The vast amounts of greenhouse gas (GHG) emissions, surging gas prices, and increasing proportion of intermittent energy sources force the energy sector to structurally modify the energy system. The reversible Solid Oxide Cell (rSOC) is considered to be part of the solution due to its high efficiency, good scalability, and ability to balance the energy grid. The rSOC is a high-temperature, electrochemical device that can convert both power-to-gas and gas-to-power during its Solid Oxide Fuel Cell (SOFC) and Solid Oxide Electrolysis Cell (SOEC) modes. The integration of the SOFC with a combined cycle gas turbine (CCGT) features exceptional synergies. Although the synergies of the SOFC and CCGT have already been widely reviewed, the combination of an rSOC and a CCGT has remained unexplored.

The research objective of this study is to assess the benefits of retrofitting an rSOC to an existing CCGT by simulating its exegetic performance, relative GHG emissions and gross profit, and comparing these results to those of an existing CCGT. During the integration of the rSOC (operating in SOFC mode) with the CCGT, the performance of the reversed SOEC mode must be taken into account because it will have to operate with the same operating conditions and the same system components. In order to decrease the system investment cost, this work examines to what extent the rSOC can be retrofitted into the currently deployed CCGTs.

This research optimizes the process plant design and scrutinizes the effect of various operating conditions on the system performance. The optimization is performed through exergy analyses of a zero-dimensional Aspen Plus model. A case study, in which the proposed system is inserted into an energy resource allocation model of the Amsterdam metropolitan area, is used to examine the gross profit of the proposed multi-energy system.

The optimization of the SOFC-CCGT system results in an exergy efficiency of 61.5%, generating 518 MWe, which enhances the performance of the existing CCGT by 3.8% and decreases the GHG emissions [CO2e t/MWh] by 21.3%. When the combined heat and power (CHP) mode of the CCGT is considered, the resulting SOFC-CCGT CHP system achieves an exergy efficiency of 61.2%, while generating 474 MWe and 103 MWth. The SOFC-CCGT CHP outperforms the exergy efficiency of the original CCGT CHP with 4.2%, while emitting 13.2% less GHG emissions. The same operating conditions of the SOFC were applied to the SOEC, which manages to operate with an exergy efficiency of 84.3%.

Implementing the rSOC-CCGT CHP system into the energy resource allocation model results in a 118% increased net present value (NPV) of the gross profit compared to the original CCGT. The proposed multi-energy system is able to adjust its operating mode to anticipate the price variations in the energy grid and thereby increases the gross profit. Adding a thermal energy storage system decouples the consumption and production of heat, which enhances the NPV of the gross profit by an additional 1.4%.

Fuel assisted electrolysis has the advantage of reducing the power demand of hydrogen production by solid oxide electrolysis with the help of assisting fuel. This thesis presents a feasibility study on the use of biogas fuelled solid oxide fuel assisted electrolysis (SOFEC) for hydrogen production on an industrial scale. The biogas is supplied as a source of hydrogen to the anode of the solid oxide electrolyser where hydrogen gets oxidised and provides electrons for the steam splitting taking place at the cathode. This results in upgrading of biogas to hydrogen and reduction in the electrical power demand. However, steam reforming of biogas (methane) is an endothermic reaction and hence,
heat has to be supplied externally.
The SOFEC system is modelled in Cycle Tempo and the modelling results are used to perform the feasibility study based on technical, economic and social aspects. Further, to corroborate the results from the study, a case study scenario of integration of SOFEC in a steelmill is presented.
With regard to technical aspects, the SOFEC cathode and electrolyte materialswere found to be in practice commercially, adequate biogas supply could be ensured by biogas production at waste water treatment plants and heat supply from high temperature waste heat sources was proposed to meet heat demand of methane reforming. Based on these conditions, the SOFEC system has high prospect of being technically feasible.
Further, for economic analysis, the net production cost of SOFEC was estimated to be less than 4.5 Eur/kg H2 which is lower than that of low temperature (7.32 Eur/kg H2) and high temperature electrolysis (5.54Eur/kg H2). Considering high temperature heat, recovered from molten slags in steel mills, being used as heat supply followed by a predicted drop in electrolyser capital costs, the SOFEC is able to compete with lower production costs of steam methane reforming (3 Eur/kg H2). Thus, low electrolyser capital costs and availability of low cost waste heat supply are the main driving factors for SOFEC to be economical.
In social aspects, the operational safety and social acceptance of SOFEC were investigated. It was concluded that for hydrogen storage challenges, existing commercial hydrogen storage solutions can work and with hydrogen fuel cells being socially accepted, the SOFEC was assumed to be accepted the same. Also the SOFEC was shown to have low CO2 (2 kg CO2 equivalent / kg H2) and low SO2 emissions provided sufficient desulfurisation of biogas is done. Therefore, it is concluded that the SOFEC has high potential to be socially feasible.
Although, the SOFEC has been presented to be a feasible technology, uncertainties
such as degradation in performance due to interruptions in biogas supply, absence of anode materials which can withstand reducing environments, absence of low cost high temperature heat and high costs of electrolyser systems are obstacles which have to be resolved.

Today’s renewables, wind and solar power, have a fluctuating nature, making the grid less stable.However, with the increasing share of intermittent sources of renewable power, novel options have to be created to stabilize the power grid. One of these options is energy storage via the conversion of excess power to hydrogen, during periods of high generation from wind and/or solar. In periods of power shortages hydrogen is converted back to power. In the literature fossil fuelled turbine cycles have been studied extensively, furthermore multiple fuelcell turbine cycles have been modelled. However, models with hydrogen and oxygen fuelled turbine cycles and fuel cell turbine cycles are scarce, leaving opportunity for further optimization of modeled hydrogen and oxygen fuelled cycles. The application of pressurized H2/O2 can lead to several improvements over conventional thermodynamic cycles and fuel cells. In this work, a number of high efficiency hydrogen and oxygen fuelled thermodynamic cycles, based upon the Graz cycle and the Toshiba Reheat Rankine cycle, both a coupled closed Brayton cycle with a Rankine cycle, are investigated. urthermore, the following thermodynamic improvements are proposed to fit the Graz cycle: an increased TIT (turbine inlet temperature), the use of a reheat combustor (the inclusion of a second combustor), condensate preheating and hybrid cooling (a combination of open loop and closed loop cooling) of the high temperature turbine blades. All upgrades together lead to an efficiency of 75% LHV. The rise of efficiency of the individual upgrades summed up is lower than the rise off all upgrades together. This is due to the fact that adding reheat and increasing TIT introduce extra high temperature turbine blade cooling needs and losses, which an improved cooling method counteracts. For this reason, the cooling method used is rather influential. Therefore, two cooling methods, open loop cooling and hybrid cooling, used in the Graz and Toshiba cycle respectively, are studied in this thesis.Next to the thermodynamic improvements, an electrochemical improvement is studied, by adding fuel cell systems to the turbine cycles. Multiple fuel cells combinations are studied: a single low temperature solid oxide fuel cell (SOFC) and a low temperature, intermediate temperature and high temperature SOFC in series. Moreover, the type of fuel cell cooling is investigated, both cooling by adding steam to the cathode and recirculating excess oxygen in the cathode are studied. The addition, of a triple SOFC cooled by oxygen recirculation, to an upgraded Graz cycle leads to a potential efficiency of 84% LHV. This efficiency is reached at a relatively low fuel cell fuel utilization of 58%. In this study the turbine cycle is not fully adapted to the fuel cell system or vice versa. Both systems are adapted to each other, leading to the unique triple fuel cell system operating in series, which is more easily coupled to a turbine cycle and can operate at an overall higher SOFC utilization, compared to a single fuel cell. However, from the fuel cell side 2 of the 3 fuel cells are less electrochemically favorable, as only one of the three fuel cells can operate in the best conditions. The overall system efficiency of the combined multiple fuel cell in series system with a turbine cycle, however is most efficient.

As a result of the Paris Agreement, energy technologies require to shift from fossil fuel based to carbon neutral. In 2015, the maritime sector was responsible for 2.6 % of the global CO2 emissions. The combination of the solid oxide fuel cell fueled by sustainable synthesized ammonia is seen as a potential solution to
reduce emissions. Ammonia is considered as a balanced solution in terms of ease of storage, volumetric energy density and cost of production. The solid oxide fuel cell is generally regarded to be a promising technology owing to its high eciency and combined heat and power usage. This MSc thesis investigates the technical viability of a sustainable SOFC propulsion system fueled by ammonia. Technical viability is expressed in equipment weight and volume, whereas sustainability is determined by efficiency and emissions. The solid oxide propulsion system is subjected to a case study: A diesel engine powered vessel from the Watertaxi Rotterdam company with an assumed shaft power of 25 kW. A model was compiled to determine the efficiency, weight and volume of the solid oxide fuel cell system. The model covers activation losses, ohmic losses and diffusion losses within the solid oxide fuel cell stack. With the model, a sensitivity study with a selected set of system parameters was performed to gain insight in the solid oxide fuel cell system. The selected system parameters are: Number of cells in the stack, single-pass fuel utilization, cathode off-gas recirculation rate and anode off-gas recirculation rate. The final solid oxide fuel cell system has a signicantly higher efficiency based on the higher heating value than the diesel engine system: 46.0 % versus 35.0 % respectively. Also, no carbon dioxide is emitted, leading to a reduction of 56.9 ton per year. Furthermore, nitrogen oxide emissions are considered to be negligible compared to the diesel engine system. However, the weight and volume of the solid oxide fuel cell system are signicantly larger: 1199 kg versus 278 kg and 1175 L versus 432 L respectively. Mainly caused by the battery module, required for compensating for temporarily imbalances between power demand and power supply. As a result, it is concluded that the solid oxide fuel cell system is unpractical for the small inland vessel selected for the case study. Larger sized vessels have more potential for the application, because large sized vessel sail more continuously, reducing the battery capacity requirement, may allow for more tolerance regarding heavy and bulky equipment and have more benefit of the higher efficiency due to a lower refuel frequency.

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.

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.

At the United Nations Climate Change Conference held in Paris in 2015, ambitious goals for the worldwide CO2 emissions were set. To achieve these goals, a huge reduction in CO2 emissions must be realized. For the energy market, the current aim is to use renewable electricity instead of fossil fuels. However, there are multiple sectors where electricity is not a suitable form of energy, due to storage issues. For example, the chemical industry is heavily based on fossil fuels as a resource to synthesize chemicals. It is therefore useful to investigate the feasibility of renewable synthetic fuels.

The goal of this thesis is to design a process that converts the hydrocarbon fuel combustion products CO2 and H2O into a fuel that is a liquid at atmospheric conditions. Methanol is selected as the liquid fuel because of its basic molecule structure. It requires much more energy to obtain methanol from CO2 and H2O than it does from natural gas. The process is determined to be container-sized to become cost competitive through mass production. The technical feasibility of a mass produced, autonomous, renewable and container-sized methanol production plant is studied in this thesis. The whole process is divided into sub processes. H2O is obtained from desalination of seawater. The H2O is split into H2 and O2 using alkaline electrolysis. The CO2 is adsorbed from the air and recovered using pressure and temperature swing. The required energy is obtained using solar PV and solar thermal. The H2 and CO2 are finally converted to methanol in the methanol synthesis sub process. The intermittent character of solar energy yields a dynamically operated process. The methanol synthesis sub process is studied further because of the small scale and dynamic operation that are new concepts for this technology. The other sub processes are considered as black boxes with fixed in- and outputs. The steady state operation of the whole process is modeled using Aspen Plus™ and the distillation process is modelled in MATLAB®. Using the results from Aspen, pinch analysis is performed for optimal use of the available heat.

From the results of the model, it is found that an autonomous container-sized methanol production plant is technically feasible. 140 kg of methanol can be produced daily with a purity of at least 96.6 %, using a set-up of three 40 feet sea containers, two of which are dedicated to the capture of CO2. 288 kW of electrical power and 24 kW of heat is required for the operation. This is equal to a solar park with an area of 1663 m2 assuming an average 6 hours of solar irradiance. Using the LHV of methanol in the calculation, the total efficiency of the process is estimated at 45 %. The results from the MATLAB® model of the distillation cannot be validated because the used equation of state of REFPROP underestimates the concentration of methanol in each iteration, yielding an invalid mass balance. Fixing this issue results in an invalid energy balance. It is therefore concluded that REFPROP is not suitable for iterative calculations of distillation columns.

Low-grade heat sources are abundant on earth but are majorly untapped due to lower thermodynamic efficiency at low temperatures and cost considerations. A cost-effective technology is needed to convert this energy resource into useful forms of energy. This work aims at optimizing Organic Rankine Cycle (ORC) based heat engine and a cogeneration system developed to produce electricity and refrigeration from a heat source below 100℃, from both thermodynamic and economic point of view. Exergoeconomics, an algebraic thermoeconomic method, was used to analyze and optimize the systems for cost-effectiveness and exergetic efficiency. Also, the prototype of the cogeneration system was experimentally tested. The results exergoeconomic optimization show that the cost-effectiveness of the cogeneration system can be significantly improved by design parameter changes. The experimental results obtained were comparable with the results obtained from theoretical simulations.