Attaching a grid tied micro inverter.

Terry Gilligan

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Nov 14, 2020
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Hi everyone, I have a grid tied 2.4kw inverter but it's not tied to the grid but I have a 24v battery bank. I have attached 9x 280w panels in 3x3 strings it works well and we have no problems with this.
I bought a 1200w mico inverter as I'd like to increase the output for an extension we're building and was wondering if I can attach the micro inverter to the unused "AC in" on my other grid tied inverter to make it easier to control as everything would be done without having to add anything extra.
Am I missing something, do people think it's a bad idea?
Regards Terry
Both inverters are no name China imports.
 
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svetz

Works in theory! Practice? That's something else
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Microinverters for the U.S. wouldn't work as they shut down if no grid is detected to be in compliance with the national electric codes. As such, the microinverters you're talking about are well beyond my experience. If they're made to be grid-tied, then one should sync up to the other thinking it's the grid.

...do people think it's a bad idea?...
Typically the answer is yes, it's a bad idea. But that's because if there isn't enough draw a grid-tied inverter should keep increasing the voltage (they're designed to suck their power sources dry as quickly as possible and push the energy up-hill onto the grid as fast as they can). It sounds like yours must be smart enough to keep from blowing up your devices. As such, I'd write the manufacturers and ask about your specific use case.
 

DThames

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Nov 22, 2019
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There are ways to do it but your grid tie system must be able to,
1. make it look like its output is the grid so the grid tie micro will come on.
2. know how to trick the micro into shutting down when the batteries are charged and the load is reduced. This is commonly done by changing the output frequency so the grid source will fall outside of exceptionable limits. For example if the micro would only output when the freq was between 59 and 61 hz, a 61.5 hz output would make it shut off.

As svetz said, not an idea you want to try without hardware that is designed to function correctly in that mode.

This might be helpful.
 
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