The sol-ark inverter seems to be a popular choice in the US and has generally very good reviews. It’s also able to operate in on-grid (hybrid) and off-grid modes and would provide a high level of backup power (9kW at 240V and 4.5kW at 120V - see specs attached). It should also be able to work directly with your existing solar array depending on the string configuration?
Simpliphi batteries are also very good, high quality, modular battery option. Although you would need closer to 30kWh of storage capacity to last several days - remember the batteries should not be fully discharged.
