Can we store more green energy with improved flow batteries?
Generating green energy, we can already manage quite well. Just think of the many wind turbines or solar panels. However, the lack of consistent energy production is a disadvantage. When there is a lot of wind or sunshine, we see peaks in production. But our energy consumption does not necessarily keeps track. Storing the generated energy for use the moment we actually need it is therefore essential.
Jonas Hereijgers is a professor of industrial sciences, with a specialisation in chemistry at UAntwerp. In his RECHARGE research project, for which he received a prestigious ERC grant, he focuses on improving flow batteries. They are used for such purposes as storing green energy efficiently.
Classic batteries versus flow batteries
‘You can’t just store electricity’, Hereijgers begins. ‘To do that, you need certain processes, like chemical reactions. For example, they take place in batteries’. Hereijgers explains how a classic battery works: ‘Inside, there are two plates in a liquid. A chemical reaction takes place on the surface of those plates: one plate gives off electrically charged particles, and the other absorbs them. This is how you get electricity’. The more liquid there is in a battery, the more electricity can be stored in it. ‘If you want more storage, the entire battery will automatically have to be expanded, so that more liquid will fit in it. That’s expensive’.
Flow batteries solve this problem: ‘In a flow battery, the liquid is not inside the battery housing, but in external vessels. From there, they are pumped to the battery and back again. This design makes it possible to expand only the vessels, and not the entire battery, which is a lot less expensive’. According to Hereijgers, flow batteries are particularly interesting for the storage of green energy. ‘The major drawback to solar and wind power is that production is not constant. During bright sunlight or high winds, there is a surplus, and there is a deficit at night or on windless days. It is therefore a challenge to maintain a balance between supply and demand. One solution is to store the excess energy and release it later. Flow batteries are ideal for doing this’.
Maximising charging speed
Hereijgers would like to make flow batteries even better. He is investigating how they can be charged faster. ‘This is crucial, because if a battery is too slow to fill up, it is not very useful for it to be large’. He is working on two improvements: ‘First, there are plates inside the battery. The larger their surface area is, the more charged particles can be absorbed and released at the same time, and thus the faster the battery can charge and discharge. For this reason, plates with a sponge-like structure are preferred, as they have a much larger surface area. One problem, however, is that the structures used now are disordered. As a result, the liquid does not flow through it evenly, and not every zone of the plates is utilised optimally’. Hereijgers’ solution is to use a 3D printer to make his own plates, with an ordered structure.
He would also like to modify exactly how the fluid is pumped through a flow battery. ‘Currently, the flow of liquid is typically constant. If the current were to be pulsed, it would create turbulence, making the charged particles in it move much faster. This would make it possible to charge and discharge the battery in less time. Compare it to a sugar cube in a cup of tea: it dissolves on its own, but slowly. If you stir, it goes much faster’.
Hereijgers would like to use these two innovations to make flow batteries faster. ‘Each of the optimisations alone is a major step forward. When the two are combined, that is truly innovative!’