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Item type:Publication, Mathematical modelling of coupled and decoupled water electrolysis systems based on existing theoretical and experimental studies(Elsevier Ltd, 2022-05-08)Since it has the potential to significantly reduce gaseous emissions in the near future, electrolytic hydrogen production using electricity generated from renewable energy sources, such as solar radiation, is key. Water splitting processes occurring in electrolyzer cells are complex phenomena. Therefore, to fully realize such processes, different technologies have been accounted for. The focus of this work is on the mathematical modeling of three different electrolyzer cells related technologies, (i) alkaline, (ii) proton exchange membrane (PEM), and (iii) decoupled water splitting. Accordingly, several existing mathematical models for alkaline and PEM electrolyzers are initially revised. Next, a comprehensive mathematical model capable of properly predicting the performance of the three electrolyzer technologies accounted for here is proposed. The developed mathematical models are then used to predict the behavior of electrolyzer cells under different operation conditions. The obtained results are finally compared in terms of cell voltages, cell efficiencies, and hydrogen production rates. When compared to other results available in the literature, the cell voltage ones obtained using the new proposed model are in relatively good agreement. Specifically, for a current density range of 0–200 mA/cm2, cell pressures between 10 and 40 bar, and a cell temperature of 60 °C, cell voltage requirements are between 1.25 and 1.75 V, with the E-TAC technology performing better than the other two ones accounted for. In addition, for current densities of more than 100 mA/cm2 and cell pressures below 5 bar, Faraday's efficiencies are almost the same for all three technologies, i.e., about 95%. However, for higher cell pressures, significant differences in Faraday's efficiency appear. Based on the work carried out, it is concluded that developing a sound mathematical model is crucial both for the comprehension of coupled and decoupled water electrolysis-related processes and for their use in the simplest and most reliable way. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Genetic algorithms-based size optimization of directly and indirectly coupled photovoltaic-electrolyzer systems(Elsevier Ltd, 2022-10-15)Since relatively high costs and low efficiencies are usually associated with photovoltaic-electrolyzer (PV-EL) systems, the coupling of a PV system to an EL one is a critical aspect when sizing PV-EL systems. Accordingly, using a genetic algorithms-based optimization approach and considering a hydrogen production target of 100 g per day, the size of different directly and indirectly coupled PV-EL systems is optimized in this work. The referred optimization processes are carried out for five PV-EL system configurations, one related to directly coupled systems and four (one per each DC/DC converter topology accounted for) to indirectly coupled ones. In addition, seeking to maximize hydrogen production, minimize losses, and increase system efficiency, four objective functions are assessed. Some of the results highlight that, when using system cost and overall efficiency as objective functions, properly sized indirectly coupled PV-EL systems feature lower implementation costs than directly coupled ones. In addition, the differences in the overall efficiencies characterizing the optimum directly and indirectly coupled PV-EL systems so determined are relatively small (>1%). One of the original contributions of this work relates to the fact that this is one of the first works dealing with optimization processes of both directly and indirectly coupled PV-EL systems, where optimum system configurations are compared with each other. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, On the application of sliding mode control to indirectly coupled photovoltaic-electrolyzer systems used in the production of clean energy(Elsevier B.V., 2024-08-01)To improve the performance of photovoltaic-electrolyzer (PV-EL) systems, it is key to operate them at the right operating conditions, not only at design point but also at off-design. In addition, when directly coupling a PV system to an EL one, an ideal sizing of the resulting PV-EL coupled system ensuring the best interaction between the PV system and the EL stack is not always possible. Coupling indirectly PV systems to EL ones, through DC/DC converters for instance, results thus advantageous. Accordingly, this work discusses the application of sliding mode control (SMC) to indirectly coupled PV-EL systems, which allows them to operate as efficient as possible. The control scheme employed here includes mathematical models for both the PV system and the EL stack, and for the DC/DC converter and the sliding mode control algorithm utilized. To determine their influence on the obtained results, two different converter topologies are assessed here. Some of the results obtained emphasize that using a DC/DC converter can significantly increase the hydrogen produced by PV-EL systems, especially when it is paired with a control algorithm like SMC. This effort represents one of the first works involving the application of sliding mode control to indirectly coupled PV-EL systems. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Effective Thermal-Electric Control System for Hydrogen Production Based on Renewable Solar Energy(Elsevier BV, 2023-12-14)This paper focuses on the design and use of a control system for a renewable energy production plant based on hydrogen. The proposed control system aims at ensuring the stability and smooth functionality of the plant, which consists of a (i) photovoltaic...