SCCER Heat and Electricty Storage Wärme und Strom Speicherung

The Orkney Islands of Scotland have been selected for the development of a new Europeanwide hydrogen project, named BIG HIT (Building Innovative Green Hydrogen systems in an Isolated Territory: a pilot for Europe).
Started in May 2016, it is a five-year demonstration project involving 12 participants based across six EU countries and coordinated by the Aragon Hydrogen Foundation (FHA).
Within BIG HIT, the otherwise curtailed energy generated from tidal and wind turbines (on average more than 30% of the annual renewable output in Orkney) is being used to produce ‘green’ hydrogen from electrolysis, which is then transported across the Orkney islands and used as fuel for transport, heat and power community end-uses.

Achieving stringent long-term climate change mitigation goals requires provision of clean fuels to endusers while intensifying the use of low carbon emissions sources (i.e. renewable energy). The growing share of intermittent renewable energy, such as wind and solar energy technologies, impose challenges related to the temporal and spatial grid balancing:

- Temporal balancing arises due to the inevitable mismatch between renewable electricity production and demand as a consequence of day/night cycles, weather effects and seasonal differences.
- Spatial balancing is necessary resulting from a possible mismatch between locations of electricity production and consumption.

Energy conversion technologies with storage, such as Power-to-Product (P2X) technologies, represent potential solutions for this multi-dimensional balancing challenge and to enhance the energy system’s flexibility. The term P2X refers to energy conversion technologies that produce synthetic gases, fuels or energy feedstock products using an electro-chemical conversion process. There is a variety of energy outputs that can be produced in P2X technologies, with methane produced in Powerto- Gas (PTG) systems being one of the most prominently discussed options. As such, P2X technology not only offers a possible flexibility solution for the electricity system, they can also connect the electricity sector with other sectors of the economy in a new way (e.g. the transport sector and industry). With the aim to derive a technical, economic and environmental assessment of Power-to-X technology with its systemic interdependencies, this research work specifically investigates the gas market, the mobility sector and the electricity market including the corresponding regulatory and innovation policy aspects. From the analysis we derive essential factors that can contribute to the successful implementation of this technology and to arrive at profitable business cases, as well as key energy market segments for P2X technology.

more less

Lithium-ion batteries enabled the success of portable electronics and find increasingly application in electric vehicles and in centralized and decentralized stationary storage for the temporal and spatial balancing of energy supply and demand. Worldwide efforts to scale production volumes for lithium-ion batteries have led to a significant cost reduction over recent years, but also result in increasing challenges in the supply of raw materials, in particular cobalt, which is already classified as critical by the European commission.¹
Within SCCER HaE, we are investigating cathode materials for next-generation lithium-ion batteries. Our research focuses on nickel-rich layered oxides with reduced cobalt content. Increasing the nickel content in layered oxides offers significantly improved lithium storage capacity, but at the price of reduced cycling stability. Employing sacrificial electrolyte additives, we were able to demonstrate a NMC811/graphite full cell with a capacity retention of >90% after 200 cycles.²

To improve operational safety and reduced cell production costs, we are also developing concepts to replace the liquid electrolytes based on highly-flammable organic solvents in lithium- and sodium-ion batteries by non-flammable aqueous electrolytes. The major disadvantage of water as electrolyte solvent is its intrinsically narrow electrochemical stability window (thermodynamically only 1.23 V) limiting maximum cell voltage and consequently the batteries energy density. We recently discovered an aqueous sodium-ion electrolyte system with a much wider electrochemical stability window of 2.6 V ³ enabling us to demonstrate a NaTi₂(PO₄)₃/Na₃(VOPO₄)₂F full cell with 85% capacity retention after 500 cycles.⁴
We are also developing solid-state electrolytes for all-solid-state batteries based on closoborate salts. We were able to stabilize a highly ionically conducting phase at room temperature using anion mixing reaching ionic conductivities on the order of 1 mS/cm at room temperature.⁵ This achievement further enabled us to assemble an all-solid-state battery with a sodium metal anode and a NaCrO₂ cathode delivering a capacity retention of 85% after 250 cycles bringing this class of materials to a technology readiness level comparable to other current all-solid-state battery concepts.⁶
We are also investigating ionic transport in Na-β’’-Al₂O₃ ceramics, an archetypical ion conductor, commercially employed as solid-state electrolytes in high-temperature sodium-nickel-chloride and sodium-sulfur batteries, but also promising for applications in future all-solid-state batteries. Although already discovered in the 1960s, Na-β’’-alumina ceramics are challenging to prepare with the desired composition, phase content, and microstructure. These parameters have a direct impact on the ion conductivity, which varies by a factor of 100 at a given temperature when comparing different studies. We developed a comprehensive model identifying the dominant factors governing ion transport in these materials.⁷

References:
¹ http://ec.europa.eu/growth/sectors/raw-materials/specific-interest/critical.
² Vidal Laveda J., Low J. E., Stilp E., Dilger S., Battaglia C., submitted.
³ Duchêne L., Kühnel R.-S., Rentsch D., Remhof A., Hagemann H., Battaglia C., Chem. Comm., 2017, 53, 4195.
⁴ Duchêne L., Kühnel R.-S., Stilp E., Cuervo Reyes E., Remhof A., Hagemann H., Battaglia C., Energy Environ. Science, 2017, 10, 2609.
⁵ Kühnel R.-S., Reber D., Battaglia C., ACS Energy Lett., 2017, 2, 2017.
⁶ Reber D., Kühnel R.-S., Battaglia C., submitted.
⁷ Bay M.-C. Heinz M. V. F., Figi R., Schreiner C., Basso D., Zanon N. Vogt U. F., Battaglia C., submitted.

more less

Thermal energy storage and the components therefore are essential in a large field of applications. In residential building applications – for example – their size i.e. volume and the efficiency is a cost driver. In solar thermal energy use the storage units are important components, because they bridge the time between diurnal conversion and demand. In case of a sensible (water) heat storage, the stratification within the tank is of key importance for the efficiency of the system. Existing recommendations for the design of storage tanks which have a good temperature stratification are generalized to any storage size. The feed flow deflection relation is identified as a relevant variable. If this deflection relation is less than 0.12 for horizontal inlet into the tank and less than 0.5 for inlet via an upward or downward elbow pipe pointing towards the top or bottom of the tank, the unintended deflection of the entering fluid stream into local vertical flows is low and an existing storage stratification is effectively maintained¹.

To increase storage density and therefore reduce storage volume an ice storage allows the storing of solar heat in a compact volume for the later use as source for a heat pump that provides heat for a building – or as a sink in a cooling system. As an example a novel ice storage with 2m³ water volume is described which contains heat exchanger plates for extracting the latent heat. A numerical model for the heat exchanger plates that was implemented into the Polysun system simulation software will be presented. The model allows the numerical simulation of an ice storages according a field installation with heat exchanger plates. The field installation will be used for the validation of the system template. The core elements of the developed model are the heat transfer values (𝑈𝑈𝐴𝐴𝑖𝑖) between the brine inside the heat exchangers plates and the water inside the storage². The UA-values limit the maximum power that can be extracted from or injected to the storage (ice or fluid) and thus, have a large influence on the simulation results. Sensible heating, sensible cooling as well as icing are treated individually as they all inflict different physical dynamics in the fluid on small scales that effect the overall heat (power and energy) balance. In all states, the UAvalues are derived from general heat transfer correlations. In the model all UA-values represent the values associated to one control volume (1 knot), while the heat exchanger has a fixed number of control volumes 12 - of 12 knots - and the water volume is modelled as 1 knot. As a further step in decreasing thermal energy storage volume an absorption desorption seasonal thermal energy storage system – a thermo-chemical storage could be applied. Such a closed sorption heat storage based on water vapour absorption in aqueous slat solutions theoretically achieves a significantly higher volumetric energy density compared to conventional hot water or ice storage systems. To this purpose, the development of an absorber-desorber unit - a prototype designed for a power output of 10 kW – is presented. In this work, the influence of two main parameters on the exchanged power is evidenced. Furthermore, a comparison with the results of the initial numerical model used to design the heat and mass exchanger is carried out. Physical explanations of the diverging results encountered during the absorption process as well as an improved heat transfer coefficient model for the desorption process are proposed³.

References:
¹Battaglia, M.; Haller, M. Y. Stratification in large thermal storage tanks. Eurosun 2018, September 10 – 13, Rapperswil, Switzerland.
²Philippen, D.; Battaglia M.; CarbonellD.; Thissen B.; Kunath L. Validation of an ice storage model and its integration into a solar-ice system. Eurosun 2018, September 10 – 13, Rapperswil, Switzerland.
³Daguenet-Frick, X.; Gantenbein, P.; Müller, J.; Fumey B.; Werber, R. Seasonal thermochemical energy storage: comparison of the experimental results with the modelling of the falling film tube bundle heat and mass exchanger unit. Renewable Energy 110 (2017) 162-173.

more less