Micro Inverters tied in a string for emergencies

[josepr]

I live in a hurricane prone area. The last one left us with no power for 3 months. Because of that, during the emergency, I installed a small off grid solar system (8 solar panels, 300w, 4 strings of 2 panel) {2 because the charge controller starts de-rating at 115v}.

I would like to connect those panels to the grid but still be able to use the system off grid during power outages and emergencies. Because of cost, changing the off-grid inverter is not an option. Because of that traditional AC couple and DC couple options are not possible. Also, because of cost, I would like to install a cost-effective grid tied solution (string inverter or microinverter). One of my options is installing a string inverter with a secure power option and use the inverter’s charger (its power factor corrected). But I think that is a very inefficient solution. The other one could be more efficient, although a little bit more expensive, is using micro inverters. But I do not know if my solution is viable. Because of that I have a question for the forum’s micro inverter experts.

The question is: can I connect the negative lead of one micro inverter to the positive lead of another micro inverter? I know that, electrically, I’m am not connecting them. Each one will only receive DC electricity from one panel. Basically, what I want to do is to preserve the 2S4P solar array configuration, but additionally adding one micro inverter to each solar panel. The micro inverters will not be on when the solar charge controller is working during a grid down situation (turned off using a two-pole breaker). It will be controlled manually. Because some micro inverters detect and turn off if they sense a DC ground fault both connections (positive and negative) from the combiner (fused) to the solar charge controller will be disconnected (DC breakers) when the micro inverters are connected (negative grounded off grid system).

I do not see anything wrong with this design. But I could be wrong. Any suggestions are welcome. Let me know if you think this will work and if not, why? Thank you very much.

[Mike90250]

All you can safely do, is at night when the array cannot produce any power, is to unhook the panel leads from the microinverter and rewire the panels into whatever string suits your charge controller. And when grid comes back. again at night, move the panel cables back to the mircoinverters.

And you will need wire, high voltage DC breakers and all the battery gear

[Ampster]

What Mike is saying, is that it is not safe to disconnect the panels under load. You can do that with a switch or breaker and then safely disconnect the microinverters and reconnect the string inverter. If your solar panels are on the roof you may want to provide an easily accessible junction box to do that.
I don't know the answer to your question but if it doesn't work out is only 8 more connections. In your situation, where you have a power outage once every 3 years that may be the most expedient and cost effective. In my case, I expect to see at least two or more outages in a year. That is why I paid the extra money for a true hybrid inverter with an automatic transfer switch.