Driven by the increasing demand for waste reduction and green energy production, an integrated system which combines an anaerobic membrane bioreactor (AnMBR) and a solid oxide fuel cell (SOFC) was proposed in this research project for blackwater treatment and energy production. The potentials of using an AnMBR for wastewater treatment and biogas production, and the feasibilities of producing energy from biogas with a SOFC have been investigated by many researchers. Although, combining the two equipment might raise new challenges and opportunities. The AnMBR pH has direct impacts on the biogas composition, which would subsequently affect the SOFC operational strategy. Therefore, this research project focused on the influence of the AnMBR pH on the SOFC operational strategy, which would provide insights for connecting AnMBR and SOFC. The AnMBR pH was controlled around 8 initially, and then reduced to 7. The composition of the biogas produced under each pH condition was analyzed before the biogas was conditioned for the SOFC operation. Biochar adsorption and CO2 addition were applied for biogas conditioning. pH 8 was favorable for biochar adsorption, whereas pH 7 was favorable for CO2 addition. The aim of biochar adsorption was to ensure that the H2S concentration remaining in the biogas after adsorption was less than 0.5 ppm, so that sulfur poisoning could be avoided at the anode of SOFC. A biochar column (BC) was attached to the AnMBR for the adsorption of sulfur compounds in the biogas. The BC was packed with biochar made of cow manure. The adsorption capacity of the biochar was measured to determine the amount of biochar required in the BC. After biochar adsorption, the ratio between CH4 and CO2 was balanced by adding CO2 to the biogas, to reduce the risk of carbon deposition at the anode of SOFC. The exhaust gas discharged by the SOFC could also be recycled as an alternative to CO2 addition. The performance of the SOFC system using the conditioned biogas as the fuel was assessed based on electric power output and fuel utilization efficiency. Based on the results of biogas production, conditioning, and utilization, the influence of the AnMBR pH on the SOFC operational strategy was analyzed. Furthermore, the potentials and the limitations of connecting AnMBR and SOFC were discussed.

The energy transition towards a fossil fuel free society presents ambitious challenges ahead. The highly potential renewable energy sources are becoming competitive and increasingly adopted for power generation, while for sectors such as residential, industrial or transportation still solutions have to be found. Sector coupling and energy storage are presented as alternatives to increase RES integration and reduce emissions. Given the different applications and requirements in each of these sectors the combination of multiple technologies with different characteristics will be needed. Among these technologies, Solid Oxide Cells have shown huge potential and increasing attention based on their unique characteristics. This research advocates for pushing further the integration of renewable energy sources trough Solid Oxide Cell based systems.

At first, a review of the state-of-the-art technologies for sector coupling and energy storage is presented, the limitations and challenges at the sector level are addressed, and the value and research status of Solid Oxide Cell systems is conveyed. A selection of suitable sector coupling applications has been done based on SOC unique characteristics. Their functional requirements have been investigated for the future system design. The selected processes have been modeled in Aspen Plus to further conduct an energy and exergy analysis with the objective to understand the effect of the operating conditions and functional requirements on the thermodynamic performance. To conclude, a techno-economic analysis has been performed to determine the economic competitiveness and feasibility of these systems.

Through the thermodynamic optimization, in electrolysis mode exergy efficiencies of 78.93% and 80.38% are achieved for the methane-based and methanol-based system respectively. When operating thermoneutral, lower temperatures are desirable for both systems, but pressurization only has positive effects in the methane case. The upgrading process has a considerable impact on the process performance highly dependent on the operating conditions. In fuel cell operation, the methane-based system achieves 60.33% in comparison with 52.10% for methanol at high temperatures and environmental pressure. From a techno-economic perspective, stack cost is the main driver of the plant capital cost highly influenced by current density and lifetime, while the operational costs are mainly determined by electricity and carbon price. Onshore wind is presented as the best alternative for renewable energy supply due to higher capacity factors, under realistic considerations a 445 EUR/tn LCOMEOH is accomplished which could become market-competitive for future carbon emission’s prices.

The International Maritime Organization (IMO) has imposed strict emission guidelines for the shipping industry to meet the Paris agreement. This has led the maritime industry to search for alternative fuels and prime movers. An electric propulsion system powered with a Solid Oxide Fuel Cell (SOFC)-Internal Combustion Engine (ICE) is one of the possible solutions. In such a system the SOFC is made to run at a constant load while the engine is expected to cover the transient loads.
The main purpose of the thesis is to get an insight into the optimum power split required between Solid Oxide Fuel Cell (SOFC) and Internal Combustion Engine (ICE) for a particular maritime load profile. This has been achieved by analyzing system performance of three different power split configurations (30-70, 50-50,70-30) between SOFC and ICE. The operational profiles from three different case studies have been considered; Cruise, Oil tanker and Yacht. The system analysis has been performed with steady state results for SOFC-ICE system modeled in Matlab Simulink. SOFC has been modeled as 1D model with 3 elements whereas, the engine has been modeled as a lookup table with datasheets for two stroke dual fuel CI engine. From the power split study it has been found that, in general, the ship with high frequency of full load operation benefits from a large installed SOFC and the ships with high frequency of anchoring load or part load benefits from small installed SOFC power. Owing to large heat demand, the Cruise ship benefits the most from the SOFC-ICE system. A 50-50 power split or SOFC installed at base load for a Cruise ship leads to carbon emission reduction by almost 56% compared to diesel electric system while achieving a system efficiency (heat and power) of 74%. Thus, the SOFC-ICE system running on natural gas can help in reducing the emissions by almost 50% while allowing high electrical and system efficiencies. Thus, allowing the maritime industry to attain the greenhouse gas emission and energy efficiency goals. With commercialization of green hydrogen and storage, the system could also help in achieving the zero emission goals.

We have set out to develop a drone, based on the existing Delftacopter, capable of soil monitoring via LiDAR remote sensing. The battery was to be replaced by a fuel cell system in order to extend the range threefold to 180km. Unfortunately, the ultimate design is likely unfeasible. Agriculture requires healthy soil and monitoring soil health is fundamental to its maintenance. Soil organic carbon in particular provides energy to the soil’s microorganisms, and is beneficial to water and nutrient retention. In addition, storing carbon in the soil is a form of carbon sequestration, which has become interesting due to the rising levels of carbon dioxide in our atmosphere. Monitoring soil organic carbon is therefore the goal of the drone design. The fuel cell system is a 650Whydrogen fuel cell by Intelligent Energy with a mass of 1290 g, which will be replacing the battery in the base design. Fuel tanks that were considered suitable are the 450 g, 0.5 L, 500 bar and 1350 g, 3 L, 300 bar fuel tanks by Meyer. It was found that one 1350 g and two 450 g fuel tanks were necessary to achieve the desired range of 180 km. However, after more careful drag estimates, this configuration turns out to be too heavy. 4 450 g fuel tanks remains feasible. Results below are based on this amount of fuel tanks. The incorporated LiDAR sensor is one by Velodyne, namely the Puck LITE, with a specified range of 100 m. The LiDAR sensor has a firing cycle of 55.296 &s, almost 20 kHz. Based on previous studies that used LiDAR to measure soil organic carbon, it has been established that a density of 5 data points per square meter is required. Fromour LiDAR parameters it turns out that the optimal flight altitude is 27.5mabove the surface that is to be measured, with a rotation rate of 10 Hz for the LiDAR sensor, when flying at a speed of 20ms¡1. With a flight distance of roughly 116km at 22.5ms¡1 (111km at 20ms¡1), an area of 21.8km2 per flight can be scanned. 1

The integration of variable renewable energy sources (RESs) in the electrical power grid leads to larger and faster variations in the power demanded from controllable power sources. This is a problem, because flexibility of (base load) power plants is limited. Solid oxide reversible cells(SORCs) can be used as load-shifting devices to reduce these power variations by converting electricity to hydrogen (solid oxide electrolysis cell (SOEC) mode) when power demand is low and converting hydrogen to electricity (solid oxide fuel cell (SOFC) mode) when power demand is high. However, the introduction of SORCs is challenging. It is a promising long-term energy storage technology, but it is in its development stage. Apart from prohibitive costs, challenges also lie within durability and efficiency under dynamic operation. Development of control strategies is essential for maintaining optimal operating conditions. Therefore, this study researches the ability of SORCs to operate in a mixed power grid by developing an SORC model and power disturbance rejection controller which ensures safe operating conditions.
A dynamic 0D SORC model was developed. It describes a single cell at the center of a large stack of identical cells, which makes it representative for large-scale SORCs. The model is based on SOFC models and uses the current density to indicate the operating mode of the SORC. The benefit of this approach is that one continuous model describes both operating modes. Validation of the model is based on comparison of static cell voltage-current density curves from literature and from a small stack experiment. Open-loop analysis of the model showed that the system is stable and can be decoupled. It also showed that development of gain-scheduling controllers was necessary to handle the exothermic, hydrogen consuming SOFC mode and endothermic, hydrogen producing SOEC mode. This motivated the design of gain-scheduling H-infinity tuned proportional-integral (PI) controller, which were used to control the positive electrode, electrolyte, negative electrode (PEN) structure temperature and fuel channel composition by manipulating the air and fuel flow rate, respectively. Two methods were compared for specifying the performance of the controller. The first method was based on the desired closed-loop bandwidths and the second method was based on the bandwidth of the disturbance. The first method was superior to the second method, because the obtainable closed-loop bandwidths are faster than the bandwidth of the disturbance.
This study shows that gain-scheduling PI controllers allow SORCs to be used for load shifting applications in a mixed power grid. Further research is needed to validate the dynamics of the model and to identify the influence of balance of plant (BOP) dynamics on controller performance.

Energy storage systems are an emerging field of interest for the future of electrical grids. With the rapid growth of renewable but intermittent sources of electricity, energy storage systems can help smooth the variations, making the grid more stable and reducing the need for maintaining an overcapacity of power production infrastructure. Among energy storage solutions, power-to-chemical storage is of particular interest due to the high energy density of chemicals and seasonal storage capabilities. Developments made in power-to-chemical technologies can also go a long way towards making the transportation and chemical industries sustainable. The chemical considered in this work is ammonia (NH3), which has advantages of being an easily liquefiable fuel, and has also been in industrial use for over a century. This thesis project aims towards the development of an efficient power-to-ammonia energy storage system using reversible solid oxide cells. The system designed in this thesis is based on direct ammonia utilisation in fuel cell mode, and steam electrolysis coupled with Haber-Bosch ammonia synthesis in the electrolysis mode. A steady state process model is designed in Aspen Plus. This is followed by extensive thermodynamic exergy analysis, used as the basis for the further design and optimisation of the system, with a goal to maximise the round trip efficiency. Exergy analysis is used to identify the sources with most scope for improvement.
The final system can attain a maximum round trip efficiency of 61.20 %, improved from a basic system efficiency of 19.79 %. The maximum round trip efficiency is comparable to values reported in recent times for thermodynamically studied models from literature using other fuels, such as 56.72 % for methanol. The optimised system attains high efficiencies without the need for thermal energy storage or an afterburner. Further, it is demonstrated that the designed system is efficient enough that heat integration across modes with high temperature energy storage does not provide any significant benefit.

In the current transition to new and durable methods of generating energy, biomass is becoming a primary source of energy. Solid Oxide Fuel Cells, when integrated in a combined heat and power system, can yield high efficiencies in the conversion from biomass to thermal and electrical energy. One of the challenges that this process faces is the damaging effects of the contaminants that are formed in the gasification of biomass fuels. These damage effects include the clogging up of lines, de-activation of the catalysts and a decreased carbon conversion. Among these contaminants, tars, particulate matter, HCl and H2S are the most prominent and can cause severe damage on downstream equipment, interfere with electrochemical reactions and pressure drops, which all negatively affect the SOFC performance. This study focuses on the effectiveness of a re-designed high-temperature gas cleaning unit on removing these contaminants. Under the FlexiFuel-SOFC project, which aims to develop a highly efficient fuel flexible biomass CHP system, an integrated system consisting of a gasifier, gas cleaning unit and a SOFC has been built in the laboratories of BIOS Bioenergiesysteme. HCl, H2S and tar contents in the syngas were analyzed at different points in the process. The operating temperatures are monitored to see if the design parameters are achieved. It is critical for each reactor/component to reach the design temperature, as this can greatly influence the gasification process, the effectiveness of catalysts and fuel cell bio- syngas to electrical energy conversion. The temperature evaluation shows a normal heating up of the gasifier and reactors during the test runs. The design temperature parameters were achieved. The tar content analysis shows the most abundant tar compounds were naphthalene, toluene and phenol. The total tar content in the syngas was measured on two test days and was found to be 3.64 and 3.37 g/nM3 before gas cleaning and 0.11 and 0.41 g/Nm3 after gas cleaning, which comes down to a 97% and 88% resp. reduction in total tar content.

Gas-to-gas membrane humidifiers are the preferred option for humidification in automotive fuel cell systems, because they are compact, induce low parasitic losses and require no moving parts or control mechanisms. Understanding the performance of the humidifier as a function of its operating conditions is crucial for the efficiency of the fuel cell system. Therefore zepp.solutions BV, a system integrator of hydrogen fuel cell systems for the clean and mobile power generation, demanded advanced insight into the performance of their humidifier. Two models were developed to describe the heat and mass transfer in a gas-to-gas shell-and-tube membrane humidifier, furthermore the performance of the humidifier was extensively determined via experiments. The novelty in the model lies in the comprehensive combination of advanced correlations describing mass and heat transfer in the humidifier. Experiments at various mass flows, temperatures and pressures were performed on a Fumatech H20N humidifier, a gas bubbler has been designed and developed to humidify the gas stream. Heat transfer was measured to increase linearly with inlet temperature difference and was limited by convective heat transfer. Water transfer was found to be limited by diffusion and to increase exponentially with wet inlet temperature, dry air mass flow only had a small impact. The impact of mass transfer on heat transfer can not be neglected, due to latent heat transfer and transfer of energy by water being transported. For the analytical and numerical model, the heat and mass transfer coefficients are based on correlations found in literature. The membrane diffusion coefficient and both convective mass transfer coefficients vary over an order of magnitude or more in literature. The numerical model can predict the latent effectiveness with acceptable accuracy, the sensible effectiveness is mainly overestimated. For eighty percent of the cases the predictions are within (+.0061 to .22) and (-.11 to +.056) for the sensible and latent effectiveness, respectively. A further improvement requires more information about the membrane diffusion coefficient of the specific membrane material and appropriate correlations for the shell side Sherwood numbers taking tube placement irregularity into account.

Emissions restrictions imposed by the International Maritime Organization (IMO) is forcing ship owners and builders to look into alternative fuels and prime movers. The high efficiency of fuel cells could help to decrease emissions in marine power generation. Solid oxide fuel cells (SOFCs) are the most fuel flexible among fuel cells, the high operating temperature and the possibilities for direct internal reforming (DIR)makes this technology of great interest for natural gas fueled systems. SOFCs operating in hybrid system configuration could even achieve higher efficiencies, due to effective utilization of left-over fuel in anode off-gas and adequate system heat integration. In literature extensive research is found about hybridization of SOFCs and gas turbines. For such hybrid configurations high efficiencies are projected, however poor part load performance and high system complexity are tempering the interest for marine applications. SOFC integration with an internal combustion engine (ICE) also has high projected efficiencies and is expected to enable system integration in marine applications with limited complexity, higher robustness, and lower costs compared to SOFC-gas turbine integration. However, due to the novelty of SOFC-ICE hybrid systems, not much research has been published as of yet and the research that is found shows a variety in system configurations and performance results. This observation justifies additional SOFC-ICE hybrid system research, particularly if the system has to operate on marine applications. In this work an integration of an SOFC and ICE is proposed. Both SOFC and ICE share the load on the system: the SOFC can operate on a base load, while the ICE can handle majority of the transient load. A pre-reformer is proposed, which supplies partially reformed methane to the SOFC. The ICE is supplied with natural gas mixed with excess fuel from the SOFC-anode. This additional natural gas supply to the engine makes it a combined cycle, instead of a bottoming cycle, and allows better dynamic load control and increases reliability. Also system heat integration is an essential requirement, as the steam required for methane pre-reforming is produced with heat from engine exhaust system. System component models are developed and individually analysed. Thereafter both component models are combined to an SOFC-ICE hybrid system model and a study is conducted to investigate the sensitivity of the following operating parameters and system configurations on system performance and efficiency: SOFC current density, SOFC fuel utilization, anode off-gas recycling, methane pre-reforming ratio, pre-reformer integration, and power split ratio. The SOFC component model provides insights of performance behaviour when varying operating parameters. The ICE model clearly indicates the advantages when hydrogen is added to natural gas, both improved engine efficiency and improved combustion stability are demonstrated. Finally, it is found that operating the hybrid system model consisting of a 375 kWe (AC) SOFC and a 375 kWe ICE leads to an electric efficiency of 45.7 % (LHV). This is a 5 to 10 percent point improvement compared to conventional diesel engines operating in this power range [1]. In this hybrid system the SOFC current density is set to 5000 Am¡2, anode off-gas recycling is not applied, and 30 % of the SOFC fuel is pre-reformed. The SOFC fuel utilization is set to 86 % in order to avoid too large hydrogen-natural gas blending ratios at the ICE intake, which are currently not substantiated with engine experiments. Future modeling of the ICE should make it possible to extend the hydrogen-natural gas blending ratio, such that even higher hybrid system efficiencies can be demonstrated. This work demonstrates that the SOFC-ICE hybrid system operating at a 50 % SOFC and 50 % ICE power split provides a firmefficiency improvement compared to conventional diesel driven power plants in the range upto 1MW. An higher efficiency means a lower fuel consumption and thus a CO2-emissions reduction. Also NOx-formation is reduced, due to the absence of expansive high temperature combustion in the fuel cell part of the system. Considering volumetric power density, the SOFC-ICE hybrid system installation volume is more than twice as large as conventional marine power plants. Taking the energy conversion efficiency into account, the LNG storage space for proposed hybrid system is two times larger than that of a diesel fueled generator set. A 50 % SOFC and 50 % ICE power split leads to these numbers, depending on the operating profile a different power split can lead to other efficiencies and volume and weight constraints. The impact of power density and energy density depend on the practical application (e.g. ship design, required power, endurance, operating profile, and costs) and must be considered case-by-case.

As all industries move towards sustainable fuels to reduce emissions, aircraft industry is still at its nascent stages. The adoption of clean energy sources has been slow particularly due to low energy density of commercially available batteries, and high volumetric density of hydrogen as a fuel. Electric aircrafts have been demonstrated but only a few are available commercially. Hydrogen powered flights have also been demonstrated, but only for experimental purposes. As the move towards clean aviation furthers, it is necessary to indicate an approach for designing a mass minimized aircraft powerplant. The aim of this thesis was to indicate exergy-gravimetric approaches towards designing an optimal minimized-mass powerplant for aircraft applications. This thesis work also aimed to use this approach to size a mass-minimized powerplant for the Pipistrel Alpha Electro aircraft. The exergy analysis of fuel cell was carried out on CycleTempo through which sources of exergy destruction were identified and quantized. A mass-minimized model was developed on MATLAB. Using these tools, a number of system configurations for varying battery combinations, endurance requirements, and fuel cell types were analysed. Overall, an exergy-gravimetric approach towards mass minimization was developed in this thesis work. Multiple fuel cell - battery hybrid powerplants were sized for the Pipistrel Alpha Electro. It was demonstrated that at least three system configurations using commercially available batteries and PEM fuel cells exist which would perform superior than the existing battery system on the aircraft, reducing the powerplant weight by as much as 20 kg from the existing battery system, while increasing endurance by about 15 minutes.

In a effort to curb climate change, more and more countries are adding solar and wind farms to their electrical grid. These solar and wind farms produce electrical energy based on environmental conditions, for example solar irradiation intensity or wind speed. As such these farms create fluctuations in the electrical grid and create a mismatch between energy supply and demand. To solve this problem the European Balance project proposes to use reversible solid oxide cell (ReSOC) systems. These systems can convert the excess energy produced by the solar and wind farms into an energy carrier when the supply of energy is bigger than the demand. At a later time this energy carrier can be reverted back to electrical energy when the energy demand is bigger than the supply. As these ReSOC systems are still in the development phase, experimental work is being carried out to develop these systems. For the Balance project the university of technology Delft (TuD) is tasked to determine the performance and the degradation, during constant operation and during cyclic operation, of a ReSOC system. To achieve these goals the university utilises a ReSOC test station. After use of the test station, the university found that the ReSOC systems showed high degradation and fractured within short use in the test station. As these results were not replicated by other balance partners, a cause for these results had to be found. In this work the test station was investigated to find the cause of the high degradation and breaking of the cells. After investigations of the voltage fluctuations and voltage spikes seen during electrolysis operation, it was found that water condensed in the fuel inlet duct. The liquid water droplets, formed as a result of condensation, caused the voltage fluctuations, high degradation and thermal gradients in the system that eventually fractured the cells. By redesigning the water injection system the fluctuations were reduced by 70% and the voltage spikes were completely removed. This indicates that the redesign solved the problem of water condensation in the fuel inlet duct. The resulting decrease in degradation rate of the ReSOC system extended the experimental duration up to a verified 1000 hours of continuous operation. The extended duration allowed the ReSOC system to complete 900% more cycles, within Balance protocol specification, whilst the current density was also increased by 60%. These improvements enable the test station to determine the objectives given by the Balance project. Whilst investigating the the high degradation, markings were found on the fuel electrode of the cells as well. A computational fluid dynamics (CFD) study confirmed that these markings indicated the fuel flow distribution. By converting the CFD data to current density and fuel utilisation data, it was shown that the overall performance of the ReSOC system was influenced negatively by the flow distribution plate. The results also showed that the ReSOC performance in the test station of the TuD can improve significantly if the fuel inlet flow is switched from a perpendicular to a tangential flow direction at the cell surface area. A redesigned flow distribution plate is therefore proposed that closely matches an ideal tangential flow distribution.

The intermittent nature of renewable energy sources makes it difficult for electric utility companies to effectively implement these technologies in the power grid due to mismatches between supply and demand. Solid oxide cells are electrochemical devices that are receiving a lot attention as an effective power grid balancing technology, given their ability to operate as Solid Oxide Fuel Cells (SOFC) for electric power generation, and as Solid Oxide Electrolysis Cells (SOEC) for chemical fuel production. Solid Oxide Reversible Cells (SORC) are capable of working alternately in these two modes, thus can be used to store electricity in the form of fuel when energy supply in the grid exceeds the energy demand and can release this energy when demand exceeds the supply from generation systems.

The purpose of this project was to design an energy storage system that uses solid oxide reversible cells and syngas as fuel, consuming it to produce electricity during operation as a fuel cell and producing it back to store electric power through the co-electrolysis of water and CO2 when working as an electrolysis cell. The design and steady-state simulation of the system was performed using the process simulation software Aspen Plus, where a base configuration of the plant was constructed and improved using as main criteria the roundtrip efficiency and exergy efficiency achieved. This approach allowed to locate the main sources of energy and exergy losses, therefore strategies could be implemented to reduce them, finally achieving a more advanced and efficient system. Overall, it was possible to attain improvements in system roundtrip efficiency from 29% to 44%; in SOFC exergy efficiency from 44% to 64%; and in SOEC exergy efficiency from 66% to 68%.

A lot of scientific research has been focusing on energy storage systems recently and there are numerous reasons for that. First of all, they can nullify the intermittent nature of renewable energy technologies, by storing excess energy in times of heightened solar irradiance and wind levels and utilizing it when electricity demand is surging. A combination of energy storage systems along with renewable energy technologies can eliminate CO2 emissions in the future. It can also lead to state development, by liberating countries from the dependency on costly fossil fuel imports. Finally, population growth will result in increased energy peaks and energy storage systems can be seen as the means for achieving those enhanced power requirements.
In the current thesis, an extensive thermodynamic investigation of an efficient energy storage system based on steam electrolysis is presented. The core of the system is a reversible solid oxide cell stack. It can operate either as electrolysis (charging mode) or as a fuel cell (discharging mode). Apart from the core, around the stack, various balance of plant components can be placed for the synthesis of a plethora of fuels. In this case study, methanol is synthesized.
At first, process design of a model capable of converting electrical energy to methanol and vice versa is formulated in process simulation software Aspen Plus®. Extensive energy and exergy analysis have been conducted on the system for the identification of process conditions which maximize energy and exergy efficiency of each mode of operation. Furthermore, extensive exergy flow diagrams have been drawn in order to pinpoint the components which mostly contribute to the total exergy losses. Finally, roundtrip efficiency optimization has also been performed and the respective process conditions have been reported. For the calculation of the hot and cold utility of the system, the pinch technology has been employed.
Results indicate that during electrolysis mode energy and exergy efficiencies of 68.74% and 77.67% respectively, can be achieved when thermoneutral operation is applied. The same results for fuel cell mode operation are 60.22% and 56.78% respectively. Exergy and energy efficiency during fuel cell mode are still limited due to the intense refrigeration system employed for CO2 condensation. For maximization of roundtrip efficiency, a thermal energy storage system was additionally employed in the process design which stores heat energy from fuel cell mode in order to satisfy the thermal requirements during the endothermic electrolytic operation. The maximum reported value of roundtrip efficiency is 56.72% while in scientific literature a maximum value of 54.3% has been cited, showing a clear improvement.

In a future scenario electric vehicles (EV) could be operated in Vehicle to Grid (V2G) mode to support the national and renewable energy electricity grid by providing ancillary services such as peak shaving and frequency regulation. While developing financial models to price these services it is important to include the impact of Vehicle to Grid operation on the power-delivery components of these Electric Vehicles. Considerable amount of academic research has been focused on understanding the impact of Vehicle to Grid operation on Battery Electric Vehicles (BEVs). However, information about the impact of Vehicle to Grid operation on the fuel cells (FCs) of Fuel Cell Electric Vehicles (FCEVs) and Fuel Cell Range Extender Electric Vehicles (FCREEVs) is scarce.

Long term tests are required to asses the impact of Vehicle to Grid operation on these fuel cells. The fuel tank volume limitation of the TU Delft Hyundai FCEV does not allow for long term Vehicle to Grid experiments using the operational Vehicle to Grid set-up at the TU Delft Green Village site. Furthermore, there exist limited control over the power management strategy programmed in the Hyundai FCEV; the power management strategy defining the load cycle it’s Fuel Cell undergoes in Vehicle to Grid operation. This study therefore proposes a method to conduct simulated long term Vehicle to Grid experiments on a laboratory test bench. The method has also been applied, and the impact of simulated Vehicle to Grid operation on the Fuel Cell of the PEMFC test bench estimated. Most importantly, the experimental conditions simulated on the laboratory test-bench were derived from data recorded in the Hyundai FCEV during actual Vehicle to Grid operation. Simulated Vehicle to Grid operation under three aging cycles: high constant load (CC1), low constant load (CC2) and cyclic load (CC3), was found to cause a performance loss in the range of 31.4 μV h 1 to 40.9 μV h 1, 62.5 μV h 1 to 63.9 μV h 1 and 36.1 μV h 1 to 92.4 μV h 1 respectively.

Power generation systems based on SOFCs provide a highly efficient alternative to traditional systems. In the present study a sensitivity analysis with cell operating temperature, pressure ratio and fuel utilization as system parameters is performed on a SOFC-GT system fed by Hydrogen and Methane. Exergy losses in different system components and their dependence on system operating parameters and fuel chemistry are investigated in detail. In the considered ranges system efficiency increased with both cell operating temperature and fuel utilization. A flat optimum with pressure ratio was found for Hydrogen (2.5) and Methane (5). The main causes of high losses in the system are found to be very different for Hydrogen and Methane which leads to different optimization strategies.
Following the optimizations comparable system exergy efficiencies were obtained with Hydrogen (76.2%) and Methane (78%). Electrical efficiencies were 74.6% and 80.9% with Hydrogen and Methane respectively. An additional study of a SOFC system without a gas turbine was also undertaken with 4 fuels (Methane, Hydrogen, Methanol and Ammonia). It was observed that it is possible to achieve a high system efficiency by minimizing the excess heat left due to the removal of the gas turbine and utilizing it completely for internal reforming of the fuel. An electrical efficiency of 73.3% was achieved with Methane without the gas turbine.

Solid oxide fuel cell exhibits its advantages such as fuel variability. Capable of running on renewable fuels, SOFCs are regarded as potential solution to carbon-neutral energy conversion path. SOFCs operate on fuel supplied to the anode and oxidant supplied to the cathode. The anode should facilitate the oxidation of fuel and transport of electrons from the reaction site to the current collector. It should also enable the diffusion of gaseous fuel to the reaction sites and reaction products away from the reaction sites. Meeting abovementioned requirements, Ni/YSZ cermets are competent SOFC anodes, where Ni is an electronic conductor, YSZ is an ionic conductor, and pores in between Ni and YSZ facilitate the fuel supply. Fuel oxidation occurs in the vicinity of triple phase boundaries (TPBs), where Ni particles, YSZ particles and pore interact. Thus, TPB length quantifies the electrochemically active sites within the anode. The fuel oxidation involves physical processes and multi-elementary reaction steps in reality, among which exists a rate-limiting step. The overall reaction rate can be represented by the rate-limiting step whose kinetics are proposed as a function of the TPB length. In many past computational studies of the cermet anode, a global electrochemical reaction expressed by Butler-Volmer equation is put forward, simplifying electrode reaction to a single step process and probably inadequately to present insights into intrinsic processes occurring within the anode. In this work, TPB-based kinetics, derived from the pattern anode experiment, are implemented in a CFD model to evaluate the performance of Ni/YSZ cermet-based cells. For model validation, simulated polarization curves are compared with the experimental ones. TPB length as a fitting parameter is determined to ensure the agreement between simulated polarization curves and experimental ones. The fitted TPB length is found to be several orders of magnitudes lower than physical TPB length of typical Ni-YSZ cermet anode, which might imply that only a small fraction of the physical TPB length actually participates in the electrochemical reactions. CFD behavior like species distribution and electrochemical behavior like overpotential breakdown are investigated. The gradient of species molar fraction in anode turns to be larger than that in fuel channel, agreeing with the fact that fluid flow is much slower in anode where species transport in porous electrode is dominated by diffusion rather than convection. The cathode activation overpotential makes the most significant contribution to the overall overpotential. The anode activation overpotential at high current density region in the case of low molar fraction of inlet hydrogen yields rapid increase, which could be explained as a consequence of rapid decrease of exchange current density in the vicinity of anode/electrolyte interface. Parametric study of operating temperature is conducted later to see its effect on the cell performance. The higher the operating temperature is, the slower drop of cell voltage with respect to cell current is observed. At a fixed cell voltage, an elevated temperature will cause intensified fuel consumption/vapor generation within anode, leading to a larger gradient of species molar fraction and accordingly a larger concentration overpotential.

Unmanned aerial vehicles (UAV) for science missions are becoming increasingly popular in the present context. Science missions require high altitude operation and long endurance (HALE). With rising awareness of climate change phenomenon it becomes imperative to look into more efficient and more sustainable means of powering these missions. A 'well-to-wheel' study is a comprehensive way of comparing different operations for powering a vehicle. For this study , the HALE UAV is powered by a solid oxide fuel cell and gas turbine (SOFC-GT) hybrid. The HALE UAV design is based on concept that has been developed before by NASA. It is also essential that a suitable fuel is selected for powering the hybrid system. Previous studies which were based on liquid hydrogen (LH2 ) concluded that liquefication of hydrogen as an avenue for major exergy losses. For the current study, use of compressed synthetic natural gas (SNG) is analysed. Exergy analysis is carried out for fuel production and the hybrid system operation at cruise altitude. To begin with, syngas is synthesised from woody biomass through gasification. The syngas is then converted into SNG and compressed for storage. This SNG is utilised in the SOFC-GT hybrid. Design calculations are made for the take -off stage. Effect of pressure variation is studied to get the optimum system size. Then the performance of the system is analysed in the cruising stage to estimate the endurance of the flight. Exergy efficiency analysis and mission endurance calculations are made for the system during cruising conditions as a means to evaluate the system performance. The effect of position of air preheater is studied in two different configurations. The exergy efficiency for compressed SNG synthesis is 59.7% and the SOFC-GT operation at cruise is 69.6% effcient. A total 'well-to-wheel ' effciency of 41.6 % is attained. Based on the results of the analysis carried out thus far, the mass for the system components is estimated. Volumetric estimates are also made and the system is fitted in the nacelle volume as defined in NASA concept. The results are eventually compared to the system working on LH2 . The results from compressed SNG study show that specific energy density of the fuel is important. The mass estimates show that the infrastructure required to carry the SNG fuel reduces the specific energy of the fuel. liquid fuels such as methanol should be analysed as another option.