Can an ESS invert from PV panels and discharge from batteries at the same time?

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rick987 asked Dec 2, '22

Can an ESS invert from PV panels and discharge from batteries at the same time?

Hello. I have a new PV system installed (by a professional) with 20 Shutten Solar panels 410 Wc, a Fronius Symo 8.2-3 (3 phases), a Fronius Smart Meter 65A-3 (for zero injection, that's a long story with my utility provider...), 3 Quattros 48/5000/70, 4 LiFePO4 batteries 25.6V/200Ah, and a back- up generator. System management is through a Cerbo GX 3 and a BMV700.

I am struggling a bit to get the configuration right. One issue I see is that, during the sunny hours, while the ESS decides to discharge from the batteries, it does not allow production from the solar panels (see screen below). This effectively reduces the efficiency of the system, especially when the loads of the house are such that it may take several sunny hours for the discharge to stop at the min. SOC (currently at 75% on Batterylife), leaving me, by the end of the sunny hours, with batteries charged at 85% or so, nor contributing much to the loads overnight. Do I expect too much from my system, or is there a way to get around this issue? Many thanks for your tips!

ess discharging

27-nov-9h39.jpg (120.7 KiB)

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ajmacleod commented · Dec 02, 2022 at 09:44 AM

I don't have a direct answer to your question but I can say that in an ESS system with DC coupled PV (i.e. with a victron MPPT ) the system will use PV to charge the batteries and, if there is sufficient PV, simultaneously power AC loads with it.

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Michelle Konzack ajmacleod commented · Dec 09, 2022 at 07:04 PM

I use the same Fronius with 3 MultiPlus-II 24/5000 and the Fronius is connected to the AC1 output.

Did you do the same?

In this configuration if you switch on any loads, the energy from the Fronius go directly to the devices and the left over energy go back into the Inverter and it charge the batteries and if they are full the rest goes into the grid (if configured)

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johnone commented · Dec 09, 2022 at 08:18 PM

This may not be relevant, but in the photo the amount of PV shown is, I've found, below the limit where the graphical display adds on the blue dots to represent flow. In these low sun winter days (in the UK) anything below around 25W (not sure how it's configured/ what the exact limit is) is not represented on the display. Above that and my system shows PV being added to AC consumption. Hope that's useful.

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