04 Fakultät Energie-, Verfahrens- und Biotechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/5
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Item Open Access Long-term capacity expansion planning with variable renewable energies : enhancement of the REMix energy system modelling framework(2017) Fichter, Tobias; Thess, André (Prof. Dr.)The large-scale integration of variable renewable energies (VRE) like Photovoltaics and wind power into the power system is crucial for the transition towards a sustainable electricity supply. However, due to the inherent characteristics of VRE, i.e. the site-specific, highly variable, and unreliable power generation, as well as their low variable generation costs, the large-scale deployment of VRE causes adequacy-, grid-related, and balancing-impacts for the residual system. These impacts and the related costs need to be considered for a concerted capacity expansion planning with VRE in order to identify cost-efficient and reliable transition pathways. Traditionally applied capacity expansion planning models have limitations to consider the value of energy at its time of the delivery of VRE and their impacts on the system due to the applied low system-operational detail. Hence, new planning methods are required to ensure a successful transition towards a sustainable electricity supply. This work enhances the REMix energy system modelling framework to allow for a concerted long-term capacity expansion planning with VRE. The outcome of this is the REMix-Capacity Expansion Model (REMix-CEM). The optimization model bridges the gap between traditional long-term capacity expansion planning and short-term power system operation models. This enables the model to consider the value and the impacts of a large-scale integration of VRE into the power system accurately within capacity expansion planning. This thesis describes the challenges of long-term capacity expansion planning with VRE and presents the developed model in detail. This includes a principle description of how REMix-CEM is typically applied by DLR for a science-based consultancy of planning authorities in developing and emerging countries. To demonstrate its capabilities, the flexible formulation of the model is used to investigate two important issues within a model-based long-term capacity expansion planning with VRE - the model foresight and the applied system-operational detail. Both issues can have a significant influence on results and computational effort of the model. These correlations are investigated within two case studies for a fictitious but representative power system of a developing country. Results of the first case study indicate that the type of model foresight (single-year myopic, multi-annual rolling horizon, or perfect foresight) has a strong influence when some of the input parameters change suddenly at one point of the planning time frame, while its influence is less pronounced when parameters changes rather continuously over the period of study. Only a large model foresight enables the model to anticipate future occurrences well in advance and to adopt its investment strategies accordingly. Furthermore, the analysis shows that the larger the model foresight the higher is the competitiveness of VRE and dispatchable RE, because their advantage to produce electricity at stable costs over the lifetime can be captured more precisely. However, it is also demonstrated that a larger model foresight means also a higher computational effort to solve the capacity expansion optimization problem. In addition, a large model foresight with perfect information over the planning time frame might not fully capture the decision frame-work of real-life decision makers. To keep computational effort manageable for long-term capacity expansion planning with VRE, investment decisions are typically based on a limited number of representative dispatch periods. These dispatch periods have the aim to represent the temporal variability of load and RE resources over the year as accurate as possible. Within the second case study it is shown that the average day method, which uses average values to assign values for RE resource availability to the utilized dispatch periods, is inappropriate for capacity expansion planning with VRE. The value of energy at its time of the delivery of VRE is modeled inaccurately and system flexibility requirements, caused by the integration of VRE, are underestimated systematically. The representative day method, which uses a sample of “real” historical days instead of average values, is significantly more suitable because extreme values are not averaged. This leads to a better approximation of VRE electricity generation, which allows a more accurate consideration of the value of energy at its time of the delivery of VRE and system flexibility requirements. System flexibility requirements can be captured within capacity expansion optimization especially by considering unit commitment constraints (UCCs) of thermal generators. However, this requires a large number of integer decision variables that describes the unit commitment status. This leads to high computational complexity. Hence, UCCs are typically neglected during capacity expansion optimization. Within the second case study it is however demonstrated that neglecting UCCs within capacity expansion planning with VRE leads to an overestimation of the competitiveness of VRE and an underestimation of the need for flexible generation and storage technologies. This work shows that by a linear relaxation for UCCs system flexibility restrictions can be captured accurately during long-term capacity expansion optimization with comparably low additional computational effort.Item Open Access An investigation of hydrogen generation via steam reforming of liquid fuels(2017) Martin, Stefan; Thess, André (Prof. Dr. rer. nat. habil.)Im Rahmen der vorliegenden Arbeit wurde die Dampfreformierung von Biodiesel, Diesel und Bioethanol experimentell und theoretisch untersucht. Flüssige Brennstoffe zeichnen sich durch eine hohe volumetrische und gravimetrische Energiedichte und eine bereits vorhandene Verteilungsinfrastruktur aus. Die dezentrale Wasserstofferzeugung aus Flüssigbrennstoffen durch Reformierung kann mit dazu beitragen, die Marktdurchdringung von Brennstoffzellenfahrzeugen zu beschleunigen. Weitere Anwendungsmöglichkeiten bestehen im industriellen Sektor, etwa für metallurgische Prozesse oder für die Herstellung von Flachglas. Im Rahmen der experimentellen Arbeiten wurde ein vertieftes Verständnis der Katalysatordeaktivierung erzielt. Insbesondere wurden geeignete Betriebsbedingungen ermittelt, um die initiale Kohlenstoffbildung auf der Katalysatoroberfläche zu verhindern. Geringe Temperaturen und hohe Brennstoffmassenströme begünstigen eine Katalysatordeaktivierung durch Verkokung. Die Kohlenstoffbildungsneigung nimmt in der Reihenfolge Bioethanol < Biodiesel < Diesel zu. Durch entsprechende Wahl der Katalysatoreintrittstemperatur und des Brennstoffmassenstromes wurde für die jeweiligen Flüssigbrennstoffe ein stabiler Versuchsbetrieb (100 Stunden) nahe am chemischen Gleichgewicht nachgewiesen. Im Falle von fossilem Diesel hat sich gezeigt, dass die Langzeitstabilität der Dampfreformierung durch eine vorhergehende Entschwefelung des Kraftstoffs weiter verbessert werden kann. Die experimentellen Arbeiten werden ergänzt durch eine Simulationsstudie. Ziel der Untersuchung ist die verfahrenstechnische Optimierung einer Wasserstofferzeugungseinheit aus Biodiesel (50 Nm3/h H2) bestehend aus den Komponenten Dampfreformierung, Wassergasshift-Stufe, Druckwechseladsorption und Gas-Flüssig-Brenner. Neben einem positiven Druckeinfluss zeigen die Ergebnisse ein Optimum des molaren Dampf:Kohlenstoff-Verhältnisses bei 2,78. Aufbauend auf einem verfahrenstechnisch optimierten System wird ein wärmeintegrierter Wasserstoffgenerator entwickelt mit einem thermischen Systemwirkungsgrad von 75,6 % (bezogen auf den unteren Heizwert).Item Open Access Entwicklung und Integration neuartiger Komponenten für Polymerelektrolytmembran- (PEM) Elektrolyseure(2018) Lettenmeier, Philipp; Friedrich, K. Andreas (Prof. Dr.)Item Open Access Hydrogen production by partial catalytic dehydrogenation of kerosene(2016) Pearson, Karolina; Thess, André (Prof. Dr. rer. nat.)Die Verknappung fossiler Energieträger erhöht den Bedarf an effizienten Technologien in der Luftfahrt. Für die Stromerzeugung an Bord eines Flugzeugs, während des Bodenbetriebs, können anstelle eines konventionellen Hilfstriebwerks alternativ Brennstoffzellensysteme eingesetzt werden. Der dafür notwendige Wasserstoff kann durch partielle katalytische Dehydrierung des an Bord verfügbaren Kerosins bereitgestellt werden. In dieser Arbeit werden zwei alternative Prozesskonzepte für die Wasserstofferzeugung aus Kerosin entwickelt und auf Ihren elektrischen Wirkungsgrad energetisch bewertet. Für diesen Zweck wird die partielle katalytische Dehydrierung von Kerosin detailliert experimentell untersucht und die Ergebnisse in die Modellierung der Prozesskonzepte eingebunden.Item Open Access Techno-ökonomische Prozessbewertung der Herstellung synthetischen Flugturbinentreibstoffes aus CO2 und H2(2016) König, Daniel H.; Thess, Andre (Prof. Dr. rer. nat.)Technologieverbesserung, Optimierung der Betriebsabläufe und effiziente Infrastrukturgestaltung tragen zur Reduzierung der Umweltwirkung des stetig wachsenden Flugverkehrs bei. Um jedoch die Ziele zur Emissionsminderung und Dekarbonisierung des Flugverkehrs zu erreichen sind alternative Treibstoffe notwendig. Die Konvertierung von H2 und CO2 in flüssigen Flugturbinentreibstoff mit dem Power-to-Liquid-Verfahren (PTL) stellt dabei einen möglichen Herstellungspfad dar, welcher in dieser Arbeit unter technischen und ökonomischen Gesichtspunkten analysiert und bewertet wird.Item Open Access Techno-ökonomische Optimierung eines Hochtemperatur-Latentwärmespeichers(2018) Hübner, Stefan; Thess, André (Prof. Dr. rer. nat.)Diese Arbeit beschreibt die technische und ökonomische Optimierung eines Hochtemperatur-Latentwärmespeichers, der z.B. in solarthermischen Kraftwerken mit Direktverdampfung zur Speicherung der Verdampfungsenthalpie des Wassers eingesetzt wird. Die Wärmeübertragung erfolgt über axial berippte Rohre, deren Form, Material und Anbindung in dieser Arbeit theoretisch optimiert wird, das Optimierungsergebnis wird anschließend mit sehr zufriedenstellenden Ergebnissen experimentell überprüft.Item Open Access The value of concentrating solar power for a sustainable electricity supply in Europe, Middle East and North Africa(2018) Hess, Denis; Thess, André (Prof. Dr.)Dispatchable solar power from concentrating solar thermal power plants (CSP) combined with thermal energy storage and co-firing option can provide energy according to demand. A transfer of such electricity from solar thermal power plants in desert regions to distant consumer centres may therefore complement regional or domestic energies. The research question of the value of this transfer was already analysed in qualitative studies that found out a high potential of this idea. However, a detailed energy system modelling showing the value of concentrating solar power plants from Middle East and North Africa (MENA) for Europe (EU) was not yet done. This thesis closes the scientific knowledge gap applying an energy system model with a least-cost approach and detailed scenario analysis for the year 2050. The thesis describes the effects of including and excluding a transfer of CSP from MENA to EU. The transfer-system consists of a power plant and a high voltage direct current transmission (HVDC) and is therefore called CSP-HVDC (concentrating solar power - high voltage direct current) power plant. The techno-economic assumptions for this composed technology are strictly chosen to avoid its overestimation. The assessment of CSP-HVDC considers energy system evaluation criteria. These multi-criteria reveal the impact of CSP-HVDC on energy infrastructure, operational behaviour, cost and emission of the energy system. To evaluate national grid expansion, a new grid methodology is introduced as composed of transmission and distribution grid. This new model reduces complexity of the grid and analyses grid expansion considering different power plant park portfolios. As a result CSP-HVDC-application proves to require a future national grid expansion to a far lesser extent than a system with high shares of wind and photovoltaic energy. This is substantiated by a validation with a high-resolution grid model. Integrating CSP-HVDC into the national grid brings about reduction of grid stress due to lower capacity peaks in the transmission lines of the grid. Cost sensitivity analyses indicate the cost uncertainty of the energy system. The examination of system cost uncertainty shows that an appropriate share of dispatchable energy including CSP-HVDC generates a minimal system cost uncertainty. Analysis of cost relations of CSP-HVDC to all other used technologies (e.g. nuclear and carbon capture and storage technologies) point out how high the probability of an integration of CSP-HVDC is. Inside the EUMENA region (Europe, Middle East and North Africa) various regions are subdivided. Due to different characteristics of regional energy systems, it depends on the model region in EU how probable it is that CSP-HVDC is integrated. For some EU regions up to 66% integration probability can be achieved. The result of multi-criteria evaluation shows that power plant capacity, electrical storage expansion, and electrical curtailment cause a lower impact when CSP-HVDC is used to supplement the energy portfolio. However, the strict model conditions lead to a higher needed transmission infrastructure altogether, when CSP-HVDC is applied in high shares because of its long transfer distance. Lower CSP-HVDC shares can reduce the total transmission infrastructure of single regions. Another result demonstrates that system cost does not play the essential role in quantifying the value of CSP-HVDC because system cost differences may be small. The right share of CSP-HVDC offers a higher degree of freedom, more options and compromises for the design of a low carbon energy system under the included evaluation criteria mentioned above. Thus, a technologically diverse energy system with low carbon emission rather benefits from CSP-HVDC.Item Open Access Storage demand in highly renewable energy scenarios for Europe : the influence of methodology and data assumptions in model-based assessments(2017) Cebulla, Felix; Thess, André (Prof. Dr.)Future low-carbon energy systems are likely to rely on power generation from variable, renewable energies (VRE) sources, thus fostering an increased demand for flexibility options which can balance mismatches of power demand and supply. Electrical energy storage (EES) is a promising option to tackle this matter and its required capacity is typically studied with model-based assessments. However, such analyses barley account for uncertainties in data assumptions or the chosen methodology, and, in consequence, lack an understanding of the robustness of the derived EES capacity. Therefore, this thesis aims to shed light on the main drivers for EES demand in highly renewable European energy systems in a comprehensive approach, considering parametric and methodological uncertainty. Using and enhancing the linear optimization model REMix, this study analyzes the required storage capacity and its utilization for northern, western, and central Europe in energy scenarios with high shares of renewable power generation (> 80%). The robustness of the storage capacity was tested against a large set of parameter variations (e.g. cost parameters or the meteorological year as input for VRE power) and methodological assumptions. The latter include different levels of technological detail (e.g. modeling approaches for thermal power plants), variations in the spatial and temporal resolution, as well as more general assumptions (e.g. restricted curtailments). In the reference scenario an overall EES capacity of approximately 200 GW and 30 TWh for Europe was derived. These results are particularly sensitive to investment costs variations of EES and VRE technologies (I) and to assumptions regarding the transmission grid infrastructure (II). (I) Reduced costs for storage and higher investment costs for VRE technologies increase the need for EES to 270 GW/55 TWh and to 235 GW/38 TWh, respectively. (II) Reducing transmission grid congestions can lower the ESS demand considerably, however, the analysis also showed that - even in the scenario which favor transmission the most (i.e. low investment costs for grid expansion) - around 120 GW of storage converter power and 13 TWh of storage unit capacity is still required for temporal balancing. In this sense, grid expansion and storage are not complete substitutes, but complementing flexibility options, both essential for future energy systems with high shares of VRE power generation. Moreover, the model-endogenously derived EES capacity mix in all scenarios is technology-diverse, underlining the necessity for a balanced storage portfolio. These findings are supported by the high dependency of the spatial capacity distribution of storage with the regionally predominant VRE technology and its temporal power generation characteristics. In this regard, significant correlations between the electricity generation from offshore and onshore wind systems with hydrogen storage charging are observed. Onshore wind power production also correlates with adiabatic compressed air storage, whereas the generation of photovoltaic systems is predominantly balanced by stationary lithium-ion batteries. To analyze the impact of the technological detail on storage demand, a comparison of two approaches for modeling thermal power plants was carried out: a detailed, mixed-integer unit-commitment approach and a simplified economic dispatch method. The results indicate that for larger observation areas (e.g. Europe) with high VRE shares, in-depth modeling is not necessarily required, however, analyses for smaller model regions in combination with lower VRE penetration levels can greatly benefit from detailed power plant modeling.