society, fuels cells powered by renewable fuels, and specifically solid waste, are seen as interesting contributors to the energy portfolio. The alternative energy industry needs to reduce costs, enhance efficiency, and demonstrate durability and reliability to be economically feasible and attractive. This paper addresses biomass waste gasification in distributed energy systems, using a solid oxide fuel cell (SOFC) to produce electricity and heat. The potential and optimal plant efficiency and layout (i.e., anode off-gas (AOG) recirculation point via small-scale turbomachinery and heat exchanger network) are analyzed through a multi-stage approach that includes scenario evaluation and multi-objective optimization via a hybrid optimization strategy with heuristics and mathematical programming. The results in this paper summarize the most convenient operating conditions and provide an optimized heat exchanger network (HEN). The AOG recirculation toward the gasifier combustor is the preferred option; the electrical and thermal efficiencies can separately go up to 49 and 47%, respectively. The combined total efficiency ranges between 76 and 82%, and the area of heat exchange, which corresponds to an amount of heat exchanged between 91 and 117 kW, is within 6–14 m2.

Despite being a mature technology, solid oxide fuel cell (SOFC) devices are still limited by lifetime issues. In SOFC stacks, cell/interconnect interaction is the main responsible for voltage degradation at the oxygen electrode side. Corrosion and chromium evaporation might in fact increase ohmic and charge transfer losses. This study presents the evolution of the degradation phenomena inside four SOFC short-stacks tested respectively for 45, 2700, 4800 and 10000 hours. An additional stack which underwent 124 thermal cycles is also analyzed to assess the mechanical reliability of the interconnect/ceramic coupling. Metal interconnect was made of K41/AISI441 ferritic stainless steel coated with MnCo2O4 porous barrier layer. Scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) characterization is applied to examine the degradation process. Observations indicate that despite a harsh initial red-ox interaction between the cathode materials and the interconnect, after 5000 h of operation the kinetic of the degradation process in the electrical contact areas slows down dramatically. An empirical model based on the scale thickness at different interconnect location gives estimation for the oxide thermal growth for a stack lifetime period. From the mechanical properties point of view, no spallation was observed and local delamination was mainly due to the sample preparation process.

This paper describes an optimization strategy for operating solid-oxide fuel-cell systems at optimal efficiency. Specifically, we present the experimental validation of a real-time optimization (RTO) strategy applied to a commercial solid-oxide fuel-cell system. The proposed RTO scheme effectively pushes the system to higher levels of efficiency and maintains the system there despite perturbations by tracking active constraints. The optimization approach uses either steady-state measurements, or transient measurements in combination with a dynamic model, and can deal effectively with plant-model mismatch. In the reported experiments, the approach drives the system to the desired power demand at optimal efficiency. The experimental fuel-cell system reached 65% DC electrical efficiency. As such, the proposed RTO scheme is a promising candidate for enforcing optimal micro-CHP operation. In addition, the approach can deal with slow drifts such as degradation without compromising on efficiency. Finally, and important from a practical point of view, we suggest guidelines for safe and optimal operation. (C) 2019 Elsevier Ltd. All rights reserved.

While high performance of SOFC systems has already been achieved, there is still a need to increase the stack lifetime, while decreasing the system's total cost of ownership, both being linked. The increase in lifetime includes the minimization of performance degradation, but also avoidance of potentially detrimental events during operation, originating from the stack, outside the stack, or a combination of both. The present paper highlights how the detection of faulty operation as early as possible is important to implement adequate mitigation strategies, wherever applicable, according to the fault and its grade of severity. Three types of faults have been considered, fuel starvation, leakage and carbon deposition. Both hardware components and algorithms to monitor, detect, isolate, and finally correct faulty system operation have been developed and will be embedded in a real SOFC system.

The current advances in the integration of devices through the internet of things (IoT) have encouraged researchers to focus on the applications of IoT in the automotive industry. Although different achievements in the in-vehicle network analysis and traffic management have been already reviewed, a comprehensive study to bring together the main applications of the IoT in the automotive industry is required. Internal combustion engines (ICEs) are established as the most common prime-mover for cars, however, with the depleting fossil-fuel resources, the interest in the usage of fuel cells and batteries has increased. In this regard, the main goal of the current study is to evaluate the application of IoT in batteries, fuel cells, and ICEs. This paper is also centralized on different types of IoT applications and combines them with empirical articles such as Random Location Detection, Vehicle Theft Prevention, Observation of vehicle performance, and industrial management of vehicles. As an output of this comprehensive review, different usages of the IoT in the automotive sector will be clarified. Also, this article can be considered as a basis for advancing the recent implementation of the IoT in the fuel cell, battery, and ICE domains.

Proton-exchange membrane fuel cells (PEMFCs) are regarded as promising alternatives to internal combustion engines (ICEs) to reduce pollution. Recent research on PEMFCs focuses on achieving higher power densities, reducing the refueling time, mitigating the final price, and decreasing the degradations, to facilitate the commercialization of hydrogen mobility. The design of bipolar plates and compression kits, in addition to their coating, can effectively improve performance, increase durability, and support water/thermal management. Past reviews usually focused on the specific aspect, which can hardly provide readers with a complete picture of the key challenges facing and advances in the long-term performance of PEMFCs. This paper aims to deliver a comprehensive source to review, from both experimental, analytical and numerical viewpoints, design challenges, degradation modeling, protective coatings for bipolar plates, and key operational challenges facing and solutions to the stack to prevent contamination. The significant research gaps in the long-term performance of PEMFCs are identified as (1) improved bipolar-plate design and coating, (2) the optimization of the design of sealing and compression kits to reduce mechanical stresses, and (3) stack degradation regarding fuel contamination and dynamic operation.

Many countries have set official targets to 100% phase out sales or registrations of new internal combustion engines (ICE) that use gasoline. Battery and fuel cell technologies have been suggested to be the best alternative for the current ICEs to be utilized in cars, buses, trucks, and boats. Although there have been studies to consider fuel cells and batteries for the cars, there are limited number of studies to consider these technologies for ferries. Different types of prime movers have been utilized to run the boats, however, most of the studies in the field are related to either the usage of fuel cell or battery as the prime mover of the boats, while the integrated system can improve the low range of batteries by maintaining high acceleration and fast re-fueling time. Two well-known types of industrial Li-Ion batteries in the market are Nickel Manganese Cobalt (NMC), and Lithium Titanite Oxide (LTO). Among the existing Li-Ion batteries in the market, LTO enjoys from the highest performance, lifespan, and safety by higher costs, whereas NMC provides acceptable performance with low costs and high specific energy. In comparison to the batteries, proton exchange membrane fuel cells (PEMFCs) have faster refueling time and higher ranges, hence the integration of batteries and fuel cells can provide the needs of ferries. In this study, the possibility of integrating the fuel cell technology and the battery is evaluated to provide 800kW electricity. PEMFC modules are integrated with a Li-Ion battery to have high ranges and efficiencies in fast refueling times for ferry applications. An optimization model was developed using the open source Julia programming language to determine the best combination of the batteries and fuel cells considering the size, weight, hydrogen consumption, and overall efficiency as the output parameters. The dynamic model captures the characteristics of the system by the changes in time and considers the impacts of batteries’ charging/discharging status on the overall performance. Two different novel scenarios are suggested to provide 800kW power for a ferry with a total length of 50.8m to transport 780 passengers considering the Lausanne-Evian round trip, which is 24km, in 70 mins. LTO and NMC type Li-Ion batteries are selected for these two different scenarios while PEMFC is the selected type of fuel cell for this ferry. Dynamic models have been developed in the MATLAB software for both the battery and fuel cell modules. Based on the presented flowchart in Fig. 1, a quasi-static optimization model has been utilized for the power split. Results indicate that the total size, and hydrogen consumption of around 8 , and 36.1 kg/h, respectively, are needed in the first scenario to reach the maximum power of 800kW with 49.5% overall efficiency. The operating power of the integrated battery and fuel cell system is between 80kW to 720 kW, which is 10% to 90% of the maximum power. In the second scenario, the corresponding values of the size, and hydrogen consumption are around 8.23 , and 36 kg/h to reach the same power by the overall efficiency of 49.6%. The first scenario uses 8 modules of PEMFCs and one module of NMC while the second scenario uses LTO as the battery with the same number of PEMFCs. Fig. 2 also shows the transient performance characteristics of the integrated system in the first scenario considering the output power and the hydrogen consumption of the fuel cells, in addition to the output energy and the state of charge of the batteries. Figure 1

Electricity production and consumption must be balanced for the electrical grid. However, the rapidly growing intermittent power sources are now challenging the supply-demand balance, leading to large flexibility needs for grid management. The plant integrating biomass gasification and reversible solid-oxide cell stacks can be potential means of flexibility, which could flexibly switch among power generation, power storage, and power neutral modes. This paper investigates the economic feasibility of such grid-balancing plants, i.e., plant capital expenditure (CAPEX) target, via a systematic overall decomposition-based methodology for real geographical zones and flexibility-need scenarios. The plant CAPEX target (€/ref-stack) is defined as the maximum affordable investment cost for each reference stack (active cell area 5,120 cm2). The results show that, for a 5-year payback time, 5-year stack lifetime, and 40 €/MWh grid balancing price, the plant concept with 10–100 MWth gasifier has high economic potential with target reaching 17,000 €/ref-stack; however, the plant concept with 100–1,000 MWth gasifier has a limited commercialization potential with the target reaching below 1,000 €/ref-stack due to high biomass supply costs. Considering the sale of chemical product, plant CAPEX target can reach up to 22,000 and 3,000–12,000 €/ref-stack for the plants with 10–100 and 100–1,000 MWth, respectively. The plant CAPEX target is decreased by increasing the total capacities of all plants deployed since more and more capacities will be put into power neutral mode (isolated from the electrical grid) via the coordination of multiple plants. The plant CAPEX target can be further increased by higher grid up/down-regulating price and longer payback years.

A microsteam turbine with a tip diameter of 15 mm was designed and experimentally characterized. At the nominal mass flow rate and total-to-total pressure ratio of 2.3 kg h−1 and 2, respectively, the turbine yields a power of 34 W and a total-to-static isentropic efficiency of 37%. The steam turbine is conceived as a radial-inflow, low-reaction (15%), and partial admission (21%) machine. Since the steam is limited in the system (solid oxide fuel cell), a low-reaction and high-power-density design is preferred. The partial-admission design allows for reduced losses: The turbine rotor and stator blades are prismatic, have a radial chord length of 1 mm and a height of 0.59 mm. Since the relative rotor blade tip clearance (0.24) is high, the blade tip leakage losses are significant. Considering a fixed steam supply, this design allows to increase the blade height, and thus reducing the losses. The steam turbine drives a fan, which operates at low Mach numbers. The rotor is supported on dynamic steam-lubricated bearings; the nominal rotational speed is 175 krpm. A numerical simulation of the steam turbine is in good agreement with the experimental results. Furthermore, a novel test rig setup, featuring extremely thin thermocouples (ø0.15 mm) is investigated for an operation with ambient and hot air at 220 °C. Conventional zero- and one-dimensional predesign models correlate well with the experimental results, despite the small size of the turbine blades.

The Solid-oxide fuel cell is a highly efficient prime mover for biogas conversion, but a part of biogas needs to be reformulated externally to facilitate the electrochemical conversion, easy control of reforming conditions, and thermal management of the stack. Carbon deposition and external mineralcarrying water should be avoided to ensure the durability of the fuel processor and stack catalysts. This paper investigates four plant layouts with different anode off-gas recirculation schemes and biogas reforming methods: (1) pre-reforming with hot recirculation (HR), (2) pre-reforming with cold recirculation (CR), (3) no pre-reforming and hot recirculation (NR), (4) partial oxidation with hot recirculation (PO). All the schemes feature an electrolyte supported SOFC working at 860°C and 0.23 A/cm2 current density. A sensitivity analysis of the plant efficiency as a function of the Recirculation Ratio (RR) and the Reformer Temperature (RT) is performed. The results show that HR and CR schemes achieve the highest efficiency (58-63%). The HR scheme benefits from the recirculated water and does not require external water for RR > 50% and RT > 600°C; the CR scheme achieves the same result for RR > 80% and RT > 700°C. The optimal RR is within 50 – 80% for the highest system efficiency, as a trade-off between the overall fuel utilization and electrochemistry performance. The RT should be between 600 and 700°C. The HR scheme is the overall best performing if the re-circulator and stack designs do not limit the flow rates at a high RR.

Solid oxide fuel cells have a proven efficiency for the direct conversion of biogas into electricity, and their full potential from European agricultural and waste-water sites still has to be fully evaluated and harnessed. Biogases are methane-rich mixtures whose composition and trace contaminants, especially of sulfur compounds, can vary greatly. To avoid carbon deposition from the carbon-rich CH4-CO2 mixtures, some amount of steam and/or extra CO2 needs to be added to process the biogas. Ideally this can be recovered from the SOFC exhaust. In a preparatory work, biogas/SOFC integrated systems were studied and compared using Aspen Plus[1]. Best performances are reached with a catalytic methane pre-reformer when a fraction of the anode off-gas is recirculated for mixing with the biogas feed. This work provided the guidelines for the present catalytic study and predicted thermodynamic equilibria of gas mixtures. Here, the overall performance of a ruthenium exsolution catalyst[2] for the reforming of methane was evaluated for these different biogas compositions at various gas hourly space velocities. Gas chromatography and material balance calculations enabled the full measurement of inlet and outlet gas compositions which, in turn, permitted to calculate precise conversion rates, reforming ratio, and the deviation from thermodynamic equilibrium. Methane conversion reached >95 % for a dry-dominant reforming mixture, which simplifies the overall system. The longer-term stability of the catalyst as well as its tolerance towards different sulfur traces that occur in biogas was then evaluated and analyzed. [1] Shuai Ma, Gabriele Loreti, Ligang Wang, Andrea L. Facci, Stefano Ubertini, Changqing Dong, François Maréchal, and Jan Van herle, E3S Web of Conferences 2021 238:04002 DOI: 10.1051/e3sconf/202123804002 [2] Muhammad A. Naeem, Paula M. Abdala, Andac Armutlulu, Sung Min Kim, Alexey Fedorov, and Christoph R. Müller, ACS Catalysis 2020 10 (3), 1923-1937 DOI: 10.1021/acscatal.9b04555

The proton exchange membrane fuel cell (PEMFC) is a prominent environmentally friendly alternative candidate to internal combustion engines in automotive applications. The recovery of the waste heat of light-duty diesel engines has been investigated recently, which is similarly relevant for PEMFCs. Thermoelectric generators (TEG) applied on the stack’s walls have been already proposed and tested as a cooling method for small scale applications of the PEMFC. For the medium scale usages of the PEMFC stack, TEG technology may be further used to recover heat lost through the cooling water required for stack thermal management, which was the focus of the present study. Using an agglomerate model for the PEMFC and a computational fluid dynamic (CFD) thermal model for the TEG heat exchanger unit, the operation and performance of the PEMFC stack and heat recovery unit were simulated, respectively. After validation, results indicated that the transferred heat from the PEMFC to the cooling channel increased the temperature of the coolant from room temperature to 330.5 K at the current density of 0.8 A/cm2. CFD analysis revealed that 37.7 W of the heated wasted by the PEMFC stack could be recovered by the currently available TEG material and geometry.

The Laboratory for Applied Mechanical Design (LAMD) designed, manufactured, and experimentally tested a novel recirculation fan for a 10 kWe solid oxide fuel cell (SOFC). The fan uses oil-free bearings, more specifically herringbone-grooved journal and spiral-grooved thrust gas bearings. The radial inducer-less fan with a tip diameter of 19.2 mm features backward-curved prismatic blades with constant height. Prior to coupling the recirculation fan with the SOFC, the fan was experimentally characterized with air at 200 °C. At the nominal point of 168 krpm, the measured inlet mass flow rate is 4.9 kgh−1, the total-to-total pressure rise 55 mbar, the isentropic total-to-total efficiency 55 %, and the power 18.3 W. This paper compares the experimental data towards a computational fluid dynamic simulation of the full fan impeller and volute suggesting an excellent correlation at the nominal point what validates the numerical approach. However, the heat flows crossing the fan fluid domain, have an increased effect at off-design conditions, thus the experimental results need careful consideration. The fan backface leakage has negligible impact on the measurements.

Thermochemical biomass-to-fuel conversion requires an increased hydrogen concentration in the syngas derived from gasification, which is currently achieved by water–gas-shift reaction and CO2 removal. State-of-the-art biomass-to-fuels convert less than half of the biomass carbon with the remaining emitted as CO2. Full conversion of biomass carbon can be achieved by integrating solid-oxide electrolyzer with different concepts: (1) steam electrolysis with the hydrogen produced injected into syngas, and (2) co-electrolysis of CO2 and H2O to convert the CO2 captured from the syngas. This paper investigates techno-economically steam- or co-electrolysis-based biomass-to-fuel processes for producing synthetic natural gas, methanol, dimethyl ether and jet fuel, considering system-level heat integration and optimal placement of steam cycles for heat recovery. The results show that state-of-the-art biomass-to-fuels achieve similar energy efficiencies of 48–51% (based on a lower heating value) for the four different fuels. The integrated concept with steam electrolysis achieves the highest energy efficiency: 68% for synthetic natural gas, 64% for methanol, 63% for dimethyl ether, and 56% for jet fuel. The integrated concept with co-electrolysis can enhance the state-of-the-art energy efficiency to 66% for synthetic natural gas, 61% for methanol, and 54% for jet fuel. The biomass-to-dimethyl ether with co-electrolysis only reaches an efficiency of 49%, due to additional heat demand. The levelized cost of the product of the integrated concepts highly depends on the price and availability of renewable electricity. The concept with co-electrolysis allows for additional operation flexibility without renewable electricity, resulting in high annual production. Thus, with limited annual available hours of renewable electricity, biomass-to-fuel with co-electrolysis is more economically convenient than that with steam electrolysis. For a plant scale of 60 MWth biomass input with the renewable electricity available for 1800 h annually, the levelized cost of product of biomass-to-synthesis-natural-gas with co-electrolysis is 35 $/GJ, 20% lower than that with steam-electrolysis.

The degradation of metal interconnects (ICs) is one of the main lifetime limiting issues in Solid Oxide Cells (SOCs). Chromium oxide thermally grows on the substrate surface that causes ohmic loss and its vapors poison the oxygen electrode reaction (OER). Mn-based spinels are presently among the materials of choice to protect ICs to prevent Cr diffusion. As the target lifetime is around 40000h, it is of interest to design accelerated ageing tests, under harsher than nominal operating conditions, to simulate the long-time ageing behavior at nominal conditions. In this study, the performance of IC coatings was investigated with accelerated ex-situ corrosion ageing tests, in which the operating condition of the air-side interconnect was simulated. Temperature and humidity were selected as test variable parameters. Area Specific Resistance (ASR) and Cr depletion/migration were studied for the stressed conditions. Tests were carried out on stainless steel substrate with Mn-Cu-Oxide and Mn-Co-Oxide as protective coatings. Ageing tests over 1000h at different temperatures (750-950°C) and humidity (above 15%RH) were run while monitoring the ASR of the samples. Fig. 1 shows the ASR results for the samples run at different temperatures and in dry condition. Based on Fig. 1a-e, it is observed that the ASR trends remain constant during the test time. Although 916°C is well above nominal operating temperature, the ASR showed constant value within a reasonable range. At a test temperature 950°C (Fig. 1f), the ASR behavior of samples containing Co-Mn Oxide protective coating is the same found for lower temperatures; however, a sharp ASR increase in Mn-Cu Oxide coated samples can be observed. Applying humidity to high-temperature conditions also may help to accelerate the test, and its results will be presented. SEM/EDX post-test characterization provides information on the scale morphology and helps to understand the different behaviors at different stressed conditions. Keywords: SOC; interconnect; protective coating; ageing test; accelerating test; Cr diffusion; ASR; Figure 1

This study examines the effect of Ni migration near the interface with the electrolyte after fuel cell (SOFC) and electrolysis mode (SOEC) operation on nickel-yttria stabilized zirconia (Ni-YSZ) electrodes. The experimental dataset consists in a series of short-stacks tested under different polarization conditions and durations. Selected zones have been imaged by 3-D FIB-SEM serial sectioning. After reconstruction and segmentation, the spatial variations of metric and topological properties have been quantified along the direction perpendicular to the interface with the YSZ electrolyte, including TPB density, volume fraction, dihedral angles and interfacial curvature. Their spatial distribution and time evolution have been analysed to advance the understanding of the driving forces that cause Ni depletion near the YSZ electrolyte.

The perovskite-type mixed oxide La0.3Sr0.55Ti0.95Ni0.05O3−δ (LSTN) is demonstrated to exhibit the remarkable property of structural regeneration, where Ni can be reversibly exsoluted from the host perovskite lattice resulting in a regenerable Ni catalyst for solid oxide fuel cell anode applications. Results of catalytic tests for the water gas shift reaction and electrochemical investigations on a button-sized fuel cell demonstrate the redox stability of LSTN, its potential application in solid oxide fuel cells, and its ability to recover catalytic activity completely after sulfur poisoning. Nickel segregation was characterized and quantified on powder samples by means of electron microscopy, X-ray diffraction, X-ray absorption spectroscopy, and temperature-programmed reduction–reoxidation cycles. Catalyst stability was much improved compared to impregnated Ni/La0.3Sr0.55TiO3−δ and Ni/Y0.08Zr0.92O2 anode materials. A full cell was tested under both open circuit voltage and polarized conditions, showing a stable cell voltage over redox cycles as well as periods of reverse potential and current overload. The area-specific resistance of the anode layer was as low as 0.58 Ω cm2 at 850 °C. This allows LSTN to be applied in redox-stable solid oxide fuel cell anodes and reversible segregation of Ni to be exploited for fast recovery from sulfur poisoning.

This paper presents a model-based investigation to handle the fundamental issues for the design of co-electrolysis based power-to-methane at the levels of both the stack and system: the role of CO2 in co-electrolysis, the benefits of employing pressurized stack operation and the conditions of promoting internal methanation. Results show that the electrochemical reaction of co-electrolysis is dominated by H2O splitting while CO2 is converted via reverse water-gas shift reaction. Increasing CO2 feed fraction mainly enlarges the concentration and cathode-activation overpotentials. Internal methanation in the stack can be effectively promoted by pressurized operation under high reactant utilization with low current density and large stack cooling. For the operation of a single stack, methane fraction of dry gas at the cathode outlet can reach as high as 30 vol.% (at 30 bar and high flowrate of sweep gas), which is, unfortunately, not preferred for enhancing system efficiency due to the penalty from the pressurization of sweep gas. The number drops down to 15 vol.% (at 15 bar) to achieve the highest system efficiency (at 0.27 A/cm2). The internal methanation can serve as an effective internal heat source to maintain stack temperature (thus enhancing electrochemistry), particularly at a small current density. This enables the co-electrolysis based power-to-methane to achieve higher efficiency than the steam-electrolysis based (90% vs 86% on higher heating value, or 83% vs 79% on lower heating value without heat and converter losses).

Urea is widely used in agriculture, industry, and food, while it is also a potential fuel. Large-scale urea production relies on fossil fuels, thus there is a strong need for green urea given the increasing penetration of renewable energy sources. A potential alternative is biomass-to-urea; however, it cannot fully convert the biomass carbon into urea. To achieve full carbon conversion, innovative integrated biomass- and power-to-urea processes are designed conceptually. The two green urea production processes are evaluated techno-economically and compared with state-of-the-art methane-to-urea. The results show that the methane-to-urea achieves a system efficiency of 58% (LHV), while biomass-to-urea only has 39% (LHV) with unconverted biomass carbon of up to 60%. The integrated power- and biomass-to-urea has outstanding heat integration performance which fixes all biomass carbon into urea, with an efficiency enhanced up to 53%. Due to the electricity demand, the levelized cost of the urea of integrated biomass- and power-to-urea is 15 – 38 and 58 – 87% points higher than those of the biomass-to-urea and methane-to-urea for the scale of 10 – 60 MWth urea production. The available annual hours and electricity price of renewable electricity have a significant impact on the levelized cost of the urea. When the available annual hours decrease from 7200 to 3600 with an electricity price of 73 $/MWh, the levelized cost of urea increases on average by 13% from 51 $/GJ with the plant capacity being 10 – 60 MWth urea. However, when electricity price is reduced from 73 $/MWh to 35 $/MWh with available annual hours of 3600, the levelized cost decreases on average by 15% from 59 $/GJ with the same plant capacity.

The global demand for fossil fuels in the transportation sector is increasing rapidly due to the continuous growth of internal combustion engine vehicles. This leads to severe environmental problems, including greenhouse gas emissions and air-quality deterioration. Thus, it is necessary to increase the use of renewable energy sources in the transportation sector as well as other off-grid applications. Battery and fuel cells are promising alternatives owing to high efficiency and low (even zero) local emissions. However, they are limited by either the low capacity or sluggish dynamic response. These shortcomings can be overcome by the hybridization of battery and fuel cells, which have been the focus of leading international automotive and shipbuilding companies. This paper presents a comprehensive evaluation and comparison of different hybrid systems of Proton Exchange Membrane Fuel Cell with battery and Solid Oxide Fuel Cell with battery for mobility and other off-grid applications from perspectives of system configurations, technical specifications, energy management strategies, and experimental validation. With the existing issues and corresponding solving strategies highlighted, the suggestions for designing high-performance fuel cell hybrid power systems are concluded accordingly. This review can serve as a reference and guide to advance the development of the fuel cell and battery hybrid power systems for mobility and off-grid applications.

Biomass-to-electricity or -chemical via power-to-x can be potential flexibility means for future electrical grid with high penetration of variable renewable power. However, biomass-to-electricity will not be dispatched frequently and becomes less economically- beneficial due to low annual operating hours. This issue can be addressed by integrating biomass-to-electricity and -chemical via ‘‘reversible’’ solid-oxide cell stacks to form a triple-mode grid-balancing plant, which could flexibly switch among power generation, power storage and power neutral (with chemical production) modes. This paper investigates the optimal designs of such a plant concept with a multi-time heat and mass integration platform considering different technology combinations and multiple objective functions to obtain a variety of design alternatives. The results show that increasing plant efficiencies will increase the total cell area needed for a given biomass feed. The efficiency difference among different technology combinations with the same gasifier type is less than 5% points. The efficiency reaches up to 50%–60% for power generation mode, 72%–76% for power storage mode and 47%–55% for power neutral mode. When penalizing the syngas not converted in the stacks, the optimal plant designs interact with the electrical and gas grids in a limited range. Steam turbine network can recover 0.21–0.24 kW electricity per kW dry biomass energy (lower heating value), corresponding to an efficiency enhancement of up to 20% points. The difference in the amounts of heat transferred in different modes challenges the design of a common heat exchange network.

The increasing penetration of variable renewable energies poses new challenges for grid management. The economic feasibility of grid-balancing plants may be limited by low annual operating hours if they work either only for power generation or only for power storage. This issue might be addressed by a dual-function power plant with power-to-x capability, which can produce electricity or store excess renewable electricity into chemicals at different periods. Such a plant can be uniquely enabled by a solid-oxide cell stack, which can switch between fuel cell and electrolysis with the same stack. This paper investigates the optimal conceptual design of this type of plant, represented by power-to-x-to-power process chains with x being hydrogen, syngas, methane, methanol and ammonia, concerning the efficiency (on a lower heating value) and power densities. The results show that an increase in current density leads to an increased oxygen flow rate and a decreased reactant utilization at the stack level for its thermal management, and an increased power density and a decreased efficiency at the system level. The power-generation efficiency is ranked as methane (65.9%), methanol (60.2%), ammonia (58.2%), hydrogen (58.3%), syngas (53.3%) at 0.4 A/cm2, due to the benefit of heat-to-chemical-energy conversion by chemical reformulating and the deterioration of electrochemical performance by the dilution of hydrogen. The power-storage efficiency is ranked as syngas (80%), hydrogen (74%), methane (72%), methanol (68%), ammonia (66%) at 0.7 A/cm2, mainly due to the benefit of co-electrolysis and the chemical energy loss occurring in the chemical synthesis reactions. The lost chemical energy improves plant-wise heat integration and compensates for its adverse effect on power-storage efficiency. Combining these efficiency numbers of the two modes results in a rank of round-trip efficiency: methane (47.5%) > syngas (43.3%) ≈ hydrogen (42.6%) > methanol (40.7%) > ammonia (38.6%). The pool of plant designs obtained lays the basis for the optimal deployment of this balancing technology for specific applications.

The longer lifetimes of solid oxide cells (SOC) – obtained and still required, both in fuel cell and electrolysis operation – exacerbate the need for accelerated stress tests, since neither reliable degradation models are currently available nor validated methodologies to evaluate expected stack durability in a practical timeframe. The project AD ASTRA ( “HArnessing Degradation mechanisms to prescribe Accelerated Stress Tests for the Realization of SOC lifetime prediction Algorithms”) started operations to tackle this on January 1st 2019, funded by the European Fuel Cells and Hydrogen Joint Undertaking. Generally, a great number of operational parameters influence SOC degradation during lifetime, each contributing according to characteristic times and intensities, often in convoluted or even contrasting fashion. Aggravation of test input parameters can thus lead to non-representative accelerated degradation of a component where concurring effects are differently influenced, leading to a biased end state of the component investigate. To systematically address, harness and accelerate the selected failure modes, a matrix was set up of degradation mechanisms, test items, test procedures and characterization methods, that was translated to protocols in such a way that consistent measurement data are generated, helping subsequent analysis and correlation of phenomena and parameters by the project’s modelling and simulation activities. The testing approach consists of a dual-focus campaign targeting: • macroscopic stack testing procedures, where short stacks will be operated in situ, in aggravated conditions with the objective of identifying test settings that will stress the stack in a representative way but minimizing testing time and resource expenditure • specific component ageing tests, to reproduce (ex-situ) the degraded condition of critical stack components or interfaces in a faster time, based on analysis of the components extracted from stacks that have been field-tested. A radical innovation of the project consists in the integration of these two methods: components specifically aged ex situ assembled into otherwise “new” stacks for in-situ testing, so that their effect on stack performance can be easily isolated from other components that in real-world conditions would also degrade. These tests allow to observe from the start (t=0) the end-of-service stack degradation, radically reducing in-situ testing time and providing powerful means to validate models simulating the long-term effects of component degradation in a stack.

The increasing penetration of intermittent renewable power challenges the stability of the electrical grid, thus coal power plants are usually required to extend the operation range by reducing the minimum load. This work proposes a concept of coupling solid-oxide cell stack based power-to-gas with coal power plants to allow for dual functions of (1) storing excess renewable electricity and (2) reducing the minimum load of coal power plants by combustion stabilization with oxygen-rich air from power-to-gas. The performance and operating strategy of such an integrated plant are evaluated with detailed off-design characteristics of the considered coal power plants. The results show that the integration of power-to-gas affects the distribution of the heat absorbed by radiative and convective heat exchangers in the boiler, stabilizes coal combustion, and reduces the superheat degree of live/reheated steam. It allows the power plant for operating at a significantly low load of down to 22% of the nominal load, compared with 40% before the coupling; meanwhile, a very limited penalty is caused with the plant efficiency reduced from 34.4% down to 34.1% (with 13% of the normalized power-to-gas capacity). Minimizing the power-to-gas contribution to the accommodated renewable power is advantageous for a minimal CO2 emission; nevertheless, maximizing the power-to-gas contribution with the coal power plant at high load allows for a maximal system efficiency.

While the global fuel utilization of solid oxide fuel cells (SOFCs) is limited by the stack aging rate, the fuel excess is typically used in a burner, and thus limiting the system electrical efficiency. Further, natural-gas-fueled SOFCs require treated water for the steam reforming process, which increases operational cost. Here, we introduce a novel micro anode off-gas recirculation fan that is driven by a partial-admission (21%) and low-reaction (15%) steam turbine with a tip diameter of 15 mm. The 30 W turbine is propelled by pressurized steam, which is generated from the excess stack heat. The shaft runs on dynamic steam-lubricated bearings and rotates up to 175 krpm. For a global fuel utilization of 75% and a constant fuel mass flow rate, the electrical gross DC efficiency based on the lower heating value was improved from 52 % to 57 % with the anode off-gas recirculation, while the local fuel utilization decreased from 75% to 61%, which is expected to significantly increase stack lifetime. For a global fuel utilization of 85%, gross efficiencies of 66% in part load (4.5 kWe) and 61% in full load (6.3 kWe) were achieved with the anode off-gas recirculation. The results suggest that the steam-driven anode off-gas recirculation can achieve a neutral water consumption.

Imbalance costs caused by forecasting errors are considerable for grid-connected wind farms. In order to reduce such costs, two onsite storage technologies, i.e., power-to-hydrogen-to-power and lithium battery, are investigated considering 14 uncertain technological and economic parameters. Probability density distributions of wind forecasting errors and power level are first considered to quantify the imbalance and excess wind power. Then, robust optimal sizing of the onsite storage is performed under uncertainty to maximize wind-farm profit (the net present value). Global sensitivity analysis is further carried out for parameters prioritization to highlight the key influential parameters. The results show that the profit of power-to-hydrogen-to-power case is sensitive to the hydrogen price, wind forecasting accuracy and hydrogen storage price. When hydrogen price ranges in (2, 6) €/kg, installing only electrolyzer can earn profits over 100 k€/MWWP in 9% scenarios with capacity below 250 kW/MWWP, under high hydrogen price (over 4 €/kg); while installing only fuel cell can achieve such high profits only in 1.3% scenarios with capacity below 180 kW/MWWP. Installing both electrolyzer and fuel cell (only suggested in 22% scenarios) results in profits below 160 k€/MWWP, and particularly 20% scenarios allow for a profit below 50 k€/MWWP due to the contradictory effects of wind forecasting error, hydrogen and electricity price. For lithium battery, investment cost is the single highly influential factor, which should be reduced to 760 €/kWh. The battery capacity is limited to 88 kW h/MWWP. For profits over 100 k€/MWWP (in 3% scenarios), the battery should be with an investment cost below 510 €/kWh and a depth of discharge over 63%. The power-to-hydrogen-to-power case is more advantageous in terms of profitability, reliability and utilization factor (full-load operating hours), while lithium battery is more helpful to reduce the lost wind and has less environmental impact considering current hydrogen market.

The present paper investigates the variation in performances in co-electrolysis of steam/CO2 on SOEC single cells caused by the progressive increase of CO2 inlet concentration and current density. Steam electrolysis and co-electrolysis were investigated on circular Ni-YSZ supported cells produced by SOLIDpower (“ASC-700” type cells). The thin film electrolyte is constituted by YSZ and the oxygen electrode by LSCF-GDC. The active area corresponds to 12.56 cm2 (2 cm of radius). The cells were fed with different H2O/CO2 mixtures, while keeping 10% H2 of the inlet molar flow in order to avoid re-oxidation of the Ni-YSZ support. A sensitivity analysis was performed looking in particular at the effects of inlet gas composition, gas flows and temperature on the performances. I-V characterization and EIS measurements at different current densities were carried out for each sequence. In steam electrolysis mode, the reference inlet molar flow was equal to 150 Nml/min (90% H20, 10% H2), at 750°C. The I-V curve showed a voltage of 0.861V at OCV, 1.049V at 0.5 A/cm2 and 1.253V at 1 A/cm2. A sensitivity analysis was performed varying the temperature (700°C, 750°C and 800°C), the inlet air flow (100 Nml/min, 300 Nml/min and 500 Nml/min) and the total inlet fuel flow (from 8 to 16 Nml/min/cm2). In this case, the steam conversion factor was kept constant equal to 50% (adjusting the current imposed). EIS analysis exhibits that ohmic and polarization resistances decrease with current densities lower than 0.4 A/cm2 and then rise with higher values. As expected, the increase of temperature has a positive impact on the performances, while the change of air and fuel flow slightly affects them. In co-electrolysis mode the CO2 and H2O content was varied, keeping constant the total molar flow and the hydrogen fraction as explained before. As shown in the enclosed image, the area specific resistance (ASR) increases with the CO2 concentration in the mixture and gas transport limitation occurs at lower current densities. Also in this case a sensitivity analysis was conducted changing the temperature (from 700°C to 800°C) and the resulting EIS plots demonstrate different ongoing processes favored at high current densities. In particular, the reverse water-gas-shift reaction plays an important role on the overall balance of the gas species, and it directly depends on temperature and inlet fuel composition. Figure 1