Wind-hydrogen systems for remote area power supply are an early niche application of sustainable hydrogen energy. Optimal direct coupling between a wind turbine and an electrolyser stack is essential for maximum electrical energy transfer and hydrogen production. In addition, system costs need to be minimised if wind-hydrogen systems are to become competitive. This paper investigates achieving near maximum power transfer between a fixed pitched variable-speed wind turbine and a Proton Exchange Membrane (PEM) electrolyser without the need for intervening voltage converters and maximum power point tracking electronics. The approach investigated involves direct coupling of the wind turbine with suitably configured generator coils to an optimal series-parallel configuration of PEM electrolyser cells so that the I-V characteristics of both the wind turbine and electrolyser stack are closely matched for maximum power transfer. A procedure for finding these optimal con figurations and hence maximising hydrogen production from the system is described. For the case of an Air 403 400 W wind turbine located at a typical coastal site in south-eastern Australia and directly coupled to an optimally configured 400 W stack of PEM electrolysers, it is estimated that up to 95% of the maximum achievable energy can be transferred to the electrolyser over an annual period. The results of an extended experiment to test this theoretical prediction for an actual Air 403 wind turbine are reported. The implications of optimal coupling between a PEM electrolyser and an aerogenerator for the performance and overall economics of wind-energy hydrogen systems for RAPS applications are discussed.

L’efficacité énergétique d’un électrolyseur alcalin est liée aux surtensions de réactions aux électrodes. Dans le but d’améliorer cette efficacité, nous avons développé de nouvelles électrodes composites polymère/particules maximisant la surface active des meilleurs catalyseurs, les propriétés de conductivité électrique et de transport des espèces en choisissant le polymère-liant le plus avantageux pour la cinétique réactionnelle. Les notions théoriques et l’état de l’art des principaux matériaux d’anodes et de cathodes et des différents paramètres régissant le fonctionnement d’un électrolyseur alcalin sont présentés afin de faire une synthèse des nombreux travaux réalisés. Des méthodes de fabrication d’électrodes au laboratoire ou lors d’essais préindustriels ont été explorées et comparées. Les performances électrochimiques des cathodes et anodes composites développées pour les réactions de l’évolution d’hydrogène et d’oxygène en milieu alcalin concentré sont étudiées par voltammétrie cyclique, polarisation linéaire et spectroscopie d’impédance électrochimique. Ce travail donne lieu à la description des différents paramètres clés du fonctionnement des électrodes composites polymère/particules. Différentes formulations de cathodes et d’anodes ont donc été étudiées afin d’établir des corrélations entre les propriétés physico-chimiques des polymères liants et des particules sur le comportement électrochimique des électrodes réalisées. Ces résultats sont discutés en termes de surtension de réactions, de cinétique électrochimique et de densités de sites actifs. Enfin, les résultats de la mise à l’échelle des cathodes composites et de leur procédé de fabrication pour une application industrielle sont rapportés avec l’objectif d’intégrer celles qui ont démontré des performances supérieures à celles de l’état de l’art dans un dispositif prototype industriel d’électrolyse. La démarche de la mise à l’échelle, les moyens expérimentaux développés, et une partie des résultats des essais y sont présentés. / The electrolyzer efficiency is directly related to the electrode reaction overpotentials. To improve this efficiency, new composite electrodes with selected binders and electrocatalysts showing large active area have been formulated to enhance the electrochemical kinetics. First, a state of the art of electrode materials and electrolysis parameters have been reported in a relevant literature survey about different topics developed in the thesis manuscript. Then, a few laboratory and preindustrial electrode fabrication processes were explored and compared on both technical and economical aspects. Moreover, the electrochemical performances of composite cathodes and anodes for hydrogen and oxygen evolution reactions have been studied by cyclic voltammetry, linear polarization and electrochemical impedance spectroscopy. This comprehensive study leads to a precise description of the interfacial phenomena at the microscopic scale during gas production and the evaluation of key parameters for the formulation of advanced electrodes. Many electrode formulations were studied for the correlation of physicochemical properties of components and corresponding electrochemical behaviors. These results are discussed in terms of overpotentials, electrochemical kinetics and active site density. Finally, scale-up of composite cathode is reported. The aim of this work is to integrate the best formulated composite electrodes in a real scale prototype. The scale-up process, experimental devices developed and some electrochemical results are presented.

Hydrogen energy sector has gained significant attention worldwide but one of the key enabling components for its success would be cheaper and sustainable hydrogen production. Hydrogen could be produced directly from natural gas or coal etc; alternatively it could be produced by electrolysis of water powered by renewable energy sources, nuclear energy or fossil fuel. Wind energy is growing rapidly, which can produce cheap hydrogen. Electrolysers can be employed to control the frequency of the electricity grid while also making fuel as a by-product. This thesis concerns the intricacies of hydrogen production by electrolysers from renewable energy sources. A generalised, input-based mathematical model of the electrolyser has been developed for various subsystems, such as current-voltage, Faraday efficiency, gas production, gas purity, differential pressure, temperature subsystem, parasitic losses, gas losses and efficiencies at various stages of operation. Some empirical equations have been developed and some adjusted parameters have been used in the model. The model has been tested and verified against the experimental measurements. A generic method has been developed for modelling the Faraday efficiency. Model simulations have been carried out to investigate the sensitivity of the results to the value of the capacitance and how this affects the dynamic response of the electrolyser. A new sizing method of the electrolyser has been developed for a stand-alone energy system such as the HARI project. The electrolyser model has also been simulated for maximum and efficient hydrogen production in a directly coupled mode of electrolysers with solar PV arrays without the maximum power point (MPP) tracker, which leads to an interesting finding that "electrolysers should not be operated at MPP". It has also been found that the dynamic and intermittent power supply from renewables can damage the stability of electrolysers and reduce the energy capture. This is especially true for pressurised electrolysers, which are favoured by the industry at present. The in-depth theoretical and practical analysis of several aspects confirms - contrary to industry trends - that "Pressurised electrolysers are less energy efficient, less durable, more costly and not adequately compatible for renewable energy powered operation, especially in the stand-alone energy systems, compared to atmospheric electrolysers".

This thesis explores the integration and dynamics of residential scale renewable-regenerative energy systems which employ hydrogen for energy buffering. The development of the Integrated Renewable Energy Experiment (IRENE) test-bed is presented. IRENE is a laboratory-scale distributed energy system with a modular structure which can be readily re-configured to test newly developed components for generic regenerative systems. Key aspects include renewable energy conversion, electrolysis, hydrogen and electricity storage, and fuel cells. A special design feature of this test bed is the ability to accept dynamic inputs from and provide dynamic loads to real devices as well as from simulated energy sources/sinks. The integration issues encountered while developing IRENE and innovative solutions devised to overcome these barriers are discussed. Renewable energy systems that employ a regenerative approach to enable intermittent energy sources to service time varying loads rely on the efficient transfer of energy through the storage media. Experiments were conducted to evaluate the performance of the hydrogen energy buffer under a range of dynamic operating conditions. Results indicate that the operating characteristics of the electrolyser under transient conditions limit the production of hydrogen from excess renewable input power. These characteristics must be considered when designing or modeling a renewable-regenerative system. Strategies to mitigate performance degradation due to interruptions in the renewable power supply are discussed. Experiments were conducted to determine the response of the IRENE system to operating conditions that are representative of a residential scale, solar based, renewable-regenerative system. A control algorithm, employing bus voltage constraints and device current limitations, was developed to guide system operation. Results for a two week operating period that indicate that the system response is very dynamic but repeatable are presented. The overall system energy balance reveals that the energy input from the renewable source was sufficient to meet the demand load and generate a net surplus of hydrogen. The energy loss associated with the various system components as well as a breakdown of the unused renewable energy input is presented. In general, the research indicates that the technical challenges associated with hydrogen energy buffing can be overcome, but the round trip efficiency for the current technologies is low at only 22 percent.

Sweden has goals to reach net-zero emissions by 2045. Although electricity sector is almost fossil free, industry & transport still rely on fossil fuels. Ambitious initiatives such as HYBRIT, growth of EV market & expansion of wind power aim to expedite emission reduction. Decarbonization of transport, industry and large-scale wind & solar PV integration in the future necessitates studying energy system of Sweden at national scale in the context of sector coupling, external transmission & storage technologies. Therefore, this study aims to evaluate the impact of thermal energy storage, hydrogen storage and batteries via Power-to-heat & Power-to-hydrogen strategies in the future Swedish energy system (2045) with high proportions of wind power. Two scenarios SWE_2045 & NFF_2045 were formulated to represent two distinct energy systems of the future. The SWE_2045 energy system still relies on fossil fuels, but to a lower extent compared to 2019 level and has increased levels of electrification and biofuels in the transport and industrial sectors. In comparison, the fossil fuels are completely removed in NFF_2045 and the industrial sector has significant demand for electrolytic hydrogen. Both the scenarios were simulated using EnergyPLAN, a deterministic energy system model, under each storage technology. The results indicate that HPs coupled with TES has the potential to increase wind integration from 29.12% to 31.8% in SWE_2045 and 26.78% to 29.17% in NFF_2045. HP & TES also reduces heat production from boilers by 67% to 72% depending on the scenario, leading to overall reduction in total fuel and annual costs by at least 2.5% and 0.5% respectively. However, for wind integration of 31.1% in SWE_2045 the annual cost increases by 5.1% with hydrogen storage compared to TES. However, hydrogen storage shows better performance in NFF_2045, wherein the wind integration increases from 26.78% to 29.3%. Furthermore, increasing hydrogen storage for a lower wind capacity (60 GW) in NFF_2045 reduces both electricity import and export while simultaneously increasing the contribution of storage in fulfilling the hydrogen demand from 1.62% to 6.2%. Compared to TES and HS, the contribution of battery storage is minimal in sector integration. For increase in wind integration of 28% to 29%, the annual cost of a system with battery storage is 1.3% to 2% higher than that of the system with TES and hydrogen storage respectively. Therefore, HPs coupled with TES can improve flexibility in both scenarios. Hydrogen storage is not a promising option if the end goal is only to store excess electricity, as shown by the results in SWE_2045. However, it demonstrates better utilization in terms of wind integration, reduction in electricity import and export when there is a considerable demand for hydrogen, as in the case of NFF_2045. / Sverige ligger i framkant när det gäller avkarbonisering och har mål att nå nettonollutsläpp till 2045. Även om elsektorn är nästan fossilfri, är industri och transport fortfarande beroende av fossila bränslen. Ambitiösa initiativ som Hydrogen Breakthrough Ironmaking Technology (HYBRIT), tillväxt av elbilsmarknaden och expansion av vindkraft syftar till att påskynda utsläppsminskningar. Dekarbonisering av transport, industri och storskalig vind- och solcellsintegrering i framtiden kräver att man studerar Sveriges energisystem i nationell skala i samband med sektorskoppling, extern transmissions- och lagringsteknik.  Därför syftar denna studie till att bestämma effekten av termisk energilagring, vätelagring och batterier via Power-to-heat & Power-to-hydrogen-strategier i det framtida svenska energisystemet (2045) med höga andelar vindkraft. Två scenarier SWE_2045 & NFF_2045 formulerades för att representera två distinkta framtidens energisystem. Energisystemet SWE_2045 är fortfarande beroende av fossila bränslen, men i lägre utsträckning jämfört med 2019 års nivå och har ökat nivåerna av elektrifiering och biobränslen inom transport- och industrisektorn. Som jämförelse är de fossila bränslena helt borttagna i NFF_2045-scenariot där transportsektorn endast är beroende av el och biobränslen, medan industrisektorn har en betydande efterfrågan på elektrolytiskt väte. Båda energisystemen simuleras med EnergyPLAN, en deterministisk energisystemmodell, för olika testfall under varje lagringsteknik. Resultatet av simuleringen bedömdes i termer av kritisk överskottselproduktion, potential för ytterligare vindintegration, total bränslebalans i systemet och årliga kostnader.  Resultatet indikerar att värmepumpar i kombination med termisk energilagring kan förbättra flexibiliteten i båda scenarierna genom att minska den kritiska överskottselproduktionen och bränsleförbrukningen samtidigt som vindintegrationen förbättras. Vätgaslagring är inget lovande alternativ om målet är att endast lagra överskottsel, vilket framgår av vindintegrationsnivåerna i SWE_2045. Det förbättrar dock vindintegration och tillförlitlighet avsevärt när det finns en betydande efterfrågan på vätgas i NFF_2045. Som jämförelse är batteriernas bidrag till vindintegration minimalt i båda scenarierna i samband med sektorintegration på grund av utnyttjandet av överskottsel av värmepumpar och extern överföring av restel. Valet av lagringsteknik i framtiden beror dock på dess tekniska ekonomiska utveckling och energipolitik.

This report travels through multiple disciplines to seek innovative and sustainable energy solutions for wastewater treatment plants. The first subject is a report about increased global temperatures and an over-exploitation of natural resources that threatens ecosystems worldwide. The situation is urgent where the current trend is a 2°C increase of global temperatures already in 2040. Furthermore, the energy-land nexus becomes increasingly apparent where the world is going from a dependence on easily accessible fossil resources to renewables limited by land allocation. A direction of the required transition is suggested where all actors of the society must contribute to quickly construct a new carbon-neutral resource and energy system. Wastewater treatment is as required today as it is in the future, but it may move towards a more emphasized role where resource management and energy recovery will be increasingly important. This report is a master’s thesis in energy engineering with an ambition to provide some clues, with a focus on energy, to how wastewater treatment plants can be successfully integrated within the future society. A background check is conducted in the cross section between science, society, politics and wastewater treatment. Above this, a layer of technological insights is applied, from where accessible energy pathways can be identified and evaluated. A not so distant step for wastewater treatment plants would be to absorb surplus renewable electricity and store it in chemical storage mediums, since biogas is already commonly produced and many times also refined to vehicle fuel. Such extra steps could be excellent ways of improving the integration of wastewater treatment plants into the society. New and innovative electric grid-connected energy storage technologies are required when large synchronous electric generators are being replaced by ‘smaller’ wind turbines and solar cells which are intermittent (variable) by nature. A transition of the society requires energy storages, balancing of electric grids, waste-resource utilization, energy efficiency measures etcetera… This interdisciplinary approach aims to identify relevant energy technologies for wastewater treatment plants that could represent decisive steps towards sustainability.