Soon I will make an off-grid system with the following equipment :
Fronius Gen24 Symo 10.0
3 x 48/5000 Multiplus II
6 x Pylontech US3000
Gerbo GX
There is no generator, the site has sometimes grid power, but very fluctuating .
Since the system is off-grid I will connect Fronius to AC Out-1 of the multiplus.
The question is what happens, when batteries are drained and the Multiplus shuts down AC-Out ?
In such a case the system itself is blocked, although the next day sun might be able to fill the batteries.
I am thinking of the following solution : I will put a separate contactor to the loads only. And with the relay from Gerbo I will disconnect the loads before the batteries are drained, let’s say at %20 SOC. So that for next day when the sun comes, the multiplus’ ac-out will still be active to turn on the Fronius inverter.
What do you think ? any suggestions or better ideas ?
You could connect your loads to AC OUT 2 and program that like you described.
Or you add a small (or big) MPPT charger to the battery, that will start charging the battery in the morning → the MultiPlus starts → the Fronius can start
Charging the battery with a MPPT is more efficient.
there is no room for additional charger, all PV is connected to the Fronius with 600 VDC, therefore it would be additional cost , which customer doesnt want. However what do you mean with AC2 ? I thought AC2 out is only active when there is grid available. As soon as the grid is gone, the loads will also be gone.
You can configure a different behaviour for the AC OUT 2 with VE.config.
For an off-grid system I would always recommend to plan with a small MPPT.
You don’t need much, a MPPT 100/20 with two panels is enough.
That doesn’t need much space and doesn’t add much cost.