SCCER Heat and Electricty Storage Wärme und Strom Speicherung

Na-Ion batteries are among the candidates for next generation battery systems and are under exploration at a fundamental level. Electrodes for Na-Ion constising of intermetallics (Sn, Sb etc.) show impressive specific charge densitiy above 500 mAh/g. Furthermore, the cyclability of the Na- battery electrodes improves if an additive such as FEC (fluoroethylene carbonate) is added. In order get from promissing electrode materials to electrodes and battery cells, a mechanically and chemically stable electrode is required. In Li-ion battery systems PVDF (Polyvinylidenfluorid) is a well established binder for the electrodes. Yet in Na-ion systems PDVF binder seems not to work. In this study the interface between the intermetallic (Sn) electrode and the binder is inverstigated via XPS to explore the failure mechanisms.

The outflow temperature of a thermal energy storage (TES) system with only sensible heat storage material drops during discharge if the tank is not large enough and not sufficiently pre-charged. This can be mitigated if the sensible heat storage is combined with a latent heat storage system. This approch is evaluated by exeriments and simulations.

Cellular ceramics are attracting materials for high temperature applications such as high-temperature thermal storage systems, thermal protection systems, burners, reformers, and solar radiation absorbers. These material structures are able to withstand oxidative environments at high temperatures and are particularly resistant to thermal shock. As typical for ceramic materials, thermal stresses are one of the major reasons of failure in these components when used in high temperature applications. The study of this phenomena is a difficult task since it couples the thermal physics and structural mechanics of ceramics with a possibly complex cellular structure. X-ray computed tomography of a commercially available SiSiC foam produced by the replica method, was used to digitally reconstruct the cellular structure. We then used the finite element method (FEM) as well as experiments to study the effect of structural features on ceramic foams’ mechanical and thermal properties. In a second step, models of lattice structures made of ordered tetrakaidecahedral unit cells – a unit cell often used to represent the microstructure of commercial foams – were simulated and their morphology (e.g. strut shape, cross section, and thickness) optimized for enhanced thermo-mechanical properties. Optimized structures made of SiSiC were produced using advanced additive manufacturing techniques in conjunction with the conventional replica method. Their mechanical properties were then tested using non-destructive techniques (acoustical emission and electrical resistance) and compared to the FEM numerical modeling.

A promising idea is to store hydrogen chemically bound to small molecules in a way that allows a quick hydrogen evolution or storage on demand. CO₂ has been proven to be suitable carrier molecule for hydrogen, by forming formic acid or formates. Beside the catalysts and carrier substances, the solvent systems play a crucial role in these processes. It mediates the interactions between the reactants, catalysts, and the products. For this purpose, we examined in detail the interactions of formic acid with some carefully selected solvents, using FT-IR, NMR spectroscopy and calorimetric methods.

Redox flow batteries (RFBs) are very well suited for storing the intermittent excess supply of renewable electricity. However, conventional RFBs cannot in many situations utilize all the available “junk” electricity due to a limited storage capacity, as they are charged and discharged electrochemically, with electricity stored as chemical energy in the electrolytes. In the RFB system reported here, the electrolytes are conventionally charged but are then chemically discharged over catalytic beds in separate external circuits.

Formic acid can be selectively decomposed into CO free carbon dioxide and hydrogen. It has been shown, that beside the ruthenium(II)-mtppts systems, the iron(II) – hydrido tris[(2-diphenyl-phosphino)ethyl]-phosphine complex also catalyses formic acid cleavage with an exceptionally high rate and efficiency. This opens the way for cheap, non-noble metal based catalysts for this reaction. Entirely rechargeable hydrogen storage devices have been developed based on the hydrogenation of bicarbonates, or CO₂ – amine systems and decomposition of formates in aqueous solution or organic solvents with the same catalysts, [{RuCl₂(mtppms)2}2][4] or [RuH₂(dppm)2], in both directions without needing to isolate either the formates or bicarbonate salts to start new cycles. For the first time, the direct hydrogenation of CO₂ into formic acid using a homogeneous ruthenium catalyst, in aqueous solution and in dimethyl sulfoxide without any additives, have been realised.

The electrochemical reduction of CO₂ is an interesting pathway since a broad range of useful products can be formed. Nevertheless, on top of the high overpotential required to drive this reaction, the electrochemical reduction of CO₂ suffers from a poor yield/selectivity of valuable products. In order to overcome these two barriers, a better fundamental understanding of this reaction is urgently needed. Especially, the yield of each reaction product should be quantified as a function of several parameters. For this purpose, we have designed a Differential Electrochemical Mass Spectrometry (DEMS) setup coupled with an electrochemical flow cell that allows the in-operando quantification of the volatile species produced in the course of the reaction. Alternatively, this reaction is studied also using an online Fourier Transformed Infra-Red (FTIR) spectroscopy setup coupled with an electrochemical cell where information about adsorbed reaction intermediates could be earned.

A promising storage system based on the combination of a heat pump, heat engine, cold and hot storage is presented. This site-independent technology can provide flexibility between power and heat while supplying electricity efficiently in the interesting power range of approximately 0.3-100 MW for several hours. Within the SCCER framework, HSLU is reviewing and extending the existing variations, as well as developing new ones. The goal is to adapt this flexible technology in order to provide application-specific, optimized storage solutions for a variety of cases from bulk electricity storage to district heating, cooling and electricity storage.

The process of Power-to-Methane transforms excess electrical energy to chemical energy in the form of methane. This process is conducted in two stages: In the 1st stage, the electrolysis, water is split into oxygen and hydrogen the latter is transformed in a 2nd stage into methane in using carbon dioxide from a suitable source. This gas can be transported over long distances in the natural gas grid and it can be stored in storages already existing today.
It is the aim of our project, to demonstrate existing technologies of the Power-to-Methane process to the public and interested expert groups.

The objective of this research (conducted in WP5 of SCCER-Storage) is to develop a uniform techno-economic and environmental assessment method for electrical and thermal storage. This assessment is intrinsically flexible because it can be applied to different energy storage (ES) technologies for both heat and electricity, for different applications and sectors. The analysis will integrate different levels including:

• the storage unit, e.g. battery unit or hot water tank.
• the application, e.g. renewable energy (RE) time-shift and demand shifting.
• the system interactions, e.g. energy prices and reference scenarios.

Within WP5, a time-dependent analysis will be conducted including RE intermittency, ES dynamics, energy prices with tariffs and demand load profiles. In first instance we focus on electricity, based on SWISSIX data; later on, we address district heating. This analysis will be compared with a time-independent approach based on pre-defined ES systems and constant energy prices in order to understand the impact of the temporal resolution on the results. The outputs of this assessment method will be used to quantify the benefits of ES for the Swiss energy system and the profitability for investors.