It is a bit more complex as well (the load on a grid has a real and an imaginary component). Many problems stem from the fact that most solar inverters can source Watts (real) but not VAs (imaginary). That means where traditional generators are able to use their inertia to deal with sudden bursts of capacitive or inductive loads in the net, inverters need to become smarter (or better coordinated) to stabilize the grid in all situations. Four quadrant inverters exist (inverters that can deal with all four quadrants of the real/imaginary coordinate system), but they are not especially wide deployed. Inverters with electronic inertia are in developement.

This aside of course one issue is storage, but it is not unsolveable at all.