Heatwave demand pulls Unigrid's sodium-ion home batteries into Europe at a premium to lithium

A household in Spain running the air conditioner off a wall battery on a heatwave afternoon wants two things from it: the box should pay for itself out of cheaper grid hours, and it should sit safely in the house ^[2]. Spain heads Darren Tan's list. "We have requests coming from Spain, France, Germany, The Netherlands," Unigrid's co-founder and chief executive said ^[3]. The demand Tan describes came with a heatwave ^[2], and the temperature figure the BBC attaches to sodium-ion is for cold, operation down to minus 40C ^[5].

Those buyers take power when the grid sells it cheaply and spend it on cooling later ^[2]. In my view nothing in that job needs sodium in particular. The category tells itself they are buying a chemistry that could end up cheaper to build and run than lithium-ion, and one potentially less likely to catch fire ^[5]. The larger prize, in the BBC's account, is batteries made in the US from entirely US-sourced materials ^[7].

On price, sodium costs more for now. Unigrid's pricing is roughly $100 per kWh, while LFP, a relatively cheap form of lithium-ion, traded at $81 last December ^[12]. The premium is $19 per kWh, about 23% ^[14], or roughly $171 across a 9 kWh unit at those rates ^[15]. The BBC did not report a retail price. Some companies told the BBC sodium-ion might fall as low as $30 per kWh ^[23]. Cell supply is a second price variable. "We can switch back and forth and choose what battery we want to work with," Tan said ^[9].

Clare Grey of the University of Cambridge, a co-founder of battery firm Nyobolt, aims her objection at the sales pitch. She told the BBC that a company going for sodium and selling it on safety should not start putting in elements that will raise red flags ^[18]. Ivana Hasa of the University of Warwick, who has no connection to Unigrid, said chromium-3 can turn into chromium-6 at very high states of charge, and that the risk can be mitigated by how voltage is controlled ^[19]. "Safety tests reported on the cell chemistry are very promising," she said ^[20]. Tan said third-party tests have not been able to make the battery form chromium-6 ^[21]. "We've tried very hard to try and produce it, we've overcharged it as much as we can... We were unsuccessful in generating chromium-6," he said ^[22]. Other manufacturers use cathodes without chromium, such as sodium iron phosphate pyrophosphate, or NFPP ^[11].

The volumes are still small. The 1,000 units Tan expects Unigrid to ship by year end add up to 9 MWh of storage ^[16].

For an installer deciding whether to stock it, I'd use a 2x2. The first test is whether the site needs something sodium claims over lithium, such as operation in deep cold or a lower fire risk where the unit will sit ^[5]. The second is whether certification is in hand for that market: Unigrid says it has passed Europe's tests and is still being evaluated for the US ^[10]. Sites that pass both are where I'd stock it, with the vendor's charge-voltage limits in writing and recorded at install, because Hasa ties the chromium-6 risk to voltage control ^[19]. A certified site that only needs afternoon load-shifting pays about $19 per kWh extra for a cost advantage that has not arrived ^[14]. For that customer I'd put an LFP quote beside the sodium one, and the tradeoff of choosing LFP is giving up sodium's temperature and fire claims ^[5]. Anything in the US column waits for the evaluation to finish ^[10].