Reversible Solid Oxide Cell System Research Articles

Hot air recirculation enlarges efficient operating window of reversible solid oxide cell systems: A thermodynamic study of energy storage using ammonia

Energy storage is vital for the energy transition, enabling reliable power grids based on intermittent renewables. Reversible solid oxide cell (rSOC) technology is promising for seasonal energy storage. The novel finding from this work is that optimised air recirculation for rSOC in endothermic electrolyser mode leads to efficiency being nearly independent of current density. Thereby the operating region of highest efficiency is expanded from the thermoneutral point to the entire endothermic region, leading to highly efficient part-load operation. Air recirculation increases fuel cell mode efficiency too, particularly at higher loads. This widens the efficient operating window in both modes. These findings emerge from a thermodynamic study of an rSOC-based energy storage system with ammonia as fuel. A process design is developed and optimised for efficiency, supported with detailed exergy analysis. First, ammonia synthesis subsystem integrated with the rSOC system in electrolyser mode is optimised. Second, rSOC outlet air recirculation is optimised for high system efficiency. Finally, rSOC operating points are optimised for highest round-trip efficiency. We find the least exergy destruction for the ammonia synthesis subsystem at 170bar synthesis pressure and 30°C condensation temperature (without needing refrigeration). The overall system achieves round-trip efficiencies up to 60.3%.

Electrochemical-energy- exergy analysis of reversible solid oxide cell-based small-scale stand-alone energy storage system

The present renewable energy systems should shift towards more storage-based systems due to their inherent intermittency. This study examines the electrochemical, energy, and exergy performances of a Reversible Solid Oxide Cell (ReSOC) based stand-alone energy storage system “with a pressurized gas tank”. The system operates in the fuel cell mode (SOFC) for power generation and electrolysis cell mode (SOEC) for syngas production. The exergy analysis gives a detailed insight into the irreversibility points in both system operation modes. The ReSOC system model is based on a validated ReSOC stack electrochemical model and system components’ mass-energy balance model. The power extraction level in the ReSOC stack was shown to determine the thermal management required through the electrochemical analysis. The energy analysis resulted in a system roundtrip efficiency of 51 % at the considered operating conditions. In addition, the highest points of exergy loss/destruction are the exhaust air (SOFC: 32 %, SOEC: 34 %), ReSOC stack (SOFC: 25 %, SOEC: 28 %), and pressure regulation valve (SOFC: 11 %, SOEC: 17 %). The results also show that the SOEC mode performed better than the SOFC mode in the energy and exergy analyses. This study may be used as a basis for stand-alone system performance improvement leading to higher efficiency.

Transient analysis and safety-oriented process optimization during electrolysis–fuel cell transition of a novel reversible solid oxide cell system

The reversible solid oxide cell (rSOC) is an emerging solution for power-gas conversion in renewable energy networks owing to its high efficiency and bi-directional operation. However, there are still many unidentified safety issues endangering the stability and lifespan of rSOC that need to be addressed before its widespread commercialization. In this paper, a novel one-dimensional rSOC stack model incorporating peripheral auxiliary components is introduced to investigate the transient behavior of the co-flow rSOC stack during electrolysis–fuel cell transition and to develop a safety-oriented optimization strategy for the switching process. This is the first comprehensive study of thermal−material safety hazards for rSOC in the system environment and the first proposal of a dual-model predictive control strategy to avoid nonlinearities in global predictive control during cross-mode switching. It is found that localized extreme temperature gradients, fuel starvation and thermal oscillations are the main safety issues faced by rSOC in switching transients. The conclusion that the current stride and the rate of current change are key factors in guaranteeing the transient safety of rSOC is obtained by evaluating targeted dispatch currents. On this basis, the constraint of current-change rate of 7 A s−1 is incorporated into the controller design, further results indicated that the proposed cooperative control strategy effectively prevents the reactant crisis with smoother thermodynamic responses, which are all within the safety threshold.

Multiscale analysis and cost optimization of a reversible solid oxide cell system with coordinated degradation and efficiency considering Ni-particle coarsening

In H2-supported microgrids, the electrochemical performance deterioration of reversible solid oxide cell (rSOC) is primarily caused by the coarsening of Ni particles. Specifically, there are still various unresolved questions from microdegradation mechanisms to macroperformance optimization of rSOC systems that require further investigation and solutions. In this study, a novel multiscale-multiphysics field model consisting of a modified Ni coarsening model incorporated into the rSOC system model is used to analyze the effects of operating modes and conditions on degradation behavior. The issue of coordination between degradation and efficiency is settled for the first time by introducing minimization of the total operating cost of an rSOC system. The results indicate that the degradation rate (rdeg) is higher in the fuel cell mode, and this is related to the partial pressure ratio pH2/pH2O within H2-electrode pores. Furthermore, rdeg is found to be most affected by the PEN temperature, followed by the fuel utilization and fuel molar fraction. The minimum total cost is approximately 0.49 $/kWh taken at a low system intake (including H2O, H2, and air) with higher temperatures. The optimization weight shifts gradually toward efficiency owing to the higher gas supply cost. These findings provide a valuable reference for the selection of the optimal operating state for the rSOC system considering degradation.

Design and Experimental Investigation of Temperature Control for a 10 kW SOFC System Based on an Artificial Neuronal Network

For a future carbon-neutral energy economy, fuel cells play an important role due their high efficiency. Especially the Solid Oxide Fuel Cell (SOFC) with demonstrated efficiencies beyond 60 % 1 can contribute to reasonable roundtrip efficiencies for hydrogen and e-fuels 2.To match the fluctuating electricity demand in a future electricity grid, dominated by renewable energy sources like wind and photovoltaic, dynamic operation of fuel cells is required. The research has shown that the degradation und therefore the lifespan of Solid Oxide Cell (SOC) stacks shows a significant dependency on the operating conditions and dynamic load changes 3. However, some research suggests that the degradation is not caused by the load changes itself but spatial temperature gradients during load changes 4–6.Therefore, controlling the temperature gradients in the stack during load changes can have a significant impact on the lifespan of SOC stacks. This is typically more dramatically for stacks with larger cell sizes or multiple cells per layer. Furthermore, a tight temperature control allows for running the stack at maximum efficiency without the risk of stack damage due to exceeding temperature limits.In this work the authors designed and experimentally evaluated different controller topologies for fuel cell operation (SOFC) of a reversible solid oxide cell (rSOC) system described previously 7. The controller design incorporates an artificial neuronal network (ANN) for real time state predictions. The training data for the ANN was generated by a dynamic model of this system. This model is implemented in Matlab Simulink and was validated against experimental data. The generated training data consists of about 1,000 simulated days of dynamic system operation with a sample interval of 10 s. Additionally, data for 16,000 different steady state operating conditions of the system were generated.One focus of this work is the robustness of the controller under real world conditions despite inaccuracies of the underlying model and SOC degradation effects over time. To compensate the aging of the stack, the ANN is trained on variable degradation states. The degradation state is then tracked by the controller during operation to maintain an accurate prediction. First system experiments showed promising results in this respect (Fig. 1).Fig 1. Maximum temperature (red) and its setpoint (red, dashed) as well as 8 other temperatures distributed over the stack (black) in response to a given current density profile (green) and the air flow (blue) set by the controller AcknowledgmentsThe authors would like to thank their colleagues at the Forschungszentrum Jülich GmbH, who helped realize this work, and the Helmholtz Society for financing these activities as part of the Living Lab Energy Campus. References(1) Peters, Ro.; Frank, M.; Tiedemann, W.; Hoven, I.; Deja, R.; Kruse, N.; Fang, Q.; Blum, L.; Peters, R. Long-Term Experience with a 5/15kW-Class Reversible Solid Oxide Cell System. J. Electrochem. Soc. 2021, 168 (1), 014508. https://doi.org/10.1149/1945-7111/abdc79.(2) Heydarzadeh, Z.; McVay, D.; Flores, R.; Thai, C.; Brouwer, J. Dynamic Modeling of California Grid-Scale Hydrogen Energy Storage. ECS Trans. 2018, 86 (13), 245–258. https://doi.org/10.1149/08613.0245ecst.(3) Kim, Y.-D.; Lee, J.-I.; Saqib, M.; Park, K.-Y.; Hong, J.; Yoon, K. J.; Lee, I.; Park, J.-Y. Degradation of Anode-Supported Solid Oxide Fuel Cells under Load Trip and Cycle Conditions and Their Degradation Prevention Operating Logic. J. Electrochem. Soc. 2018, 165 (9), F728–F735. https://doi.org/10.1149/2.1391809jes.(4) Hagen, A.; Høgh, J. V. T.; Barfod, R. Accelerated Testing of Solid Oxide Fuel Cell Stacks for Micro Combined Heat and Power Application. Journal of Power Sources 2015, 300, 223–228. https://doi.org/10.1016/j.jpowsour.2015.09.054.(5) Nakajo, A.; Wuillemin, Z.; Van herle, J.; Favrat, D. Simulation of Thermal Stresses in Anode-Supported Solid Oxide Fuel Cell Stacks. Part I: Probability of Failure of the Cells. Journal of Power Sources 2009, 193 (1), 203–215. https://doi.org/10.1016/j.jpowsour.2008.12.050.(6) Jiang, W.; Luo, Y.; Zhang, W.; Woo, W.; Tu, S. T. Effect of Temperature Fluctuation on Creep and Failure Probability for Planar Solid Oxide Fuel Cell. Journal of Fuel Cell Science and Technology 2015, 12 (5), 051004. https://doi.org/10.1115/1.4031697.(7) Peters, R.; Tiedemann, W.; Hoven, I.; Deja, R.; Kruse, N.; Fang, Q.; Blum, L.; Peters, R. Development of a 10/40kW-Class Reversible Solid Oxide Cell System at Forschungszentrum Jülich. ECS Trans. 2021, 103 (1), 289–297. https://doi.org/10.1149/10301.0289ecst. Figure 1

Reversible solid oxide cells: Early performance and microstructural evolution during electrolysis and switched mode operation

Incorporating more renewables into our energy mix will require a diversity of technological solutions. Reversible solid oxide cell systems (RSOCs) operating reversibly between fuel cell and electrolysis modes with high round-trip efficiencies offer one such solution. However, questions remain about the stability of the oxygen and fuel electrodes under reversible operation. In this study, single cells with the configuration Ni-YSZ|YSZ|GDC10|NNO-NDC50|NNO are operated by reversible cycling under potentiostatic conditions. Test conditions are chosen to be representative of average stack conditions that are likely to be encountered during operation of a stack constructed of such cells. The results of reversible cycling over 500 h (21 cycles) are compared with operating the cells under potentiostatic conditions in the electrolysis-only mode (i.e., without cycling). Voltage-current density (DC), AC complex impedance spectroscopy, distribution of relaxation times (DRT) analysis, and scanning electron microscopy (SEM) indicate excellent reversibility and stability of the neodymium nickelate-based oxygen electrodes in both electrolysis and reversible cycling modes. Degradation behavior is attributed to the loss and coarsening of connected Ni particles in the fuel electrode, particularly in the active layer. However, reversible operation mitigates this degradation compared to operation in the electrolysis-only (SOEC-only) mode.

Experimental Results of a 10/40 kW-Class Reversible Solid Oxide Cell Demonstration System at Forschungszentrum Jülich

In 2018, a 5/15 kWDC reversible solid oxide cell system was developed and successfully operated by Forschungszentrum Jülich. Based on the knowledge gained with this first system, an optimized system in the power class of 10/40 kWAC was developed afterwards in 2019 that uses the well-established Integrated Module. This module consists of four 20-layer sub-stacks, two heat exchangers and five heating plates. It represents the main components of the system. The basic system layout was retained in general from the previous system and adjusted in accordance with the higher power level, as well as the supporting balance of plant components. The layout of the demonstrator system and its results are described. During the experimental evaluation in fuel cell mode, the system could provide an electrical output power from 1.7 to 13 kWAC. The maximum system efficiency of 63.3% based on the lower heating value (LHV) could be reached at a system power of 10.4 kWAC. This operating point was also analyzed regarding the temperature distribution in the stack and efficiency losses. In electrolysis mode, a maximum efficiency of 71.1% (LHV) was achieved with an electrical power input of −49.6 kWAC. At this operating point, about 11.7 Nm3 h−1 of hydrogen are generated. The stack temperature distribution and the efficiency losses are also analyzed for the electrolysis mode. Finally, the potential for the efficiency optimization through higher heat integration in this mode is experimentally evaluated and discussed.

Efficiency analysis of a novel reversible solid oxide cell system with the secondary utilization of the stack off-gas: A model-based study

Systems with reversible solid oxide cells (rSOCs) can potentially overcome the spatio-temporal mismatch between intermittent generation from renewables and continuous electricity demand by operating bi-directionally. Achieving high energy conversion efficiency is one of the critical design objectives for a typical rSOC system. However, only a few papers discuss the effect of parameters and system processes on efficiency, and thermal management designs considering gas flow rates of the fuel and air loops are not yet seen. This work presents a novel rSOC-based system that employs a heat recovery unit for absorbing thermal energy as parasitic power gain and a water-gas heat exchanger instead of the electric evaporator to utilize the stack off-gas secondarily. Modeling and efficiency analysis of such a system is performed using a physically finite element method-based rSOC stack model coupled with extra auxiliary component models. Results indicate that efficiencies of 92%, 71.1%, and 62.4% can be achieved at 1,023 K and 1.23 bar in electrolysis, discharge, and the round-trip, respectively. The parasitic gain can significantly improve system efficiency and output performance and reduce the power loss in regulating the temperature uniformity of the stack with increased airflow. The outcomes can serve as guidelines for the thermal management design of real rSOC systems and control strategies optimization.

Design and partial-load operation of a reversible Solid Oxide Cell system with molten salts thermal storage

The increasing penetration of renewable energy sources in the electricity mix requires efficient storage solutions on the seasonal scale. Reversible Solid Oxide Cell (rSOC) systems are receiving increased attention as viable options to fulfil this requirement. In this work, a MW-scale rSOC system capable of working over a large operating window is studied via modelling on Aspen Plus®. To ease the thermal integration, a molten salt thermal storage is coupled to the system, enabling heat recovery in fuel cell mode, which is then exploited for water evaporation in electrolysis mode. The rSOC stack is designed to operate exothermically in the electrolysis mode at nominal load. In both modalities, the air mass flow rate is regulated to control the stack temperature, while limiting the in-out gradients within 100°C. At nominal load, the system achieves an electrical efficiency of 52% in fuel cell mode and of 87% in electrolysis mode. The operation at low partial loads, due to the decrease of the air flow rate, requires an additional high-temperature heat source to guarantee the heat integration. In this regard, the adoption of an electrical resistance in electrolysis mode and a hydrogen-fed combustor in fuel cell mode are selected as viable solutions to amplify the operating range of the system. As a results, the system can be operated down to the 30% of the stack nominal power in both modalities, where the system achieves an electric efficiency of 44% and 80% in fuel cell and electrolysis mode, respectively.

Correcting for Inductance in Low-Impedance Electrochemical Systems

Electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) analysis are central tools in the study of solid oxide cells because of their application to the characterization and deconvolution of cell processes. Reliable analysis of these processes, however, depends on reproducible electrochemical characterization. In this study, we explore the impact of inductance correction on the EIS and DRT spectra of a cutting edge, low-impedance reversible solid oxide cell system. Our analyses demonstrate the importance of inductance correction for the deconvolution of cell processes with DRT analysis. An open-source set of inductance-correcting functions, written in Python, is also presented.

Dynamic simulation of a reversible solid oxide cell system for efficient H2 production and power generation

Reversible solid oxide cell (rSOC) can flexibly switch between the electrolysis mode and the fuel cell mode for electrical energy storage and power generation. For practical application, sweeping gas is needed to bring in the reactants and take out the products timely. In this study, we use steam as anode sweeping gas in electrolysis to decrease the overpotential loss and collect pure O2, which is then used as the fuel cell cathode oxidant. The real fluctuating power generated from solar photovoltaic is used as the power supply, which allows rSOC to generate H2 from 6:45 a.m. to 5:45 p.m. and produce electricity in the night. Compared with the conventional strategy, the proposed system can utilize more than 35% electricity in electrolysis, and its efficiency and total H2 production can be increased by 8% and 50%, respectively. The total power generation and the power density are also increased by 290% and 160%, respectively. Overall, this new strategy results in a doubled round-trip voltage efficiency due to the much-decreased overpotential losses in the electrochemical processes. This study provides a guidance for the optimization of practical rSOC application with dynamic operating conditions.

Modeling and control-oriented thermal safety analysis for mode switching process of reversible solid oxide cell system

A reversible solid oxide cell (rSOC) system can balance the surplus and shortage of electricity generated from renewable energy grid by working either in energy conversion or in storage mode. A dynamic model of the rSOC system was developed and validated against experimental data. It can be used to determine the dynamic thermal characteristics during mode switching. This work focuses on the influence of different operating parameters on the temperature distribution in the rSOC stack along the gas flow direction in the system environment. The extremum of local temperature gradient in the dynamic process is proposed for the first time, and it hardly changes when adjusting air excess ratio (AR) and fuel utilization (FU). In addition, the results show that the maximum PEN temperature (MaxT_PEN) increases with the decrease of AR in the transients, but FU has little effect on the local MaxT_PEN. AR and FU affect the MaxT_PEN (Compared with FU, AR is more significant) and the maximum temperature gradient (MaxT_grad) in steady-state, but the control current does not. The proposed control currents significantly decrease the MaxT_PEN and MaxT_grad in the transient process, and the ramp current works better than the multi-step current. Overall, this work identified the effects of operating parameters on the thermal characteristics of the rSOC stack in switching from electrolysis to fuel cell mode under the system environment. It guides the development of the thermal management strategy of the rSOC system.

Capacity configuration optimization of a hybrid renewable energy system with hydrogen storage

ABSTRACT Different from low-temperature electrolysis systems, the large power consumption for the balance of plant (BOP) of the reversible solid oxide cell (RSOC) system for a high-temperature operating condition needs to be considered in the determination of the capacity configuration of the hybrid renewable energy (HRE) system. To address this issue, a power-based model of the RSOC system is developed and the corresponding capacity configuration strategy especially for the HRE system is also proposed in this paper. An optimization program of a hybrid energy system model composed of the wind turbines (WT), photovoltaic panels (PV), reversible solid oxide cell (RSOC) system, hydrogen storage tank (HST), and battery are presented to urge the minimization of the total system cost, power redundancy, and power shortage. Particle swarm optimization (PSO) algorithm is utilized to determine the optimum size and operational energy management within the system. The results show that after the regulation of the energy storage system, the power redundancy and shortage of the hybrid energy system are greatly reduced with the decreases by 85.08% and 64.42%, respectively. Moreover, the power mismatch is still significantly affected by seasons. It is also found that the energy storage efficiency of the RSOC system is within 20% due to the fact that part of the electric energy is consumed by the BOP to maintain the operation of the RSOC system. Thus, more improvements should focus on simplifying the BOP system of the RSOC system and reducing the excess power consumption in the future.

A New Sweeping Gas Strategy of a Reversible Solid Oxide Cell System for Efficient H2 Production and Power Generation During Dynamic Operation

A New Sweeping Gas Strategy of a Reversible Solid Oxide Cell System for Efficient H2 Production and Power Generation During Dynamic Operation

Development and Demonstration of a Decentralised Hydrogen rSOC System

The quality of life and economic prosperity of the population depends to a large extent on a secure and sustainable electricity supply. In order to ensure this for generations to come, a comprehensive integration of renewable, decentralized electrical energy sources is necessary. Such developments are already evident in the world's largest markets. Inevitably, electricity production is increasingly being distributed over larger areas and energy supply systems are tending towards decentralization. Traditional role distributions, such as centralized feed-in and load adjustment by large power plants and decentralized demand, are being replaced by decentralized feeders at all grid levels and prosumers. Security of supply can only be achieved by balancing fluctuating output and demand. Therefore, in order to achieve the EU's 2050 climate targets, in addition to flexibility on the consumer side and sector coupling strategies, increased balancing options in the form of storage systems are required. Currently available storage technologies such as pumped storage power plants, etc. can be considered as complementary solutions. In Europe, their capacities are limited by almost exhausted utilization potentials. Since the fluctuating generation profiles also contain a significant seasonal component, long-term storage solutions are essential. In order to offer appropriate long-term storage services, the additional use of gaseous energy carriers enabled by PtG (Power-to-Gas) technologies is the only alternative.Currently, however, PtG storage technologies are still in the development and demonstration phase, so that further research is required primarily at the system but also at the component level. Another major issue is the commercial viability related to full-load operating hours and installation cost of PtG technologies, if the operation is only given when surplus electricity is available. Fuel cell technologies like reversible solid oxide cell systems (rSOC) that combine both electrolysis and electricity generation in one unit offer great potentials to address these issues.Within the Austrian funded R&D project FIRST (Fully Integrated Reversible Solid oxide cell system) a compact, reversible, high-temperature solid oxide (rSOC) system with a rated power of 15 kWel in SOEC operation and a rated power of 5 kWel in SOFC operation is being developed and demonstrated.In order to realize a compact and thus economically operable system, the Balance of Plant (BoP) components are being optimized for both SOEC and SOFC operation compared to two separate units. In addition, the stand alone system targets a fast switching between gas and electricity production and enables intelligent linking with electricity, gas and heat grids.The reversible solid oxide cell (rSOC) demonstrator shall be capable to produce H2 with > 70 % efficiency, or electricity with > 50% efficiency, in a simplified system with low operating costs. Flexible operation by rapidly switching between electrolysis and fuel cell modes within minutes to enable optimal use of electricity from fluctuating energy sources such as wind and solar. Load forecasting models are applied to respond in advance to changes in demand or yield, bringing new system control strategies to bear.The project aims to test the usability of the technology beyond test bed operation under real operating conditions as a long-term application. Therefore, the results will be relevant to industrial stakeholders as well as utilities.Within this work the status of the FIRST project will be presented including results from the simulative investigation and optimization within a dynamic model.

Comparison of Reversible SOC-Based Renewable Energy Storage Systems for the Netherlands and India

The present study explores a hybrid energy storage system (HESS) for a microgrid, with Li-ion batteries for short-term storage coupled with a reversible solid oxide cell (rSOC) system for seasonal energy storage in hydrogen. A comparison of system size and capital cost shows that using a HESS leads to significant savings compared to a system with only batteries, with a capital cost reduction of up to 75 %. The study also reveals that Jodhpur (India) has greater needs for seasonal storage, and sees greater benefits from the use of a HESS than a temperate region like Groningen (Netherlands), due to the very high variability of wind energy, combined with the high share of wind energy in India. This shows that reversible solid oxide cell systems are a serious contender for energy storage in different climatic regions.

Development of a 10/40kW-Class Reversible Solid Oxide Cell System at Forschungszentrum Jülich

In 2018, a 5/15 kW reversible solid oxide cell system was developed and successfully operated. Based on these positive outcomes, a larger system in the power class of 10/40 kW was planned, with the well-established “Integrated Module” constituting a core element. This module consists of four 20-layer sub-stacks, two heat exchangers, and five heating plates. The basic structure was retained as per the previous system and the surrounding balance of plant components were adjusted in accordance with the higher power level. This adaptation is outlined using the example of an air heat exchanger. A possible efficiency optimization in electrolysis mode via a highly efficient steam generation process is also described and substantiated by experimental results.

Experimental Investigation of Efficiency Maximization in Solid Oxide Electrolysis Systems by Internal Steam and Heat Recovery

This study presents the development of a scalable steam generator for a reversible solid oxide cell system with 40 kW of power in electrolysis mode. As solid oxide electrolysis can be conducted under thermal-neutral conditions, efficiency is primarily governed by the system’s heat and steam loss. The steam generator presented herein recovers heat and steam from the fuel side off-gas in order to preheat the feed water and superheat the electrically-generated saturated steam. The design is based on a pinch analysis intended to optimize the temperature levels. In the considered system, the steam generator was estimated to increase electrolysis efficiency from 70% to more than 74%.

Characteristics of Oxygen Electrode Supported Reversible Solid Oxide Cells

Oxygen-electrode-supported solid oxide cells (OESCs) have potential advantages over fuel-electrode-supported cells, including reduced fuel-electrode concentration polarization, better oxygen electrode current collection, and flexibility in the fuel electrode choice. However, there are serious drawbacks including the difficulty of co-firing the oxygen electrode and electrolyte, and oxygen electrode concentration polarization. This paper explores the characteristics of OESCs with La0.8Sr0.2MnO3−δ -Zr0.92Y0.16O2−δ (LSM-YSZ) electrode-support enhanced by SrTi0.3Fe0.6Co0.1O3−δ (STFC) infiltration, thin YSZ electrolyte, and SrTi0.3Fe0.7O3−δ (STF) fuel electrodes. The STFC infiltration increases fuel cell maximum power density by >1.5 times and electrolysis current density (at 1.3 V) by >2 times. Cell performance in pure oxygen is compared to that in air, exploring a possible reversible solid oxide cell system configuration where oxygen produced during electrolysis is stored and subsequently used during fuel cell operation. The fuel cell maximum power density is increased from 0.88 W cm−2 in air to 1.37 W cm−2 in oxygen, with limiting current increased from 1.7 to >5.6 A cm−2; the electrolysis performance is essentially unchanged, probably because the electrode air becomes enriched with oxygen during electrolysis.

Potential Deployment of Reversible Solid-Oxide Cell Systems to Valorise Organic Waste, Balance the Power Grid and Produce Renewable Methane: A Case Study in the Southern Italian Peninsula

The large market penetration of non-dispatchable renewable power sources (vRES), i.e., wind and photovoltaic, may be hampered by an increasing need for large scale energy storage capacity and the challenges of balancing the power grid. Novel technologies integrating waste gasification with reversible Solid-Oxide Cell systems have been proposed to provide flexible grid balancing services. The rSOC system operated in electrolysis mode uses excess power from vRES to generate hydrogen (H2), which is combined with syngas derived from waste gasification to produce methane (CH4). The rSOC system can also be operated in fuel cell mode by oxidising syngas to produce electricity. This paper presents a well-defined case study which aimed to estimate the potential deployment of a novel rSOC technology in a future power system dominated by intermittent renewables. The hourly power grid residual loads (i.e., the difference between load and vRES power generation) and the availability of low-grade organic waste and residues are quantified and matched for the southern Italian peninsula in 2030. The results show that the theoretical grid flexibility needs approximately 10 TW h of overproduction and 5 TW h of underproduction in 2030 to ensure the complete disposal of the municipal organic waste generated in 2030 (6.7 Mt) and that production of renewable CH4 will need to be 1.4–2.4 Mt, pointing to an intriguing perspective for the deployment of rSOC systems at a large scale. The multifunctionality of the system proposed is an added value that can make it a convenient and efficient piece of the puzzle of technologies required in a climate-neutral and circular economy. The results and methods here presented are intended to form the basis for estimations of future potential deployment and economic and environmental assessments of competing technologies.