Trying to understand

[ronquick]

In my previous post my understanding was that by back feeding my existing micro inverter panels with a generator or battery back up when the grid is down that when the panels powered up that there would be a surge looking for the grid that would fry something.
Since I have 2 strings at 4.4 kw each, if I back fed the inverter prior to them waking up would that eliminate the issue as they wake up slowly? I could also only power up only one string if that would help.
I believe I would also need a pure sign wave inverter for my battery back up and only use it for imitating the grid not to power anything after dark.

[inetdog]

The problem is that since any current GTI, whether string or micro, will convert the full amount of power available from the panels into AC output. If that power is greater than the total of your loads at any time, the excess power will try to backfeed the generator or the off grid inverter.

In addition, the anti-islanding circuitry of some GTIs will simply not recognize the generator or inverter as a low enough impedance source to fill in for the actual grid.

Waking up slowly will not help, since they will continue to increase their output match the growing panel input. Sooner or later, especially if you turn off some loads, the GTI output power will exceed the load power and you will be in trouble.

PS: The AC coupled systems that do work in this environment have control circuitry that insures that the battery powered inverter is always delivering some power to the loads.

[ronquick]

In my previous post my understanding was that by back feeding my existing micro inverter panels with a generator or battery back up when the grid is down that when the panels powered up that there would be a surge looking for the grid that would fry something.
Since I have 2 strings at 4.4 kw each, if I back fed the inverter prior to them waking up would that eliminate the issue as they wake up slowly? I could also only power up only one string if that would help.
I believe I would also need a pure sign wave inverter for my battery back up and only use it for imitating the grid not to power anything after dark.

Thanks,
I knew I was missing something. I guess I need to enjoy what I have and not be concerned with the occasional outage.

[SunEagle]

Thanks,
I knew I was missing something. I guess I need to enjoy what I have and not be concerned with the occasional outage.

A lot of design went into the anti-islanding features of the GTI equipment to keep Utility personnel safe. While a lot of people would like to continue to generate power from their PV system when the grid is down it is just too dangerous.

So backup power would have to come from other sources like generators, batteries and some GTI inverters that have a separate emergency circuit as long as they have been totally isolated from the grid. It is an inconvenience but a person's life is more important.

[inetdog]

Hybrid inverters, on the other hand, are generally capable of working when the grid is down as well as working in GTI mode and even selling back to POCO, but they typically have a built-in transfer switch that isolates them from the grid while they are in that mode.
And that transfer switch is part of their UL listing evaluation.