I think they covered this question pretty well here:

> Invinity’s vanadium flow batteries are used to ‘front-end’ the energy asset, acting as a first line of response when the system is called into service; only after the required response exceeds the capacity of the Invinity battery does the lithium-ion battery get called into service. Since Invinity’s flow battery does not degrade with use and can cycle indefinitely, it performs much of the ‘heavy-lifting’ required from the system while reducing wear on the lithium-ion battery.

What I think this means, is the the 5Mhw of flow batter covers demand spikes and the 50Mhw allows for larger longer draws during off peak renewable times.

I am just an enthusiastic auteur in this field and could be very wrong.