The grid-tied inverters need to have a grid voltage and frequency to be in a certain defined range orelse they switch off (this behaviour can be changed via firmware for some inverters). In theory you could use a pure sinus UPS for that, but in practice it is not designed to receive power on the outlet side and will overload/burn out.

There are specific battery/diesel backed solar grid-tied inverter solutions which can smoothly separate and reconnect from the grid during outages while providing power to the consumers. These are far more expensive than simple grid-tied solar inverters.