With the raise of renewable energies, a new landscape for the energy production ecosystem is in front of us. However, the intermittent nature of renewable energy sources creates a need for efficient and low-cost energy storage. In such context, redox flow batteries arise as an alternative to current technologies, aiming to offer an increased durability at a competitive cost. At UCT Prague, as part of the FlowCamp project, we work on the development of next generation redox flow batteries for large-scale energy storage systems using abundant and inexpensive materials.
Over the past two decades, there has been a significant shift in the energy production landscape towards renewable energies. Such change has been promoted by an increased social awareness about the negative effects of CO2 emissions produced by fossil fuel combustion. However, renewable energies present technological challenges due to their fluctuating nature as they cannot ensure a constant energy supply. For example, solar energy can be obtained only during daytime and wind energy heavily depends on weather conditions. This issue can be solved by means of stationary energy storage accumulating energy surpluses and releasing it afterwards as required.
Currently, the widespread energy storage solutions are pumped-hydro stations covering 95% of the energy stored in the world (2017); batteries represent less than 2% of the grand total. Pumped-hydro provides a low-cost solution but requires large volumes of water at different altitudes which limits the installations to mountainous areas. On the other hand, batteries can store up to 1000 times more energy than pumped-hydro for the same volume. But the cost of storing electrical energy in batteries is up to 10 times higher than the production cost of the same energy and, therefore, research is needed to achieve competitive costs.
Lithium-ion batteries are widely used for portable applications (such as mobile phones or electric vehicles) and lately also stationary systems based on this technology have been produced. However, as the rising demand for lithium will soon overcome its availability, alternative technologies using more abundant and economical materials are desired. In this context, redox flow batteries present a suitable solution for stationary energy storage. They operate like a common battery converting chemical energy into electricity but, instead of being a closed system, there is a flow of active materials in and out of the battery. Their operation can be thought of as similar to combustion in a heater: an “electrochemical fuel” is fed into the battery where it reacts producing electricity, but such “fuel” can also be regenerated (recharged) by reversing the system feeding electricity to the cell. This approach allows the use of the same battery design in wind/solar stations of diverse sizes as the capacity only depends on the external tanks that store the “electrochemical fuel”.
Within this search for suitable redox flow battery technologies for stationary energy storage, the FlowCamp project is funded by the EU as part of the Horizon 2020 framework (Grant Agreement no. 765289). During this four-year project (2017-2021), 15 PhD students in 11 different institutions will work on the development of prototype redox flow batteries for three different next generation systems: hydrogen-bromide, organic, and zinc-air. The main goal of this project is to decrease the cost of energy storage in considered systems to a level comparable to the energy production cost. Kosek group at Department of Chemical Engineering of UCT Prague (VSCHT v Praze) participates on this project by providing computer models to assist with the design of a zinc-air redox flow battery. The zinc-air technology is commonly used as a primary (non-rechargeable) battery in, for example, hear-aid devices. The technological challenge comes with the scalability into a redox flow system suitable for large-scale energy storage. The main advantages of this technology are its high storage capacity (energy density) and the broad availability of the employed materials.
The development of accurate and reliable computer models constitutes an essential part in the research and development of battery technologies. Computer modelling has two primary goals: Firstly, it provides necessary insight into what happens under the hood, since not all aspects of the system can be directly observed experimentally. Secondly, it provides tools for optimization and thus saves money and time spent on building prototypes with non-optimal design. This is especially important in the design of batteries as the optimization of the geometry (where the liquid flows) would require building and testing several prototypes resulting in prohibitive costs. Therefore, we work in close collaboration with the partners of the FlowCamp project that are developing different battery components providing constant feedback on upcoming development steps. Ultimately, our models will simulate how the battery behaves under different operating conditions during both charging (when the renewable energy source is producing electricity which is fed to the battery) and discharging (when the power has to be supplied from the battery to the customer). Accordingly, the modelling tools developed for the research phase can also be used for monitoring of the battery during operation as means for early diagnose of faults.
In summary, development of large scale reliable energy storage systems is a crucial need if renewable energy sources are to overcome the fossil sources. UCT is a proud member of the European FlowCamp consortium, that is pushing the frontier of that research forward developing next generation redox flow batteries.