Just about any storage inverter will do this and there are plenty lower cost than the 18K pv or the Solark 15K
Of the top of my head and far from complete:
Solis 5G HVES ( 6kw backup )
Solis S6 ( just coming to market, 11.2kw backup top model )
Goodwe GW7600A-ES ( upto 11kw backup top model )
Growatt XH series ( upto 10kw Backup top model )
Generac ( do not recommend )
Solax X1
Tigo TSI ( looks like a relabed Growatt )
All of the above are less than half the cost, UL9540 certified. Note this are high voltage, not 48V and the UL9540 listings are for a small set of listed batteries, not DYI or flavor of the month rack batteries.