There are inverters available that are specifically not for grid tie. What this means is that you would have to have two separate systems as the non-grid tie type inverter is not compatible to feed the grid meter, it will not sync thus shorting out situations and destroyed equipment possible if tied to the grid.
You will effectively double your cost for little gain.
I also recommend a generator. And the inverter "may" as Steve put it, work while the generator is operating. For small loads I recommend an inverter type generator, often called a low speed generator, where the AC output frequency is created and has nothing to do with the speed of the motor. They save on fuel as the generator can slow right down and save fuel under low and no load situations. This is again as Steve mentioned.
UPS's and generators don't like each other. The UPS sees good AC, switches the load to the generator, the voltage dips as the generator ramps up to accept the load (unless a high speed generator oversized), mean while the UPS sees the voltage dip and removes the load back to it's battery, creating an endless cycle.
