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Off-Grid (Parallel) 48v AC "Smart" Grid Charging as Winter/Backup "Generator" in Germany

In Germany an Off-Grid system with any kind of AC Grid connection (even totally disconnected) on the same piece of land is considered "parallel operation". If we indirectly or directly connect any "generator" (including Multiplus or Quattro regardless of configuration) to the grid we are no longer in parallel operation and a ton of rules, bureaucracy, tax, and even remote control is applicable! So long as the sun shines everything is okay, until winter...

Even with an oversized "full roof" solar array, in winter especially with EVs, the only way I see to cover the couple of months with poor sun BUT keeping ALL the electronics Off-Grid is to trickle CHARGE the batteries from the Grid for a few days/week at a time. For example, like an ad-hoc/mobile EV charger or electric oven we can draw up to 3,6kVA from a "charger" 24/7 without breaking rules to deliver 86kWH/day. Using the battery as a buffer, we can then trickle charge the EVs for a few hours each day, cover heating and entertainment requirements. On the DC side everything is perfect with Multis/Quattros even using DC power directly to reduce battery cycles.

It's important for me to keep ALL the electronics Off-Grid so that I have (almost) complete freedom to choose the power rating and technology within my system. My Grid distribution box will only contain a couple of power sockets for testing plus chargers split evenly across all phases, that's it. The energy company has nothing to say about the rest (common electrical safety respected). ;-)1641965825516.png

Of course, the basic assumption here is "not direct or indirectly connected" regards AC/Grid power. Here we only have DC connectivity between the Grid and Off-Grid systems, technically they are only "connected" via magnetic fields.

Now the question...

The Skylla 48v 25A charger appears to be the only option (x3 <= 3.6kVA), is expensive at 900€ each as I have to buy 3 (2700€), but not very smart at all. There is no way to share temperature, voltage sense and BMS control via any VE bus (Direct or CAN). I could get a Multiplus or Quattro at similar prices but those can feed energy back to the grid which is not allowed. I guess I have to use them as dumb chargers with the remote switch/relay and shunt to fill-in for the missed capability.

The Skylla may even have to be set in power supply mode to prevent its charge logic conflicting with the BMS or much higher than spec capacity house battery? :-( I'd really like to keep a pure Victron installation but if it comes down to power supply mode then are there any 3rd party 48v chargers which integrate with VenusOS or a VE bus?

I hear the rules are very simple in the Netherlands, perhaps why Victron don't see this requirement? Then Victron don't make "Smart" 48v chargers because they feel the demand is covered by the Multiplus and Quattro? But these devices CAN return energy to the Grid, so considered "energy production" devices, which IS a problem for evermore people seeking Off-Grid as a solution to the politics or just want freedom of choice.

Or is there something I missed here... For example, is it impossible to return power via the AC2 input of a Quattro with physical/electronic limitation (it would have to be documented also with a schematic as proof for the energy provider)?

chargeroffgrid48v battery
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bbmz avatar image bbmz commented ·

A short comment beforehand - you (and maybe your electrician) have to decide, what you want to do … if you really want to build a system like this, it is technically possible. You will need quite a lot of equipment, and you will have a lot of losses, but legally your “system“ is not not allowed (in Germany)!


In more detail - also for other potetcial users - as long as there is a electrical connection („Hausanschluss“ bzw. „Netzanschluss“) on the same property a system will always be considered as (at least indirect) coupled. For further details search at the „EEG-Clearingstelle“. You have to remove your ground-cable to the grid on your property (permantly) to be considered as „off-grid system“ without regulations. Even your DC-coupled system will still be considered as grid-coupled.

[Annotation - to be clear: that´s not my personal opinion! I also don‘t understand these rules, but they are explicit in this case.]


I think I don‘t have to go into details, what regulations you therefore still have to fulfill - only a short enumeration: compliance to VDE AR-N 4105 (for all devices), probably central grid-protection („NA-Schutz“), metering concept (probably via CTs), registration at BNetzA („Marktstammdatenregister“), „Netzanschlussbegehren“, and so on …


My personal advice: do what you want to do (but on your own responsibility). Your huge effort for the „DC-coupling“ will not change anything compared to a „simple“ AC-coupling (from the legal perspective).

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tnt369 answered ·

Ich habe ein ähnliches System am laufen. Ich nutze aber den Eingang AC IN 1 am Quattro. Davor habe ich ein Relais mit dem ich das Netz vom Quattro trenne wenn es nicht benötigt wird. Damit wird unnötiges Einspeisen sicher verhindert.

Sobald das Netz benötigt wird schaltet das Relais zu und versorgt AC IN1 vom Quattro. Dabei gebe ich über Modbus einen hohen "Grid Setpoint" vor um die Batterien zu laden und die Verbraucher zu versorgen. Ein Rückspeisen ins Netz wird so zuverlässig unterbunden.

Es handelt sich dabei genau genommen nicht um eine "Off Grid" Anlage, aber der Netzbetreiber bekommt nichts davon mit und weiß auch gar nichts davon ;-)

Durch die Modbus-Kommunikation und die Regelung des Grid-Setpoint kann ich Verbrauch, Erzeugung, Bezug und Akkunutzung gut aufeinander abstimmen. Zur Steuerung und Visualisierung verwende ich Loxone.

Bitte beachte dass die Geräte (Multiplus/Quattro) je nach Anzahl und Baugröße einen nicht unerheblichen Ruheverbrauch haben. Auch im Betrieb sind die Verluste nicht ganz ohne. Bei mir (2 Quattro zu je 5kW) beläuft sich das auf ca. 10-20% (ca. 3-4kWh/Tag).


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code-chief avatar image code-chief commented ·

Danke, Ja mein Offiziell On-Grid Verteilerkiste beinhaltet "Test" Steckdosen und Ich konnte auch in Winter plötzlich 3 Kabel einstecken von dem Multi/Quattros ;-) Aber mit Neubau Ich suche ein Langfristige Lösung das gilt als "Geek Free" zum Beispiel wann das Haus war verkauft oder geerbt, dass es funktioniert, laut Standards ohne besondere Workarounds/besondere Technisches Know-How.

English for the community - Thanks (to the suggestion to just connect AC IN and set parameters like Grid Setpoint to prevent feed-in), yes my official distribution panel will only contain "Test" power sockets which I could just "accidentally" connect to the Multi/Quattros. ;-) But with a new house build I'm looking for a long-term solution which is "Geek Free", e.g. if the house is sold or inherited, that it works according to standards without special workarounds/special technical knowledge.

What I'm really trying to suggest to Victron is, what others have already asked... Please update your Charger products to include VE.Bus or VE.Direct, e.g. Skylla 48/25 "Smart" and consider 3 phase clustering or 3 phase in one box like one of the lower voltage Skylla versions supports.

And my remaining question is, if you have a Quattro, is AC2 unidirectional (impossible to return energy to the Grid as "backup/winter generator")? Or are both AC1 and AC2 bidirectional?

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