So does anyone really know the answer?
Good point about other solar panels pumping electricity on to the grid. How do they know the “grid iis down”?
Yes, the answer is well known and has been more or less stated in this thread. The inverter can sense the voltage on the output and since the stereotypical grid-tied inverter is programmed to just put out the maximum available current, if you remove the grid the voltage will quickly go out of bounds--high for an open circuit (say just your house is disconnected) and low for an overload (say where the substation disconnects and now your inverter is trying to power the neighborhood). IOW, the whole premise of a grid-tied inverter is that it has to be connected to a low-impedance (stiff) AC voltage source with the voltage within the specified limits, otherwise it trips off for at least 5 minutes.In theory, if you were to carefully balance load and supply, you could trick the inverters into remaining operational even though they aren't connected to an actual grid. Schneider has/had a product that essentially did something like this, using a battery, inverter and charger combo to simulate a grid in an isolated system. As long as it is able to keep the voltages in range, the inverter(s) should keep working. Some newer inverters and microinverters can regulate their output and operate in a specific island mode, provide reactive power and other neat tricks. Absent any of these solutions, a standard grid-tied inverter will trip off immediately without the grid.
off grid inverter......no demand no output
grid tie inverter....generated as much power as available and assumes that the grid can use it all
Grid tie .............grid tie inverters must monitor the grid for 5 minutes and watch voltage and frequency. EDIT: and not output any power until the 5 minute clock is up. END EDIT. If there is one cycle where frequency or voltage is out of limits then the 5 minute clock restarts again. This is to prevent a grid collision where the grid has shut down and then comes back up again, sometimes the grid will come up for 8-15 seconds, determine that all is not well, shut down and then restart. It’s coded into the National energy policy set by the federal government the DOE.......U.S. Department of Energy.
Rule number 1 in doing this.....your loads must always be greater than the grid tie inverter can output. I have done this but it is not for newbie’s....you can do massive damage if you mess it up.
Some smart hybrid off grid inverters have a way of dealing with this for instance the MagnaSine MS4048PAE when paired with a grid tie inverter will “bump” its frequency up to 66 hz for a cycle or two when the output voltage goes out of range which will cause the grid tie inverter to shut down.
Not recommended unless you have a big system with MagnaSine, Schneider, or Outback or some such “hi-end” inverters