This should help you understand it a bit better.
I don't believe I've had any trouble understanding what you're saying from the start. I just disagree that it practically applies to PV inverters.
Actual load is not a heating element. Picture you're pedaling a cement roller bicycle with the rear wheel coupled by gears. When you're pedaling, you're exporting power. But if your foot gets caught in the gears "a fault condition", then the roller will extrude you through the gears, because it is directly coupled. In other words, grid is "backflowing" into DG system or feeding the fault energy.
This, I think, is a horrible analogy, for many, many reasons. For example, gears have pretty much nothing in common with electrical circuits. Perhaps the most salient reason, though, is that if I were a PV inverter I would be pedaling in the
opposite direction of the grid.
In a non-isolated inverter, a fault would cause energy to flow from the grid back into the point of fault.
Only if it overcame several physics and engineering constraints that would keep that from happening.
Since the grid is AC, it would initially start like a half wave diode put between hot and neutral. Fast acting current limiting will prevent the static converter from erupting into a giant ball of flame, but there's a fair chance that power components will fry.
Fast acting current control is how a PV inverter
operates. So I think it has the ability to quickly limit fault current. Also, you keep referring to 'static converters', and a PV inverter, I think, is not one.
I pulled the PV out of circuit just for shows. You can mentally put it back in, but you can see how it makes no difference in fault current.
It makes all sorts of difference. The key difference is that the DC current is flowing the
opposite way. Think about that. Draw it out if you need to. (I did). Physics and UL 1741 dictate that if the inverter can inject energy into the grid in the
opposite polarity of the grid voltage, then a fault on one of the DC conductors must result in one of two things:
a) the inverter causes DC current to flow from the faulted conductor (i.e. on the EGC)
b) the inverter must stop operating, if it can no longer be correctly pushing against the grid voltage
If (a) then the fault current is DC on the EGC and flows the opposite direction (on the AC grounded conductor) of how the utility fault current would flow
If (b) then the inverter has shut down, meaning the DC conductors are now isolated, meaning AC fault current can't flow. (See response to previous quote in this post.)
I actually have no idea which of these will prevail; it could be either one, I suppose, depending on a lot of other factors. What I
can see is that neither scenario involves AC fault current through the DC conductor. And if it's (a), then the GFDI is supposed to detect it and shut down the inverter.
Solar marketing companies have significant interest in promoting non-isolated design to reduce hardware costs since it would increase the filler gap between retail price and manufacturing cost. As for the effect on final installed cost, it could be rather insignificant.
The largest expenses are soft cost such as parasitic losses of money such as markups in each layer of multi-leveled marketing structure.
Actually non-isolated inverters have brought along significant end-user cost reductions. And 'soft costs' in the PV industry is everything that
isn't hardware. That post really shows you are not familiar with solar industry economics.