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With the increasing share of renewable energies and the nuclear phase-out, the energy transition is accelerating. From the perspective of building technology, there is great potential to support this transition given its large share in total energy consumption and the increasing number of flexible and controllable components and storages. However, a question often asked at the plant level is: "How do we use this flexibility to support the regional grid?". In this work, a grid-supportive controller of a real-world building energy plant was developed using mathematical optimisation methods and its technical feasibility was demonstrated. The results could convince actors from the energy industry and academia about the practicality of these methods and offer tools for their implementation.
Passive hybridization refers to a parallel connection of photovoltaic and battery cells on the direct current level without any active controllers or inverters. We present the first study of a lithium-ion battery cell connected in parallel to a string of four or five serially-connected photovoltaic cells. Experimental investigations were performed using a modified commercial photovoltaic module and a lithium titanate battery pouch cell, representing an overall 41.7 W-peak (photovoltaic)/36.8 W-hour (battery) passive hybrid system. Systematic and detailed monitoring of this system over periods of several days with different load scenarios was carried out. A scaled dynamic synthetic load representing a typical profile of a single-family house was successfully supplied with 100 % self-sufficiency over a period of two days. The system shows dynamic, fully passive self-regulation without maximum power point tracking and without battery management system. The feasibility of a photovoltaic/lithium-ion battery passive hybrid system could therefore be demonstrated.
This paper shows the results of an in-depth techno-economic analysis of the public transport sector in a small to midsize city and its surrounding area. Public battery-electric and hydrogen fuel cell buses are comparatively evaluated by means of a total cost of ownership (TCO) model building on historical data and a projection of market prices. Additionally, a structural analysis of the public transport system of a specific city is performed, assessing best fitting bus lines for the use of electric or hydrogen busses, which is supported by a brief acceptance evaluation of the local citizens. The TCO results for electric buses show a strong cost decrease until the year 2030, reaching 23.5% lower TCOs compared to the conventional diesel bus. The optimal electric bus charging system will be the opportunity (pantograph) charging infrastructure. However, the opportunity charging method is applicable under the assumption that several buses share the same station and there is a “hotspot” where as many as possible bus lines converge. In the case of electric buses for the year 2020, the parameter which influenced the most on the TCO was the battery cost, opposite to the year 2030 in where the bus body cost and fuel cost parameters are the ones that dominate the TCO, due to the learning rate of the batteries. For H2 buses, finding a hotspot is not crucial because they have a similar range to the diesel ones as well as a similar refueling time. H2 buses until 2030 still have 15.4% higher TCO than the diesel bus system. Considering the benefits of a hypothetical scaling-up effect of hydrogen infrastructures in the region, the hydrogen cost could drop to 5 €/kg. In this case, the overall TCO of the hydrogen solution would drop to a slightly lower TCO than the diesel solution in 2030. Therefore, hydrogen buses can be competitive in small to midsize cities, even with limited routes. For hydrogen buses, the bus body and fuel cost make up a large part of the TCO. Reducing the fuel cost will be an important aspect to reduce the total TCO of the hydrogen bus.
This work presents the results of experimental operation of a solar-driven climate system using mixed-integer nonlinear model predictive control (MPC). The system is installed in a university building and consists of two solar thermal collector fields, an adsorption cooling machine with different operation modes, a stratified hot water storage with multiple inlets and outlets as well as a cold water storage. The system and the applied modeling approach is described and a parallelized algorithm for mixed-integer nonlinear MPC and a corresponding implementation for the system are presented. Finally, we show and discuss the results of experimental operation of the system and highlight the advantages of the mixed-integer nonlinear MPC application.
Der verstärkte Einsatz von Wärmepumpen bei der Realisierung einer klimaneutralen Wärmeversorgung führt zu einer signifikanten Zunahme und Änderung der elektrischen Lasten in den Verteilnetzen. Daher gilt es, Wärmepumpen so zu steuern, dass sie Verteilnetze wenig belasten oder sogar unterstützen.
Inhalt des Projekts „PV²WP - PV Vorhersage für die netzdienliche Steuerung von Wärmepumpen“ (Projektlaufzeit 1.07.2018 – 30.06.2021) war die Demonstration eines neuen Ansatzes zur Steuerung von Heizungssystemen, die auf Wärmepumpen und thermischen Speichern basieren und in Kombination mit einer Photovoltaikanlage betrieben werden. Das übergeordnete Ziel war dabei die Verbesserung der Netzintegration und Smart-Grid-Tauglichkeit entsprechender Heizungssysteme durch eine kostengünstige Technologie bei gleichzeitiger Erhöhung der Wirtschaftlichkeit.
Dabei wurden drei zukunftsweisende Technologien in Kombination genutzt und demonstriert: wolkenkamerabasierte Kurzfristprognosen, prädiktive Steuerung und Regelung sowie machinelearning-basierte Systemmodellierung als Basis für die Optimierung. Als Demonstrationsumgebung diente mit dem Projekthaus Ulm ein real bewohntes Einfamilienhaus.Umweltforschung
Bifaziale Photovoltaikmodule werden durch ihre höhere Leistung, bezogen auf den Flächenbedarf immer attraktiver. Die meisten der bislang hergestellten Photovoltaik Module sind Monofazial ausgeführtund schöpfen damit nicht ihr vollständiges Potential aus. Weiterhin bestehen die konventionell hergestelltenPhotovoltaik(PV) Module aus einem Verbund aus Glas und Kunststoff sowie verschiedenen Metallen, was die Entsorgung oder ein Recycling kostenaufwendig und kompliziert gestaltet. Die Firma Apollon greift diese Punkte auf und versucht, beides in dem NICE-Modul(Siehe Anhang 12.1)zu vereinen,nämlich ein bifaziales Modul, bei dem die PV-Zellen zwischen zwei Glasplatten, anstelle von zwei Kunststoffen eingespannt werden. Die Hochschule Offenburg ist F&E-Partner der Firma Apollon und betreibt ein kleines Labor zur Herstellung von NICE-Modulen. Zu Testzwecken werden diese der Witterung ausgesetzt und so der Energieertrag,sowie deren Lebensdauer unter geltenden Witterungsbedingungen ermittelt. In der Masterarbeit von Benjamin Smith[1]stellte sich heraus, dass sich bei den Modulen nach weniger als zwei Wochen im Freien die Klebefläche zwischen den Glasplatten löste. Somit fielen die Module beim Witterungstest unter realen Bedingungen durch.Im Anschluss an die Arbeit von Benjamin Smith besteht diese Arbeit darin,einen Außenteststand zu konzipieren und aufzubauen, um das in Zwischenzeit neu entworfene Klebe-konzept, welches einem TC 50 Test standhielt, auf die Lebensdauer im Freien und das PV Modul selbst auf den elektrischen Ertrag zu untersuchen. Für den elektrischen Ertrag werden Strom-und Spannungsverlauf aufgezeichnet. Außerdem musste für eine Charakterisierung der Module die Bestrahlungsstärke,der Temperaturverlauf, sowie die Inho-mogenität der Bestrahlungsstärke auf der Rückseite und die Windgeschwindigkeit ermittelt werden. Um eine Alterung des Modulwechselrichters auszuschließen, werden speziell dafür die Wechselspannung und Leistung auf der Ausgangsseite des Modulwechselrichters aufgezeichnet. Sämtliche modulrelevanten Messwerte werden im 3-5 s Intervall abgespeichert und sind auf einem Webserver sowie für eine spätere Datenanalyse als .csv Datei abrufbar. Somit eignet sich die Messeinrichtung lediglich für eine Bilanzierung,nicht aber für eine Leistungsmessung.
Für den Außenteststand musste eine Unterkonstruktion, geeignet für bifaziale Module entworfen und aufgebaut werden. Die Konstruktion ist vollständig aufgebaut. Das Messsystem wurde auf deren Funktion erfolgreich geprüft und steht bis auf die Strahlungsinhomogenitätsmessung im Technikum am Campus Nord der Hochschule Offenburg bereit zur Inbetriebnahme.
Lithium‐ion battery cells are multiscale and multiphysics systems. Design and material parameters influence the macroscopically observable cell performance in a complex and nonlinear way. Herein, the development and application of three methodologies for model‐based interpretation and visualization of these influences are presented: 1) deconvolution of overpotential contributions, including ohmic, concentration, and activation overpotentials of the various cell components; 2) partial electrochemical impedance spectroscopy, allowing a direct visualization of the origin of different impedance features; and 3) sensitivity analyses, allowing a systematic assessment of the influence of cell parameters on capacity, internal resistance, and impedance. The methods are applied to a previously developed and validated pseudo‐3D model of a high‐power lithium‐ion pouch cell. The cell features a blend cathode. The two blend components show strong coupling, which can be observed and interpreted using the results of overpotential deconvolution, partial impedance spectroscopy, and sensitivity analysis. The presented methods are useful tools for model‐supported lithium‐ion cell research and development.
This article presents a comparative experimental study of the electrical, structural and chemical properties of large‐format, 180 Ah prismatic lithium iron phosphate (LFP)/graphite lithium‐ion battery cells from two different manufacturers. These cells are particularly used in the field of stationary energy storage such as home‐storage systems. The investigations include (1) cell‐to‐cell performance assessment, for which a total of 28 cells was tested from each manufacturer, (2) electrical charge/discharge characteristics at different currents and ambient temperatures, (3) internal cell geometries, components, and weight analysis after cell opening, (4) microstructural analysis of the electrodes via light microscopy and scanning electron microscopy, (5) chemical analysis of the electrode materials using energy‐dispersive X‐ray spectroscopy, and (6) mathematical analysis of the electrode balances. The combined results give a detailed and comparative insight into the cell characteristics, providing essential information needed for system integration. The study also provides complete and self‐consistent parameter sets for the use in cells models needed for performance prediction or state diagnosis.
Lithium-ion batteries play a vital role in a society more and more affected by the spectre of climate change: hence the need of lowering CO2 emissions and reducing the fossil fuel consumption. At the moment, lithium-ion batteries appear as the ideal candidates for this challenge but further research and development is required to understand their behaviour, predict their issues and therefore improve their performance. In this regard, mathematical modelling and numerical simulation have become standard techniques in lithium-ion battery research and development and have proven to be highly useful in supporting experimental work and increasing the predictability of model-based life expectancy.
This study focuses on the electrochemical ageing reactions at the anode, especially on the topic of lithium plating and its interaction with the solid electrolyte interface (SEI). The purpose of this work is a deeper understanding of these degradation processes through the construction of refined modelling frameworks and the analysis of simulations carried out over a wide range of operating conditions. The governing equations are implemented in the in-house multiphysics software package DENIS, while the electrochemistry model is based on the use of the open-source chemical kinetics code CANTERA.
The development, parameterisation and experimental validation of a comprehensive pseudo-three-dimensional multiphysics model of a commercial lithium-ion cell with blend cathode and graphite anode is presented. This model is able to describe and simulate both multiscale heat and mass transport and complex electrochemical reaction mechanisms, including also as extra feature the capability of reproducing a composite electrode where multiple active materials are subject to intercalation/deintercalation reaction.
A further extension to include reversible lithium plating process and predict ageing behaviour over a wide range of conditions, with a focus on the high currents and low temperatures particularly interesting for the fast charging topic, follows. This extended model is verified by comparison with published experimental data showing voltage plateau and voltage drop as plating indicators and optionally includes an explicit re-intercalation reaction that is shown to suppress macroscopic plating hints in the specific case of a cell not showing evident plating signs. This model is used to create degradation maps over a wide range of conditions and an in-depth spatiotemporal analysis of the anode behaviour at the mesoscopic and microscopic scales, demonstrating the dynamic and nonlinear interaction between the intercalation and plating reactions.
A deeper outlook on the SEI formation and growth is presented, together with the qualitative description of three different 1D-models with a decreasing level of detail, developed with the purpose of ideally being included in future in more comprehensive multiscale frameworks.
Finally, the extended model is successfully coupled with a previously developed SEI model to result in an original modelling framework able to simulate both degradation processes and their continuous positive feedback.