Unsolicited long-duration energy storage thoughts:
1. round trip efficiency didn't matter much for project economics when doing ancillary services or real time energy trading, matters a lot for long duration storage applications

2. Having a "long duration storage technology" is mostly a bad thing. It means you can't do higher value / higher power activities when the need/opportunity arises.

3. On the other hand, having an incredibly low cost energy storage technology is a good thing, obviously, and in fact it is the only way you will ever get over the "long duration storage technology" handicap sitting in the Minuses column in your buyer's evaluation

4. The biggest challenge is achieving manufacturing scale:
*Solar panels spent decades being improved in calculators, satellites, offshore oil rigs, etc. before being deployed at MW scale
*Li-Ion did same w/ camcorders, phones, laptops, cars

Scale carefully, iron out the kinks.

5. Grid tied projects in the 100s of MW need:
A) safety
B) proven multi-year track record
C) bankable OEM (multi-B $ balance sheet)
D) lower capex on a $/kwh basis than any competitor
E) high round trip efficiency
F) development/permitting path

6. The items above only describe Lithium Ion today for new build projects (yes, even for 8+ hours).
They also hold for existing Pumped Hydro projects. Many but not all new PHS projects tend to fail on items D-F.

7. Finally, I'm not a lithium-ion investor or booster, just stating the facts as I see them. I keep a file on every flow battery, thermal storage, etc. new technology I come across and wish them all luck and hope they're a viable option soon. But you can only rush this so much.