Solid oxide fuel cell (SOFC) powertrains can be considered as a promising solution for future zero-emission shipping, yet the decrease in electrical efficiency at low load remains a barrier for full-scale marine adoption. This work provides the first comprehensive quantification of hot standby power demands for marine SOFC modules and evaluates its impact on the multi-modular powertrain efficiency. A thermodynamic process system model of a 112 kW el rated SOFC module was utilized, including anode recirculation, autothermal pre-reforming in hot standby, heat losses and off-design heat exchanger behavior. Assessing five hot standby heat integration variants, combined fuel-equivalent standby demands ranging from 5.2 to 15.3 kW chem per module were obtained. The highest-performing configurations are those employing cathode off-gas recirculation, motivating their integration in a multi-modular marine SOFC concept. At the multi-module powertrain level, non-uniform operation strategies, in which individual modules either operate close to their maximum-efficiency point or remain in hot standby, can significantly increase low-load efficiency. At a typical cruise-ship operating point near 15% rated power, efficiencies of up to 55% (LHV to AC) are achieved, compared to only 26% for uniform operation of all modules. The results highlight the importance of incorporating hot standby strategies into future marine SOFC system design.

This study investigates hybridization of a solid oxide fuel cell with a gas turbine (SOFC-GT) for application in an ATR 72 regional aircraft. Several challenges hinder its viability, including the low gravimetric power density of SOFC stacks and stringent heat integration constraints. A steady-state model sweeps the cell voltage, overall pressure ratio (OPR), and a bounded turbine inlet temperature (TIT). This study introduces a new corrected power-share metric. This metric accounts for operating-point-dependent SOFC power density. It also enables weight-relevant comparisons. We analyze two types of coupling: direct and indirect. In the direct coupling, SOFC cooling fixes the core airflow and a TIT ceiling imposes a minimum power share. In the indirect coupling, a bypass decouples SOFC and gas turbine operation, incurring an efficiency penalty. We compare two heat-integration architectures: preheating with SOFC cathode exhaust versus low-pressure turbine (LPT) exhaust. Results show that direct coupling achieves efficiencies above 65% at high-corrected power shares, whereas indirect coupling offers greater operational flexibility but lower efficiency. Cathode exhaust preheating improves feasibility and outperforms LPT recuperation by more than 15% efficiency at low-to-mid-corrected power shares. However, LPT recuperation attains higher peak efficiency only at high-corrected power shares and within a narrow OPR window, which is limited by recuperator pinch.

Solid oxide electrolysis cells (SOECs) enable efficient hydrogen production by utilizing waste heat for steam evaporation, providing strong synergies with exothermic ammonia synthesis. However, there is a need for efficient systems designs to couple these processes for renewable ammonia production. Here, the influence of operating pressure and system configuration on power-to-ammonia (PtA) efficiency is investigated using an experimentally validated model of electrolyte-supported cell (ESC)-based stacks. Main findings were: (1) PtA efficiencies increase with SOEC pressurization in systems without sweep air, reaching 72% at 8 bar, while sweep air systems peak at similar to 69% at 2 bar due to air compression demand at elevated pressures. (2) Part-load operation in modular plants reduces efficiency, dropping to 45% at 10% load because of module hot standby consumption. (3) Waste heat from the Haber-Bosch process combined with SOEC off-gas recovery, meets steam demand in most cases, with up to 62% supplied by the SOEC itself. (4) At high pressure without sweep air, electrical steam generation is required due to reduced off-gas heat and higher boiling points. In such a case, increasing the recirculation ratio can increase system efficiency by reducing evaporator load.

Power-to-Methane (PtM), which converts renewable electricity into synthetic methane, provides a promising approach for long-term energy storage and industrial decarbonization. High temperature solid oxide electrolysis cell reactors (SOECs) are critical to PtM due to their high efficiency and synergy with the exothermic methanation process. Their ability to perform H2O/CO2 co-electrolysis further enhances their process integration potential. However, co-electrolysis remains understudied, especially compared to steam electrolysis in industrial applications. This study develops a modelling framework to assess the thermodynamic potential of two PtM process configurations, comparing steam and co-electrolysis pathways. For a system with idealized components, the maximum achievable exergetic efficiency for different SOEC operating temperatures (750-850 degrees C) and pressures (1-23 bar) was determined. Results indicate that both systems perform best at the lowest temperatures, however co-electrolysis achieves higher system exergy efficiencies (85.0 % vs. 76.7 % in steam electrolysis). While steam electrolysis is more efficient at low pressures, co-electrolysis outperforms at high pressures due to increased in-situ methanation, reaching up to 59.2 % yield at 23 bar. This reduced cell voltage and specific power demand but also current density, revealing a reactor size-efficiency tradeoff for fixed methane output. Methane formation in co-electrolysis alters the internal recycle ratio needed to maintain the reducing gas inlet composition, which affects the isothermal operational voltage and reduces freshwater and specific power demand of compressors and evaporators. These findings demonstrate the potential of SOECs especially in co-electrolysis operation to achieve high efficiencies for PtM and its thermodynamic constraints at the system level.

Solid Oxide Electrolysis Cells (SOECs) offer the lowest specific electrical energy demand among electrolysis technologies, making them highly suitable for large-scale hydrogen production, where electricity accounts for 70%–85% of the levelized cost of hydrogen. To comply with guarantees of origin for green hydrogen, SOEC systems must operate reliably in power-following mode with fluctuating renewable energy sources (RES). However, transient operation induces thermal gradients within SOEC stacks, accelerating degradation and increasing the risk of premature failure.This study proposes a dynamic control concept that enables rapid power modulation with limited thermal stress, based on an experimentally validated multi-stack SOEC reactor model. A large-scale SOEC plant is considered, consisting of multiple modules, each comprising a multi-stack reactor and independent balance-of-plant components. The module-level power control employs a PI controller, augmented with model-based current slew-rate limit correlations and feed-forward step changes between hot standby and thermoneutral operation. For a moderate thermal gradient limit of ±5Kmin-1, optimised control parameters enables transitions from hot standby to 80% nominal power in 35s and to 100% in 3min – approximately six times faster than conventional linear current ramps. The control concept is further applied to a modular SOEC plant under a real wind park power profile. Two key factors influencing power-following capability are identified: the number of modules and the lower power limit of an individual module’s operating range (Pmod,low). The proposed control concept improves power-following capability by reducing power mismatch by 45% and significantly decreases the required module count, enhancing both system efficiency and scalability.

Integrating high-temperature solid oxide electrolysis cells (SOECs) with exothermic Fischer-Tropsch (FT) synthesis can unlock significant synergies for enhancing process efficiency. In such a coupled system, syngas is generated via co-electrolysis, while the excess heat from the FT reactor is utilized to produce steam for the SOEC which can significantly improve energy utilization and system performance. In industrial FT reactors, single-pass syngas conversion typically ranges from 60–85% to avoid hot spot formation, necessitating recycling to boost conversion. This recycling leads to the accumulation of light hydrocarbons (C1–C6) in the gas phase, requiring a substantial purge stream that reduces product yield and overall carbon efficiency. To address these challenges, this work proposes a long-recycling approach, where FT tail gas is recycled into the SOEC, enabling hydrocarbon reforming directly within the system. This integration reduces the purge gas stream and introduces a cooling effect in the SOEC, facilitating higher current densities under isothermal operating conditions. A combined experimental and simulation study was conducted to explore the transient thermal effects of introducing FT tail gas into a 120 kW SOEC module, which consists of 24 stacks of electrolyte-supported cells (ESCs). Emulated FT tail gas compositions, representative of an industrial FT synthesis reactor, were introduced into the system. Transient simulations, performed using the validated TEMPEST reactor model, evaluated spatial and temporal temperature gradients within the SOEC, identifying operating regimes that could pose risks to system stability. From these analyses, optimized operating strategies were developed to minimize temperature gradients and enhance system reliability. Experimental validation demonstrated the efficacy of these strategies in maintaining stable and safe SOEC operation. This study highlights the potential of the proposed SOEC-FT integration to improve system performance, reduce carbon losses, and advance the development of sustainable, high-efficiency energy solutions.

Introduction Solid Oxide Fuel Cells (SOFCs) represent a promising alternative to conventional propulsion systems for seagoing vessels, offering significantly higher fuel to AC electricity conversion efficiencies and lower carbon dioxide (CO₂) emissions. In comparison to liquefied natural gas-fueled (LNG) internal combustion engines, the utilization of SOFC systems with the identical fuel almost exclusively eliminates methane slip and achieves a notable reduction in non-greenhouse gas emissions, such as nitrogen oxides (NOₓ) [1]. Despite their potential, multi-MW SOFC systems are in the developmental phase and have yet to achieve large-scale implementation on seagoing vessels. In the recent EU-funded project Nautilus [2], coordinated by the authors, the suitability of SOFC systems for marine applications was demonstrated in terms of electrical conversion efficiency, emissions reduction, seaworthiness [3] and operating flexibility. The experimental results of the 60 kW el functional demonstrator are addressed in a separate submission to this conference (Heddrich et al.). Building on these experimental results and a recently published SOFC powertrain sizing study for cruise ships [4], this submission investigates the design and operational challenges of a modular SOFC powertrain at part load demand. A simulation study is presented, analyzing a configuration composed of multiple 1 MW el SOFC units, providing both propulsive and hotel load demands for a reference cruise ship with an installed SOFC capacity of 53 MW el . Each 1 MW el unit consists of nine 110 kW el modules, which each include stacks, anode off-gas recirculation, pre-reforming, afterburners, and heat recuperation. The modules are independently controllable in their power output and fuel supply. Need for efficient module hot standby modes in maritime FC powertrain application A well-known characteristic of SOFC systems is the significant drop of electrical efficiency at low part load operation as the stack temperature decreases due to the effects of both lower SOFC heat dissipation and overall worse performance of heat integration, thus needing to heat the module by means of additional combustion or electric heating. Recent experimental investigations, presented both in a field demonstration study of commercial SOFC systems [1] and the Nautilus functional demonstrator testing, confirm this behavior and are reproducible by thermodynamic steady-state simulations, all of which are depicted in Figure 1a). LHV to AC electrical efficiencies well below 30 % can be observed below 20 % of the rated SOFC system power. While not an issue for most stationary applications, this presents a significant challenge for maritime powertrain applications, as many ship types operate for extended periods at low part-load conditions. For instance, during harboring of cruise ships, when only the smaller hotel load is required, a substantial portion of the powertrain's operating time may be spent at reduced power levels. Analysis of demand profiles obtained in the project for a typical one-week Mediterranean cruise ship revealed that approximately 25% of the operating time occurs at power levels below 15% of the installed SOFC capacity, while 40% of the operating time is spent below 25% of installed SOFC power. As described above, uniform operation of all SOFC modules under such low part-load conditions is not feasible. This approach would (i) unnecessarily increase overall fuel consumption during the mission and (ii) lead to a higher level of unfavorable nitrogen oxides (NOₓ) and particulate matter emissions in sensitive areas, such as ports located within Tier III and Tier IV IMO Emission Control Areas [5]. As an additional degree of freedom, a modular powertrain design allows for a non-uniform operation during part load demand, where only the number of modules whose combined output near their most efficient operating point corresponds to the required overall load demand is actively operated. The remaining modules are placed into a dedicated hot standby mode. Ideally, this would enable the powertrain to maintain its peak efficiency throughout the part load range, depicted as black circles in Figure 1b). However, to sustain the stack's standby setpoint temperature during hot standby mode, high-temperature heat to compensate heat losses in the range of roughly 2 to 3 kW th per 110 kW el module has to be provided, typically by heating up the inlet gases, either (A) indirectly via fuel combustion and heat exchangers or (B) directly via electric heaters. For case (A) and a multi-modular unit consisting of nine modules, Figure 1b) exemplarily compares the powertrain efficiency along the load range assuming a pre-defined target value of 5 kW chem,LHV of fuel per 110 kW el module in hot standby (blue circles) against the reference uniform operation of all modules, identical to the red dashed line in Figure 1a). As can be seen, a significant increase in part load electrical efficiency is possible, with values above 50 % even at low part load operation of 15 % installed power. However, this benefit would diminish with rising hot standby fuel demand, eventually reaching a point where no significant efficiency advantage is gained, or overall performance is even worse, compared to the uniform operation of all modules. For case (B) with electric heaters, the heat source can be located closer to the stacks avoiding disadvantages concerning heat integration. However, this comes with an additional penalty of conversion loss, as the electric power has to be provided by active modules, ideally running at highest conversion efficiencies. To enable the practical implementation of SOFC powertrains on ships, particular attention thus must be given to a design allowing efficient operation both in nominal and hot standby conditions. In this study, two core research tasks are investigated: On a modular level : Identification of most suitable hot standby operating mode by means of a comparative steady-state thermodynamic simulation study, evaluating the required energy flows in the form of fuel or supplied electric power, the potential to lift low part load efficiencies as well as the demand for additional components exclusively for hot standby. On a multi-module unit level : Assessment of rule-based algorithms to prescribe module load setpoints and transition commands to/from hot standby, enabling load-following of the ship power demand while minimizing the mission fuel consumption. Methodology of performed simulations In order to adequately address hot standby characteristics, a thermodynamic model containing detailed component models with regard to heat losses, heat integration and pressure losses is required. In the DLR in-house framework TEMPEST [6], such a system model was established for the proposed system layout depicted in Figure 2. A special focus was drawn to the correct depiction of the decreasing performance of heat exchangers in hot standby, which were designed for high effectiveness in nominal operation at moderate pressure drops. Utilizing Nusselt correlations obtained from dedicated high-temperature heat exchanger testing [7], the simulation model gives a realistic depiction of the module’s ability of heat integration at significantly reduced mass flows. In addition to maintaining the stack above a specified temperature setpoint, ensuring a reducing atmosphere and sufficiently high oxygen-to-carbon (O/C) ratios in the pre-reformer and anode channels of SOFCs is critical to prevent catalyst oxidation or deactivation caused by carbon deposition. However, the use of forming gas typically used in stationary applications is not viable, as it is unavailable in sufficient quantities and reserved only for emergencies. A suitable, though not exhaustive, set of components to meet these requirements is highlighted in yellow in the process flow diagram in Figure 2. Heat provision can be achieved through several methods, including: (i) utilizing the standard built-in afterburner combined with thermal integration via heat exchangers and the optional addition of extra fuel and air supply; (ii) employing an electric heater or (iii) an auxiliary burner upstream of the cathode; or (iv) recirculating a significant share of the hot cathode off-gas. To minimize fuel demand on the anode side, the existing off-gas recirculation blower can be utilized at even higher ratios than in nominal operation. Additionally, a controllable air stream introduced into the pre-reformer enables catalytic partial oxidation (CPOX) of the fuel. This process generates steam, maintains adequate pre-reformer temperatures, and supports a sufficient pre-reforming reaction rate, thereby reducing the amount of endothermic internal reforming in the stack. In addition, the SOFC stacks can either be but into OCV or operated at low electrical current to provide a share of required electrical power demand of the module itself. For all viable combinations of the aforementioned components, steady-state simulations are conducted to evaluate the fuel flow and electrical power demands of all balance-of-plant components. Using a multi-day cruise ship operational profile that features significant time spent in low part-load conditions, the total mission fuel consumption is calculated and compared to the uniform operation approach of all modules. In an initial step, the stack standby temperature is maintained within the range of active operation to enable rapid transitions to high power output. A subsequent sensitivity study is performed to evaluate the trade-off between maintaining lower standby temperatures associated with reduced heating demand, and the longer ramp-up times or limited ability of the module to achieve high power outputs quickly. Conclusion This study provides a comprehensive analysis of suitable hot standby operating strategies of a modular LNG-fueled SOFC powertrain which can overcome the fundamental disadvantage of low part load efficiencies. The results serve as a realistic estimation of fuel consumption during all phases of typical cruise ship profiles with a focus on low part load operation, thus providing system developers and shipbuilders with operational data that was until now not available. References Gandiglio, M., Marocco, P., Nieminen, A., Santarelli, M., & Kiviaho, J. (2024). Energy and environmental performance from field operation of commercial-scale SOFC systems . International Journal of Hydrogen Energy, 85, 997–1009. https://doi.org/10.1016/j.ijhydene.2024.08.332 Nautilus Project Website: https://nautilus-project.eu/ (last access on 05.02.2025) van Veldhuizen, B. N., Zera, E., van Biert, L., Modena, S., Visser, K., & Aravind, P. V. (2023). Experimental evaluation of a solid oxide fuel cell system exposed to inclinations and accelerations by ship motions . Journal of Power Sources, 585, 233634. https://doi.org/10.1016/j.jpowsour.2023.233634 van Veldhuizen, B. N., van Biert, L., Ünlübayir, C., Visser, K., Hopman, J. J., & Aravind, P. V. (2025). Component sizing and dynamic simulation of a low-emission power plant for cruise ships with solid oxide fuel cells . Energy Conversion and Management, 326, 119477. https://doi.org/10.1016/j.enconman.2024.119477 International Maritime Organization: Nitrogen Oxides (NOx) – Regulation 13: https://www.imo.org/en/OurWork/Environment/Pages/Nitrogen-oxides-(NOx)-%E2%80%93-Regulation-13.aspx (last access on 05.02.2025) Srikanth, S., Heddrich, M. P., Gupta, S., & Friedrich, K. A. (2018). Transient reversible solid oxide cell reactor operation – Experimentally validated modeling and analysis . Applied Energy, 232, 473–488. https://doi.org/10.1016/j.apenergy.2018.09.186 Hollmann, J., Fuchs, M., Spieker, C., Gardemann, U., Steffen, M., Luo, X., & Kabelac, S. (2022). System Simulation and Analysis of an LNG-Fueled SOFC System Using Additively Manufactured High Temperature Heat Exchangers . Energies, 15(3), 941. https://doi.org/10.3390/en15030941 Figure 1

Introduction Recent demonstrations of commercial stationary natural gas-fed Solid Oxide Fuel Cell (SOFC) Systems have successfully demonstrated LHV to AC electrical efficiency values well above 60% [1,2]. This represents a highly attractive alternative to conventional Diesel- or LNG-fueled gensets of seagoing vessels, as the utilization of SOFC technology can both significantly reduce CO 2 emissions and almost entirely avoid combustion byproducts such as nitrogen oxides (NO x ), carbon monoxide (CO), particulate matter (PM) as well as methane slip. However, there are presently no such gensets demonstrated in a relevant power class and overall uncertainty regarding applicability, transient capability, genset sizing and emission reduction potential remains. The recently completed project Nautilus set its objective to close this research gap by developing and testing a novel maritime genset, consisting of LNG-fueled SOFC modules coupled with battery sets to enable reliable load-following while operating at overall high conversion efficiencies. Apart from marine component qualifications such as ship motion inclination testing of SOFC modules [3] and laboratory validation of energy management systems (EMS) [4], one of the core objectives of the Nautilus project consisted of a land-based demonstration of the proposed hybrid SOFC-battery genset to emulate ship-like operating conditions. This contribution aims to give an overview on the core demonstrator results, which include steady-state and transient testing of the SOFC module itself as well as battery-coupled operation in load-following mode of scaled-down real cruise ship profiles for both hotel and propulsive load. During all relevant operating conditions, CO 2 and non-CO 2 emissions of the SOFC module exhaust were measured and are compared to conventional genset data. Functional Demonstrator Layout The land-based demonstrator with a total rated power of 80 kW el,AC was commissioned on DLR premises in Stuttgart and is connected both to the local natural gas grid and the electricity grid. The arrangement and overall layout of the system is shown in Figure 1), depicting the (i) SOFC System, (ii) Battery, Controls and EMS and (iii) emission analysis subunits. The SOFC System with a rated electrical power of 60 kW el consists of a set of 40 G8 SolydEra stacks assembled in a system environment including anode off-gas recirculation with pre-reforming, air supply, fuel gas pre-cleaning, internal heat recuperation as well as a heat recovery unit for combined heat and power (CHP) application, the latter one not being used in the testing period shown here. The natural gas is provided by means of a compressor to ensure the required fuel supply pressure of 4 bar, which is meant to emulate the fuel supply on a ship after LNG evaporation. Thus, the compressor power is not accounted for in the efficiency calculation of the genset. In the second subunit, a marine certified 40 kWh Li-Ion battery along with a bidirectional DC-DC converter is installed. Both the battery and the DC output of the SOFC module are connected to a 600 V busbar, which feeds electrical power into the local 3-phase 400 V/50 Hz electricity grid by means of a frequency inverter and a transformer. From an external PC, the instantaneous power demand value, either set manually or coming from a timeseries of the cruise ship profiles, is fed to the EMS. Depending on the employed power distribution algorithm, the EMS sends power demands to the power electronics of SOFC and battery (charge/discharge) subsystems. The performance of EMS strategies was tested in a prior laboratory environment by coupling a single-pass multi-stack arrangement with a Li-Ion battery [4]. Finally, the exhaust emission analysis subunit consists of a Fourier transform infrared spectroscopy (FTIR) gas analyzer (ppm range), ppb range analyzers for NO x and SO 2 , as well as array particle monitors to measure several properties including particle number, mass concentration, and black carbon. Demonstrator Testing and Selected Results At the time of submission, the demonstrator has been operated for a total time of 1600 h and provided a total amount of electrical energy of 62.6 MWh. The testing campaign consisted of several distinct measurement tasks, which are briefly described: SOFC module steady-state electrical efficiencies along the load range , recorded in regular intervals throughout the testing campaign. Each operating point, defined by a constant electrical current, was held for 3 hours, while only the last 30 min were utilized to determine the steady-state performance. The corresponding LHV to AC electrical efficiency measurement points and a respective curve fit are depicted in Figure 2a) in red and are compared to a recently published field demonstration study by Gandiglio et al. [2] (blue). A peak efficiency of 63.4 % LHV to AC could be observed at 73 % of rated electrical power, with the characteristic drop towards lower part load operation. Both qualitatively and quantitatively, the obtained data is in close agreement with Gandiglio et al.. In addition, the potential thermal and combined CHP efficiency achievable with the built-in heat exchanger was estimated assuming exhaust recuperation down to 100°C, reaching values of up to 85 %. SOFC module load ramp tests to identify the transient performance without battery assist, at varying ramp rates (0.5, 2 and 4 % of rated module power per minute). The highest chosen ramp rate was given as a constraint from the SOFC system integrator due to balance of plant performance limitations. All load ramps tested on the demonstrator could be followed precisely (see Figure 2b) and without signs of negative impact of fuel and air supply dynamics on the stack, such as drops in stack voltage due to short-term fuel starvation, thus confirming the internal SOFC system control functionality for the depicted ramp tests. Higher ramp rates were tested in a dedicated SOFC single-pass lab test environment with identical stacks, exemplarily shown by a 10 %/min ramp as green line in Figure 2b). While downward ramps could be performed as intended, the upwards ramping capability was constrained due to minimum voltage constraints for cases where the stacks had remained at low part load for an extended period, resulting in lower stack temperatures. As longer time periods at low part load are to be expected in maritime applications, this characteristic represents a possible system constraint relevant for EMS design. CO 2 and non-CO 2 exhaust emissions along the steady-state load range and during transient operation . The non-CO 2 exhaust emissions, such as NO x and CO gas emissions, were found to vary substantially with load. Part load operation below 50% was particularly unfavorable, while 50% and above had low emission factors, especially for NO x . The emissions were not severely impacted by transient load changes other than that of the described effect from the load. The methane slip was practically negligible, with slightly increased emissions at very high load ramp rates. SOFC module continuous load ramp cycling between minimum and maximum permissible load at 4 % rated power per minute for a total repetition of 240 cycles, to stress the system and investigate if these operating regimes lead to degradation of the stacks. During and after completion of cycling, the steady state performance as described in (i) was repeated regularly, indicating that no relevant degradation could be observed, confirming that load ramps up to 4%/min are not significantly stressing the system. Performance during non-normal operation in a genset context , such as load rejection and black start capability. It could be demonstrated, that after a load rejection from the electrical grid, the SOFC module itself was able to switch into a safe electrically isolated hot standby mode at low electrical current by using the generated stack power to run the BoP consumers and electrically heating the inlet gases to sufficient temperatures, thus not requiring forming gas. It further could be shown that only the battery power was required to return the busbar to nominal voltage enabling resumption of energy flow to the grid, confirming the envisioned black start capability concept. Coupled SOFC-battery operation in load-following mode : Load profiles, deducted from real cruise ship power demands, including both propulsive and hotel load, were scaled to the demonstrator’s rated power to emulate the operation on a seagoing vessel under realistic conditions. Successful co-operation of battery and SOFC could be demonstrated, utilizing two rule-based power distribution strategies, investigated in prior laboratory tests [4]. For a given SOFC System load ramp rate of 2 %/min and cruise ship profiles, the required battery capacities were determined and recently published [5]. Conclusion By presenting these results in detail, the authors aim to provide a profound overview and reliable basis to the scientific community for designing and sizing hybrid SOFC battery gensets for MW-powertrain applications on seagoing vessels. Emission analysis has further confirmed the overall positive environmental impact of employing such systems to reduce the maritime carbon footprint. References Åström, K.; Hakala, T.; and Fontell, E. (2020), Product development and experiences of a new Convion SOFC system , Proceedings of the 14 th European SOFC & SOE Forum, A0602, 124-130. Gandiglio, M.; Marocco, P.; Nieminen, A.; Santarelli, M.; and Kiviaho, J. (2024). Energy and environmental performance from field operation of commercial-scale SOFC systems . International Journal of Hydrogen Energy, 85, 997–1009. https://doi.org/10.1016/j.ijhydene.2024.08.332 van Veldhuizen, B. N., Zera, E., van Biert, L., Modena, S., Visser, K., & Aravind, P. V. (2023). Experimental evaluation of a solid oxide fuel cell system exposed to inclinations and accelerations by ship motions . Journal of Power Sources, 585, 233634. https://doi.org/10.1016/j.jpowsour.2023.233634 Ünlübayir, C., Youssfi, H., Khan, R. A., Ventura, S. S., Fortunati, D., Rinner, J., Börner, M. F., Qaude, K. L., Ringbeck, F., and Sauer, D. U. (2024). Comparative analysis and test bench validation of energy management methods for a hybrid marine propulsion system powered by batteries and solid oxide fuel cells . Applied Energy, 376, 124183. https://doi.org/10.1016/j.apenergy.2024.124183 van Veldhuizen, B. N., van Biert, L., Ünlübayir, C., Visser, K., Hopman, J. J., & Aravind, P. V. (2025). Component sizing and dynamic simulation of a low-emission power plant for cruise ships with solid oxide fuel cells. Energy Conversion and Management, 326, 119477. https://doi.org/10.1016/j.enconman.2024.119477 Figure 1

Hydrogen produced via water electrolysis from renewable electricity is considered a key energy carrier to defossilize hard -to -electrify sectors. Solid oxide cells (SOC) based reactors can supply hydrogen not only in electrolysis but also in fuel cell mode, when operating with (synthetic) natural gas or biogas at low conversion (polygeneration mode). However, the scale -up of SOC reactors to the multi -MW scale is still a research topic. Strategies for transient operation depending on electricity intermittency still need to be developed. In this work, a unique testing environment for SOC reactors allows reversible operation, demonstrating the successful switching between electrolysis (-75 kW) and polygeneration (25 kW) modes. Transient and steady state experiments show promising performance, with a net hydrogen production of 53 kg day -1 in SOEL operation with ca. -75 kW power input. The experimental results validate the scaling approach since the reactor shows homogenous temperature profiles.

The ability of high-temperature solid oxide cell (SOC) electrochemical reactors to efficiently convert atmospheric carbon to high value chemicals for industrial and energy storage applications via CO2 and co-electrolysis makes them a key technology for active carbon utilisation. However, due to additional operational risks from thermochemical reactions on thermal management, limited experimental capacity, and relative novelty, CO2 and co-electrolysis lag behind steam electrolysis in large-scale adoption. Here, a 1D+1D SOC model based on fundamental first principles considering three-dimensional heat transfer was improved via a unique method for representing co-electrolysis electrochemistry, solving with low computational effort. Validation against experimental data for two compositions and pressures, showed high levels of accuracy with respect to characteristic cell voltages, temperatures, and outlet compositions. The model also showed CO2 reduction during co-electrolysis mainly occurred via reverse water gas shift, while CO2 electrolysis still accounted for up to 35% of the total share. Pressurised co-electrolysis operation promotes exothermic methanation, causing pronounced heating of the reactor, consequently reducing the isothermal current density. Therefore, low to moderate pressurisation is likely most suited for coupling with downstream synthesis processes to avoid the installation of unnecessarily large systems and associated high costs.

Solid oxide electrolysis cell (SOC) systems offer a promising solution for generating green syngas crucial in decarbonizing challenging sectors like chemicals, steel, and transport. In this steady-state system modeling study, three distinct system concepts for SOC-based tailored syngas production from steam and CO2 have been investigated. The system models are implemented within ASPEN, and an experimentally validated SOC reactor model has been utilized. At the system level, a parametric analysis is performed by varying inlet composition, fuel utilization, SOC operating pressure, and maximum oxygen content in the SOC exhaust. The results are used to identify system design challenges that differ for the three routes and the most preferable system based on energy efficiency, system complexity, and feasible syngas compositions. System configurations involving purely electrochemical conversion of steam and CO2 are found to have 2-7% higher system efficiencies. Pressurized electrolysis leads to 5-8% lower system efficiencies when taking into account the maximum O-2 concentration constraint for the exhaust air.

The emulated coupling of a 100 kW SOC reactor with an emulated tail gas recirculation of a Fischer-Tropsch reactor was investigated. Different syngas ratios (H 2 /CO) were studied, not only experimentally but also with the support of the in-house simulation framework from DLR, TEMPEST, which is specialized for transient simulations on electrochemical reactors. Different operating conditions were evaluated by: (i) adding CH 4 at open circuit voltage (OCV) and under current and (ii) by performing an experimental ramp of the emulated Fischer-Tropsch gas composition into the inlet gases of the SOC reactor. These results allowed to evaluate the performance of the SOC reactor with the temperature profile along the cells and the stacks, as well as with the syngas ratio behavior. Operation strategies are analyzed and discussed with the aim to mitigate failure conditions on SOC reactors, while operating in transient conditions in the frame of syngas production via high temperature co-electrolysis.

Defossilization of the global energy system requires a transition towards intermittent renewable energy sources and approaches that enable efficient conversion of primary energy sources into electrical energy. Due to their high efficiency in converting chemical into electrical energy and vice versa, solid oxide cell (SOC) systems provide solutions for both of these aspects. However, mode transitions in SOC operation require operating strategies to ensure that thermal gradients in the reactors are suppressed. In this study, two researched cases utilizing SOC’s are presented, based on simulation studies and experiments with an SOC multi-reactor module. The transient module model is validated in 75 kW electrolysis and polygeneration, and applied to analyze the effect of internal steam methane reforming on the temperature profile of the reactors. Subsequently, it is coupled with a validated Li-ion battery model, to test a rule-based power split control strategy suitable for a demand curve characteristic of a ship.

An in-depth investigation of operation strategies for hydrogen and synthesis gas production using reactors with solid oxide cells.

The efficient use of CO2 and its conversion into CO via high temperature electrolysis is considered as a suitable route for the de-fossilization of anthropogenic activities. Within electrochemical solid oxide cells reactors (SOCs), the co-electrolysis of H2O and CO2 at high temperature (above 800 °C) yields syngas (H2 + CO), one of the most important feedstocks for the production of synthetic fuels and chemicals, e. g. via the Fischer-Tropsch process. At the Institute of Engineering Thermodynamics of the German Aerospace Center (DLR) in Stuttgart Germany, a unique test environment (Galactica) for investigating SOC reactors has been designed and constructed with the aim to deepen the research at the 100 kW-scale reactor in commercial systems. State-of-the-Art SOCs have shown promising results that allow the scale-up to larger, industrially relevant systems sizes. With Galactica, DLR was able to demonstrate successfully how 100 kW-scale reactors are a suitable stepping stone towards multi MW-scale process systems. However, operating strategies are required in order to understand how these systems would perform when steady-state operation cannot be guaranteed and unexpected shortages on the feedstocks and electricity could arise. In this work, the coupling of a 100 kW SOC reactor (consisting of 24 single SOC stacks) with the tail gas recirculation of a Fischer-Tropsch reactor will be presented. The main motivation is to improve the overall process efficiency, increase the conversion (since tail gas hydrocarbons will be reformed) and reduce the net material consumption [1] [2]. By emulating the tail gas composition from the Fischer-Tropsch reactor, different syngas ratios (H2/CO) were investigated in Galactica, not only experimentally but also with the support of the in-house simulation framework TEMPEST [3], specialized for transient simulations on electrochemical reactors. Different operating conditions were evaluated by: (i) adding CH4 at open circuit voltage (OCV) and under current, (ii) performing an experimental ramp of the emulated Fischer-Tropsch gas composition into the inlet gases of the SOC reactor and (iii) by simulating a Feed-Forward controller in the case of H2O and CO2 shortages by varying the current and the air flow values in order to keep the operating temperature and reactor conversion in stable conditions. These results will allow to evaluate the performance of the SOC reactor with the temperature profile along the cells and the stacks, as well as with the syngas ratio behaviour. In this regard, operation strategies will be analyzed and discussed with the aim to mitigate failure conditions on SOC reactors, while operating in transient conditions in the frame of syngas production via high temperature co-electrolysis. [1] Herz, G.; Reichelt, E.; Jahn, M., Techno-economic analysis of a co-electrolysis-based synthesis process for the production of hydrocarbons. Applied Energy 2018, 215, 309-320 [2] Cinti, G.; Baldinelli, A.; Di Michele, A.; Desideri, U., Integration of Solid Oxide Electrolyzer and Fischer-Tropsch: A sustainable pathway for synthetic fuel. Applied Energy 2016, 162, 308-320. [3] Tomberg, M.; Heddrich, M. P.; Sedeqi, F.; Ullmer, D.; Ansar, S. A.; Friedrich, K. A., A New Approach to Modeling Solid Oxide Cell Reactors with Multiple Stacks for Process System Simulation. J. Electrochem. Soc 2022, 169, 054530.

Considering the transformation of the energy system, there are two main challenges. First, efficient and cost competitive longterm energy storage on a large scale. Second, making renewable energy accessible for hard-to-electrify sectors like transport and heavy industry. Converting renewable electricity into green hydrogen in Solid Oxide Electrolysis Cells (SOEC) is considered a viable solution for both challenges. Besides the superior efficiency, SOEC offer the possibility to supply part of the energy demand by industrial waste heat or by renewable sources, such as solar thermal energy. The SOEC technology is mature but the integration within large systems and coupling with up- and downstream processes still requires research to be done on the SOEC's transient behaviour as well as identifying safe and efficient operating strategies. In this contribution, a solar-SOEC coupled system concept analysed for its capability to cope with fluctuations in solar irradiance. Different operating parameters, namely current, feed gas temperature and reactant conversion, are varied. Results show the effects on the SOEC. Additionally, an improved operating strategy for a fluctuating scenario of two hours of overcast is presented. An exergy efficiency increase of about 4% could be achieved in comparison to a reference strategy.

Chemie Ingenieur TechnikVolume 94, Issue 9 p. 1322-1322 Vortrag Critical Operating Conditions for Co-SOEC Reactors for Syngas Production with Fischer-Tropsch Recirculation D. M. Amaya Dueñas, Corresponding Author D. M. Amaya Dueñas diana.amayaduenas@dlr.de German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanyCorrespondence: D. M. Amaya Dueñas (diana.amayaduenas@dlr.de), German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorD. Ullmer, D. Ullmer German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorM. Riedel, M. Riedel German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorM. Tomberg, M. Tomberg German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorM. P. Heddrich, M. P. Heddrich German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorS. A. Ansar, S. A. Ansar German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this author D. M. Amaya Dueñas, Corresponding Author D. M. Amaya Dueñas diana.amayaduenas@dlr.de German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanyCorrespondence: D. M. Amaya Dueñas (diana.amayaduenas@dlr.de), German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorD. Ullmer, D. Ullmer German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorM. Riedel, M. Riedel German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorM. Tomberg, M. Tomberg German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorM. P. Heddrich, M. P. Heddrich German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorS. A. Ansar, S. A. Ansar German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this author First published: 25 August 2022 https://doi.org/10.1002/cite.202255067AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume94, Issue9Special Issue: (Bio)Process Engineering – a Key to Sustainable Development: ProcessNet and DECHEMA-BioTechNet Jahrestagungen 2022 together with 13th ESBES SymposiumSeptember 2022Pages 1322-1322 RelatedInformation

One promising way of facing recent challenges to slow down the climate crisis or to reduce dependencies on fossil energy sources, e.g. natural gas, is using renewable methane and other e-fuels for storage and distribution via existing infrastructure. Solid oxide cell (SOC) reactors play an important role in the conversion of sustainable electric power into chemicals as they can be obtained from combined steam and CO2 co-electrolysis for syngas production. The pressurised electrolysis operation is a key factor for increasing the system efficiency of PtX-processes, including balance-of-plant (BoP) components, electrochemical reactors and high pressure downstream processes. In general, the yield of CO2 electrochemical reduction at atmospheric and pressurised conditions in high temperature co-electrolysis is still controversially discussed. Previously, several SOC short stacks were thoroughly analysed in pressurised steam- and co-electrolysis operation in a test-rig environment. These experimental results indicate marginal influence of pressure on the performance of electrolyte supported cells (ESC). In contrast, electrochemical impedance spectroscopy (EIS) suggests that pressurisation of pure CO2 electrolysis significantly reduces the fuel electrode impedance contribution, especially at lower temperatures around 700 °C [1,2]. This work aims to experimentally determine the kinetic behaviour of pure CO2 electrolysis by varying operating conditions like pressure, temperature, reactant conversion and feed gas composition. The investigation of kinetic parameters during these experiments could complement the formerly described research. Furthermore, the kinetic expressions can be used when studying co-electrolysis operation to identify the shares of: (i) the reverse water-gas-shift (rWGS) and (ii) the CO2 electrochemical reduction. Polarisation curves were dynamically recorded and different current densities were evaluated in steady-state operation. Additionally, EIS measurements were performed at open circuit voltage (OCV), as well as under different current densities. The kinetic parameters were estimated by curve-fitting analysis of the experimental results. The resulting expressions will be implemented in the in-house modelling framework, TEMPEST, based on [3,4] with the aim to increase the accuracy of modelling high-temperature CO2 electrolysis and co-electrolysis systems. [1] Riedel, M., Heddrich, M. P., & Friedrich, K. A. (2020). Experimental Analysis of the Co-Electrolysis Operation under Pressurized Conditions with a 10 Layer SOC Stack. Journal of The Electrochemical Society, 167(2), 024504, DOI: 10.1149/1945-7111/ab6820. [2] Riedel, M. (2020, October 20–23). Experimental analysis of SOE stacks under pressurized co- and CO2 electrolysis operation [Paper presentation]. 14th European SOFC & SOE Forum, Lucerne, Switzerland. [3] Tomberg, M., Santhanam, S., Heddrich, M. P., Ansar, A., & Friedrich, K. A. (2019). Transient Modelling of Solid Oxide Cell Modules and 50 kW Experimental Validation. ECS Transactions, 91(1), 2089, DOI: 10.1149/09101.2089ecst. [4] Srikanth, S., Heddrich, M. P., Gupta, S., & Friedrich, K. A. (2018). Transient reversiblesolid oxide cell reactor operation–Experimentally validated modeling and analysis. Applied Energy, 232, 473-488, DOI: 10.1016/j.apenergy.2018.09.186.

Chemie Ingenieur TechnikVolume 94, Issue 9 p. 1321-1321 Vortrag Operation Analysis of a Flexible Solid Oxide Cell Module for Power to Hydrogen and Polygeneration S. Salas Ventura, Corresponding Author S. Salas Ventura Santiago.SalasVentura@dlr.de German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanyCorrespondence: S. Salas Ventura (Santiago.SalasVentura@dlr.de), German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorM. Metten, M. Metten German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorM. Tomberg, M. Tomberg German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorD. Ullmer, D. Ullmer German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorM. P. Heddrich, M. P. Heddrich German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorS. A. Ansar, S. A. Ansar German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this author S. Salas Ventura, Corresponding Author S. Salas Ventura Santiago.SalasVentura@dlr.de German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanyCorrespondence: S. Salas Ventura (Santiago.SalasVentura@dlr.de), German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorM. Metten, M. Metten German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorM. Tomberg, M. Tomberg German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorD. Ullmer, D. Ullmer German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorM. P. Heddrich, M. P. Heddrich German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this authorS. A. Ansar, S. A. Ansar German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, GermanySearch for more papers by this author First published: 25 August 2022 https://doi.org/10.1002/cite.202255103AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume94, Issue9Special Issue: (Bio)Process Engineering – a Key to Sustainable Development: ProcessNet and DECHEMA-BioTechNet Jahrestagungen 2022 together with 13th ESBES SymposiumSeptember 2022Pages 1321-1321 RelatedInformation