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Comment by apendleton | Hacker News Reader

The mix of lithium ion and flow batteries here (50MWh of the former vs. 5MWh of the latter) kind of makes this feel like a proof of concept to me on the flow battery side -- I'd sort of expect the reverse, and to want to mostly lean on the flow batteries because of their suitability for long-duration storage and their tolerance of lots and lots of cycles, and mostly only use the lithium ion when you needed lots of power or to handle rapid changes in demand. But maybe I misunderstand the dynamics here?

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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.

I think you're basically right. I know some people that looked in to building a flow battery (it didn't pan out for other reasons). The utility wanted it for frequency regulation - in other words, extremely short timescale response times.

But why? I thought one of the chief advantages of flow batteries was a lower cost per kWh at scale, as the expensive electrodes can be sized for peak power, while the cheaper electrolyte can be sized for capacity. Perhaps the economies of scale in lithium-ion batteries have had a bigger impact on cost than this clever split, so lion is actually cheaper per kwh?

Yes, exactly, this was my question as well. I understand their explanation for how they're using it, but it seems like the economics would be much better if configured differently.

Kind of battery cache?

FYI I think you are using “auteur” incorrectly.

If you think of the flow battery as a fast cache and the Lithium Ion as a slower one then that might help you form a better picture.

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