Please have a look at this image:
At this moment, the Fronius is delivering about 4KW more than the load (AC + Critical) needs. This 4KW is thus charged into the battery, as can be seen (The battery is receiving about 4kw more than the DC MPPT is delivering)
At this moment, the Multiplus input and output is connected - that is the only way that you will get the Fronius’ power into the AC loads.
With the Fronius connected to the grid, no frequency control is possible - it is running at full power.
I want to understand what will happen when the battery is full:
- The Fronius still delivers more than the (AC + Critical) and has to be throttled down
- The AC coupling feedback mechanism means that the AC frequency of the Fronius needs to be increased
- The only way that the Multiplus can change the frequency is to disconnect from the grid - the “Critical Loads” side is then driven by the Multiplus + Fronius.
- The Multiplus then varies the frequency of its output to throttle down the Fronius
- But the main AC load is still 10.9 KW, and since the Fronius is disconnected from the grid / Main AS load, it can not contribute power to the main load.
Am I right in this description? The main AC load will then have be switched to the grid and draw full power from the grid? All PV power will then only be used for the critical loads?