RE: EV’s11 Dec 2019 13:44
In mobile transportation it is possible to use the movement to drive air over either the Lithium-ion cells or their liquid based cooling systems plus radiators. This potentially reduces the space taken up by the airconditioning/cooling systems that need to be used on Lithium-ion batteries when they are used for stationary storage applications. It is the need to provide space for these systems (plus power of course is needed to run them), plus the additional space needed to provide individual access to each specific Lithium-ion battery module that bulks up LiB systems when used for stationary storage and makes them, in practise, much closer to the volumetric density that can be obtained with VRFBs. Remember that stationary energy storage applications are also quite a lot more demanding in that the battery can be on full power for many tens of minutes, even hours, unlike in eVs your traditional 5 seconds blasting off the lights to beat the RS turbo next door.
Also in mobile applications it is not just the volumetric energy density that is important it is also the specific energy density that is important (i.e. per unit weight). In fast moving machines (rockets, planes, cars and perhaps to a lesser extent trains) the more mass you have to accelerate and take around corners the greater the forces you need to apply, and the greater the kinetic energy of the moving vehicle. Ships go quite slowly and ferries often only have short distances to go so perhaps there is an argument for VRFBs there for the more weighty VRFB systems.
I'm actually looking at applications at present where the additional weight of a VRFB system is beneficial in providing a ballasting counterweight for PV panel systems, so weight is not always a bad thing.