The thermochemical properties of Na2Zn(SO4)(2) are systematically analyzed under dynamic conditions at various partial vapor pressures ranging from 50 mbar to 700 mbar, aiming to evaluate its potential as a material for Thermochemical Energy Storage (TCES). At 50 mbar, dehydration to Na2Zn(SO4)(2) starts at similar to 94.5 degrees C and rehydration begins at 60.6 degrees C. At 700 mbar, onset temperatures shift to 105 degrees C for dehydration and 117.9 degrees C for hydration. Na2Zn(SO4)(2) exhibits a favorable charging temperature interval and high cycle stability during the transition from dihydrate to anhydrate, indicating its promise for TCES applications. The introduction of dopants significantly influences system performance, resulting in: (a) a reduction in dehydration onset temperatures by 7-20 degrees C; (b) an increase in hydration onset temperatures by 3-7 degrees C; (c) complete vapor uptake reaching the stoichiometric 2 mol H2O/mol Na2Zn(SO4)(2); and (d) shorter induction times with accelerated reaction kinetics. LiCl-doped samples also show improved stability and reduced mass loss over multiple hydration cycles. However, the complete hydration of tetrahydrate is not fully achieved, suggesting a need for further investigation into optimal dopant compositions and their effects on hydration kinetics. Overall, addressing thermodynamic challenges and optimizing hydration processes position Na2Zn(SO4)(2)2H(2)O as a potential candidate for efficient and sustainable thermal energy storage, contributing to advancements in the field of TCES.

The authors would like to make the following corrections to the published paper [...]

Wind energy is considered a pillar of the low-carbon energy system of the future. Whereas the side effects and social costs of fossil energy sources (coal, oil and gas), as well as those of nuclear energy, are well-documented and quantified, understanding of the analogous questions with respect to wind energy is far less advanced. However, such understanding is crucial in order to minimize the influence of wind energy on the environment and to compare its social costs with those of conventional energy sources. Here, we summarize the state of knowledge of three side effects of wind energy that have not been convincingly evaluated to date. We focus our analysis on three topics, namely (1) the impact of wind energy on insects; (2) the impact of wind energy on the spatiotemporal distribution of air velocity, temperature, moisture and precipitation in the vicinity of wind parks; and (3) the impact of wind energy on humans through noise emission. For each topic, we formulate open research questions that should be addressed by responsible policy incentives in order to comprehensively assess the social costs of wind energy and to develop wind farms with minimal impact on their environment.

Asa practical contribution to the energy transition from fossil to renewable energy, this paper addresses a wellness product with high energy demand: the sauna. The overall goal of the presented research project is to develop and demonstrate a so-called Zero-Energy-Sauna. In this paper, the development by means of numerical simulations is discussed. In a preliminary study, multiple concepts have been systematically derived and assessed. One innovative concept has been patented and an extended version of this concept is being implemented in this research project. The implemented concept utilizes solar energy and applies two types of thermal energy storage: a pressurized, stratified hot water storage and a closed low-pressure adsorption storage. The main purpose of the hot water storage is the heat supply, while the purpose of the adsorption storage is to provide steam. We formulate and investigate two numerical models for these thermal energy storages. For the hot water storage, an one-dimensional model is applied which considers the effect of natural convection. With this model, different charging and discharging scenarios are examined, proving the applicability of this type of hot water storage for a Zero-Energy-Sauna. For the adsorption storage, a previously developed and published model is adopted and extended by a metal plate for manual steam generation. Based on this model, various configurations of the adsorption storage are studied, revealing an optimum design for maximum steam generation. The storage designs derived by numerical simulations serve as blueprints for the two thermal energy storages. Both storages are currently being implemented and experimentally investigated in the Zero-Energy-Sauna of the ongoing research project. (c) 2021 Elsevier B.V. All rights reserved.

Ob Dezentralisierung, Dekarbonisierung oder Digitalisierung – BWK berichtet praxisnah und kompetent über alle relevanten Themen der Energiebranche. BWK beschreibt Trends und innovative Geschäftsmodelle, präsentiert neue Lösungen und liefert hochkarätige Fachinformationen für die tägliche Praxis. Charakteristisch ist die Kombination von breitem Überblick und in die Tiefe gehender Berichterstattung. BWK ist konsequent ausgerichtet auf den Informationsbedarf von Entscheidern bei Energieversorgern und -verteilern, bei Herstellern und Dienstleistern, bei Anlagenbetreibern und Energieanwendern.

The Future Fuels project combines research in several institutes of the German Aerospace Center (DLR) on the production and use of synthetic fuels for space, energy, transportation, and aviation. This article gives an overview of the research questions considered and results achieved so far and also provides insight into the multidimensional and interdisciplinary project approach. Various methods and models were used which are embedded in the research context and based on established approaches. The prospects for large-scale fuel production using renewable electricity and solar radiation played a key role in the project. Empirical and model-based investigations of the technological and cost-related aspects were supplemented by modelling of the integration into a future electricity system. The composition, properties, and the related performance and emissions of synthetic fuels play an important role both for potential oxygenated drop-in fuels in road transport and for the design and certification of alternative aviation fuels. In addition, possible green synthetic fuels as an alternative to highly toxic hydrazine were investigated with different tools and experiments using combustion chambers. The results provide new answers to many research questions. The experiences with the interdisciplinary approach of Future Fuels are relevant for the further development of research topics and co-operations in this field.

We formulate the concept of a multi-functional energy system, called storage plant, as a possible solution to cover the variable residual load that appears in most countries after introducing renewables in the power sector. A storage plant consists of a photovoltaic power plant, a heat storage system with electric heater to transform solar power, a steam power cycle to convert stored heat to dispatchable power, a backup heating unit for the storage based on the combustion of biomass or other renewable hydrocarbons, and a gas turbine with waste heat recovery for peak loads. After explaining the storage plant concept, the paper describes a simulation model of the German power sector and its transformation from the year 2020 with roughly 40% renewable electricity share to 2040 with a hypothetic 90% renewable electricity share. Multi-indicator benchmarking over that period shows that storage plants can have a key role to achieve emission goals and at the same time sustain full supply security within the German power sector.

Background Many governments take the view that voluntary national targets to reduce greenhouse gas emissions are sufficient to avoid negative climate effects. In the absence of independent verification, however, pledges are unlikely to be sufficient for a rapid and strong reduction of emissions. It is often claimed that a global carbon tax could be an effective instrument. However, such a tax is difficult to set and to collect, especially in countries with poor administrative infrastructure. Results Here, we formulate and discuss a novel approach, the Global Carbon Surcharge (GCS), that mimics a carbon tax but does not require tax collection by governments. We define GCS as a requirement or a voluntary commitment encompassing all companies extracting carbon-carrying raw materials, namely coal, oil, gas and limestone, with the aim to burden their extraction with costs proportional to their carbon intensity. GCS mandates all companies to store these materials immediately after mining for a given period of time in the vicinity of the production site. Thereby, GCS generates additional costs that propagate through all sectors of the global economy. We elucidate how the investment costs for the storage infrastructure translate into surcharges on the raw materials. Conclusions We show that by a proper choice of the storage time and the size of the storage unit, GCS becomes equivalent to a carbon tax in the range between 50 and 100 € per ton of CO 2 that is assumed to be necessary for the transition to a carbon-neutral energy system. An attractive feature of GCS is that it can be verified, in particular by citizens themselves, using publicly available satellite data. Finally, if compulsory storage is coupled to blockchain-based smart contracts and a mandatory (expensive) mining of cryptocurrency, GCS can be operated without governmental protectionism, corruption and fraud. However, the main uncertainties of the GCS approach lie in the substantial expansion of infrastructure and the fact that the induced price effects must be sufficient to achieve a rapid and far-reaching substitution of fossil fuels.

Die Verringerung des weltweiten CO2-Ausstoßes ist ein zentrales Ziel internationaler Energie- und Klimapolitik. Oft hören wir in diesem Zusammenhang in Deutschland jedoch auch Aussagen über weitergehende Ziele, wie etwa: „Mit erneuerbarer Energie kann sich Deutschland von Energieimporten unabhängig machen und energieautark werden.“ Wie wichtig ist eigentlich Energieautarkie? Für alle, die daran glauben, dass eine Volkswirtschaft sich nach Möglichkeit autark mit Energie versorgen sollte, sind die beiden Artikel von Axel Kleidon (S. 120) und Klaus Stierstadt (S. 128) in dieser Ausgabe gute Nachrichten. Die beiden Kollegen berechnen – jeder aus einer etwas anderen Perspektive – das theoretische Potenzial erneuerbarer Energie in Deutschland. Dabei greifen Kleidon und Stierstadt weder auf raumzeitlich hochaufgelöste Satellitendaten zurück, noch bedienen sie sich ausgefeilter Computersimulationen. Sie verwenden für ihre Berechnungen vielmehr die gute alte „Back-of-the-Envelope“-Methode und kommen zu dem Schluss, dass Deutschland zumindest theoretisch seinen Energiebedarf aus heimischen Quellen decken kann. Aber wozu brauchen wir im Zeitalter von Satellitenfernerkundung und Digitalisierung noch solch altmodische Rechnungen? Warum soll Energieautarkie ein wertvolles Gut sein? Ich finde die Betrachtungen von Kleidon und Stierstadt aus drei Gründen wissenschaftlich lehrreich und intellektuell anregend. Erstens befriedigen sie jenseits praktischer Erwägungen unsere physikalische Neugier, ähnlich wie das Sammeln von Exoplaneten oder das Inventarisieren von Elementarteilchen. Zweitens helfen sie uns, Plausibilität und Konsistenz computergenerierter Energieszenarien zu prüfen. Einfache Abschätzungen zeigen oft, dass hinter mancher beeindruckenden numerischen Fassade ein simples physikalisches Gebäude steckt. Mit ähnlich einfachen Abschätzungen hätten nüchtern denkende Forscher beispielsweise schon im Jahr 1972 die vom Club of Rome in der Studie „Grenzen des Wachstums“ aufwendig berechneten Weltuntergangsszenarien schnell als numerische Artefakte enttarnt. Drittens schärfen einfache Größenordnungsbetrachtungen, auf die wir in der Physik zu Recht stolz sind, das Gespür für den Umgang mit unscharfem Wissen und eignen sich deshalb sehr gut für die schulische und universitäre Lehre. Doch wie steht es um die Energieautarkie Deutschlands? Ich habe nie verstanden, wieso in einer globalisierten Welt Energieautarkie ein besonders wertvolles Gut sein soll. Schließlich versorgt sich Deutschland weder autark mit Bananen noch mit Eisenerz und schon gar nicht mit Smartphones oder Internet-Suchmaschinen. Im Gegenteil. Die Globalisierung führt zu einer immer engeren weltweiten Vernetzung auf allen Gebieten. Warum sollte das bei der Energieversorgung anders sein? Ich glaube, dass erneuerbare Energie eine große Chance für einen friedlichen weltumspannenden Handel mit den Energieprodukten Strom, Mobilität und Wärme bietet. Die künftige weltweite Nachfrage könnte Menschen in Afrika und anderen sonnenreichen Regionen Arbeit und Wohlstand bringen. Strom aus afrikanischen Solarkraftwerken könnte in Zukunft mittels Hochspannungsleitungen zu uns übertragen werden. Flüssige Mobilität in Form von CO2-neutral erzeugter synthetischer Treibstoffe lässt sich mit Tankern zu uns verschiffen. Und wenn ich noch etwas spekulieren darf: Wer weiß, ob wir nicht eines Tages sogar Zeugen eines Wärmehandels auf der Basis preiswerter thermochemischer Energiespeicher wie beispielsweise Kalk werden, ein Konzept, das ich als „Limestone-Economy“ bezeichne. Den verbleibenden Teil unseres Energiebedarfs können wir dann aus heimischen erneuerbaren Quellen gewinnen. Die maximal möglichen Mengen haben Kleidon und Stierstadt für uns sehr plausibel berechnet und verständlich dargestellt. Die Kosten sollten wir dabei freilich stets im Blick behalten. Kurzum, ich glaube, dass ein energieautarkes Deutschland eine reizvolle Vision ist. Was ihre Umsetzung anbelangt, so stimme ich eher dem Ausspruch eines ehemaligen Bundesministers zu: „Wenn Autarkie entscheidend für das Funktionieren einer Volkswirtschaft wäre, dann müsste Nordkorea das wirtschaftlich erfolgreichste Land der Welt sein.“ André Thess ist Professor für Energiespeicherung an der Universität Stuttgart und Direktor des Instituts für Technische Thermodynamik des Deutschen Zentrums für Luft- und Raumfahrt.

We report a combined experimental and numerical investigation of a melting process representative of latent thermal energy storage systems. The purpose of the work is to assess the accuracy of numerical models of melting governed by natural convection with a benchmark experiment. The experiment consists of a rectangular box filled with a model liquid (n-octadecane) and heated symmetrically from both sides such as to allow access for shadowgraph imaging and particle image velocimetry to measure the phase state and velocities, respectively. Our numerical method for computing fluid flow, temperature, and phase state involves two different approaches: the first is a detailed model using variable thermophysical properties and the volume of fluid method to allow volume expansion in an additional air phase that we solve in two dimensions. The second is a simplified model using constant thermophysical properties and the Boussinesq approximation that we solve either in two or in three dimensions. In the first part of the work, we systematically compare the simplified (Boussinesq) with the detailed (volume of fluid) model. We find that for the given set of parameters (Ra = 2.10(8), A = 4, Ste = 0.092, Pr = 52), the difference between the detailed and the simplified model in predicting global quantities such as the liquid phase fraction and the total heat flow rate is smaller than 4%, whereas velocities differ up to 20%. In the second part of the work, we compare the simulations of the simplified Boussinesq model in three dimensions with the benchmark experiment. We find that the simulation predicts the liquid phase fraction and temperatures with deviations below 4%, but significantly overestimates the velocity magnitudes. Our experimental and numerical tools provide a rational framework in which the accuracy of latent thermal energy storage simulations can be systematically and comprehensively assessed.