Fronius, Multi, ESS, 3-phase switch

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hanswurst asked Jun 13, '22

Fronius, Multi, ESS, 3-phase switch

Hi there,

I want to build the system below:

15.0-3-M Fronius with 20kWp panels, 1 array east of 8kWp and 1 west with 12kWp
3 * Multiplus-II 48/5000
Cerbo GX
4 * Pylontech US3000C
SmartSolar Charger with 2-4 panels (just as backup to be able to start the system if the battery is empty)
3-phase switch

My supplier demands, that the PV system feeds directly to the grid through an own grid meter. 100% of the production has to be measured (and sold first). But I have the possibility to use the production immediately myself and it will be discounted from my electricity bill. So if I charge the batteries (from the grid) when there is a lot of production from the PV system, it'll cost nothing.

To me, this can be solved with this setup and ESS (correct me if I'm mistaken, hopefully not... ;-) ). But there are a few questions:

Is another energy meter needed to measure the production of the Fronius, or will the Cerbo GX communicate with Fronius directly?
As this setup does not allow the system to produce electricity in case of a longer black out, I wanted to add a 3-phase switch to get the Fronius "behind" the Multis. This might not be legal, but who cares in case of a longer black out?
- So, is this safe (if done properly), or will it lead to problems with the Multis?
- How about ESS? Will it have to be reconfigured to meet this new position of the Fronius?
- How will the Multis then limit the Fronius production? Only via frequency shifting? Are there other options?

I've studied the documentation for two weeks now, but it is simply too much information to get to the bottom of it. Hopefully this community can give me advise and reassurance. Thanks in advance for your help!

Kind regards,
Hans

Multiplus-II ESS Fronius

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Buckley Davy commented · Jun 14, 2022 at 10:05 AM

Hi @HansWurst,

I hope this is of some use to you:

Is another energy meter needed to measure the production of the Fronius, or will the Cerbo GX communicate with Fronius directly? Typically with micro-grids, with Fronius and Victron, you need to install a smart meter (in your case a three phase one obtainable from your Victron Distributor) on the input at source, this is used to feed information to the Cerbo you are installing, and is necessary to measure the flow of current. The Cerbo then communicates with the Fronius direct, and it is best to set it to communicate via Modbus to give the Victron the "Master" status in the system and allow it to control the Fronius. Setup is required on both systems.
As this setup does not allow the system to produce electricity in case of a longer black out, I wanted to add a 3-phase switch to get the Fronius "behind" the Multis. This might not be legal, but who cares in case of a longer black out? (*Laughing face), I cannot officially condone this but technically it is possible but complicated. Typically one should adhere to the Grid Code Standards of your country.
- So, is this safe (if done properly), or will it lead to problems with the Multis? I think anything done properly should be safe, although refer to my next point
- How about ESS? Will it have to be reconfigured to meet this new position of the Fronius? Yes you would need to reconfigure the system each time
- How will the Multis then limit the Fronius production? Only via frequency shifting? Are there other options? I am assuming this is in reference to when the Fronius is on the output of the Victrons. In this case my experience has taught me that controlling the Fronius via Modbus is preferable. If there is a generator on the system as well, you will need to consider utilising the Fronius input/outputs to create a rule using the DNO editor, that causes the Fronius to throttle back when the incoming grid source is a generator as your intention is to net meter. As far as I am aware, if you are netmetering, and there is no generator, the need for throttling via frequency shifting is void, as the loads will be catered for as a priority, and any excess PV will be banked in the grid.

I hope this is of some use to you, I am sure there are some other guys out there who might like to chip in. I stand to be corrected on any of the above, but have installed many of these systems now and they work exceptionally well. Nothing better than Victron and Fronius!

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hanswurst Buckley Davy commented · Jun 19, 2022 at 10:12 PM

Dear Davy,

thanks a lot for your reply! This helps out a lot.

In the meantime I found the 1:1 rule to apply to the batteries too. So basically I would need about 60 kWh of battery capacity to comply with this rule. This is not an option.

So I changed my mind and instead of making the Fronius "switchable" I would just put the switch in the PV pannel string. So I can get more power to the SmartSolar (of course I would then use a big one like SmartSolar MPPT RS 450/100). As I understand, this will not need reconfiguration of ESS?

As I understood the Fronius does communicate its live production over the TCP Modbus. Can't the Cerbo GX use this information to get the Multis to do their jobs in ESS? I'd like to work without an extra smartmeter in the Fronius setup as it might not be legal here...

Another question regarding ESS: I can feed 100% of the Fronius production to the grid, no limits here. But the part with the Multis is only allowed to feed back 800W (less to zero would be preferable). And of course I would like to use ESS to get all the PV power saved in the batteries. Can I set feed back to the grid per device?

I want to charge the batteries at max. power and power my loads, if Fronius PV power is available and if they're full I'd like to sell 100% of the PV power (that is not used for my loads). Can this be achieved with ESS?

I hope you get my point... :-)

Thanks again for giving a newbie some extra help!

Kind regards,
Hans

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