Dissertations / Theses on the topic 'Hydrogen Power'

In this thesis, solar-hydrogen Stand-Alone Power System (SAPS) which is planned to be built for the emergency room of a hospital is designed. The system provides continuous, off-grid electricity during the whole period of a year without any external electrical power supply. The system consists of Photovoltaic (PV) panels, Proton Exchange Membrane (PEM) based electrolyzers, PEM based fuel cells, hydrogen tanks, batteries, a control mechanism and auxiliary equipments such as DC/AC converters, water pump, pipes and hydrogen dryers. The aim of this work is to investigate the optimal system configuration and component sizing which yield to high performance and low cost for different user needs and control strategies. TRNSYS commercial software is used for the overall system design and simulations. Numerical models of the PV panels, the control mechanism and the PEM electrolyzers are developed by using theoretical and experimental data and the models are integrated into TRNSYS. Overall system models include user-defined components as well as the default software components. The electricity need of the emergency room without any shortage is supplied directly from the PV panels or by the help of the batteries and the fuel cells when the solar energy is not enough. The pressure level in the hydrogen tanks and the overall system efficiency are selected as the key design parameters. The major component parameters and various control strategies affecting the hydrogen tank pressure and the system efficiency are analyzed and the results are presented.

Heavy-duty trucks are in idle operation during long periods of time, providing the vehicles with electricity via the alternator at standstill. Idling trucks contribute to large amounts of emissions and high fuel consumption as a result of the low efficiency from fuel to electricity. Auxiliary power units, which operate independently of the main engine, are promising alternatives for supplying trucks with electricity. Fuel cell-based auxiliary power units could offer high efficiencies and low noise. The hydrogen required for the fuel cell could be generated in an onboard fuel reformer using the existing truck fuel. The work presented in this thesis concerns hydrogen generation from transportation fuels by autothermal reforming focusing on the application of fuel cell auxiliary power units. Diesel and dimethyl ether have been the fuels of main focus. The work includes reactor design aspects, preparation and testing of reforming catalysts including characterization studies and evaluation of operating conditions. The thesis is a summary of five scientific papers. Major issues for succeeding with diesel reforming are fuel injection, reactant mixing and achieving fuel cell quality reformate. The results obtained in this work contribute to the continued research and development of diesel reforming catalysts and processes. A diesel reformer, designed to generate hydrogen to feed a 5 kWe polymer electrolyte fuel cell has been evaluated for autothermal reforming of commercial diesel fuel. The operational results show the feasibility of the design to generate hydrogen-rich gases from complex diesel fuel mixtures and have, together with CFD calculations, been supportive in the development of a new improved reformer design. In addition to diesel, the reforming reactor design was shown to run satisfactorily with other hydrocarbon mixtures, such as gasoline and E85. Rh-based catalysts were used in the studies and exhibit high performance during diesel reforming without coke formation on the catalyst surface. An interesting finding is that the addition of Mn to Rh catalysts appears to improve activity during diesel reforming. Therefore, Mn could be considered to be used to decrease the noble metal loading, and thereby the cost, of diesel reforming catalysts. Dimethyl ether is a potential diesel fuel alternative and has lately been considered as hydrogen carrier for fuel cells in truck auxiliary power units. The studies related to dimethyl ether have been focused on the evaluation of Pd-based catalysts and the influence of operating parameters for autothermal reforming. PdZn-based catalysts were found to be very promising for DME reforming, generating product gases with high selectivity to hydrogen and carbon dioxide. The high product selectivity is correlated to PdZn interactions, leading to decreased activity of decomposition reactions. Auxiliary power systems fueled with DME could, therefore, make possible fuel processors with very low complexity compared to diesel-fueled systems. The work presented in this thesis has enhanced our understanding of diesel and DME reforming and will serve as basis for future studies.
QC 20100804

The work includes an exergy analysis of the steam reforming process for conversion of natural gas to hydrogen rich gas for use in hydrogen-fired gas power plant. Based on the analysis two sustainability indicators were calculated, the exergetic efficiency and the renewability fraction. The same analysis has been performed for a system using auto thermal reformer (Zvolinschi, Kjelstrup, Bolland and van der Kooi 2002) instead of steam reformer, and the results were compared in order to find the better system of the two based on the indicators. The system using an auto thermal reformer had the best exergetic efficiency, and the renewability fraction was 0 for both systems. One should be aware of insecurities in the results, mainly related to assumptions and limitations with respect to the simulation process.

The two indicators were proposed by Zvolinschi et. al, as a contribution to the introduction of exergy analysis as a tool for industrial ecology. It was concluded that this will be a useful contribution, especially when using system boundaries that include the closure of material cycles. Then one can also calculate the third indicator proposed by Zvolinschi et al., namely the environmental efficiency.

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.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.
Includes bibliographical references (p. 91-92).
Power supply systems for cell phone base stations using hydrogen energy storage, fuel cells or hydrogen-burning generators, and a backup generator could offer an improvement over current power supply systems. Two categories of hydrogen-based power systems were analyzed: Wind-hydrogen systems and peak-shaving hydrogen systems. Modeling of base station requirements and alternative power supply system performance was carried out using MATLAB. Final results for potential alternative systems were compared to those for the current power systems. In the case of the wind- hydrogen systems, results were also compared to those of a wind-battery system. Overall feasibility was judged primarily on the net present cost of the power supply systems. Other considerations included conformity to present regulations. Sensitivity analysis of the wind-hydrogen model was carried out to identify the controlling variables. Numerous parameters were varied over realistic ranges. Important parameters were found to include wind resource, electrolyzer size, distance from electricity grid, price of diesel fuel, and electrolyzer and fuel cell cost. The model verified cell phone industry figures regarding the geographical conditions favorable to diesel genset use. Final results for wind-hydrogen systems suggest that for today's electrolyzer and fuel cell costs, wind-battery-diesel systems are the most suitable power system more than 8km from the existing electricity grid, with an annual average wind speed of 7m/s or more, and where diesel costs more than $2.20/gallon.
(cont.) Thinking to the future, with 20% reduced electrolyzer and fuel cell costs, a wind-fuel cell-diesel system with a 15kW electrolyzer is the most suitable system at locations greater than 8km from the existing electricity grid with an annual average wind speed of 7rn/s or more and total diesel costs greater than $2/gallon. Within 8km the grid, in all cases, grid connection is most suitable. Outside this range, with diesel prices below $2/gallon, a genset only system is most suitable in most cases. Analysis of the peak-shaving hydrogen system suggests that it is not suitable for deployment under any realistic circumstances. Replenishment of hydrogen stores has a substantial power requirement.
by Rory F.D. Monaghan.
S.M.

L’hydrogène propre est une solution d’avenir pour le stockage d’électricité renouvelable. Cependant, une cellule multi-sources pour la production d’hydrogène présente de multiples phénomènes physiques, par exemple électriques, électro-chimiques, thermiques, fluidiques, etc. et la représentation des flux d’énergie y est très complexe. De plus, les échanges de puissance entre les composants de la cellule (sources renouvelables, pile à combustible, électrolyseurs, batteries) doivent être évalués de manière globale tout en préservant les réserves de puissance de chaque composant.Cette thèse propose une représentation d’état port-Hamiltonienne, dérivée d’un bond-graph, de chacun des composants d’une cellule de puissance pour la production d’hydrogène. A partir de cette représentation et des propriétés de passivité, il est possible de concevoir des algorithmes de commande. La notion de marge de passivité est introduite pour évaluer la robustesse par rapport aux incertitudes paramétriques ou aux perturbations connues. Pour chaque composant, la variation de puissance alimente un réservoir virtuel d’énergie. L’ensemble des réservoirs constitue ainsi une image des réserves de puissance du système. Au lieu d’utiliser un échange direct de puissance entre les composants et le réseau, nous proposons de gérer les flux de puissance entre les réservoirs, ce qui permet également de contrôler leurs niveaux d’énergie. La méthodologie permet de superviser en même temps la puissance et l’énergie, ce qui conduira à terme à gérer les modes opératoires de la cellule à partir des niveaux d’énergie. La méthodologie est appliquée à une plate-forme comportant des sources renouvelables, une pile à combustible et une batterie conventionnelle
Green hydrogen is emerging as a powerful solution for the storage of surplus electricity which is generated through renewable energy sources. However, a green hydrogen power cell involves multiphysics phenomena as electrical, fluidic, thermal, etc. and the representation of dynamical power flows therein is quite complex. Furthermore, the power exchange between the different components of the cell (Fuel cell, Electrolyzer, storage units, renewable sources) needs to be thought in terms of global performance while taking care of the energy reserves.This thesis proposes a Bond Graph derived port-Hamiltonian representation of all the components of a green hydrogen power cell. From this representation, it is possible to design passivity-based control algorithms. The notion of passivity margin is introduced to account for the robustness with respect to modeling uncertainties or known disturbances. For each component, the excess or shortage of power feeds an Energy Tank, which behaves as a virtual storage unit. Hence, the set of Energy Tanks is an image of the power reserves in the power cell. Instead of using conventional power routing between each component, we propose to manage power flows between the Energy Tanks, which allows us to control not only the power intensity, but also the level of energy within the tanks. Hence, the methodology enables to control both power and energy at the same time, paving the way to Operating Mode Management triggered by energy levels. An application is given on a platform including a fuel call, renewable energy sources, and a conventional storage unit

With an ever-increasing need to find alternative fuels to curb the use of oil in the world, many sources have been identified as alternative fuels. One of these sources is hydrogen. Hydrogen can be produced through an electro-chemical process. The objective of this report is to model an electrochemical process and determine gains and or losses in efficiency of the process by increasing or decreasing the temperature of the feed water. In order to make the process environmentally conscience, electricity from a geothermal plant will be used to power the electrolyzer. Using the renewable energy makes the process of producing hydrogen carbon free. Water considerations and a model of a geothermal plant were incorporated to achieve the objectives. The data show that there are optimal operating characteristics for electrolyzers. There is a 17% increase in efficiency by increasing the temperature from 20ºC to 80ºC. The greater the temperature the higher the efficiencies, but there are trade-offs with the required currents.

Modern society increasingly depends on reliable and secure energy supplies for economic growth and social prosperity. Thus, it is crucial to implement a low-carbon energy carrier based on renewable energy sources to ensure energy security and tackle climate change. Hydrogen (H2) is undoubtedly one of the most promising energy carriers to achieve a low-carbon energy future scenario. However, before the hydrogen economy can become completely viable, the safe and compact storage of H2 is an issue that must be overcome. This thesis concentrates on the development of potential “modular” solid state H2 storage solutions for portable power applications. A wide range of potential H2 storage materials was investigated with the aim of providing an improved performance in the form of a low desorption onset temperature, fast desorption kinetics and a high H2 gravimetric capacity. This research work focused on the study of light metal hydride – hydroxide systems, in particular the nanostructured MgH2-Mg(OH)2 system, and ammonia borane (AB) composites, specifically AB within a porous carbon-based matrix composites. The nanostructured MgH2-Mg(OH)2 “modular” H2 release system was investigated as a candidate exothermic filler material combined with an industrial MgH2 matrix to produce a novel solid state H2 storage hybrid tank. It was postulated that the heat of the reaction of the exothermic filler material could initiate and propagate a reaction in the matrix hydride and additionally contribute to the H2 yield. Detailed information about the thermodynamic and kinetic behaviour of the MgH2-Mg(OH)2 system, under operational conditions, was obtained. The thermal decomposition of this system was found to be a two-step process, associated with two H2 releases, resulting from: 1) almost simultaneous decomposition of Mg(OH)2 and hydrolysis of MgH2 at 616 K (exothermic event) and 2) decomposition of unreacted MgH2 at 743 K (endothermic event). The formation of a MgO layer on the unreacted MgH2 resulting from the previous hydrolysis was found to retard the H2 release. The formation of MgH2-MgO core-shell structures was investigated and confirmed by kinetic measurements, ex-situ Scanning Electron Microscopy / Energy Dispersive X-ray Spectroscopy (SEM/EDX) analysis and ex-situ Powder X-ray Diffraction (PXD) experiments. Kinetics measurements performed under operational conditions proved the H2 release of the system to be very slow (≈ 20 hours at 573 K). The mechanism for H2 evolution of this system was elucidated by in-situ Powder Neutron Diffraction (PND) performed at the Institut Laue-Langevin (ILL) in Grenoble, confirming the observations by thermal analysis methods and ex-situ PXD experiments. The use of additives (graphite and silicon carbide) was investigated to enhance the kinetic and thermodynamic properties in the system. The incorporation of SiC proved to be successful in improving the H2 release of the first step. However, no further kinetic improvements were observed by incorporating additives. Besides, the H2 capacity was slightly reduced by the introduction of 10 wt. % of C/SiC and traces of water were released alongside H2. AB-based nanocomposites and nanoconfined samples were also investigated with the aim of synthesising novel solid-state H2 storage materials with enhanced desorption properties. Highly ordered mesoporous carbons (FDU-25, CGY-1), activated carbons (AX21, Sigma AC, MAST Carbon TE7), and graphene (Angstron, Alfa), were employed to prepare nanocomposites (via ball milling or solution impregnation) in different ratios. A double-solution impregnated composite with a 2:3 weight ratio of AB to activated carbon (AC) showed the best performance with a dehydrogenation onset of 353 K and the suppression of borazine and boron-based by-products. The use of an external NiCl2 filter absorbed any released gaseous ammonia and no by-products were detected with a mass spectrometer sensitivity of 100 ppb. The nanoconfinement of AB in AC hosts was investigated by simultaneous Small Angle X-ray Scattering (SAXS) and Wide Angle X-ray Scattering (WAXS) at the Elettra synchrotron in Trieste. The results confirm that the nanoconfinement of ammonia borane was successfully induced and central to the performance improvements of the H2 storage material. To underpin the validity of the results and allow a quantitative comparison of the performance of these new developed materials with previously assessed systems, the reproducibility and repeatability of the measurements was ensured by means of intra and inter-laboratory comparisons. This was accomplished by using the facilities at the European Commission Joint Research Centre (JRC), Energy Storage Unit in Petten (The Netherlands) and the laboratories of the School of Chemistry in University of Glasgow (UK).

Dans le contexte de la transition énergétique, les grandes technologies de stockage d’énergie à grande échelle sont considérées comme l’une des options qui peut faciliter une pénétration élevée des sources d’énergie renouvelables. La thèse est concentrée sur l’évaluation de la mise en œuvre le Power-to-Gas sur le marché énergétique roumain, qui a enregistré une croissance significative des énergies renouvelables et les enjeux auxquels devra faire face. Après avoir établi l’approche générale, les deux voies techniques du Power-to-Gas, l’Hydrogène et SNG, sont techniquement dimensionnés et économiquement évalués du point de vue des investisseurs dans deux scénarios temporels (2015 et 2030), afin d’évaluer la situation économique actuelle et les prix appliqués pour atteindre une rentabilité positive. Les résultats indiquent que des facteurs de grande capacité sont nécessaires afin de compenser les coûts d’investissement élevés, mais même dans cette situation un prix élevé est nécessaire pour la faisabilité économique, 68,1 Euro / MWh pour la voie Hydrogène et 112 Euro/MWh pour Power-to Gas SNG. Le marché d’équilibrage est également étudié comme un marché à haute valeur ajoutée dans le contexte français, avec des résultats indiquant une amélioration de 4% de la NPV, mais soulignant également les limites dans le cadre de l’analyse. Un avantage significatif, en termes d’impact GWP et utilisation de l’énergie fossile, a été identifié dans l’évaluation du cycle de vie de base de plusieurs scénarios d’alimentation au gaz, qui a également révélé l’importance de la source d’électricité utilisée pour la compression d’hydrogène
In the energy transition context, large scale energy storage technologies are considered as one of the options that can facilitate a high penetration of renewable energy sources. The Thesis focuses on evaluating the implementation of Power-to-Gas in the Romanian energy market that recorded a significant growth in the share of renewables and will potentially face the related issues. After establishing a general approach, the two technical pathways of Power-to-Gas, Hydrogen and SNG, are technically sized and economically evaluated from an investor’s point of view in two temporal scenarios (2015 and 2030), in order to assess the current economic feasibility and the required price premiums that have to be put in place in order to reach a positive business case. Results indicate that high capacity factors are needed to compensate for the high capital costs, but even in this situation price premiums are required for economic feasibility, 68.1 Euro/MWh for the Hydrogen pathway and 112 Euro/MWh for Power-to-Gas SNG. The balancing market is also investigated as a high-value market in the French context, with results indicating a 4% improvement in NPV, but also highlighting the limitations of the proposed analysis framework. A significant benefit in terms of GWP impact and fossil energy use has been identified in. the basic life cycle assessment of multiple Power-to-Gas scenarios that also revealed the importance of the source of electricity used for hydrogen compression

Contestualmente al processo di decarbonizzazione del settore energetico mondiale, risulta necessario individuare soluzioni alternative in grado di consentire l’abbattimento delle emissioni climalteranti. L’idrogeno può assumere un ruolo chiave nel raggiungimento di questi obiettivi: grazie al Power to Hydrogen è infatti possibile intraprendere la conversione dei settori “hard to abate” e stoccare ingenti quantità di energia, cooperando inoltre alla stabilizzazione della rete elettrica. Con il presente elaborato si intende approfondire la tematica idrogeno, tramite l’analisi di potenzialità, limiti ed applicazioni presenti e future. A seguito della descrizione dei principali metodi di produzione, vengono considerate le tecnologie di generazione a basso impatto ambientale e, in particolare, l’elettrolisi dell’acqua. In accordo con i progetti di “Hydrogen Valley” e con il recente PNRR pubblicato dal Governo Italiano, particolare interesse è stato rivolto al territorio dell’Emilia Romagna, con l’obiettivo di individuare informazioni relative a realtà industriali coinvolte nella produzione e/o nell’utilizzo di idrogeno, con valutazioni attinenti a volumi interessati e potenzialità future. La trattazione dei risultati ottenuti confluisce nella descrizione tecnica delle attività riscontrate di maggiore interesse, ed assume espressione conclusiva nell’elaborazione di un caso di studio specifico, rispetto al quale è condotta un’analisi tecnico-economica volta a valutare la sostituzione di “idrogeno grigio” con un impianto di autoproduzione di “idrogeno verde”, basato sullo sfruttamento di risorse rinnovabili. La competitività economica di una soluzione di tale natura consentirebbe la realizzazione di una delle prime realtà nazionali adibite alla produzione industriale di idrogeno a basso impatto ambientale e dunque consentirebbe l’implementazione di sinergie e connessioni tra le attività, presenti e future, coinvolte nella catena del valore dell’idrogeno.

The topic of this thesis is the study of energy storage systems operating with wind power plants. The motivation for applying energy storage in this context is that wind power generation is intermittent and generally difficult to predict, and that good wind energy resources are often found in areas with limited grid capacity. Moreover, energy storage in the form of hydrogen makes it possible to provide clean fuel for transportation. The aim of this work has been to evaluate how local energy storage systems should be designed and operated in order to increase the penetration and value of wind power in the power system. Optimization models and sequential and probabilistic simulation models have been developed for this purpose.

Chapter 3 presents a sequential simulation model of a general windhydrogen energy system. Electrolytic hydrogen is used either as a fuel for transportation or for power generation in a stationary fuel cell. The model is useful for evaluating how hydrogen storage can increase the penetration of wind power in areas with limited or no transmission capacity to the main grid. The simulation model is combined with a cost model in order to study how component sizing and choice of operation strategy influence the performance and economics of the wind-hydrogen system. If the stored hydrogen is not used as a separate product, but merely as electrical energy storage, it should be evaluated against other and more energy efficient storage options such as pumped hydro and redox flow cells. A probabilistic model of a grid-connected wind power plant with a general energy storage unit is presented in chapter 4. The energy storage unit is applied for smoothing wind power fluctuations by providing a firm power output to the grid over a specific period. The method described in the chapter is based on the statistical properties of the wind speed and a general representation of the wind energy conversion system and the energy storage unit. This method allows us to compare different storage solutions.

In chapter 5, energy storage is evaluated as an alternative for increasing the value of wind power in a market-based power system. A method for optimal short-term scheduling of wind power with energy storage has been developed. The basic model employs a dynamic programming algorithm for the scheduling problem. Moreover, different variants of the scheduling problem based on linear programming are presented. During on-line operation, the energy storage is operated to minimize the deviation between the generation schedule and the actual power output of the wind-storage system. It is shown how stochastic dynamic programming can be applied for the on-line operation problem by explicitly taking into account wind forecast uncertainty. The model presented in chapter 6 extends and improves the linear programming model described in chapter 5. An operation strategy based on model predictive control is developed for effective management of uncertainties. The method is applied in a simulation model of a wind-hydrogen system that supplies the local demand for electricity and hydrogen. Utilization of fuel cell heat and electrolytic oxygen as by-products is also considered. Computer simulations show that the developed operation method is beneficial for grid-connected as well as for isolated systems. For isolated systems, the method makes it possible to minimize the usage of backup power and to ensure a secure supply of hydrogen fuel. For grid-connected wind-hydrogen systems, the method could be applied for maximizing the profit from operating in an electricity market.

Comprehensive simulation studies of different example systems have been carried out to obtain knowledge about the benefits and limitations of using energy storage in conjunction with wind power. In order to exploit the opportunities for energy storage in electricity markets, it is crucial that the electrical efficiency of the storage is as high as possible. Energy storage combined with wind power prediction tools makes it possible to take advantage of varying electricity prices as well as reduce imbalance costs. Simulation results show that the imbalance costs of wind power and the electricity price variations must be relatively high to justify the installation of a costly energy storage system. Energy storage is beneficial for wind power integration in power systems with high-cost regulating units, as well as in areas with weak grid connection.

Hydrogen can become an economically viable energy carrier and storage medium for wind energy if hydrogen is introduced into the transportation sector. It is emphasized that seasonal wind speed variations lead to high storage costs if compressed hydrogen tanks are used for long-term storage. Simulation results indicate that reductions in hydrogen storage costs are more important than obtaining low-cost and high-efficient fuel cells and electrolyzers. Furthermore, it will be important to make use of the flexibility that the hydrogen alternative offers regarding sizing, operation and possibly the utilization of oxygen and heat as by-products.

The main scientific contributions from this thesis are the development of

- a simulation model for estimating the cost and energy efficiency of wind-hydrogen systems,

- a probabilistic model for predicting the performance of a gridconnected wind power plant with energy storage,

- optimization models for increasing the value of wind power in electricity markets by the use of hydrogen storage and other energy storage solutions and the system knowledge about wind energy and energy storage that has been obtained by the use of these models.

Paper 1 is reprinted with kind permission of ACTA Press. Paper 2 is reprinted with kind permission of Elsevier/ Science Direct. http://www.elsevier.com, http://www.sciencedirect.com Paper 3 is reprinted with kind permission of IEEE.

The energy transition taking place in various parts of the world will have many effects on the current energy systems as an increasing amount of intermittent power supply gets installed every year. In Sweden, just as many other countries, this will cause both challenges and opportunities for today´s energy producers. Challenges that may arise along with an increasingly fluctuating electricity production include both power deficits at certain times and regions but also hours of over-production which can cause electricity prices to drop significantly. Such challenges will have to be met by both dispatchable power generation and dynamic consumption. Conversely, actors prepared to adapt to the new climate by implementing new technologies or innovative business models could benefit from the transition towards a fully renewable energy system.  This thesis evaluates the techno-economic potential of green hydrogen production at a combined heat and power plant with the objective to provide decision support to a district heat and electricity producer in Sweden. It was in the company’s interest to investigate how hydrogen production could help reduce the production cost of district heat as well as contribute to the reduction of greenhouse gases.  In the project, two separate business models: Power-to-gas and Power-to-power were evaluated on the basis of technical and economic performance and environmental impact. To do this, a mathematical model of the CHP plant and the hydrogen systems was developed in Python which optimizes the operation based on costs. The business models were then simulated for two different years with each year representing a distinctly different electricity market situation.  The main conclusions of the study show that Power-to-gas could already be profitable at a hydrogen retail price of 40 SEK per kg, which is the projected retail price for the transportation sector. The demand today is however limited but is expected to grow fast in the near future, especially within heavy transportation. Another limiting factor for hydrogen production showed to be the availability of storage space, as hydrogen gas even at pressures up to 200 bar require large volumes.  Power-to-power for frequency regulation was found to not be economically justifiable as the revenue for providing grid services could not outweigh the high investment costs for any of the simulated years. This resulted in a high levelized cost of energy at over 3000 SEK per MWh which was mostly due to the low capacity factor of the power-to-power system.  Finally, green hydrogen has the potential of replacing fossil fuels in sectors that is difficult to reach with electricity, for example long-haul road transport or the shipping industry. Therefore, green hydrogen production in large scale could help decarbonize many of society’s fossil-heavy segments. By also serving as a grid-balancer, hydrogen production in a power-to-gas process has the potential of becoming an important part of a renewable energy system.
Energiomställningen som äger rum i olika delar av världen kommer att ha många effekter på de nuvarande energisystemen eftersom en ökande mängd väderberoende kraftproduktion installeras varje år. I Sverige, precis som många andra länder, kommer detta att medföra både utmaningar och möjligheter för dagens energiproducenter. Utmaningar som kan uppstå tillsammans med en alltmer fluktuerande elproduktion inkluderar både kraftunderskott vid vissa tider och regioner men också timmar av överproduktion som kan få elpriserna att sjunka avsevärt. Sådana utmaningar måste mötas av både planerbar kraftproduktion och dynamisk konsumtion. Omvänt kan aktörer som är beredda att anpassa sig till det nya klimatet genom att implementera ny teknik eller innovativa affärsmodeller dra nytta av övergången till ett helt förnybart energisystem.  Denna rapport utvärderar den tekno-ekonomiska potentialen för produktion av grön vätgas vid ett kraftvärmeverk med målet att ge beslutsstöd till en fjärrvärme- och elproducent i Sverige. Det var i företagets intresse att undersöka hur vätgasproduktion kan bidra till att sänka produktionskostnaden för fjärrvärme samt bidra till att minska växthusgaser.  I projektet utvärderades två separata affärsmodeller: Power-to-gas och Power-to-power baserat på teknisk och ekonomisk prestanda samt miljöpåverkan. För att kunna göra detta utvecklades en matematisk modell i Python av kraftvärmeverket och vätgassystemen som optimerar driften baserat på kostnader. Affärsmodellerna simulerades sedan för två olika års elpriser för att undersöka modellens prestanda i olika typer av elmarknader.  De viktigaste slutsatserna i studien visar att Power-to-gas redan kan vara lönsamt till ett vätgaspris på 40 SEK per kg, vilket är det förväntade marknadspriset på grön vätgas for transportsektorn. Efterfrågan är idag begränsad men förväntas växa snabbt inom en snar framtid, särskilt inom tung transport. En annan begränsande faktor för vätgasproduktion visade sig vara tillgången på lagringsutrymme, eftersom vätgas även vid tryck upp till 200 bar kräver stora volymer.  Power-to-power för frekvensreglering visade sig inte vara ekonomiskt försvarbart, eftersom intäkterna för att tillhandahålla nättjänster inte kunde uppväga de höga investeringskostnaderna under några av de simulerade åren. Detta resulterade i en hög LCOE på över 3000 SEK per MWh, vilket främst berodde på Power-to-power-systemets låga utnyttjandegrad.  Slutligen kan det sägas att grön vätgas har stor potential att ersätta fossila bränslen i sektorer som är svåra att elektrifiera, exempelvis tunga vägtransporter eller sjöfart. Därför kan storskalig grön vätgasproduktion hjälpa till att dekarbonisera många av samhällets fossiltunga segment. Genom att dessutom fungera som balansering har väteproduktion i en Power-to-gas-process potential att bli en viktig del av ett system med stor andel förnybar energi.

Thesis (Ph. D.)--Missouri University of Science and Technology, 2009.
Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed December 15, 2009) Includes bibliographical references (p. 72-80).

en Español:
Se propone un modelo de FC basado en ecuaciones electroquímicas para predicción del exceso de oxígeno y de la temperatura de la pila, permitiendo además una conexión circuital con la carga. Así mismo, se presenta una técnica de modelado basada en Fuzzy, orientada a la emulación, obteniendo gran precisión con carga computacional reducida. Usando este último modelo se diseña e implementa un emulador. Estos modelos y el sistema de emulación fueron validados usando un sistema experimental.
Adicionalmente, diferentes topologías de sistemas de potencia basados en FC se proponen y analizan, obteniendo un criterio de selección dependiendo de la aplicación. Así mismo, se presentan criterios de control para una operación segura y eficiente del sistema. Finalmente, se proponen una metodología para la caracterización de los puntos óptimos de operación, y una estructura de control para operar en esas condiciones óptimas, siendo validados en un sistema experimental representativo del estado del arte.
in English:
A new FC modeling approach based on electrochemical equations for thermal and oxygen excess ration prediction with a circuit-based load connection is introduced. A fuzzy-based modeling technique is also proposed for emulation purposes, it reproducing the fuel cell dynamics with a high accuracy and a short computational time. The implementation of a fuel cell emulation system, based on this model, is described and analyzed. The models and the emulation system are experimentally validated by using a benchmark fuel cell system.
Different topologies for fuel cell-auxiliary storage devices interaction are also proposed and analyzed, thus giving an architecture selection criterion based on the load profile. Controllers, dynamic constrains and control objectives are designed for a safe and efficient fuel cell operation. Finally, a methodology for the identification of the fuel cell optimal operation conditions has been proposed, and a control strategy for operating in that optimal profile is introduced and validated.

Remote area power supply (RAPS) is a potential early market for renewable energy - hydrogen systems because of the relatively high costs of conventional energy sources in remote regions. Solar-hydrogen RAPS systems commonly employ photovoltaic panels, a Proton Exchange Membrane (PEM) electrolyser, a storage for hydrogen gas, and a PEM fuel cell. Unitised Regenerative Fuel Cells (URFCs) use the same hardware for both electrolyser and fuel cell functions. Since both of these functions are not required simultaneously in a solar hydrogen RAPS system, URFCs based on PEM technology provide a promising opportunity for reducing the cost of the hydrogen subsystem used in renewable-energy hydrogen systems for RAPS. URFCs also have potential applications in the areas of aerospace, submarines, energy storage for central grids, and hydrogen cars. In this thesis, a general theoretical relationship between cell potential and current density of a single-cell PEM URFC operating in both fuel-cell (FC) and electrolyser (E) modes is developed using modified Butler-Volmer equations for both oxygen- and hydrogen-electrodes, and accounting for mass transport losses and saturation behaviour in both modes, membrane resistance to proton current, and membrane and electrode resistances to electron current. This theoretical relationship is used to construct a computer model based on Excel and Visual Basic to generate voltage-current (V-I) polarisation curves in both E and FC modes for URFCs with a range of membrane electrode assembly characteristics. The model is used to investigate the influence on polarisation curves of varying key parameters such charge transfer coefficients, exchange current densities, saturation currents, and membrane conductivity. A method for using the model to obtain best-fit values for electrode characteristics corresponding to an experime ntally-measured polarisation curve of a URFC is presented. The experimental component of the thesis has involved the design and construction of single PEM URFCs with an active area of 5 cm2 with a number of different catalyst types and loadings. V-I curves for all these cells have been measured and the performance of the cells compared. The computer model has then been used to obtain best-fit values for the electrode characteristics for the URFCs with single catalyst materials active in each mode on each electrode for the corresponding experimentally-measured V-I curves. Generally values have been found for exchange current densities, charge transfer coefficients, and saturation current densities that give a close fit between the empirical and theoretically-generated curves. The values found conform well to expectations based on the catalyst loadings, in partial confirmation of the validity of the modelling approach. The model thus promises to be a useful tool in identifying electrodes with materials and structures, together with optimal catalyst types and loadings that will improve URFC performance. Finally the role URFCs can play in developing cost-competitive solar- hydrogen RAPS systems is discussed, and some future directions for future URFC research and development are identified.

The world faces a major problem. Fossil fuel sources are finite and the economic and environmental cost of those that actually remain make finding an alternative one of the great technological challenges of our age. Nearly 70% of refined oil is used for transportation making it one of the key sectors where change could yield large-scale global benefits. Combustion engine passenger vehicle technology is after a long period of stagnation progressing at a pace. Hybrid electric vehicles (HEVs) and battery electric vehicles (BEVs) are also starting to penetrate the mass market. Unfortunately, HEVs do not remove our dependency on oil and the prospects of battery technology advancing sufficiently to allow BEVs to progressively replace the entire oil fuelled vehicles are currently slim. Their limited range and long recharge times prohibit them being useful for most modes of driving. One solution to the problem may be hydrogen fuel cell electric vehicles (H2FCEVs) as they offer great promise, but realistically face many challenges. The fuel cell allowed man to voyage to the moon in the 1960s and recent material advances have enabled them to be packaged into motor vehicles, so providing a zero emission replacement for the internal combustion engine. However, substantial infrastructure and geopolitical changes are required to make hydrogen production and delivery economic but this gas potentially offers a clean and sustainable energy pathway to entirely replace fossil fuels in motor vehicles. Few reported studies have comprehensively examined the optimal method of building power drive train subsystems and integrating them into an architecture that delivers energy from a fuel cell into driven road wheels. This project investigated the optimisation on the most efficient drive train topology using critical analysis and computer modeling to determine a practical system. No single drivetrain was found suitable for all driving modes and worldwide markets as the current ones typically offered either optimal performance or optimal efficiency. Consequently, a new drivetrain topology was proposed, developed, tested with a simulation environment that yielded efficiency and performance gains over existing systems. Also analysed was the effect of wider vehicle design optimisation to the development of sustainable hydrogen powered passenger vehicles and this was set against the wider social, scientific and engineering challenges that fuel cell adoption will face.

The member states of European Union aim to promote the reduction of harmful emissions. Emissions from combustion processes cause effects on human health and pose environmental issues, for example by increasing greenhouse effect. There are two ways to reduce emissions; one is to promote renewable energy sources and the other to utilize more effectively the available fossil fuels until a long-term solution is available. Hence, it is necessary to strive for CO2 mitigation technologies applied to fossil fuels. Low natural gas prices together with high energy efficiency have made gas turbines popular in the energy market. But, gas turbine fired with natural gas come along with emissions of CO2, NOx and CO. However, these disadvantages can be eliminated by using gas turbine with precombustion CO2 capture, separating carbon from the fuel by using fuel reforming process and feeding pure hydrogen as a fuel. Hydrogen fired gas turbines are used in two applications such as a gas turbine with pre-combustion CO2 capture and for renewable power plants where hydrogen is stored in case as a backup plan. Although the CO2 emissions are reduced in a hydrogen fired gas turbine with a pre-combustion CO2 capture, there are still several challenges such as high flame temperatures resulting in production of thermal NOx. This project suggests a method for application of hydrogen fired gas turbine, using exhaust gas recirculation to reduce flame temperature and thus reducing thermal NOx. A NOx emission model for a hydrogen-fired gas turbine was built from literature data and used to select the best operating conditions for the plant. In addition, the economic benefits of switching from natural gas to pure hydrogen are reported. For the techno-economic analysis, investment costs and operating costs were taken from the literature, and an economic model was developed. To provide sensitivity analysis for the techno-economic calculation, three cases were studied. Literature review was carried out on several journal articles and websites to gain understanding on hydrogen and natural gas fired gas turbines. Results showed that, in the current state, pure hydrogen has high delivery cost both in the US and Europe. While it’s easy to access natural gas at low cost, therefore in the current state gas turbine fired with natural gas are more profitable than hydrogen fired gas turbine. But, if targeted hydrogen prices are reached while fuel reforming process technology are developed in the coming future the hydrogen fired gas turbine will compete seriously with natural gas.

Fossil fuel will eventually become exhausted. Also, fossil fuels produce large amounts of carbon dioxide, which cannot only bring environment pollution, but can also cause global warming. Therefore, clean and renewable energy sources should be investigated. In this project, renewable wind power was considered. Wind energy is free, clean and available in large quantities, although it is difficult to use due to its stochastic variability. Energy storage can reduce this variability allowing energy production to match energy demand. In this study, different kinds of energy storage approaches were introduced, compared, and simulated by using half hourly wind data from the Met Office, UK, and half hourly load data from the University of Bath, UK. Hydrogen has higher mass energy density than all other energy storage methods. It is seen as a versatile energy carrier of the future, complementary to electricity and with the potential to replace fossil fuels due to its zero carbon emissions and abundance in nature. On the other hand, because hydrogen is the lightest element under normal conditions; the same amount of hydrogen must occupy a huge volume compared to other elements. The mature technology for converting hydrogen into electricity has high cost and low efficiency. These are big issues that limit the usage of hydrogen energy storage methods. Using wind and load data, a new algorithm was developed and used for sizing the wind turbine, and energy storage requirements. The traditional way to supply energy is distributing electricity, but in this PhD research, there are some discussions about a new method, hydrogen transport-hydrogen pipeline. From the results of the comparison and algorithm, a practical hydrogen energy storage system for the University of Bath network was proposed and designed. In the proposed design the energy from a wind turbine was directed to the load and the remaining excess power was used to produce hydrogen by water electrolysis. The hydrogen was stored in a high pressure compressed tank, and finally a hydrogen fuelled combined cycle gas turbine was used to convert the hydrogen to electricity. In this thesis, the dynamics of the complete hydrogen cycle energy storage and recovery mechanism are discussed, identifying potential applications such as power smoothing, peak lopping and extending power system controller ranges. The results of calculations of the payback time and revenue verify the feasibility of the designed hydrogen energy storage system. The main objective of the PhD was to design a practical hydrogen energy storage system for micro-grid applications. During this research, hydrogen energy storage was investigated to show that it does solve the problems arising from renewable energy.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 87-90).
This thesis studies a hybrid PEM fuel cell system for use in low power, long life sensor networks. PEM fuel cells offer high efficiency and environmental friendliness but have not been widely adopted due to cost, reliability, and the problem of hydrogen storage. This thesis focuses on the problem of hydrogen storage. Lithium hydride is selected for study because of its high hydrogen content and because it produces hydrogen through a chemical reaction with water. Control of the lithium hydride hydrolysis reaction is investigated. Active and passively-controlled hydrogen generators that rely on lithium hydride are designed and experimentally studied. A model is created to explain the system's pressure response. The passive hydrogen generator is experimentally tested in a 2 month benchtop fuel cell experiment. The results of the study suggest that it is possible to design a simple, passive generator that controls the hydrogen pressure at an operating point. However, over longer time periods of 1-3 months, the rate of reaction slows significantly and byproduct formation prevents full utilization of the lithium hydride. These limits complicate the design of a power supply relying on lithium hydride.
by Daniel DeWitt Strawser.
S.M.

Hydrogen is a potential future energy storage medium to supplement a variety of renewable energy sources. It can be regarded as an environmentally-friendly fuel, especially when it is extracted from water using electricity obtained from solar panels or wind turbines. The focus in this thesis is on solar energy, and the theoretical background (i.e., PSCAD computer simulation) and experimental work related to a water-splitting, hydrogen-production system are presented. The hydrogen production system was powered by a photovoltaic (PV) array using a proton exchange membrane (PEM) electrolyser. The PV array and PEM electrolyser display an inherently non-linear current-voltage relationship that requires optimal matching of maximum operating power. Optimal matching between the PV system and the electrolyser is essential to maximise the transfer of electrical energy and the rate of hydrogen production. A DC/DC converter is used for power matching by shifting the PEM electrolyser I-V curve as closely as possible toward the maximum power the PV can deliver. By taking advantage of the I-V characteristics of the electrolyser (i.e., the DC/DC converter output voltage is essentially constant whereas the current increases dramatically), we demonstrated experimentally and in simulations that the hydrogen production of the PV-electrolyser system can be optimised by adjusting the duty cycle generated by the pulse-width modulation (PWM) circuit. The strategy used was to fix the duty cycle at the ratio of the PV maximum power voltage to the electrolyser operating voltage. A stand-alone PV energy system, using hydrogen as the storage medium, was designed. The system would be suitable for providing power for a family's house located in a remote area in the Libyan Sahara.

This master thesis investigated how a hydrogen energy storage could be used anddimensioned to reduce the problem of power shortage in the local distributiongrid in Uppsala, Sweden. By implementing such a storage system in mobilityhouses, which are parking garages with integrated charging stations for electric vehicles and smart renewable energy solutions for power generation, the problem with power shortage could be decreased. The results showed that by integrating a hydrogen storage together with battery packs, it was possible to reduce power peaks in mobility houses. Further, it was clear that more power peaks facilitated the dimensioning of these type of systems. It was also shown that due to today's initial cost of hydrogen storages, the total savings related to a limited purchase of electricity from the grid were insignificant. It was therefore found that this type of hydrogen storage would not reduce costs in the short term for the mobility houses considered in this study. However, implementing a smaller kW storage could generate and improve knowledge in the hydrogen/hybrid field, which could facilitate the implementation of larger systems in the future. Furthermore, the results showed that it could be interesting to implement hydrogen storages on a bigger scale for municipalities or actors, who would want to reduce the power shortage in the local distribution grid.

This thesis encompasses CO2 mitigation using three different processes: i) natural gas-fired combined cycle with chemical looping combustion (CLC), ii) trigeneration of electrical power, hydrogen and district heating with extended CLC, iii) steam-based gasification of biomass integrated in an advanced power cycle. In CLC, a solid oxygen carrier circulates between two fluidised-bed reactors and transports oxygen from the combustion air to the fuel; thus, the fuel is not mixed with air and an inherent CO2 separation occurs. In this thesis, CLC has been studied as an alternative process for CO2 capture in a natural gas-fired combined cycle (NGCC). The potential efficiency of such a process using a turbine inlet temperature of 1200 °C and a pressure ratio of 13 is between 52 and 53 % when including the penalty for CO2 compression to 110 bar. It is shown that this efficiency cannot be further improved by including an additional CO2 turbine. Two conceivable reactor designs for CLC in an NGCC are presented. Top-firing has been studied as an option to overcome a temperature limitation in the CLC reactor system. The degree of CO2 capture is shown versus the temperature in the CLC reactor and its combustion efficiency. CLC has the potential to reach both a higher efficiency and a higher degree of CO2 capture than conventional post combustion CO2 capture technique. However, further research is needed to solve technical problems as, for example, temperature limitations in the reactor to reach this potential. Extended CLC (exCLC) is introduced, in which hydrogen is not only produced but also inherently purified. The potential efficiency of a novel tri-generation process for hydrogen, electricity and district heating using exCLC for CO2 capture is investigated. The results show that a thermal efficiency of about 54% might be achieved. A novel power process named evaporative biomass air turbine (EvGT-BAT) for biomass feedstock is presented. This process contains a steam-based gasification of biomass, which is integrated in an externally fired gas turbine cycle with top-firing. In the EvGT-BAT process, the steam-based gasification is conducted in an entrained-flow tubular reactor that is installed in the SFC as a heat exchanger. The EvGT-BAT process has the potential to generate electrical power from biomass with an efficiency of 41 %.

The use of hydrogen is predicted to increase substantially in the future, both as chemical feedstock and also as energy carrier for transportation. The annual world production of hydrogen amounts to some 50 million tonnes and the majority is produced using fossil fuels like natural gas, coal and naphtha. High temperature nuclear reactors (HTRs) represent a novel way to produce hydrogen at large scale with high efficiency and less carbon footprint. The aim of this master thesis has been to evaluate the feasibility of HTRs for hydrogen production by analyzing both the reactor concept and its potential to be used in certain hydrogen niche markets. The work covers the production, storage, distribution and use of hydrogen as a fuel for vehicles and aviation and as chemical feedstock for the oil refining and ammonia production industry.

The study indicates that HTRs may be suitable for hydrogen production under certain conditions. However, the use of hydrogen as an energy carrier necessitates a widespread hydrogen infrastructure (e.g. pipe-lines, refuelling stations and large scale storage), which is associated with major energy losses. Both mentioned industries could benefit from nuclear-based hydrogen with less infrastructural changes, but the potential market is by far smaller than if hydrogen is used as an energy carrier. A maximum of about 60 HTRs of 600 MWth worldwide has been estimated for the ammonia production industry. The Swedish refineries are likely too small to utilize the HTR but in the larger refineries HTR might be applicable.

For applications that require small amounts of H₂O₂ or have economically difficult transportation means, an alternate, on-site H₂O₂ production method to the current industrial anthraquinone auto-oxidation process is needed. Thus far neutral production of H₂O₂ has been limited to bench-top laboratory scaled research with low yield of H₂O₂ [1]. To produce neutral H₂O₂ on-site and on-demand for drinking water purification, the electroreduction of oxygen at the cathode of a solid polymer electrolyte (SPE) cell could be a possible solution. The work presented here has utilized a SPE cell operating in either fuel cell mode (power generating) or electrolysis mode (power consuming) to produce H₂O₂. The SPE cell reactor is operated with a continuous flow of cathode carrier water flowing through the cathode to remove the product H₂O₂. Two catalysts were chosen for further study in this work, one is the inorganic cobalt-carbon composite catalyst, to be used in both fuel cell mode and electrolysis mode operation. The other is the riboflavin-anthraquinone-carbon composite catalyst, to be used in only the electrolysis mode operation. Through parametric experiments in both modes of operation, the Co-C catalyst was able to achieve peroxide production rate of ~200 μmol hr-¹ cm-² and 4 mW cm-² operating at a cell temperature of 60°C with a current density of 30 mA cm-² and 30% current efficiency in fuel cell mode operation. Long term recycle experiments over a period of 72 hours showed an accumulated H2O2 concentration of over 1400 ppm. Investigation of both catalysts in electrolysis mode operation showed that the AQ-C catalyst achieved maximum H₂O₂ production of 580 μmol hr-¹ cm-² operating at 40°C and a current density of 240 mA cm-² with an 8% current efficiency; while the Co-C catalyst had a maximum H₂O₂ production rate of 360 μmol hr-¹ cm-² operated at 240 mA cm-² with 8% current efficiency. Long term recycle study of both catalysts in electrolysis mode generated maximum H₂O₂ concentrations of over 3000 ppm in 72 hours. Water sample analysis showed no degradation of the catalysts in either mode of operation.
Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate

Fuel cell is a device that can directly convert chemical energy into electrical energy. For low-temperature fuel cells, catalysts are required. Fuel cells using Pt-based or other non-biological materials as catalysts are known as conventional fuel cells. Inspired from Nature, enzymes can be used as catalysts in fuel cells known as enzyme-based fuel cells. The conventional and enzymatic fuel cells share the same underlying electrochemical principles, while enzyme-based fuel cells have their intrinsic advantages and disadvantages due to enzyme properties. The objective of this thesis is to investigate the current/voltage/ power/stability capabilities of enzyme-based membrane-less H2 fuel cells in order to design the enzymatic fuel cells with improved performance. This thesis presents a facile, effective method for the construction of 3D porous carbon electrodes. The 3D porous carbon electrodes are constructed by compacting suitable carbon nanomaterials into discs. The 3D porous carbon electrodes, with large roughness, high specific surface area, and optimized pore size distribution, are able to increase the loading density of enzymes, that is, reaction sites per unit geometric electrode area. The high loading density of enzymes can result in the high current/power density of the enzyme-based membrane-less H2 fuel cells. Moreover, the large enzyme loading can bring about the improvement in fuel cell stability because current becomes limited by mass transport of dissolved gases rather than enzyme immobilization so that neither inactivation nor desorption of enzymes would influence the current output. Based on one type of 3D porous carbon electrodes, the maximum power density of enzyme-based membrane-less H2 fuel cells has increased to the mW•cm2 level by at least one order of magnitude and the half-life has also increased from several hours to one week. This thesis presents a method for the increase in power density otherwise limited by low cathodic currents due to meagre O2 in non-explosive H2-rich H2-air mixtures. The power density of enzyme-based membrane-less H2 fuel cells can be increased by re-proportioning cathode/anode geometric area ratio to balance the cathodic and anodic currents under such an unusual H2-air mixture. This thesis also demonstrates that the 3D porous carbon electrode can improve the apparent O2 tolerance of anodic catalysts – hydrogenases, which are very important for the fuel cell performance. The degrees of apparent O2 tolerance for both O2-tolerant and O2-sensitive [NiFe]-hydrogenases are greatly increased based on the 3D porous carbon electrodes, so that even an O2-sensitive [NiFe]-hydrogenase can be used as an anodic catalyst in the enzyme-based membrane-less H2 fuel cell under a non-explosive H2-rich H2-air mixture. This thesis presents a design of a test bed in which series and parallel connections of sandwich-like electrode stacks can be varied. The fuel cell test bed has demonstrated low-loss interconnects and efficient stack configuration. Operated under a non-explosive H2-air mixture containing only 4.6% O2 at 20 °C, the maximum volume power density of the fuel cell test bed exceeds 2 mW•cm3, capable of powering electronic gadgets, which is a good demonstration of electricity that originates from the buried active sites of enzymes and is transmitted by long-range electron hopping in accordance with Marcus theory.

Many communities around the world have no access to an electricity grid. To supply power to these people, stand-alone power systems are often used, the majority of which are based on diesel generators. Rising fuel costs and environmental concerns make the use of renewable energy in stand-alone systems increasingly attractive. The research reported in this thesis was to demonstrate a stand-alone power system based exclusively on renewable energy sources. To achieve this, a DC electrical backbone is used. Power electronic converters are used to interconnect the loads and generators and hydrogen is used as an inter-seasonal energy store. The design and control of the DC based stand-alone power system forms the primary focus of this research. A demonstration system has been implemented at West Beacon Farm in the UK. Substantial data has been collected that confirms the successful operation of the system.

A miniature, ultra-low power, sensitive, microbridge gas sensor has been developed.The heat loss from the bridge is a function of the thermal conductivity of thegas ambient. Miniature thermal conductivity sensors have been developed for gaschromatography systems [1] and microhotplates have been built with MEMS technologywhich operates within the mW range of power [2]. In this work a lower power microbridgewas built which allowed for the amplification of the effect of gas thermalconductivity on heat loss from the heated microbridge due to the increase inthe surface-to-volume ratio of the sensing element. For the bridge fabrication,CMOS compatible technology, nanolithography, and polysilicon surfacemicromachining were employed. Eight microbridges were fabricated on each die,of varying lengths and widths, and with a thickness of 1 μm. A voltagewas applied to the sensor and the resistance was calculated based upon thecurrent flow. The response has been tested with air, carbon dioxide, helium,and nitrogen. The resistance and temperature change for carbon dioxide was thegreatest, while the corresponding change for helium was the least. Thus the selectivity of the sensor todifferent gases was shown, as well as the robustness of the sensor. Another aspect of the sensor is that it hasvery low power consumption. The measuredpower consumption at 4 Volts is that of 11.5 mJ for Nitrogen, and 16.1 mJ forHelium. Thesensor responds to ambient gas very rapidly. The time constant not only showsthe fast response of the sensor, but it also allows for more accuratedetection, given that each different gas produces a different correspondingtime constant from the sensor. The sensor is able to detect differentconcentrations of the same gas as well. Fromthe slopes that were calculated, the resistance change at 5 Volts operation wasfound to be 2.05mΩ/ppm, 1.14 mΩ/ppm at 4.5 Volts, and 0.7 mΩ/ppm at 4 Volts. Thehigher voltages yielded higher resistance changes for all of the gases thatwere tested. Theversatility of the microbridge has been studied as well. Experiments were donein order to research the ability of a deposited film on the microbridge, inthis case tin oxide, to act as a sensing element for specific gases. In thissetup, the microbridge no longer is the sensing element, but instead acts as aheating element, whose sole purpose is to keep a constant temperature at whichit can then activate the SnO film, making it able to sense methane. In conclusion,the microbridge was designed, fabricated, and tested for use as an electrothermalgas sensor. The sensor responds to ambient gas very rapidly with differentlevels of resistance change for different gases, purely due to the differencein thermal conductivity of each of the gases. Not only does it have a fastresponse, but it also operates at low power levels. Further research has beendone in the microbridge's ability to act as a heating element, in which the useof a SnO film as the sensing element, activated by the microbridge, was studied. REFERENCES: 1. D. Cruz,J.P. Chang, S.K. Showalter, F. Gelbard, R.P. Manginell, M.G. Blain," Microfabricated thermal conductivity detector for themicro-ChemLabTM," Sensors andActuators B, Vol. 121 pp. 414-422, (2007). 2. A. G. Shirke, R. E. Cavicchi, S. Semancik, R. H. Jackson, B.G. Frederick, M. C. Wheeler. "Femtomolar isothermal desorption usingmicrohotplate sensors," J Vac Sci TechnolA, Vol. 25, pp. 514-526 (2007).

Thesis (Honors)--Ohio State University, 2007.
Title from first page of PDF file. Document formatted into pages: contains [64] p.; also includes graphics. Includes bibliographical references. Available online via Ohio State University's Knowledge Bank.

High voltage power transformer is one of the most important and expensive components in today's power transmission and distribution systems. Any overlooked critical fault generated inside a power transformer may lead to a transformer catastrophic failure which could not only cause a disruption to the power system but also significant equipment damage. Accurate and prompt information on the health state of a transformer is thus the critical prerequisite for an asset manager to make a vital decision on a transformer with suspicious conditions. Partial discharge (PD) is not only a precursor of insulation degradation, but also a primary factor to accelerate the deterioration of the insulation system in a transformer. Monitoring of PD activities and the concentration of PD generated combustible gases dissolved in the transformer oil has been proven to be an effective procedure for transformer health state estimation. However current commercially available sensors can only be installed outside of transformers and offer indirect or delayed information. This research is aimed to investigate and develop several sensor techniques for transformer health monitoring. The first work is an optical fiber extrinsic Fabry-Perot interferometric sensor for PD detection. By filling SF6 into the sensor air cavity of the extrinsic Fabry-Perot interferometer sensor, the last potential obstacle that prevents this kind of sensors from being installed inside transformers has been removed. The proposed acoustic sensor multiplexing system is stable and more economical than the other sensor multiplexing methods that usually require the use of a tunable laser or filters. Two dissolved gas analysis (DGA) methods for dissolved hydrogen or acetylene measurement are also proposed and demonstrated. The dissolved hydrogen detection is based on hydrogen induced fiber loss and the dissolved acetylene detection is by direct oil transmission measurement.
Ph. D.

Alltmer intermittent elkraft byggs idag i Sverige för att öka andelen förnybar el i energisystemet. Detta leder till mer ojämn elproduktion, vilket skapar problem i form av mer volatila och oförutsägbara elpriser. Ett sätt att dämpa effekten av den ökande intermittenta kraften är att använda förnybar vätgasproduktion som lastutjämning. På detta sätt kan vätgasen potentiellt bli en viktig del i den fossilfria energimixen. Att använda vätgas som energilager i en Power-to-Power-applikation (P2P) möjliggör även utnyttjandet av prisarbitrage på elmarknaden. Ett ökat klimatfokus har återuppväckt intresset för hur vätgasproduktion kan göras lönsamt. Några tecken på att satsningar sker är att flera länder satsar stora pengar på vätgastekniker och infrastruktur, där flertalet samarbeten över nationella gränser har etablerats.Denna studie syftar till att undersöka de tekno-ekonomiska förutsättningarna för produktion av förnybar vätgas där lönsamheten av arbitragehandel på elmarknaden Elspot bedöms. Detta innefattar en gedigen granskning av kommersiella tekniker lämpade för Linköpings energisystem, däribland elektrolys, ångreformering och bränslecell. Tre fall konstruerades med olika uppsättningar av ingående komponenter. Sedan utfördes en driftoptimering som tog fram övre och undre prisgränser för produktion respektive konvertering av vätgas mot spotpriset. Optimeringsverktyget Problemlösaren i Excel användes för att få fram dessa gränser. Visual Basic (VBA) användes sedan för att genomföra en lagersimulering som visualiserar lagersaldot för alla årets timmar. För att få fram kostnaden för varje kilogram producerad vätgas användes nuvärdesberäkningen Levelised Cost of Energy (LCOE), vilket även underlättade jämförelsen av de tre fallen. Vilka effekter i form av växthusgasutsläpp de olika anläggningarna medför utvärderades också genom beräkningssättet konsekvensanalys. Där jämfördes effekten i form av nettoutsläpp i koldioxidekvivalenter för integrering av respektive anläggning. Resultaten visar på att det finns kommersiella tekniker som kan integreras med det befintliga energisystemet på ett resurseffektivt sätt, däremot är de ekonomiska förutsättningarna inte lika bra och P2P-lösningarna är idag långt ifrån lönsamma. Anledningen tros vara en kombination av otillräckliga elprisfluktuationer samt låg total systemverkningsgrad (som högst 14%) för samtliga konstruerade fall. De årliga intäkterna från elförsäljningen motsvarar cirka 1 procent av de årliga kostnaderna för anläggningen, och LCOE landade på cirka 1500 kronor. Resultaten från investeringskalkyleringen visar på att en högre utnyttjandegrad leder till en lägre LCOE. Lagersimuleringen visar på att säsongslagring krävs för denna typ av anläggning då fluktuationerna inte är tillräcklig stora på en daglig, veckovis eller månatlig basis. Känslighetsanalys på LCOE och driftoptimeringen visar inte heller på lönsamhetsmöjligheter i P2P-fallen även vid gynnsamma justeringar på parametrarna investeringskostnad, elpris och verkningsgrad. Ur ett klimatperspektiv visar samtliga fall, med ett undantag, på en minskade växthusgasutsläpp i regionen.  Slutsatsen som dras av resultaten från fallstudien är att, trots goda tekniska förutsättningar och positiv inverkan på lokala växthusgasutsläpp, kan en P2P-applikation med vätgaslagring inte göras lönsam i en svensk kontext inom en nära framtid. Däremot visar ett Power-to-Gas-fall potential för lönsamhet, då dess investeringskostnad är mindre samt att systemverkningsgraden är högre.
More and more intermittent electric power is being built in Sweden today to increase the share of renewable electricity in the energy system. This leads to more uneven electricity generation, which creates problems in terms of more volatile and unpredictable electricity prices. One way to dampen the effect of the increasing intermittent power is to use renewable hydrogen production as load shedding. In this way, the hydrogen gas can potentially become an important part of the fossil-free energy mix. Using hydrogen as energy storage in a Power-to-Power application (P2P) also enables the use of price arbitrage in the electricity market. An increased climate focus has rekindled interest in how hydrogen production can be made profitable. Some signs that investments are taking place are that several countries are investing big money on hydrogen technologies and infrastructure, and collaborations across national borders have been established. This study aims to investigate the techno-economic prerequisites for renewable hydrogen production where the profitability of arbitrage on the Elspot market is explored. This comprises a thorough investigation of commercial technologies suited for Linköping’s energy system. Three cases where constructed with different component constellations. Then the operational strategy was optimised which generated a lower and upper price limit for production and conversion of hydrogen with input price data from Elspot. The optimisation tool in Excel was used in order to obtain these price limits. Visual Basic (VBA) was then used for storage simulation in order to get a perception of the storage development through all the hours of the year. The cost of every kilogram of hydrogen produced was then calculated through Levelized Cost of Energy (LCOE), which made the comparison of the three cases easier. The resulting greenhouse gas emissions when integrating the facilities in each case were also evaluated with a so-called impact analysis. The effect was compared in net emissions in carbon dioxide equivalents for an integration of each facility.     The results show that there are commercial technologies that can be integrated with the existing energy system in a resource efficient manner, whereas the economic prerequisites are not as good, where today’s Power-to-Power (P2P) solutions are not profitable. The reason seems to be the combination of insufficient spot price fluctuations and a low system efficiency (14% at best) for each case. The annual revenues correspond to 1 percent of the annual costs and that LCOE lands at about 1500 SEK. A higher utilization percentage of the plant shows a lower LCOE in the investment calculation. The storage simulation indicates that a seasonal storage is needed for this type of facility because of that the spot price fluctuations are not big enough on a daily, weekly or monthly basis. The sensitivity analysis made on the investment calculation and operational strategy also shows that there is no profitability in the P2P cases where parameters regarding investment cost, efficiency and electricity price were set optimistically. The Power-to-Gas case on the other hand shows potential for profitability, all because of lower total investment costs and higher efficiency. All cases except the case with steam methane reforming shows reductions in greenhouse gas emissions when integrated in the regional energy system.   The conclusion that can be drawn from the results in the case study is that, in spite of good technological prerequisites and a positive effect on local greenhouse gas emissions, a P2P-application with hydrogen storage cannot be made profitable in a Swedish context in the near future. However, a Power-to-Gas case shows potential for profitability because of its lesser investment cost and that the system efficiency is higher.

Distributed hydrogen generation from liquid hydrocarbon fuels to supply portable fuel cells presents an attractive, high energy density alternative to current battery technology. Traditional unit operation reactor design for hydrogen generation becomes inadequate with decrease in scale because of the unique challenges of size and weight minimization. To address the challenge of reactor scale-down, the concept of multifunctional reactors has emerged, in which synergistic combination of different unit operations is explored to achieve improved performance. The direct droplet impingement reactor (DDIR) studied here is based on this approach in which the liquid feed is atomized using a regularly spaced array of droplet generators with unparalleled control over droplet characteristics, followed by vaporization and reaction directly on the catalyst surface. Considering each droplet generator in the array as a unit cell, a comprehensive, first-principles model of the DDIR has been developed by considering the intimately coupled processes of 1) droplet transport, heating, evaporation, and impingement on the catalyst surface, 2) liquid reagent film formation, capillary penetration, and vaporization within the catalyst layer, and 3) gas phase heat and mass transfer and catalytic reactions. Simulations are performed to investigate the effect of reactor operating parameters on performance. Experimental validation of the model is carried out by visualizing droplet impingement and liquid film accumulation while simultaneously monitoring reaction product composition over a range of operating conditions. Results suggest an optimal unit cell shape for reaction selectivity based on a balance between reagent back diffusion and catalyst bed thermal resistance. Further, achieving a target throughput is best accomplished by adding together a larger number unit cells with optimized geometry and lower throughput (per unit cell) to more effectively spread heat and avoid hotspots at the catalyst interface. At the same time, conditions must be satisfied for ensuring droplet impingement on the catalyst surface, which become more stringent as unit cell throughput is decreased.

This thesis encompasses CO₂ mitigation using three different processes: i) natural gas-fired combined cycle with chemical looping combustion (CLC), ii) trigeneration of electrical power, hydrogen and district heating with extended CLC, iii) steam-based gasification of biomass integrated in an advanced power cycle.

In CLC, a solid oxygen carrier circulates between two fluidised-bed reactors and transports oxygen from the combustion air to the fuel; thus, the fuel is not mixed with air and an inherent CO₂ separation occurs. In this thesis, CLC has been studied as an alternative process for CO₂ capture in a natural gas-fired combined cycle (NGCC). The potential efficiency of such a process using a turbine inlet temperature of 1200 °C and a pressure ratio of 13 is between 52 and 53 % when including the penalty for CO₂ compression to 110 bar. It is shown that this efficiency cannot be further improved by including an additional CO₂ turbine. Two conceivable reactor designs for CLC in an NGCC are presented. Top-firing has been studied as an option to overcome a temperature limitation in the CLC reactor system. The degree of CO₂ capture is shown versus the temperature in the CLC reactor and its combustion efficiency. CLC has the potential to reach both a higher efficiency and a higher degree of CO₂ capture than conventional post combustion CO₂ capture technique. However, further research is needed to solve technical problems as, for example, temperature limitations in the reactor to reach this potential.

Extended CLC (exCLC) is introduced, in which hydrogen is not only produced but also inherently purified. The potential efficiency of a novel tri-generation process for hydrogen, electricity and district heating using exCLC for CO₂ capture is investigated. The results show that a thermal efficiency of about 54% might be achieved.

A novel power process named evaporative biomass air turbine (EvGT-BAT) for biomass feedstock is presented. This process contains a steam-based gasification of biomass, which is integrated in an externally fired gas turbine cycle with top-firing. In the EvGT-BAT process, the steam-based gasification is conducted in an entrained-flow tubular reactor that is installed in the SFC as a heat exchanger. The EvGT-BAT process has the potential to generate electrical power from biomass with an efficiency of 41 %.

The topic of this thesis is investigation of a small-scale stand-alone power system, based on both experimental work and computer simulations. The power system in this study uses solar energy as energy input, lead-acid batteries as short-term energy storage, and hydrogen as long-term energy storage. The main focus is upon operation and control of the hydrogen subsystem, as a robust controller is needed in order to prevent excessive use of the components in this subsystem. The laboratory power system comprises of: Hydrogen subsystem (PEM electrolyser, metal hydride, and PEM fuel cell), a lead-acid battery, programmable power supply for emulation of PV arrays, wind turbines, and controlled characterisation of the individual system components, and a programmable electronic load.

The intention was to build the laboratory power system as simple and energy efficient as possible. The components were connected directly in parallel on a common 48 V DC bus bar, no power electronics were applied between the components. Furthermore, the metal hydride and the fuel cell were air-cooled, avoiding auxiliaries required for water- cooling. The electrolyser, however, needed water-cooling. But with the electrolyser delivering hydrogen at 16 bars to a low pressure metal hydride, no use of compressor was required. On the other hand, metal hydrides needs purified hydrogen gas, > 99.999 %, in order to maintain its capacity as specified by the manufacturer.

The actual work in this thesis is divided in three main parts:

1. Design, construction, and operation of a laboratory hydrogen power system

2. Establishment of a computer model of the laboratory hydrogen power system, which interpolates and extrapolates its outputs based on experimental data collected from the laboratory system

3. Establishment of control algorithms for high-level energy management of the laboratory hydrogen power system based on the developed computer model. It is a goal to make the implementation and maintenance of these control algorithms as simple as possible. Furthermore, the control algorithms must enable efficient usage of the system components and secure energy supply to the end user

The results of this thesis are divided in two main parts:

The first part of the main results relates to the proposal and development of two types of control algorithms for high-level energy management, which will be denoted as the Control Matrix and the Fuzzy controller in the thesis. These control algorithms are suggested as opposed to the more traditional battery five-step charge controller. Identification of important system parameters and choosing proper settings for control parameters must be implemented into the control algorithms in order to finalise a complete control strategy. It will be shown that the electrolyser annual runtime decreases while the electrolyser annual hydrogen production remains the same by using the proposed control strategies, thus running the electrolyser more efficient.

Furthermore, with a reduction in the total number of electrolyser start-ups, a more stable system operation is achieved.

The second part of the main results relates to the operational experience of the small-scale laboratory hydrogen power system. Due to the amount of power required by the local control system integrated into the fuel cell and the electrolyser, the energy efficiency of the fuel cell and the electrolyser is lower at partial loads. Thus, with the additional energy needed for hydrogen purification, the round-trip efficiency of the hydrogen subsystem is found to be rather low (< 30 %), when the fuel cell and the electrolyser runs at low partial loads. However, it is encouraging that the hydrogen subsystem can reach 35 – 40 % when the fuel cell and the electrolyser are allowed to run at nominal power levels, in addition to optimal arrangement of the hydrogen purification unit. These energy efficiencies are higher than efficiencies achieved with diesel-fuelled generators. Besides, stand-alone power systems often resides in remote areas where transportation of diesel is costly, thus local production of the fuel by means of electrolyser and excess renewable energy can be profitable.

Regarding the difficulty of measuring the true amount of hydrogen present in the metal hydride, and because this system parameter is important in the control strategy, a pressurised vessel is recommended instead of the air-cooled metal hydride. Furthermore, it is recommended to use DC/DC converters in the hydrogen power system in order to ensure power quality within specifications and robust operation.

This thesis work is the continuation and final part of a joint project between the Department of Materials Technology, NTNU and Norsk Hydro Research Center in Porsgrunn, looking at the possibility of using fuel cells for production of hydrogen chloride and electric power. The experimental work encompass an evaluation of three hydrogen - chlorine fuel cell design concepts, development and implementation of a mathematical fuel cell model and a kinetic study of the chlorine reduction reaction.

The evaluated fuel cell designs consisted of a) a conventional PEM fuel cell applying a Nafion membrane, b) a composite system applying an aqueous HCl electrolyte and Nafion membrane and c) a phosphoric acid doped PBI membrane fuel cell operating at intermediate temperatures of 150 - 175 ◦C. From the evaluation it was found that the chlorine reduction kinetics are much faster than the corresponding oxygen reduction reaction, leading to low activation losses on the fuel cell cathode. However, the nature of the reactant, chlorine, and the product, HCl, places strict demands on the corrosion resistance of the construction materials and drastically increases the difficulties related to water management in the cells. Due to these effects, none of the investigated systems were able to demonstrate stable operation under the conditions used in this study. The PBI cell showed best potential and seems to be the system in which the humidification and corrosion difficulties easiest can be remedied. The first design criteria for such a system should be the minimisation of the existence of liquid water, ideally a hydrogen - chlorine fuel cell system should operate in totally water free environment and consist of a high temperature proton conductor.

A two dimensional, isothermal mathematical model of a hydrogen - chlorine single fuel cell with an aqueous HCl electrolyte is presented. The model focuses on the electrode reactions in the chlorine cathode and also includes the mass and momentum balances for the electrolyte and cathode gas diffusion layer. There is good agreement between the model predictions and experimental results. Distributions of physical parameters such as reactant and product concentrations, solution and solid phase potentials and local current densities and overpotentials as a function of cell voltage are presented. Effects of varying the initial electrolyte concentration and operating pressure are analysed. It was found that an electrolyte inlet concentration of 6 mol dm−3 gave the best cell performance and that an increase of operating pressure gave a steady increase of the fuel cell performance.

The rate and mechanism of the electroreduction of chlorine on electrochemically oxidised Pt and Ru electrodes has been investigated relative to the state of oxide formation. Current/potential curves for the reduction process in 1 mol dm−3 HCl solution saturated with Cl2 have been obtained for electrode surfaces in various states of preoxidation with the use of the rotating disc electrode technique (RDE). In the case of chlorine reduction on platinum, the results indicate that adsorption of chlorine molecules with a subsequent rate determining electrochemical adsorption step is the dominant mechanism. The exchange current density seems to decrease linearly with the logarithm of the amount of surface oxide. Chlorine reduction on ruthenium is best described by a Heyrovsky-Volmer mechanism with the first charge transfer reaction as the rate determining step. The Krishtalik mechanism incorporating adsorbed O•Cl+ intermediates is also able to describe the reaction successfully. The reaction order is constant for all oxide coverages while the exchange current density apparently moves through a maximum at intermediate oxide coverages (∼100 mC cm−2). The results show that the electrocatalysis of the cathodic reduction of chlorine is very sensitive to the state of the oxidation of the electrode surface.

The rate and mechanism of the electroreduction of chlorine on electrooxidised ruthenium has further been investigated with focus on the effect of solution pH. Current/potential curves for the reduction process in solutions with constant chloride concentration of 1.0 mol dm−3 and varying H+ concentration have been obtained with the use of the rotating disk electrode technique (RDE). It was found that the chlorine reduction rate is highly inhibited in solutions with high H+ concentrations and that it can be satisfactorily described by the Erenburgh mechanism, previously suggested for the chlorine evolution on RuO2 and ruthenium titanium oxides (RTO). The expression of the kinetic current as a function of chlorine and H+ concentration was obtained by solving the elementary rate equations of the kinetic mechanism. The kinetic constants obtained from the correlation of the kinetic current expression to the experimental data were used to simulate the dependence of the surface coverages and elementary reaction rates on overpotential.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

The diploma thesis is focusing on the seasonal energy storage in synthetic fuels and the Power to Gas system (P2G). The P2G enables the conversion of electrical energy in times of electricity surplus, for example by using the surplus from renewable energy sources to produce synthetic gas, particulary hydrogen and synthetic methane. The main focus is on the technical and economic assessment of P2G of the Gazela natural gas pipeline. Furthermore, it identifies the limits of production, transportation, and storage capacities of these synthetic gases. The technical analysis assumes the injection of hydrogen of a certain molar concentration, according to the four proposed scenarios, into the natural gas transmission system in the Gazela pipeline. The results have showen that an increase in the molar fraction of hydrogen in natural gas will cause problems in gas transport and will lead to an increase in the pressure losses, an increase in flow rate, and a decrease in the storage capacity of the pipeline. The economic analysis examines the use of P2G technology in Czech conditions. It demonstrates the amount of production costs for the production of 1 MWh of synthetic gas depending on the electricity price and the operating time of the production facility. The sensitivity analysis has shown that neither hydrogen nor synthetic methane is competitive next to cheap natural gas unless measures like an increased price of emission allowances or a carbon tax are taken.

This research investigates the energy, financial and environmental performance of an innovative integrated gasification fuel cell combined cycle fuelled by municipal solid waste that includes hydrogen storage and electrolysis. The suitability for fuel cells to run on synthesis gas coming from the gasification of waste is determined by the sensitivity of the fuel cell to run on contaminated fuel. Out of the available fuel cell technologies solid oxide fuel cells (SOFCs), because of their ceramic construction and high operating temperatures, are best suited for syngas operation. Their high operating temperature ( > 650°C) and the presence of nickel at the anode means that it is possible to reform hydrocarbons to provide further hydrogen. A major contaminant to be considered in gasification systems is tar which can foul pipework and cause substantial performance losses to the plant. Experimental research on the effects of tar on a SOFC at varying concentrations and operating conditions show; that some carbon deposition serves to improve the performance of the fuel cell by reducing the ohmic resistance, and there is a tendency for the tar to reform which improves overall performance. These improvements are seen at moderate tar concentrations but at higher concentrations carbon deposition causes substantial performance degradation. Numerical simulations representing all aspects of the proposed system have been developed to understand the energy performance of the system as a whole as well as the financial and environmental benefits. Taking into account variations in the waste composition, and the wholesale electricity price the proposed system, scaled to process 100,000 tonnes of waste per year (40,000 removed for recycling), has a simple payback period of 7.2 years whilst providing CO2 savings of 13%. Over the year the proposed system will provide enough electricity to supply more than 23,000 homes and enough heat for more than 5,800 homes (supplying 25% of the electrically supplied homes).

Renewable energy-hydrogen systems for remote area power supply (RAPS) constitute an early niche market for sustainable hydrogen energy. The primary objective of this research has been to investigate the possibility of direct coupling of a PV array to a proton exchange membrane (PEM) electrolyser by appropriate matching of the current-voltage characteristics of both the components. The degree to which optimal matching can be achieved by direct coupling has been studied both theoretically and experimentally. A procedure for matching the maximum power point output of a PV array with the PEM electrolyser load to maximise the energy transfer between them has been presented. The key element of the matching strategy proposed is to vary the series-parallel stacking of individual cells in both the PV array and the PEM electrolyser so that the characteristic current (I) -voltage (V) curves of both the components align as closely as possible. This procedure is applied to a case study of direct coupling a PV array comprising 75 W panels (BP275) to a PEM electrolyser bank assembled from 50 W PEM electrolyser stacks (h-tec StaXX7). It was estimated theoretically that the optimal PV-electrolyser combination would yield an energy transfer of over 94% of the theoretical maximum on annual basis. This combination also gave the lowest hydrogen production cost on a lifecycle basis. An experimental test of this theoretical result for direct coupling was conducted over a period of 728 hours, with an effective direct-coupling operational time of about 467 hours (omitting the hours of zero solar radiation). Close agreement between the theoretically predicted and actual energy transfer from the PV array to the electrolyser bank in this trial was found. The difference between theoretical and experimental hydrogen production was less then 1.2%. The overall solar-to-hydrogen energy conversion efficiency was found to be 7.8%. The electrolysers were characterised before and after the direct coupling experiment, and showed a small decline in Faraday efficiency and energy efficiency. But this decline was less than the uncertainties in the measured values, so that no firm conclusions about electrolyser degradation can be drawn at this stage. Another direct-coupling experiment, using a larger scale PV-electrolyser system, that is, a 2.4 kW PV array at RMIT connected to the 'Oreion Alpha 1' stand-alone 2 kW PEM electrolyser developed by the CSIRO Energy Technology, was also successfully conducted for a period of 1519 hours (with 941 hours of effective operational time of the electrolyser). Energy-efficient direct coupling of a PV array and electrolyser as examined in this thesis promises to improve the economic viability of solar-hydrogen systems for remote power supply since the costs of an electronic coupling system employing a maximum power point tracker (MPPT) and dc-to-dc converter (around US$ 700/ kW) are avoided.

Orientador: Ennio Peres da Silva
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: Neste trabalho foram analisadas as viabilidades técnica e econômica de sistemas de rodução de hidrogênio eletrolítico utilizando energia elétrica fora do horário de ponta e, reconversão deste hidrogênio em eletricidade durante o horário de ponta utilizando células a combustível. Para tanto foi construído um sistema piloto de produção e reconversão de hidrogênio com a finalidade de determinar-se as melhores condições de operação e eficiência energética para cada componente do sistema. Os resultados obtidos foram utilizados para uma análise econômica de viabilidade destes sistemas para uso industrial. Como resultados foram obtidas uma eficiência energética global de 16,4% e, para grandes diferenças de tarifa elétrica entre a ponta de carga e fora dela, foi encontrada a possibilidade da utilização desse tipo de sistema em industrias de médio e grande porte
Abstract: This work analyses the technical and economical viability of electrolytic hydrogen generation systems which used power during off-peak power demand and reconverted the energy stored in the form of hydrogen during peak hours by means of fuel cells. For this purpose, a pilot system for producing and reconverting hydrogen was built in order to determine the best operating conditions and power efficiency for each component if the system. The results obtained were used for the economical viability analysis of these systems in industrial use. For the pilot system analyzed, the results show a global energy efficiency of 16.4% and, for significant differences between the peak and off-peak power tariffs, that this kind of system may be used in medium and large companies
Mestrado
Mestre em Planejamento de Sistemas Energéticos

Världen står inför utmaningen att minska sin klimatpåverkan som till en del beror på utsläpp av växthusgaser såsom koldioxid. Detta samtidigt som behovet av energi spås öka markant. Förnybara källor, företrädesvis vind- och solkraft, spås öka sin andel av den globala energiförsörjningen. Förnybar elkraftgenerering är dock inte oproblematisk då produktionen är svår att förutspå. När solen lyser eller vinden blåser sammanfaller dessutom inte alltid med när behovet av elektricitet finns vilket skapar stabilitetsproblem i elnätet. Att lagra energi för att sedan kunna återföra är ett sätt att både lösa stabilitetsproblem i elnätet och säkerställa att energi finns när den behövs. I den här studien undersöks möjligheten att, med el från vindkraft, genom elektrolys framställa vätgas som sedan lagras för att senare återföras som el via bränslecell eller säljas som råvara. Avsikten är att motverka negativa ekonomiska konsekvenser vid försäljning av intermittent vindkraft. I studien används modeller som gör simuleringar utifrån historiska data för 2019 från en vindpark. Detta för att undersöka om regleravgifter vid prognosavvikelser går att undvika eller delvis motverka samt om det går att flytta elproduktion i tid med en vätgasanläggning för att förbättra det ekonomiska utfallet för en vindkraftsproducent. Resultaten visar att detta i dagsläget inte är lönsamt utifrån de antaganden som gjorts. Detta främst för att alltför få drifttimmar uppnås i båda fallen. Studien visar att det dock kan vara lönsamt om syftet är att producera vätgas istället för att vara ett stöd för en vindkraftsproducent.
The world faces the challenge of reducing the emissions of greenhouse gases in order to mitigate climate change. At the same time, global energy demand is predicted to increase significantly. Renewable power generation like wind and solar power are believed to dominate the increase of needed power generation. These renewables power sources do not come without problems. Power fluctuations, due to their variable production causes grid stability problems and does not necessarily correspond to the demand for energy. Energy storage is a possible solution for both grid stability as well as for non-corresponding production/demand situations. This study investigates the feasability of hydrogen production by water electrolysis with electricity from a wind park. The produced hydrogen could either be sold or stored and used in a fuel cell to generate electricity at a later point in time. The aim is to mitigate negative economic consequenses from selling intermittent wind power. In the study simulations are made with historic data from 2019 from a wind park. Two models were created to investigate if imbalance costs due to forecast errors could be avoided or partially avioded and to investigate the possibility to move production of electricity in time and avoid unfavourable spot market prices. This in order to enhance the finacial results. The results from the study shows that at the present moment this is not a profitable approach with the assumptions made. The foremost reason for this is that too few system operating hours is obtained in each case. However, the results also shows that if the objective shifts from supporting wind power to producing hydrogen, the outcome could be profitable.

Strong dependency on fossil fuels and the associated price and supply chain risk increase the need for more efficient utilisation of existing non-renewable energy sources. Carbon capture and hydrogen purification technologies are expected to play a key role in the future low-carbonised energy matrix. Integrated Gasification Combined Cycles (IGCCs) are one of the emerging clean coal technologies which pave the way for producing power from coal with a higher net power efficiency than conventional PC-fired boiler power plants. It is also advantageous that in an IGCC power plant a carbon capture unit can be applied to a stream having a very high CO2 partial pressure ahead of gas combustion that would not be available in case of a PC-fired boiler power plant, leading to less energy penalty involved in carbon capture. At the same time, the production of ultrapure hydrogen is both a sought target and an appropriate environmental solution because it is commonly utilised as feedstock in refineries’ hydrotreaters and hydrocrackers as well as energy carrier in fuel cells. A high purity of hydrogen has been commercially produced out of raw synthesis gas using a Hydrogen Pressure Swing Adsorption (H2 PSA) process. In this thesis, it was aimed to design and optimise a bespoke H2 PSA system tailored for a decarbonised syngas feed originating from a carbon capture unit. Therefore, a novel H2 PSA has been studied that is applied to an advanced IGCC plant for cogenerating power and ultrapure hydrogen (99.99+ mol%) with pre-combustion CO2 capture. In designing the H2 PSA, it is essential to increase the recovery of ultrapure hydrogen product to its maximum since the power consumption for compressing the H2 PSA tail gas up to the gas turbine operating pressure should be minimised to save the total auxiliary power consumption. Hydrogen recovery was raised by increasing the complexity of the PSA step configuration that allows a PSA cycle to have a lower feed flow to one column being used for adsorption and more pressure equalisation steps. An in-depth economic analysis was carried out and discussed in detail. The industrial advanced IGCC performances have also been improved by process integration between the H2 PSA unit and other units in the plant.

Orientador: Ennio Peres da Silva
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: A produção de hidrogênio para as células a combustível é um desafio para a ampla disseminação dessa tecnologia. Produzi-lo a partir de fontes renováveis de energia, como o etanol da cana-de-açúcar, é a opção analisada neste trabalho, enfocando principalmente a tecnologia dentro do conceito da geração distribuída de energia elétrica. O objetivo da tese é avaliar a viabilidade técnica e econômica da reforma do etanol para produção de hidrogênio com a qualidade necessária para o uso em uma célula a combustível tipo membrana de troca de prótons (PEMFC). A metodologia utilizada foi o desenvolvimento de um protótipo de geração de energia elétrica baseado em um reformador de etanol e um sistema de purificação de hidrogênio. Os principais dados obtidos nesse experimento foram a eficiência global de conversão do protótipo e a quantidade e qualidade das emissões advindas da operação do mesmo. O reformador de etanol alcançou eficiência de conversão de 69%, produzindo hidrogênio ¿ após o sistema de purificação¿ com nível de monóxido de carbono (CO) inferior a 20 µmol.mol, emissões globais de 460,85 g CO2.kWh-1, 0,812 g CO.kWh-1, 2,416 g CH4.kWh-1, sem emissão de NOx e SOx para uma vazão de entrada de 0,33 mol.etanol.hora-1. Com esses valores, foi realizada a análise da viabilidade técnica e econômica, comparando o protótipo desenvolvido com outras tecnologias de geração de energia elétrica. A análise econômica baseou-se em curvas de aprendizado do comportamento do custo inicial do reformador, calculado em 8.000,00 R$.kW-1, em relação à sua produção acumulada para calcular-se o custo de geração do hidrogênio e da energia elétrica produzida ao acoplar-se o experimento a uma célula a combustível tipo PEMFC com eficiência de conversão elétrica de 45%
Abstract: The hydrogen production for fuel cells is a challenge for wide dissemination of this technology. To produce it from renewable sources of energy, such as sugar cane¿s ethanol, is the option analyzed in this work, focusing mainly the fuel cell technology inside of distributed generation concept. The objective of the thesis is to evaluate the technical and economical feasibility of ethanol reforming for hydrogen production with the necessary quality for use in a proton exchange membrane fuel cell (PEMFC). The methodology used was the development of a power generation prototype based on an ethanol reformer and a hydrogen purification system. The main data obtained in that experiment were the prototype global efficiency conversion and the quantity and quality of emissions resulted from prototype operation . The ethanol reformer reached conversion efficiency of 69%, producing hydrogen - after the purification system ¿ with carbon monoxide (CO) level lower than 20 µmol.mol-1, overall emissions of 460.85 g.CO2.kWh- 1, 0.812 g.CO.kWh-1, 2.416 g.CH4.kWh-1, without emissions of NOx and SOx for a 0.33 mol.ethanol.hour-1 flow inlet. Those values were used for the technical and economical feasibility analysis comparing the prototype with others electric power generation technologies. The economical analysis based on learning curves concept of the reformer initial cost behavior, which was estimated in R$ 8,000.00 /kWe, in relation to its accumulated production to calculate the hydrogen and electric power generation production cost when joining the reformer system to a PEMFC fuel cell with 45% electric efficiency conversion
Doutorado
Planejamento de Sistemas Energeticos
Doutor em Engenharia Mecânica

Mestrado em Economia e Gestão de Ciência, Tecnologia e Inovação
As alterações climáticas e os seus efeitos nefastos vieram reforçar a necessidade de uma alteração do paradigma energético, nomeadamente nos modelos de consumo, de forma a atingir a neutralidade carbónica em 2050. O hidrogénio assume um papel de destaque na transição energética uma vez que permite a produção de energia limpa, cria e dinamiza indústrias e serviços e promove novas utilizações para as infraestruturas existentes de gás natural. O presente relatório de estágio tem como objetivo perceber as consequências e custos de um processo de inovação tecnológica orientado para uma resposta mais sustentável e eficiente, baseada no hidrogénio, para uma utility portuguesa do setor energético, a REN – Redes Energéticas Nacionais. O relatório encontra-se organizado em três seções, i) clarificação de conceitos e termos relativos à inovação, transição energética e hidrogénio e contextualização do tema; ii) análise económica com enfoque na estrutura de custos sobre a adoção das tecnologias associadas à cadeia de valor Power-to Gas e iii) apresentação de parecer técnico e económico resultante da análise efetuada.
Climate changes and its negative impacts reinforce the need for change in the energy sector, namely in the consumption patterns, in order to achieve carbon neutrality by 2050. Hydrogen stands out as an energy transition driver since it allows clean energy production, industry and services development and promotes new uses for the existing natural gas infrastructures. This internship report aims to understand the costs and consequences of a technological innovation process oriented towards a more sustainable, efficient and hydrogen-based response for a Portuguese utility in the energy sector, REN - Redes Energéticas Nacionais. This report is organized in three chapters, as follows: i) presentation of concepts and terms related to innovation, energy transition and hydrogen, and theme overview; ii) economic analysis focusing on the cost structure of the adoption of technologies within the Power-to-Gas value chain and iii) technical and economic evaluation based on the carried out analysis.
info:eu-repo/semantics/publishedVersion