The reason we have batteries for off grid systems is mainly that our use of power will likely not correspond to when the sun is brightest, so we generally want to store any harvestable energy to make the most out of the solar panels we have. Yes, an PV array could drive an inverter without batteries to AC supply loads so long as the sun is shining bright enough to power those loads. And then a cloud comes and people are angry that the power has cut out. So the reason off grid systems "need" batteries is practical not technical. It's because human uses of electricity won't or can't adapt that closely to the sun's brightness.
In any case Haji, I'm pretty sure you're still wrong about the role of an MPPT component. I'm pretty sure I could send a PV source through a simple voltage regulator of some kind to a cheap voltage-source inverter (the kind made to plug into your car battery), and it would power an AC load. That is provided, of course, that the sun is shining enough and the load is not too great to cause the voltage from the regulator to drop to where the inverter trips off due to not enough input voltage.
Now if I replace the cheap voltage regulator with some more exotic kind of MPPT device, then probably I can run a larger load because the MPPT device will be better at finding an array voltage that can maintain the required input power to the inverter. But the proviso is of course still the same: the sun has to shine, the load can't be too large.
You can't talk about MPPT devices or inverters as if they are a particular types of things that all behave the same way. There are different types of each that are made for different purposes and will behave differently if hooked together.
And none of this really gets at the problem that this thread was originally about, which is how to configure a solar inverter to run in parallel with an ICE generator, and to do that safely and with an economic benefit.
