Field calibration for multidirectional spectroradiometers

A mobile calibration system for a multidirectional spectroradiometer (MUDIS) to transfer the absolute radiometric calibration from the laboratory to the location of the outdoor-measurement (field calibrator) has been developed. The main part of the calibration system comprises an aluminium sphere with a diameter of 40 cm, mounting adapters and a ventilation system. The MUDIS device is capable of measuring spectral radiance from 320 to 600 nm in 113 different directions simultaneously within 1 s. When repeating radiance measurements inside the mobile field sphere, the relative standard deviation (RSD) for wavelengths between 320 and 600 nm is less than 1.8% (320 nm) for all directions with minimum RSD of 0.6% at 382 nm. The reproducibility depends not only on the wavelength but also on the individual fibre position on the hemispherical input optics, with maximum of 4.5% RSD, but most directions show a lower deviation. On average, the RSD for the channels is less than 0.9%. The calibrator enables measurements of the spectral radiance with less uncertainty than with the previous indirect calibration method, which uses measurements of a scanning reference array spectroradiometer

MILP Model for Energy Supply Design to overcome the Cannibalization of Solar Thermal Plants and large-scale Heat Pumps in Urban District Heating Systems

Urban infrastructure is accountable for a large share of carbon emissions, especially energy supply to meet the demand for thermal heat and domestic water. Regarding the climate agreements these systems have to be decarbonized. In urban neighbourhoods, district heating systems (DHS) are efficient solutions to supply heat and favoured by locally or regionally operating municipal utilities. To integrate renewable heat from solar thermal plants or waste heat from lakes or rivers by using heat pumps, DHS in highly densed agglomerations face major problems. On the one hand the availability of land respectively free space is limited. On the other hand operating times of solar thermal plants and large-scale heat pumps are similar considering a long-term planning horizon. In this contribution a mixed integer linear programming (MILP) model is developed todetermine the implementation of both options solar thermal plants as well as large-scale heat pumps in DHS with adjustable generation plants in an optimal way. The model computes minimal investment costs and related emission savings for different alternatives integrating heat of renewable sources. The results can support the decision-making regarding the feasibility. Furthermore, good combinations of different renewable energy sources and their integration into a DHS can be identified even though the sources are distributed over the DHS. Main decision variables are the choice of possible plant sizes under consideration of the (existing) DHS-network layout and available space in highly densed urban districts. The networktopology as well as energetic and ecological constraints (e.g. maximum flow capacity in pipes or operating times of heat pumps due to boundary conditions of heat sources) lead to a selection of plant combinations which represent the optimal solution to lower the emissions at acceptable investment costs. The developed model is applied to a case study for an DHS in a newly built neighbourhood with several available heatsources for heat pumps and free areas for solar thermal collectors. The results proof the function of the model and illustrate that an energetic improvement of the DHS is possible by integrating solar thermal plants and large-scale heat pumps at economically acceptable conditions

Hochwärmeleitfähige Polymer-Compounds

Nach dem aktuellen Stand der Technik werden wärmeleitfähige thermoplastische Compounds vermehrt für Bauteile mit Entwärmungsaufgaben eingesetzt und haben somit metallische Bauteile zum Teil verdrängt. Einsatzbereiche finden sich in der Elektronik, Mechatronik aber auch in technischen Teilen in der Automobilindustrie, da bspw. die Verarbeitbarkeit im Spritzgießverfahren mehr Freiheiten bei der Formgebung ermöglicht. Weiterhin besitzen wärmeleitfähige Kunststoff-Compounds gegenüber metallischen Materialien eine wesentlich geringere Dichte und sie erlauben eine gezielte Einstellung der Materialeigenschaften durch die Variation der Füllstoffe und des Füllstoffanteils. Als Füllstoffe für wärmeleitfähige Kunststoffe haben sich organi-sche Füllstoffe (z.B. Graphit), metallische Füllstoffe (z.B. Kupfer) und keramische Füllstoffe (z.B. Bornitrid) durchgesetzt. Die Wärmeleitfähigkeitswerte von kommerziell erhältlichen Compounds liegen laut den Herstellerangaben zwischen 1 W/mK und 20 W/mK und somit um den Faktor 10 bis 100 über dem von ungefüllten Polymeren. Diese Werte konnten jedoch im Rahmen der hier vorgestellten Untersuchungen auf bis zu 30 W/mK gesteigert werden. Zum Erreichen solch hoher thermischen Leitfähigkeiten wurden bis zu 80 Gew.% an Füllstoffen in verschiedene Polymere eingebracht. Mittels einer Vielzahl an Versuchsreihen wurden neben der Wärmeleitfähigkeit auch der Einfluss auf die mechanischen Kennwerte sowie die Verarbeitbarkeit der Materialien im Extrusions- und Spritzgießprozess betrachtet. Durch den Spritzgießprozess kommt es bei gefüllten Compounds zur einer strömungsinduzierten Orientierung der Füllstoffpartikel im Bauteil. Mittels Raster-Elektronen- Mikroskop-Aufnahmen von verschiedenen Probekörpern konnte eine anisotrope Schichtstruktur nachgewiesen werden, die die Wärmeleitfähigkeit signifikant beeinflusst und eine Differenzierung der Wärmeleitfähigkeit in „through-plane“ und „in-plane“-Richtung erfordert

Energy Storage as Part of a Secure Energy Supply

The current energy system is subject to a fundamental transformation: A system that is oriented towards a constant energy supply by means of fossil fuels is now expected to integrate increasing amounts of renewable energy to achieve overall a more sustainable energy supply. The challenges arising from this paradigm shift are currently most obvious in the area of electric power supply. However, it affects all areas of the energy system, albeit with different results. Within the energy system, various independent grids fulfill the function of transporting and spatially distributing energy or energy carriers, and the demand-oriented supply ensures that energy demands are met at all times. However, renewable energy sources generally supply their energy independently from any specific energy demand. Their contribution to the overall energy system is expected to increase significantly. Energy storage technologies are one option for temporal matching of energy supply and demand. Energy storage systems have the ability to take up a certain amount of energy, store it in a storage medium for a suitable period of time, and release it in a controlled manner after a certain time delay. Energy storage systems can also be constructed as process chains by combining unit operations, each of which cover different aspects of these functions. Large-scale mechanical storage of electric power is currently almost exclusively achieved by pumped-storage hydroelectric power stations. These systems may be supplemented in the future by compressed-air energy storage and possibly air separation plants. In the area of electrochemical storage, various technologies are currently in various stages of research, development, and demonstration of their suitability for large-scale electrical energy storage. Thermal energy storage technologies are based on the storage of sensible heat, exploitation of phase transitions, adsorption/desorption processes, and chemical reactions. The latter offer the possibility of permanent and loss-free storage of heat. The storage of energy in chemical bonds involves compounds that can act as energy carriers or as chemical feedstocks. Thus, they are in direct economic competition with established (fossil fuel) supply routes. The key technology here – now and for the foreseeable future – is the electrolysis of water to produce hydrogen and oxygen. Hydrogen can be transformed by various processes into other energy carriers, which can be exploited in different sectors of the energy system and/or as raw materials for energy-intensive industrial processes. Some functions of energy storage systems can be taken over by industrial processes. Within the overall energy system, chemical energy storage technologies open up opportunities to link and interweave the various energy streams and sectors. Chemical energy storage not only offers means for greater integration of renewable energy outside the electric power sector, it also creates new opportunities for increased flexibility, novel synergies, and additional optimization. Several examples of specific energy utilization are discussed and evaluated with respect to energy storage applications. The article describes various technologies for energy storage and their potential applications in the context of Germany’s Energiewende, i.e. the transition towards a more sustainable energy system. Therefore, the existing legal framework defines some of the discussions and findings within the article, specifically the compensation for renewable electricity providers defined by the German Renewable Energy Sources Act, which is under constant reformation. While the article is written from a German perspective, the authors hope this article will be of general interest for anyone working in the areas of energy systems or energy technology

Influence of Cell Reversals on Cr/a-C Pre-coated vs Post-coated Metallic Bipolar Plates in Automotive PEMFC Systems

The results of the measurements presented in this manuscript show that none of the coatings has a significant impact on the performance degradation over the course of cell reversal cycling. However, for the EOL polarization curves, the voltage is significantly decreased for the carbon coatings compared to the Au coating. Further experiments should be performed here to determine if these are measurement inaccuracies or if the trend is confirmed. The BIP coatings Cr/a-C also perform worse in the resistance measurements of the HFR and ICR, with the pre-coat variant having the highest values after the tests. The surface changes, which can be seen in the area of the BIP deflections, probably also have an influence here. These appear to be more distinct for the BIP coating Cr/a-C pre-coat. Here, it should be analyzed in more detail how the surface changes and whether metal ions can emerge. The use of the BIP coatings Cr/a-C post- and pre-coat offers a lot of potential, both economically and technically, but cannot be recommended without reservation, as further investigations are still required.Die Ergebnisse der in diesem Manuskript vorgestellten Messungen zeigen, dass keine der Beschichtungen einen signifikanten Einfluss auf die Leistungsverschlechterung im Verlauf der Cell Reversal Zyklen hat. Bei den EOL Polarisationskurven ist die Spannung bei den Kohlenstoffbeschichtungen jedoch deutlich niedriger als bei der Au-Beschichtung. Hier sollten weitere Experimente durchgeführt werden, um festzustellen, ob es sich um Messungenauigkeiten handelt oder ob der Trend bestätigt wird. Die BIP-Beschichtungen Cr/a-C schneiden auch bei den Widerstandsmessungen des HFR und ICR schlechter ab, wobei die pre-coat nach den Tests die höchsten Werte aufweist. Wahrscheinlich haben auch hier die Oberflächenveränderungen, die im Bereich der BIP Umlenkungen zu sehen sind, einen Einfluss. Diese scheinen bei der BIP Beschichtung Cr/a-C pre-coat deutlicher ausgeprägt zu sein. Hier sollte noch genauer analysiert werden, wie sich die Oberfläche verändert und ob Metallionen austreten können. Der Einsatz der BIP Beschichtungen Cr/a-C post- und pre-coat bietet sowohl wirtschaftlich als auch technisch viel Potenzial, kann aber nicht uneingeschränkt empfohlen werden, da noch weitere Untersuchungen erforderlich sind

Power Management Optimization of an Experimental Fuel Cell/Battery/Supercapacitor Hybrid System

In this paper, an experimental fuel cell/battery/supercapacitor hybrid system is investigated in terms of modeling and power management design and optimization. The power management strategy is designed based on the role that should be played by each component of the hybrid power source. The supercapacitor is responsible for the peak power demands. The battery assists the supercapacitor in fulfilling the transient power demand by controlling its state-of-energy, whereas the fuel cell system, with its slow dynamics, controls the state-of-charge of the battery. The parameters of the power management strategy are optimized by a genetic algorithm and Pareto front analysis in a framework of multi-objective optimization, taking into account the hydrogen consumption, the battery loading and the acceleration performance. The optimization results are validated on a test bench composed of a fuel cell system (1.2 kW, 26 V), lithium polymer battery (30 Ah, 37 V), and a supercapacitor (167 F, 48 V)

Influence of Cell Reversals on Cr/a-C Pre-coated vs Post-coated Metallic Bipolar Plates in Automotive PEMFC Systems

The results of the measurements presented in this manuscript show that none of the coatings has a significant impact on the performance degradation over the course of cell reversal cycling. However, for the EOL polarization curves, the voltage is significantly decreased for the carbon coatings compared to the Au coating. Further experiments should be performed here to determine if these are measurement inaccuracies or if the trend is confirmed. The BIP coatings Cr/a-C also perform worse in the resistance measurements of the HFR and ICR, with the pre-coat variant having the highest values after the tests. The surface changes, which can be seen in the area of the BIP deflections, probably also have an influence here. These appear to be more distinct for the BIP coating Cr/a-C pre-coat. Here, it should be analyzed in more detail how the surface changes and whether metal ions can emerge. The use of the BIP coatings Cr/a-C post- and pre-coat offers a lot of potential, both economically and technically, but cannot be recommended without reservation, as further investigations are still required.Die Ergebnisse der in diesem Manuskript vorgestellten Messungen zeigen, dass keine der Beschichtungen einen signifikanten Einfluss auf die Leistungsverschlechterung im Verlauf der Cell Reversal Zyklen hat. Bei den EOL Polarisationskurven ist die Spannung bei den Kohlenstoffbeschichtungen jedoch deutlich niedriger als bei der Au-Beschichtung. Hier sollten weitere Experimente durchgeführt werden, um festzustellen, ob es sich um Messungenauigkeiten handelt oder ob der Trend bestätigt wird. Die BIP-Beschichtungen Cr/a-C schneiden auch bei den Widerstandsmessungen des HFR und ICR schlechter ab, wobei die pre-coat nach den Tests die höchsten Werte aufweist. Wahrscheinlich haben auch hier die Oberflächenveränderungen, die im Bereich der BIP Umlenkungen zu sehen sind, einen Einfluss. Diese scheinen bei der BIP Beschichtung Cr/a-C pre-coat deutlicher ausgeprägt zu sein. Hier sollte noch genauer analysiert werden, wie sich die Oberfläche verändert und ob Metallionen austreten können. Der Einsatz der BIP Beschichtungen Cr/a-C post- und pre-coat bietet sowohl wirtschaftlich als auch technisch viel Potenzial, kann aber nicht uneingeschränkt empfohlen werden, da noch weitere Untersuchungen erforderlich sind

Influence of Cell Reversals on Cr/a-C Pre-coated vs Post-coated Metallic Bipolar Plates in Automotive PEMFC Systems

The results of the measurements presented in this manuscript show that none of the coatings has a significant impact on the performance degradation over the course of cell reversal cycling. However, for the EOL polarization curves, the voltage is significantly decreased for the carbon coatings compared to the Au coating. Further experiments should be performed here to determine if these are measurement inaccuracies or if the trend is confirmed. The BIP coatings Cr/a-C also perform worse in the resistance measurements of the HFR and ICR, with the pre-coat variant having the highest values after the tests. The surface changes, which can be seen in the area of the BIP deflections, probably also have an influence here. These appear to be more distinct for the BIP coating Cr/a-C pre-coat. Here, it should be analyzed in more detail how the surface changes and whether metal ions can emerge. The use of the BIP coatings Cr/a-C post- and pre-coat offers a lot of potential, both economically and technically, but cannot be recommended without reservation, as further investigations are still required.Die Ergebnisse der in diesem Manuskript vorgestellten Messungen zeigen, dass keine der Beschichtungen einen signifikanten Einfluss auf die Leistungsverschlechterung im Verlauf der Cell Reversal Zyklen hat. Bei den EOL Polarisationskurven ist die Spannung bei den Kohlenstoffbeschichtungen jedoch deutlich niedriger als bei der Au-Beschichtung. Hier sollten weitere Experimente durchgeführt werden, um festzustellen, ob es sich um Messungenauigkeiten handelt oder ob der Trend bestätigt wird. Die BIP-Beschichtungen Cr/a-C schneiden auch bei den Widerstandsmessungen des HFR und ICR schlechter ab, wobei die pre-coat nach den Tests die höchsten Werte aufweist. Wahrscheinlich haben auch hier die Oberflächenveränderungen, die im Bereich der BIP Umlenkungen zu sehen sind, einen Einfluss. Diese scheinen bei der BIP Beschichtung Cr/a-C pre-coat deutlicher ausgeprägt zu sein. Hier sollte noch genauer analysiert werden, wie sich die Oberfläche verändert und ob Metallionen austreten können. Der Einsatz der BIP Beschichtungen Cr/a-C post- und pre-coat bietet sowohl wirtschaftlich als auch technisch viel Potenzial, kann aber nicht uneingeschränkt empfohlen werden, da noch weitere Untersuchungen erforderlich sind