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Comment by c2h5oh | Hacker News Reader

The small handful of sodium batteries that are currently available retail all seem to have rather bad roundtrip efficiency compared to LFP and voltage drop starting at a high state of charge.

Also LFP prices dropped enough that shipping cost from China became a significant part of the price. This will be even more of a factor should the less energy dense sodium batteries ever reach the promised $30/kWh.

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One thing I hadn't groked about Sodium Ion was the enormous Voltage range leads to a bit of an issue when it comes to current. You have a 4x voltage from top to bottom of the battery and this also means your current is 4x as well for the same power output. This becomes a bit of an issue and it is part of the efficiency equation, not just externally to the battery where wires have to be much larger than LFP or LI but internally due to internal resistance.

Ehhh not really a problem unless you idolize 12/48 V style systems that aren't adequate for these modern chemistries (i.e., non-lead-acid based) that scale down effectively to single digit amp hours per cell. You can keep the current around a comfortable 20A at any pack size, just by increasing the voltage. Say 5Ah cells. At 1.5kV (the highest easily practical with mainstream transistors and sticking to the "simple" circuit designs), that's 7.5kWh per such battery string.

That's a small home solar setup's entire battery.

Sodium gravimetric density is same. Volumetric is worse. Shipping containers generally cost by volume, but given how dense batteries are I suspect this won't matter.

I'd agree if you could stick them in the containers discharged, but you can't. This means that even safer chemistry like sodium battery is still hazardous cargo.

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