Renewable energy resources like wind and solar have the potential to revolutionize our energy infrastructure and enable a decarbonized society. The intermittent nature of renewables poses a challenge to ensuring a consistent and reliable electricity supply. Hydrogen technology is emerging as a promising solution for stabilizing renewable energy systems. There is still significant technological development required to cost-effectively integrate hydrogen with renewable energy assets. Conventional PV solar installations require power electronics for their operation, like charge controllers and inverters. Not only are these power electronic components costly and in high demand, but they also degrade faster than PV solar panels. Removing power electronic components could significantly lower the investment costs associated with a PV solar park.

This work focuses on how PV solar panels can be directly coupled to a modular alkaline electrolyzer, without grid-based buffering or the use of an inverter. Literature research revealed that hydrogen technology has seen little exploration in on-grid Hybrid Renewable Energy Systems (HRES) and no exploration in off-grid HRES. To appropriately investigate whether a directly-coupled HRES would be technically feasible, a megawatt-scale system was modelled and simulated. All elements of the HRES were modelled, duly accounting for physical limits and constraints. Components were sized and configured to complement one another, optimizing for maximum hydrogen production. To experimentally verify the validity of the proposed HRES, a 5 kW pilot system was constructed. To control the HRES, a new algorithm was developed using the Incremental Conductance maximum power point tracking algorithm as a basis. Within the new Maximum Hydrogen Production (MHP) algorithm, the step sizing was discretized and a variable step size was implemented which can be applied to any target slope. This allows for the system to target operational points which optimize hydrogen yield instead of electricity yield. Furthermore, the addition of tracking bias helped adjust for the asymmetric nature of the interaction between electrolyzer stacks and the PV solar park.

Simulation results in The Netherlands demonstrated that the feasibility of the HRES is dependent on the configuration of the PV solar park and on the number of electrolyzer stacks in the system. Compared to industrial and research benchmarks, the proposed HRES increased hydrogen production by 14.9% and 4.2%, respectively. Dynamic 'm-tracking' of the MHP algorithm goal increased hydrogen production by 0.8% in months of high irradiance. Months with a lower average irradiance experienced an artefact in the MHP algorithm, resulting in prolonged periods of zero power output. An experimental setup confirmed the simulation results, showing that it is possible to control a system of PV solar panels directly coupled to a modular alkaline electrolyzer. Experimental results revealed the need for moving average filtering to prevent fluctuations due to changing conditions of the electrolyzer and the weather from causing poor algorithm tracking ability. The low performance of the experimental setup can be attributed to a low iteration and measuring frequency, which increase the likelihood of a tracking error due to rapidly changing operating conditions. Economic analysis of the proposed HRES yielded an LCOH of €3.44 per kg, 20% and 13% lower than industrial and research benchmarks, respectively. Therefore, an HRES featuring PV solar and modular alkaline electrolysis is technologically and economically viable without the use of charge controllers and inverters.

Emissions of greenhouse gases (GHG) are the main cause of climate change, with as effect a rise in global temperature. The culprit in these emissions is carbon dioxide (CO2). Carbon capture and utilization (CCU)Emissions of greenhouse gases (GHG) are the main cause of climate change, with as effect a rise in global temperature. The culprit in these emissions is carbon dioxide (CO2). Carbon capture and utilization (CCU) can mitigate a part of these emissions, by converting carbon species to useful products. The typical route for CCU involves: carbon capture, compression, transportation and utilization. This thesis takes on a slightly different approach. Instead of utilization at a centralized location, the utilization of carbon species will be realized on location. This is beneficial, since no transportation of CO2 is required. Three different high partial pressure carbon sources will be addressed: tail-gas (TG) from steam methane reforming, blast furnace gas (BFG) from the steel industry and biogas from the bacterial degeneration of biomass. Each of these gas streams are composed of up to 50-60 mol % CO2 and or CO. By capturing the carbon species in these gases or removing some of the inert components, different ratios of CO2, CO, H2 and inerts can be obtained. Electrolysis technologies will be used to upgrade the captured gases, with the addition of hydrogen or by adjusting the CO/CO2 ratio. The electrolysis technologies considered are PEM and SOEC. The advantage of electrolysis is the potential for integration with renewable energy sources such as, wind, solar and hydro power. Depending on the electrolysis technology and carbon source, syngas with CO/CO2 ratios varying between 0-4 can be obtained. Five different cases were defined with CO/CO2 ratios equal to 0, 0.25, 1, 3 and 4. The upgraded syngas can then be used in the conversion towards several liquid fuels, such as methanol and Fischer-Tropsch (FT) liquids. Both methanol and FT liquids require a stoichiometric ratio of at least 2. For these two product routes a techno-economic analysis was performed. As a first production route, methanol synthesis was discussed. The feasibility for each of the five cases was assessed, by comparing the cost price of the methanol with the respective market price. A reference methanol plant from literature was implemented in Aspen Plus to obtain the energy and mass balances for each case. The mass balances showed the amounts of hydrogen and carbon species required to produce one ton of methanol. The total cost price of the methanol consists of the operational expenses (OPEX) and capital expenses (CAPEX). The OPEX reflects the costs required to run the process. This includes the prices for the feedstock and labour costs for example. The CAPEX consists of the capital investments. Based on the CO/CO2, Case 3 with CO/CO2 = 4, should be the cheapest case as less hydrogen has to be added to produce one ton of methanol. However, Case 4 with a CO/CO2 = 0.25 is the cheapest option. Case 4 originated from the TG stream, which already had a high fraction of H2 present in the TG. Therefore, Case 4 requires less addition of hydrogen. Capture costs were also lower in Case 4, compared to the other cases. At a market price for methanol of €400 per ton, a maximum electricity price of €30 per MWh was allowable. FT liquids were overall found to be an unfeasible product, when considering renewable production of hydrogen and CO from CO2 electrolysis. In FT liquids, waxes (C20+) are a requirement in the product fraction as these can be sold at the highest price. When considering the production of gasoline and diesel, the renewable FT route proved to be unfeasible. In general it was found that for each case, irrespective of product, more than 50 % of the product cost price, was included in the costs for electrolysis. And as the electrolysis technologies require electricity to operate, it can be concluded that electricity is the determining factor.
can mitigate a part of these emissions, by converting carbon species to useful products. The typical route for
CCU involves: carbon capture, compression, transportation and utilization.
This thesis takes on a slightly different approach. Instead of utilization at a centralized location, the utilization of carbon species will be realized on location. This is beneficial, since no transportation of CO2 is
required. Three different high partial pressure carbon sources will be addressed: tail-gas (TG) from steam
methane reforming, blast furnace gas (BFG) from the steel industry and biogas from the bacterial degeneration of biomass. Each of these gas streams are composed of up to 50-60 mol % CO2 and or CO. By capturing
the carbon species in these gases or removing some of the inert components, different ratios of CO2, CO, H2
and inerts can be obtained. Electrolysis technologies will be used to upgrade the captured gases, with the
addition of hydrogen or by adjusting the CO/CO2 ratio. The electrolysis technologies considered are PEM
and SOEC. The advantage of electrolysis is the potential for integration with renewable energy sources such
as, wind, solar and hydro power. Depending on the electrolysis technology and carbon source, syngas with
CO/CO2 ratios varying between 0-4 can be obtained. Five different cases were defined with CO/CO2 ratios
equal to 0, 0.25, 1, 3 and 4. The upgraded syngas can then be used in the conversion towards several liquid
fuels, such as methanol and Fischer-Tropsch (FT) liquids. Both methanol and FT liquids require a stoichiometric ratio of at least 2. For these two product routes a techno-economic analysis was performed.
As a first production route, methanol synthesis was discussed. The feasibility for each of the five cases was
assessed, by comparing the cost price of the methanol with the respective market price. A reference methanol
plant from literature was implemented in Aspen Plus to obtain the energy and mass balances for each case.
The mass balances showed the amounts of hydrogen and carbon species required to produce one ton of
methanol. The total cost price of the methanol consists of the operational expenses (OPEX) and capital expenses (CAPEX). The OPEX reflects the costs required to run the process. This includes the prices for the feedstock and labour costs for example. The CAPEX consists of the capital investments. Based on the CO/CO2,
Case 3 with CO/CO2 = 4, should be the cheapest case as less hydrogen has to be added to produce one ton
of methanol. However, Case 4 with a CO/CO2 = 0.25 is the cheapest option. Case 4 originated from the TG
stream, which already had a high fraction of H2 present in the TG. Therefore, Case 4 requires less addition
of hydrogen. Capture costs were also lower in Case 4, compared to the other cases. At a market price for
methanol of €400 per ton, a maximum electricity price of €30 per MWh was allowable.
FT liquids were overall found to be an unfeasible product, when considering renewable production of hydrogen and CO from CO2 electrolysis. In FT liquids, waxes (C20+) are a requirement in the product fraction as
these can be sold at the highest price. When considering the production of gasoline and diesel, the renewable
FT route proved to be unfeasible. In general it was found that for each case, irrespective of product, more than
50 % of the product cost price, was included in the costs for electrolysis. And as the electrolysis technologies
require electricity to operate, it can be concluded that electricity is the determining factor.

Renewable energy projects, such as wind and solar (PV) parks, are rapidly being built to replace fossil fuel based energy sources. The major drawback of electricity production from renewable sources is that they are intermittent and therefore lead to amismatch between the supply and the demand of energy. Energy storage in the form of hydrogen production is a potential candidate to overcome this problem. However, due to its lowvolumetric energy density, hydrogen must be compressed to use it for storage or transportation purposes. HYET BV has developed an Electrochemical Hydrogen Compressor (EHC) that is capable of compressing hydrogen up to P = 1000 bar, and have the potential of bringing compression costs down to 3 kWh/kg. As the compressed hydrogen is saturated with water, it must be dehydrated before it is used for refuelling Fuel Cell Electric Vehicles (FCEV), as the ISO 14687-2:2012 standard has limited the water concentration to 5 ¹mol water per mol gas mixture. In this work, a landscaping studywas performed to search for potential drying methods, includingmembrane separation, adsorption, absorption and cooling. To select the best method for hydrogen dehydration, it is essential to have a good understanding of the thermodynamics at the given pressure conditions, beginningwith the saturated water content in compressed hydrogen. To the best of our knowledge, the only experimental data describing the water content in the H2-H2O mixture for pressures exceeding 300 bar are from 1927 and are limited to T = 323.15K [J. Am. Chem. Soc., 1927, 49, pp 65-78]. In this thesis, it was concluded that conventional Equations of State (EoS) failed to predict the equilibrium coexistence compositions of the liquid and gas phase. Therefore, molecular simulations were used, which adequately predicted the water content in compressed hydrogen. The second part of this thesis was to select the best drying method for hydrogen dehydration. Previous work showed that absorption using Ionic Liquids (IL) could be an interesting alternative to traditional dryingmethods. Therefore, absorption experiments were performed on the ILs 1-Ethyl-3-methylimidazolium acetate [EMIM][Acetate], 1-Butyl-3-methylimidazoliumchloride [BMIM][Chloride], and 1-Butyl-3-methylimidazolium octyl sulfate [BMIM][Octyl Sulfate] to test the feasibility of ILs for hydrogen dehydration. The ILs were selected on stability, safety, and on the activity coefficient of water in the given IL. The experiments showed that ILs can be used as an absorbent to dry hydrogen gas. A part from the initial selection criteria, the experiments showed that surface tension is an important criterion for future IL selection, as it is strongly related to foam production. Finally, the very hygroscopic ILs tested turned out to be capable of absorbing large amounts of water, but a lot of energy was required to regenerate the ILs, making them less attractive as a potential absorbent.