Gigafactory For Flow Batteries in China, page-31

In a true flow battery like Vanadium Redox the storage capacity is directly related to the volume of electrolyte - double the tank size and you get twice the storage capacity (but still the same power ouput).

The Redflow battery is a "Hybrid Flow Battery", where the charge-discharge cycle involves plating zinc metal onto the electrode and disolving it back into the electrolyte solution. So doubling the storage capacity would require doubling the capacity of the electrode to accept zinc deposition as well as doubling the volume of electrolyte solution. In fact the Gen 2.5 battery contains two 5kW electrodes bolted together - while the Gen 3 battery contains a single new 10kWh electrode.

Personally I don't see why ZBMs shouldn't be just as suitable as VRB's for large scale storage. After all, large-scale lithium batteries are built using many small cells (a Tesla Model 3 with a 50kWh battery contains nearly 3000 indivudual battery cells). If a single cell fails, the battery suffers little degradation in power output or storage capacity. Similarly, a megawatt/megawatt hour ZBM-based battery would only lose 1% of its power/capacity if one ZBM was out of action for repair or it's maintenance cycle. Furthermore, ZBMs have better round trip efficiency, and can be readily transported as a completed item ready to be installed and connected to the network.