Hydrogen is getting great attention as a key energy carrier for a cleaner energy future, with demand projections up to 20% of global energy demand by 2050. However, the low volumetric density of hydrogen leads to a challenge for storage and transport purposes, making liquefaction a promising solution that also ensures high purity. However, at the current time, the high energy consumption of liquefaction remains a major obstacle. Within this process, the precooling stage is the second most energy-intensive step, covering the broadest temperature range but offering flexibility in terms of refrigerant choice, cycle configuration, and operating conditions.

However, most of the study of the hydrogen precooling omits economic analysis, refrigerant freeze-out discussion, and employs a portion of a non-environmentally sustainable substance as the refrigerant. This study focused on addressing the gap by conducting multi-objective optimization (MOO) on specific energy consumption (SEC) and levelized precooling cost (LPC) to find out the optimal trade-off between the technical and economic competitiveness of the precooling stage, while ensuring the freeze-out risk in the streams was avoided and using environmentally friendly mixed refrigerant (MR) mixtures.

Two cycles, namely single mixed refrigerant (SMR) and dual mixed refrigerant (DMR), are modeled in Aspen HYSYS V12, where the configurations are defined based on freeze-out consideration. Nine MR mixtures for SMR and DMR are defined based on their thermophysical properties. A Non-dominated Sorting Genetic Algorithm-II (NSGA-II) algorithm was used for MOO through the pymoo library package in Python, which was then coupled with Aspen HYSYS. The decision variables to be optimized include MR composition, MR flow rate, compressor discharge pressure, and JT valve outlet pressure. Several constraints are also introduced, such as vapor fraction at the inlet compressor, minimum internal temperature difference (MITD) of heat exchangers, JT valve temperature difference, and several temperature constraints to ensure thermodynamic behavior is not violated.

In this study, Mixture 8 (for SMR) and Mixture 6 (for DMR) appear to be the top-performing mixtures, achieving specific energy consumptions (SEC) of 1.25 kWh/kg_H2 and 1.13 kWh/kg_H2, respectively, with levelized precooling costs (LPC) of €0.47/kg_H2 and €0.60/kg_H2. The study indicates that aligning the boiling points of mixed refrigerant components to enhance temperature glide, combined with tuning of operating conditions, is the key to achieving both energy efficiency and cost competitiveness. Furthermore, the optimized results in DMR also suggest that the intermediate-compression stage in the MR2 cycle could be removed.

From the sensitivity analysis, it was observed that as the precooling temperature target increased, the gap in SEC between the SMR and DMR configurations narrowed. Starting from 95 K, both systems reached similar SEC values, highlighting equal technical performance. However, the LPC further SMR dominant over the DMR. This indicates that beyond this temperature target, DMR was no longer economically competitive. Additionally, variations in pressure drop across heat exchangers and coolers had a stronger impact on the SMR configuration. The percentage increase in SEC and LPC was more severe due to the accumulation of pressure losses within a single-loop cycle. In contrast, the DMR system distributes losses across two separate loops, making it less sensitive to pressure drop effects.

This thesis explores the integration of solid sorbent direct air capture (DAC) with two types of concentrated solar power, to create a renewable and scalable approach for carbon dioxide removal. Parabolic trough collector (PTC) and solar power tower (SPT) systems are modelled dynamically on an hourly basis, combined with the energy requirement and performance of the DAC model. Because system output is highly sensitive to climatic conditions, two high-irradiance locations in Almeria, Spain and Alice Springs, Australia are evaluated using typical meteorological year data.

The results show that SPT outperforms PTC in achieving the lowest levelised cost of CO2 removal (LCOD), primarily due to its lower thermal energy storage costs. The configuration optimised for LCOD involves significant oversizing of the solar field and storage, far larger than the configuration optimized for cost of heat. This increases the capacity, and utilises the CAPEX-intensive DAC installation to a greater extent. These DAC costs are the main cost driver accounting for 68% of the cost for a conservative scenario. A sensitivity analysis reveals that lowering the DAC costs is found not to change the optimal configuration significantly, allowing the LCOD of a lower CAPEX scenario to be determined accurately from the results.

The weather conditions in Alice Springs result in a reduction of the LCOD by up to 27% compared to Almeria, due to higher and more constant solar availability combined with lower humidities. While PTC systems have higher LCOD, they require significantly less land. Overall, the combination of CSP and DAC is technically viable and it offers a scalable, land efficient alternative to nature based carbon dioxide removal methods.

The viability of hydrogen as a sustainable energy carrier is significantly affected by the costs linked to its transportation and storage. Transporting and storing hydrogen in its liquid form offers remarkable advantages, as liquid hydrogen has unique characteristics, including lower weight and volume, as well as a higher energy content compared to gaseous hydrogen. However, current industrial hydrogen liquefaction processes face significant challenges related to efficiency and cost, with a second-law efficiency of less than 25% and costs ranging from 2.5-3.0 US$/kgLH2.

Large energy storage systems can address the issue of energy demand fluctuations in renewable energy grids by storing excess energy produced and compensating for any energy shortfalls. The development of hydrogen energy storage systems will thus support the advancement and increased utilization of renewable energy sources. The demand for liquid hydrogen is expected to rise in the near future, driven by environmentally friendly applications and use in mobility sector. As a result, large-scale hydrogen liquefaction (LHL) plants will become increasingly important in the clean energy efficient hydrogen supply chain.

This thesis aims to develop a Large-scale Hydrogen Liquefaction (LHL) plant based on the Brayton cycle concept of 86 TPD. The plant is modeled using Aspen HYSYS, with preliminary designs for key equipment—such as compressors, turbines, and plate-fin heat exchangers, ensuring compatibility with current technological constraints. State properties of the fluid used in the design of compressors and turbine equipment were obtained from REFPROP software, utilizing the Peng-Robinson Equation of State (EOS). For the design of plate-fin heat exchangers, Aspen Exchanger Design and Rating (EDR) was employed. Subsequently, a techno-economic analysis was conducted using the Aspen Process Economic Analyzer (APEA) to estimate both capital and operating expenditures, based on the process simulation model and preliminary equipment designs.

The specific energy consumption (SEC) of the plant, accounting for power recovery from turbine shafts, is determined to be 6.9025 kWh/kgLH2. The plant’s exergy efficiency is calculated at 43.665%, and the specific liquefaction power is found to be 3.014 kWh/kgLH2. Assuming an electricity price of 0.1 €/kWh, modelled 86 TPD Brayton-cycle concept yielded specific liquefaction cost (SLC) of 1.57 €/kgLH2.

A sensitivity analysis was conducted to identify the parameters that influence the specific liquefaction cost (SLC) of the plant. The analysis focused on two key parameters: 1) electricity price and 2) feed pressure. The results reveal that fluctuations in electricity prices have a substantial impact on the plant’s economic performance. Additionally, the analysis indicates that the plant’s efficiency and economic viability are significantly sensitive to decreases in feed hydrogen pressure.

Interest in incorporating renewable energy systems into current infrastructure has surged as a result of the growing need for sustainable energy solutions in urban settings. This thesis investigates the optimization of a heating and cooling system designed for residential and commercial buildings, with a focus on Dutch climate conditions. The system consists of photovoltaic thermal (PVT) collectors, aquifer thermal energy storage (ATES), heat exchanger and heat pumps. By using these technologies, buildings will be able to satisfy energy demand sustainably without the need for fossil fuels.

Through dynamic simulations, the research aims to optimize the energy system's performance while taking into account a range of operational scenarios and parameter values. Critical components, including the ATES and PVT collectors, are modeled to evaluate their working and performance with heat pumps to provide heating and with heat exchanger for cooling.

The Photovoltaic Materials and Devices research group at TU Delft uses the PVMD Toolbox, a sophisticated modeling tool. Few models from the toolbox are utilised in developing an integrated model, which is later implemented in the toolbox. Later on, it is optimized to improve its effectiveness through dynamic sizing of collectors and aquifers, and implementation of operational modes, making overall the integrated system more robust and redundant. The performance of the integrated system is then studied for a base scenario with 10 PVT collectors and 27,000 m^3 aquifer volume for the current scenario. It showcases promising results. To assess its applicability, the system is analysed under various scenarios. The first scenario is a season-wise performance assessment, where it is showcased that PVT produce energy during summer months and the rest of the year there is a consistent performance by ATES. On comparing the performance of different insulation levels of the buildings, it is found that the future scenarios require half or one-fourth of the energy as compared to the current scenario and the system performs better for them in terms of power consumption by heat pumps. The system's performance under different flow rates of water from PVT and ST is assessed. It is found that at a higher flow rate, a higher amount of energy is generated by both of the collectors, while ST shows better performance than PVT.

For the case when the system provides underfloor heating, it shows that the heat pumps require almost 25% of the energy required for radiator heating. The integrated system is then compared to that of conventional energy systems, demonstrating similar costs but almost no environmental impact and better energy efficiency.

The research findings present a compelling argument for the implementation of such energy systems in urban environments, as they indicate the possibility of substantial energy savings and a decrease in carbon emissions. The report also offers suggestions for future work, such as the application of advanced software, location feasibility studies, and various ATES to precisely model and scale such systems in various real-world circumstances.

This thesis contributes significant insights into the subject of renewable energy systems and lays the groundwork for further study and development of sustainable heat networks by offering a thorough analysis of an innovative method of sustainable energy management.

With the adoption of the Paris Agreement, 196 countries worldwide committed to the limitation of the global temperature rise. In order to achieve this goal more energy needs to be produced in a sustainable way. However, the industrial sector is still mainly fossil driven and therefore has to adapt to be able to utilize sustainable produced power, which most often is in the form of electricity. More than a quarter of the total heating demand is in the 100 ◦C to 200 ◦C range. In this temperature range heat pumps are a strong alternative to fossil fuels. Heat pumps can absorb energy from a low temperature heat source and deliver it at a higher, usable temperature. Various technologies for waste heat recovery were investigated in this thesis. It was identified that existing heat pump technologies are suitable to upgrade waste heat, but are limited to lower temperatures of around 120 ◦C. This limitation is mostly due to the high compressor discharge temperatures, which degrade the lubrication oil. Compression resorption heat pumps utilizing wet compression (CRHP’s) limit the superheating during compression and are able to operate oil free, because the working fluid acts as a lubricant. This increases the achievable compressor discharge temperature. The wet compression however is not yet a mature technique and an isentropic efficiency of 70% is required to be competitive with existing technologies. Absorption cycles show promising results for upgrading waste heat due to their non-isothermal heat source and sink, which can be matched to the waste heat temperature. At the Process and Energy lab experiments have been performed on a wet compressor using an ammonia water mixture. This thesis proposes a new method of analysing existing experimental data through a cycle energy balance model. In order to create a model of the experimental setup, four limitations of the setup were identified. First the influence of the gap seal flow, which is the flow from the high pressure to the lower pressure side of the compressor. Second, the mixture inside the compressor can not be assumed homogeneous, which means that both phases are not in equilibrium. Third, there is cooling oil flowing through the compressor housing which cools the process side, this results in a non-adiabatic compression. Finally the pressure drop on the high pressure side is not measured, resulting in an error when calculating the composition of the working fluid. In order to model these limitations a model of the experimental setup was created in Aspen Plus. This model was supplemented with Matlab code to account for the non-equilibrium compression as well as the pressure drop and gap seal flow. Empirical relations were used to determine the heat and mass transfer between the phases during compression. The isentropic efficiency of the modelled compressor was varied until the output matches the input indicating that the steady state solution has been found. The influence of the non-adiabatic compression and the gap seal flow seem to have a significant impact on compressor performance. It was found that the compressor has the highest volumetric and isentropic efficiency when the inlet vapor quality is around 0.85 and the performance decreases with higher vapor qualities. Isentropic efficiencies of up to 0.88 were calculated. The results were compared against previous analysis of the same experimental data which used different assumptions and did not consider the whole cycle. Finally, a case study was performed to analyse the applicability of heat pump technology to upgrade waste heat in a paper recycling plant. A conventional vapor compression heat pump (VCHP) and an electric boiler were compared to a CRHP. To deal with the uncertainty of wet compression performance a range of isentropic efficiencies were considered as well as different ammonia concentrations. The CRHP proved to be energetically and economically viable and outperformed both the VCHP and electric boiler in this case study.

Photovoltaic-Thermal (PVT) modules, alongside Solar Thermal (ST) and Photovoltaic (PV) technologies, offer solutions to energy demands such as electrical consumption, space heating, and domestic hot water of residential buildings. This research employs a model-based approach to analyze how building insulation, solar collector configurations, and seasonal heating modes impact system design. Enhanced insulation scenarios demonstrate potential space heating demand reductions up to 70\%, highlighting the relevance of proper insulation selection.
The findings identify that using a PVT/PV configuration with one module per string is optimal, reducing roof area usage while achieving balanced thermal and electrical energy exchange. The analysis further reveals that higher indoor temperature settings substantially increase heating demands, suggesting significant energy savings potential through temperature set point adjustments. Operational heat supply strategies are adapted to seasonal variations, optimizing the use of solar energy and effectively incorporating aquifer thermal energy storage (ATES) systems as seasonal storage for winter months. But notably, the integration of PVT modules with heat pumps emerged as the primary driver of heat supply, contributing approximately 67\% of the total heat demand.

Electrification and decarbonization of industrial process heat is an important next step in the energy transition to reduce greenhouse gas (GHG) emissions. This study provides an in-depth analysis of how in the current industrial landscape the combination of commercially available electric heating technologies with the implementation of thermal energy storage (TES) can realize the electrification of
medium-temperature industrial process heat on the short-term. Moreover, it explores what potential novel high-temperature heat pump (HTHP) technologies, specifically the supercritical CO2 (sCO2) reversed Brayton HTHP, have to realize this electrification even more efficient in terms of electricity demand in the future. Thereby, it also briefly highlights the opportunities and challenges to combine HTHP technology and TES in the future to realize an optimal electrification.

In order to reduce greenhouse gas (GHG) emissions, fleets of medium- and heavy-duty vehicles are transitioning from conventional fossil fuels to fully electric drivetrains. To utilize these medium- and heavy-duty electric vehicles (MHDEVs) without significantly disrupting their operations, Megawatt Charging Systems (MCS) are being developed, which enable charging rates up to 4.5 MW. However, these charging rates are associated with substantial heat generation in the vehicle’s battery pack. To regulate the battery temperature and maximize battery lifetime, performance, and safety, the development of a battery thermal management system (BTMS) for this application is crucial.

The study provides a methodology that adopted a system engineering approach for the design of a BTMS for the application of MHDEVs which utilize MCS. The study defined the requirements for the BTMS which include the optimal temperature range for battery cells and determined the battery heat generation rate when using MCS. Furthermore, the study investigated the magnitude of temperature gradients in battery cells as a result of MCS.
Subsequently, two assessment stages have been proposed to assess BTMS strategies, which include forced air BTMS, immersion cooling BTMS, cooling plates with coolant BTMS, and cooling plates with refrigerant BTMS. This assessment resulted in design requirements for heat transfer areas and mass flow rates to maintain the battery cells below 35 ℃. Moreover, the concepts of utilizing cooling plates with refrigerant in a vapor-compression refrigeration system and storing charging session heat by thermal energy storage (TES) have been developed. This included the dimensioning of a condenser and compressor for the vapor-compression refrigeration cycle and included the dimensioning of the required mass and volume of TES medium for the TES system. The study found that these two BTMS strategies are the most favorable. Thermal energy storage with hydrated salt as phase change material (PCM) appeared as the most effective and feasible option subsequent to conducting comparisons with immersion coolant and paraffin PCM. However, a BTMS with a vapor compression refrigeration system might be needed when the BTMS is used for both driving and charging. Analysis of refrigerants R717, R134a, and R1234yf, indicated that R717 is the most effective in this BTMS with a COP of 3.52 and a lower required mass flow rate and compressor power consumption, however, is associated with several safety considerations that must be addressed when selecting R717 over other refrigerants. Lastly, the study utilized a MATLAB Simulink model to identify the effects of dynamic phenomena that occur during operation of the BTMS and the study determined the impact of BTMS weight on MHDEV driving range.

Recommendations for future research are given related to the need for increased fidelity of heat generation prediction and BTMS models. Furthermore, future research should be conducted on combining the BTMS with other thermal management systems in the vehicle to maximize overall effectiveness.