# question

## AC and DC coupling - Co ordination

I just watched the webinar for Victron/Fronius Micro grids.

I want to understand what happens when the Fronius inverter is ramped down through the frequency control.

There are two parts to this question which are closely related.

First question is simple.

Can a common PV array feed both the string inverter and the Victron solar charge controller? So they would be connected in parallel and share a common dc energy source.

Secondly,

Let's say the house is only using 200 watts. Let's also assume we are using a 3KW fronius string inverter. The PV array is producing 4KW and the battery is 50% SOC.

Once the fronius inverter ramps lowers its output through frequency control can the solar charge controllers demand more of the PV energy and send that energy to the batteries?

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One PV array either feeds the fronius or a charge controller, not both.

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Can anyone answer this question more thoroughly?

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Well your second question doesn't apply since you can't do what you want to do in the first. What additional detail would you like to know? You need to decide if you want to AC couple the solar array, or DC couple it, you can't do both with a single solar array.

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Hi @project eco ,

You need to read a bit more about AC coupled vs DC coupled systems.

The battery inverter (for example MultiPlus) will shift the frequency based on the SOC of the batteries and the loads. If there is energy available and required for the batteries that is not required for the loads, that energy will surely go to your batteries. In other words, the battery inverter will ramp the PV inverter(s) down and up.

The reason you also need a MPPT DC coupled charge controller in an off grid situation is so you can automatically recover from a LVD (low voltage disconnect). I'd still recommend to also have that in grid-tied systems with a battery backup but that topic is beyond the scope of this post.

And @daryl is quite right: each (PV inverter and MPPT charge controller) need their own dedicated solar array.

Jan

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