Making a Grid-Tie system function without grid?

[awls]

I am working on a project to allow a grid-tie system to continue to function when the grid goes down. (Southern California)
From what I have read, this involves "tricking" the grid-tie inverters into thinking they are connected to the power grid by providing a 240V/60Hz signal. I am using a pure sine wave generator (powered by a 12V battery), and connecting it in place of the grid to the solar inverter (Note the grid is disconnected for all of these experiments). This generator provides a clean 60Hz signal at the voltage required by the inverter, but so far I have not been able to get it functioning (brand is Sunpower, but I believe this process to be the same for all inverters).
Has anyone done something like this successfully or have any ideas on the matter? I have been able to get the inverter to the "flashing green light" stage in which it senses a grid connection and is attempting to sych with it, but no farther.

My thoughts are that maybe the inverter needs to "see" more power from the sine-wave generator (my generator can produce 600W) or that there is the possibility that the generator is not producing a signal of 60Hz +- 1Hz required for inverter operation.

Any advice is appreciated!
Thank you

[Naptown]

What Sunpower inverter do you have.
If a rebranded SMA you would need to add a sunny Island and a much larger battery bank.
The reason it wont work as you currently have it is the impedence on the microgrid is too high and the inverter is sensing this and shutting down.

[awls]

Sorry, I don't have the exact model on me right now. What functionality does the Sunny Island add?
It was my thought that the inverter simply needed a clean grid signal of the proper voltage/frequency to sync with, is this incorrect?

[Naptown]

If it is a Sunnyboy inverter it will add the functionality you desire in a system that will actually work.
There are other methods but the way you are going about it will trip off or not start. This is because your grid tie inverter will send a high voltage ping to the grid and see what happens. With your microgrid the voltage rises beyond specification on the inverter and it will not continue starting up.

[bcroe]

Grid Tie Inverter Without a Grid

Besides the grid impedance test, there is the issue of matching solar power to
your load (without battery buffers). Standard PV inverters will try to find the
solar MPPT and raise the output AC voltage to pump all that power into the
grid. With no real grid or load, the voltage rise out of range and shut down.

Only an inverter that can switch to matching the load (fixed output voltage)
instead of MPPT can solve the problem. And when the load exceeds the sun,
it all will die. Bruce Roe

[Mike90250]

What will your sine wave inverter do when the GT inverter pumps 280VAC into it, as it pulses the "grid" and then starts dumping power into a 240VAC circuit ? Are both your phases balanced ?

The only way it can send power into the grid, is to raise it's voltage to backfeed the transformer. Without the Grid to load it down, the voltage will rise, till the safety cuts it off (about 1/2 second) then a 5 minute re-sync before it trys again.