• Energy Research
• 7. Clean energy close
• 11. Sustainability close
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• University of Stuttgart close

AbstractAlthough the road-map of the oxy-fuel process seems to be very advanced, there are still plenty of open questions. One of the significant ones is the corrosive behaviour of the heat exchanger surfaces. The Institute of Combustion and Power Plant Technology, University of Stuttgart, performs research on the fireside corrosion under oxy-fuel and conventional combustion conditions for the current and supercritical power plants considering the influence of combustion modus, gas atmosphere and fly ash deposits on the waterwall and superheater surfaces. Since the oxy-fuel-combustion atmosphere is composed of recirculated flue gases and pure oxygen, significantly higher concentrations of CO2, SO2 and H2O are present compared to the conventional combustion of coal with air as an oxidizer. In the here presented study the influence of an oxy-fuel combustion of a hard-coal on the surface of selected superheater materials is discussed and compared to the results obtained for lignite. Especially the interactions between the flue gas atmosphere, ash deposits and heat exchanger materials are studied in detail. The investigation encompassed in this paper has been focused on impacts of oxide-scale growth, carbon enrichment of the materials and sulphur-induced corrosion.Increased sulphur-induced corrosion has been observed in samples exposed to the oxy-combustion atmosphere. The noticed higher depth of corrosive attack of the oxy-fuel samples might be explained by a higher partial pressure of SO2 which is characteristic for oxy-fuel process. Moreover in certain cases the sulphur might be released by the deposits. Beside that, the oxy-fuel samples were exposed to much higher partial pressures of carbon dioxide comparing to the air-case leading apparently to rapid and massive internal carbon enrichment in the oxide scale. Moreover dependence between the chromium content and oxidation ability of the austenitic materials surfaces was noticed under oxy-fuel conditions.

This contribution provides the simulated data and surrogate models for the DTU 10 MW reference wind turbine in an onshore configuration simulated with FAST v8.16.00. The dimensions include mean wind speed, turbulence intensity, and power level, as well as the application of an individual blade control (IBC) loop. Down-regulation up to 50% is considered using two controller trajectories. The constTSR trajectory considers only pitching for down-regulation, maintaining a constant tip speed ratio, and the lin70 trajectory considers both pitch and rotational speed reduction to achieve down-regulation. Power boosting is performed up to 130% power level by following the optimal Cp trajectory until the requested power level is reached. The regression is done with two methods: a spline-based interpolation and a Gaussian Process Regression (GPR). The raw data, smoothened data, and the trained GPR models are provided along with scripts for generating the surrogate model's predictions with both methods. A short description of the simulation parameters and variables considered is given in the supplementary pdf file. The dataset is part of the doctoral thesis 'Wind Turbine Operational Optimization Considering Revenue and Fatigue Objectives' by Vasilis Pettas at the University of Stuttgart (http://dx.doi.org/10.18419/opus-13959) and the journal publication 'Surrogate Modeling and Aeroelastic Analysis of a Wind Turbine with Down-Regulation, Power Boosting, and IBC Capabilities' (https://doi.org/10.3390/en17061284). Detailed analysis of the controller design and validation of the surrogate models can be found in these publications. 

Die Stromerzeugung aus Windenergie hat in den vergangenen Jahren, insbesondere unterstützt durch das Erneuerbare-Energien-Gesetz (EEG), stark zugenommen und belief sich im Jahr 2006 auf einen Anteil von rund 4,8 % an der Bruttostromerzeugung. Aufgrund des fluktuierenden Charakters der Windstromerzeugung ist die Integration und Einspeisung dieses Anteils in das Netz der öffentlichen Versorgung bereits heute mit teilweise erheblichen Problemen verbunden. Diese werden sich in Zukunft weiter verstärken, wenn der geplante Einstieg in die Offshore-Windenergienutzung wie geplant stattfindet und in den kommenden Jahren einige GW Leistung Offshore installiert werden. Grundsätzlich bieten sich zwei Lösungsansätze für die angesprochene Problematik an, die sich gegenseitig ergänzen: Zum einen können durch exaktere Prognoseverfahren die zu erwartenden Windstrommengen besser vorhergesagt und damit zugleich die Fahrpläne der konventionellen (Schatten-)Kraftwerke genauer erstellt werden. Der Bedarf an Ausgleichsenergie wird durch dieses Verfahren minimiert. Im Fall von Windflauten muss jedoch die gesamte nachgefragte Leistung durch konventionelle Kraftwerke bereitgestellt werden. Zum anderen kann durch den Einsatz von Speicherkraftwerken eine zeitliche Entkopplung von Energieangebot und –bedarf realisiert werden, indem in Zeiten hohen Windenergieangebots ein Teil des Windstroms zwischengespeichert wird und umgekehrt in Windflauten das Speicherkraftwerk die Strombereitstellung übernimmt. Mit Hilfe dieses Verfahrens erfolgt dementsprechend eine Anpassung des Angebots an die Nachfrage. Die vorliegende Arbeit konzentriert sich auf den zweiten Ansatz und entwickelt ein Simulationsmodell, mit dessen Hilfe ein Windpark-Speicher-System abgebildet und eine Vergleichmäßigung des Windstroms durch Integration verschiedener Speichertechnologen (diabates/adiabates Druckluft-Speicherkraftwerk, Pumpspeicherkraftwerk) simuliert wird. Ziel der Vergleichmäßigung ist die kontinuierliche Bereitstellung einer garantierten Leistung. Die verbleibenden Fluktuationen werden durch einen Abgleich mit der Nachfrageseite in Form der Netzlast berücksichtigt. Für unterschiedliche Systemvarianten werden sowohl die Stromgestehungskosten als auch die spezifischen CO2-Emissionen berechnet, um auf dieser Basis einen Vergleich der einzelnen Systeme zu ermöglichen. Grundlegende Parameter wie beispielsweise die energetische Speicherkapazität, die spezifischen Investitionskosten der Windenergieanlagen und des Speicherkraftwerks oder auch die Bezugskosten für Ausgleichsenergie werden anschließend in Form von Sensitivitätsanalysen und Parametervariation detailliert untersucht. Auf diese Weise können die unter konstant gesetzten Parametern gewonnenen Ergebnisse bestätigt bzw. kritisch hinterfragt werden, wobei insbesondere der Einfluss der verschiedenen Eingangsgrößen auf die Stromgestehungskosten im Detail analysiert wird. In der Folge werden vielversprechende Systemkonfigurationen unter dem Zielkriterium möglichst geringer Stromgestehungskosten identifiziert. Zudem wird geprüft, welche Anforderungen an die Kostenentwicklung speziell von Druckluft-Speicherkraftwerken zu stellen sind, um mit einem konventionellen Vergleichssystem konkurrenzfähig zu werden. Power generation from wind energy has increased significantly in the past years reaching 4.8 % of the gross power generation. This development was especially promoted by the re-newable energy law (Erneuerbares-Energien-Gesetz). The integration and feed-in of this power into the grid is associated with considerable problems as the wind power generation is characterised by its fluctuating nature. These diffi-culties will grow and accelerate if the planned wind parks in the North or Baltic Sea with some GW power are realised in the following years. In principle there are two methods of resolution for this kind of problem which com-plement one another: On the one hand it’s possible to develop better forecasting models in order to forecast the wind power generation more accurately. By this means also the operation of the conventional power plants can be planned more accurately. In the consequence the de-mand for balancing power is minimized. Nevertheless it’s inevitable to provide the total sum of demanded power in times of wind calms by conventional power plants. Concerning the second method the operation of storage facilities is involved in the system in order to realise a temporal decoupling of energy supply and demand. In times with high wind power generation the storage unit is filled and vice versa in wind calms the storage facility is able to provide power. Thus the supply side is adapted to the demand side. The following thesis focuses on the second method. A tool is developed, simulating the operation of a windpark-storage system, in order to equalise the wind power generation by the help of different storage technologies (diabatic/adiabatic compressed air energy storage, pumped hydro). The equalisation aims at the continuous supply of a guaranteed power. Re-maining fluctuations of wind power are considered by a comparison of demand and supply side, whereas the demand side is represented by the system load. The costs of generating electricity as well as the specific CO2-emissions are calculated for different configurations resulting in a comparison of the different systems. Following fun-damental parameters as the energy storage capacity, the specific investment costs of the wind power plants and the storage facility or the price of balancing power are examined in detail by the help of a sensitivity analysis. In so doing it is possible to confirm or to question the results calculated with fixed parameters. In this context especially the influence of different parame-ters on the costs of generating electricity is analysed. Finally promising system configurations with the aim of reducing the costs of generat-ing electricity are identified. Moreover the requirements concerning the reduction of invest-ment costs especially of compressed air energy storage systems in order to achieve competi-tiveness with a conventional system are examined.

Lipase‐catalyzed transesterification of triglycerides and alcohols to obtain biodiesel is an environmentally friendly and sustainable route for fuels production since, besides proceeding in mild reaction conditions, it allows for the use of low‐cost feedstocks that contain water and free fatty acids, for example non‐edible oils and waste oils. This review article reports recent advances in the field and focus in particular on a major issue in the enzymatic process, the inactivation of most lipases caused by methanol, the preferred acyl acceptor used for alcoholysis. The recent results about immobilization of enzymes on nano‐materials and the use of whole‐cell biocatalysts, as well as the use of cell‐surface display technologies and metabolic engineering strategies for microbial production of biodiesel are described. It is discussed also insight into the effects of methanol on lipases obtained by modeling approaches and report on studies aimed at mining novel alcohol stable enzymes or at improving robustness in existing ones by protein engineering.

The companies of the photovoltaic industry have experienced considerable growth in recent years. And further growth is forecasted for the coming years. By now, nearly two million single photovoltaic (PV) installations generate electricity from sunlight around the world. Thereby, the wafer-based PV products have a market share of about 80-85%. The interim shortage of silicon and the increasing cost pressure in the market give rise to ever thinner and larger wafers. Thus, the "PV Roadmap for Crystalline Silicon" of the German cell producers expects an average wafer thickness of 100 µm until 2020 and the next generation of wafer thickness in 2015. This trend brings about new challenges for the PV industry: due to the manual and automated handling in the manufacturing the silicon-based wafers are exposed to mechanical stress. If the wafers, however, become ever thinner they lose their mechanical stability and might form cracks when exposed to huge forces during the handling.These cracks, however, cause a higher breakage rate and are one of the main reasons for breakdowns of the finished modules. The damage-free handling of the very fragile silicon wafers will gain in importance due to the expected increase in the throughput. Therefore, the handling systems and components must not only handle the sensitive substrates as gently as possible but also with high speed and precision in the µm range. For this purpose, new adjusted handling components are required. This thesis aims at making a contribution to the optimal selection of handling components for the photovoltaic industry. The primary target is the development of an objective and vendor-independent evaluation procedure for grippers especially used in the cell and module manufacturing. The procedure to be developed should be suitable for cell, equipment and machine manufacturers as well as for component suppliers. Furthermore, the procedure should be applicable to identical and variable grippingprinciples. The result of the method should be the optimal decision guidance for the user and should enable an adequate and neutral classification of the tested gripper. Der enorme Ausbau der Produktionskapazitäten der Photovoltaik-Industrie in den vergangenen Jahren hat auch die Anforderungen an den Maschinen- und Anlagenbau erhöht. Die Automatisierung in der Fertigung von Solarzellen spielt dabei zur Sicherung von Qualität und Ausbeute und somit auch für die Kostenreduktion eine entscheidende Rolle. Die sich erhöhenden Materialtransportintensitäten zwischen den einzelnen Prozessschritten stellen dabei eine nicht zu vernachlässigende Herausforderung dar: Die zunehmend dünneren und fragilen Substrate bei verkürzten Zykluszeiten bringen insbesondere die Handhabung an deren physikalische Grenzen. Vor diesem Hintergrund gewinnt eine Bewertung der Leistungsfähigkeit von Handhabungskomponenten verstärkt an Bedeutung. Die Ausgangssituation zeigt, dass in der Zellfertigung aktueller Fertigungslinien insbesondere die greiferbasierte Handhabung mit Pick-and-Place-Charakter bereits parallel eingesetzt wird, um den hohen Durchsätzen gerecht zuwerden. Hierbei muss der Aufnahme- und Ablagevorgang so schnell und schädigungsarm durchgeführt werden, dass sowohl der geforderte Durchsatz, wie auch die erforderliche Qualität erreicht werden können. Durch diese Randbedingungen sind neue und erhöhte Anforderungen an die Greiferauswahl und die optimale Parametereinstellung des eingesetzten Greifers zu stellen. Die vorliegende Arbeit beschreibt ein neues, angepassten Verfahren für die Leistungsbewertung von Greifern für Silizium-Wafer. Im Vordergrund steht die Entwicklung eines objektiven und herstellerunabhängigen Bewertungsverfahrens für Greifer, die insbesonders in der Zell- und Modulfertigung eingesetzt werden. Das zu entwickelnde Verfahren kann sowohl von Zellherstellern, Anlagen- und Maschinenbauern, aber auch von Komponentenlieferanten eingesetzt werden. Das daraus resultierende Ergebnis soll eine optimale Entscheidungshilfe für den Anwender darstellen aber auch eine adäquate, neutrale Klassifizierung der getestetenGreifer ermöglichen.

The increasing number of Distributed Generation Units (DGs) in distribution grids is challenging the way electrical systems are designed and operated. For traditional power systems, Low Voltage (LV) networks play a passive role in voltage regulation, but when DGs are present the LV network may play an active role in voltage control. In this paper, a voltage control strategy using mini Combined Heat and Power (mCHP) is proposed. For this aim, the electrical and thermal dynamics of a mCHP plant are considered, a voltage controller is designed and a voltage control mode is developed, which prolongs the regulation action of the mCHP unit using heat storage. Simulations are conducted considering thermal and electrical demand of a typical multi-family house in the climate region of North Rhine-Westphalia, Germany. Aspects of resulting voltage and thermal profiles, compared to a traditional heat lead mode, are discussed for an exemplary day.

Lithium-ion cells are widely used in various applications. For optimal performance and safety, it is crucial to have accurate knowledge of the temperature of each cell. However, determining the temperature for individual cells is challenging as the core temperature may significantly differ from the surface temperature, leading to the need for further research in this field. This study presents the first sensorless temperature estimation method for determining the core temperature of each cell within a battery module. The accuracy of temperature estimation is in the range of ΔT≈1 K. The cell temperature is determined using an artificial neural network (ANN) based on electrochemical impedance spectroscopy (EIS) data. Additionally, by optimizing the frequency range, the number of measurement points, input neurons, measurement time, and computational effort are significantly reduced, while maintaining or even improving the accuracy of temperature estimation. The required time for the EIS measurement can be reduced to 0.5 s, and the temperature calculation takes place within a few milliseconds. The setup consists of cylindrical 18,650 lithium-ion cells assembled into modules with a 3s2p configuration. The core temperature of the cells was measured using sensors placed inside each cell. For the EIS measurement, alternating current excitation was applied across the entire module, and voltage was measured individually for each cell. Various State of Charge (SoC), ambient temperatures, and DC loads were investigated. Compared to other methods for temperature determination, the advantages of the presented study lie in the simplicity of the approach. Only one impedance chip per module is required as additional hardware to apply the AC current. The ANN consists of a simple feedforward network with only one layer in the hidden layer, resulting in minimal computational effort, making this approach attractive for real-world applications.

Sustainability aspects and their verification are becoming indispensable for companies in the textile industry from both an economic and a legal perspective. The reason for this is that there is a large number of different certificates, specifications, and labels, such as Global Organic Textile Standard, Fairtrade, or OekoTex, as well as legislation, such as the German Act on Corporate Due Diligence Obligations in Supply Chains issued in 2021. Hence, the requirements for keeping the proof, e.g. for the batch-accurate world-wide tracing of organic cotton for clothing, or for the necessary transparency to determine the carbon footprint or the recycling percentage, are becoming more and more associated with considerable effort, especially for small and medium-sized enterprises (SMEs). Depending on the certificate or specification, SMEs need not only to determine their own sustainability information (gate-to-gate), but also that of the upstream stages of the value chain (cradle-to-gate). The multi-stage value chains of the SME-dominated textile industry, together with the vast and fast-changing variety of materials and products, lead to high complexity in processes and communication. In addition, when confronted with batch-related sustainability criteria and a variety of sustainability and labelling requests from different customers, SMEs have to spend an increasing amount of time and effort on the reliable provision and communication of the respective information. The paper describes the challenges and existing approaches, e.g. the use of blockchain technology, associated with the provision of cradle-to-gate sustainability information in textile SMEs and proposes a holistic framework enabling SMEs along the value chain to configure and implement an infrastructure for efficient, fully digital cloud-ready workflow, based on process models and textile product master trees, in order to address these challenges.