Yes solar is variable but if you will watch around bad storms (atleast in my area) the few days after the storm. Being ice or tornados or snow is usually sunny. Bad Storms don't come through and then leave clouds around for days, they use up what ever energy is in the atmosphere and then leave clear skies. My thoughts were about low usage times. Running a gas or wood heaters blower. A fridge and freezer when needed.
Maybe it come down to another post. Not as much about is it possible but is it feasible.
TnAndy is a great resource for this discussion. If I understand his system, he is set up to switch his grid-tied system output into his off-grid system when the power is off. The off-grid system has a battery bank and that is very useful for electrical loads.
The batteries do what the grid does in a grid-tied system. They fill on-demand calls for power that exceed the solar panels current (in time) output, and they are somewhere to store power when the load is below the panels' outputs, and of course supply 100% of the power at night.
On a partly cloudy day the output of a solar system will be all over the place from low to maximum. That brownout condition is not what AC electric motors will function well on. You could use variable speed DC motors and allow them to run at whatever voltage is available directly from the panels, but that has drawbacks too.
I don't know how well inverter generators handle having power applied to their output terminals. That would be the situation if the generator and a grid-tied system were combined in a service panel. They would each have their own dedicated circuit breaker that they feed the panel through. Generators are designed to be power sources, not sinks. Whether that is not an issue with inverter gens, I don't know.
Assuming the generator is going to work that way, it would supply the clocking for 60 cycles that the grid-tied system would sync to. The loads on the panel would draw from the combined generator and solar inverter output with the generator filling the grid function.
Where trouble would start is if the load exceeds that combined capacity; there is no grid or battery bank to make up the difference. Let's say the load is 4 kW, the generator is a 2 kW unit, and the solar system has a 4 kW capacity. You won't always get the 2 kW needed from the solar system to meet the 4 kW load unless it is a cloudless day. It could easily vary from .5 kW to 4 kW. In any case at dawn and dusk you won't get the 2 kW either. If motors are starting and stopping, the start-up loads need to be met too.
The price differential between a 2 kW and 5 kW generator (needed for a 4 kW load) is a lot less than the cost of the solar system. Plus it works in the dark of night, during storms, and on cloudy days. I don't see much advantage in trying to use a grid-tied solar system as a generator fuel saver or capacity extender/booster.
You can open the main service disconnect and take care of the utility line backfeed safety issue. A manual breaker lock-out meets code, but lock-outs are not designed for two backfeed breakers IIRC. There is likely a reasonable solution for that problem.
