Flow batteries: more cost effective for residential and utility-scale installations?


Before joining Imergy, Watkins served as chief executive of Bridgelux, Inc., a leading developer and manufacturer of solid state lighting technologies and solutions. Before that, Watkins served as CEO of Seagate Technology, the world’s leading disc drive and storage solutions company, from 2004 to 2009. During his tenure at Seagate, Watkins was named Forbes Magazine 2006 CEO of the year.

pv magazine: How much cheaper are Imergy vanadium-based batteries to comparable lithium and lead-acid batteries for use in conjunction with either residential rooftop solar arrays or large utility-scale PV installations?

Bill Watkins: For anything that needs long-duration storage, the flow battery will win every time, simply because it can provide very short duration cycles, for the stability – rapid cloud cover type of things – and it can do very long duration, whereas the lithium ion and lead acid can’t do long duration very well. They’re extremely expensive when duration gets longer than an hour to 90 minutes and they need to be largely oversized to avoid deep discharge, so you’ve got a clear winner from the point of view of long-duration. The only issue is space. If it’s a residential environment, and the footprint is really small, then lithium ion has an advantage, but then it can’t do long-duration. So long-duration lithium is going to be much bigger than short-duration lithium, and long-duration lead acid is bigger than a flow battery. For example in Germany they’re selling small residential systems for about €11,000 for a 2.5 kW/10 kWh system, and I think those are lithium. Imergy’s flow batteries are about 50% more cost effective for both residential and utility-scale installations.

Lithium has won a lot of projects for short, quick duration and it may be fine for that. In order to do long duration with lithium you have to continue to oversize it. The other thing which none of the lithium manufacturers talk about is what we call mid-balance – you want to be able to charge and discharge, which means you have to be below full. And if you hold a lithium ion battery below full for long periods it just dies. So you don’t want to operate lithium in that mode at all, whereas a flow battery can operate in that middle band without any impact for any number of cycles.

How much are Imergy batteries at the moment?

The cost of an Imergy battery depends on several factors – the power size and the discharge duration are typical examples of the factors driving that cost. As I noted previously, our cost structure is substantially below the pricing for an equivalent capability delivered by lithium batteries. Because an Imergy battery is very long-lived, we can deliver the lowest levelized cost of stored energy (LCOSE) of any competitor in the market. Just as the LCOE for PV is much higher in Germany than in the U.S. Southwest due to sunshine availability, the LCOSE for storage depends on factors ranging from ambient air temperature, depth of discharge, initial costs, O&M, equipment replacement costs, and discharge duration, to name a few. We have analyzed many use case comparisons to know that in case after case, Imergy can deliver a lower LCOSE than any other battery in the market. You add to that LCOSE the benign environmental characteristics of the Imergy battery and you have a clear winner.


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