I’m planning an ESS system with backup power for the whole house, but I’m having trouble figuring out the right configuration and certification for the grid connection application with Westnetz.
Planned setup
3 × MultiPlus-II 48/10000/140-100 in a three-phase configuration
Fronius Symo GEN24 10.0 SC on the AC-Out
MPPT RS 450/200, LFP battery approx. 64 kWh
Apparent power = 3 × 10 kVA + 10 kVA = 40 kVA, so a central grid protection device (Ziehl UFR1001E + grid coupling switch) is required anyway
The devices are to be installed about 65 m from the meter cabinet in an outbuilding
Grid protection certificate 2622/0478-A-2-E3-CER: integrated grid protection, single unit
Certificate for a three-phase configuration 250041RECO01-A-CER: According to the wiring diagram on page 3, this is the External Transfer Switch setup with current transformers, K1/K2 and Ziehl.
The certificate for the smaller models (3k to 6k5) explicitly states that multiple single-phase devices may be combined into a three-phase system. I can’t find that in the certificate for the 8/10/15 kVA models.
I think there are two possible configurations here:
Option A: Backup-power switchover via the MultiPlus internal transfer relays
In the meter cabinet: central Ziehl UFR1001E grid protection device, which controls a 4-pole grid coupling switch in the supply line to the MultiPlus AC-In.
Cable 2 (5×35, 65 m): MultiPlus AC-Out → house distribution board. The whole house is connected to the AC-Out.
Disconnection from the grid in backup-power mode is handled by the MultiPlus internal transfer relays.
Can a three-phase configuration of 3 × 48/10000 be registered in Germany under VDE-AR-N 4105 in this setup, i.e. with internal transfer relays and additional central grid protection?
What documentation for the MultiPlus should be submitted: the individual certificates, a manufacturer’s declaration, or an additional certificate for three-phase operation (in particular, regarding phase imbalance > 4.6 kVA)?
Option B (preferred): External Transfer Switch, components in the meter cabinet
In the meter cabinet: transfer contactors K1/K2, current transformers and Ziehl UFR1001E as shown in the ETS wiring diagram. The Ziehl would therefore also serve as the central grid protection device at the meter point.
In grid mode, the house is connected directly to the grid.
Only one power cable runs to the outbuilding (MultiPlus AC-Out ↔ house busbar downstream of the ETS), along with the AC-In measurement cable, current transformer cables and control cables.
Advantages: No need for a 5×35 power cable over 65 m; the Ziehl is installed directly at the meter point; and this would be the three-phase configuration certified by Victron.
Because it is significantly cheaper, Option B is my preferred solution, provided it is permitted despite the distance. Option A would be the fallback.
Problem: According to the ETS manual, the devices must be no more than 20 m from the main distribution board because of the current transformer cables (100 A : 50 mA, extendible up to 20 m using 0.75 mm² cable).
Is the 20 m limit a hard technical limit or a certification requirement? Can the current transformer cables be extended to about 65 m, for example by using a larger cross-section or shielded, twisted-pair cable?
Is there an approved alternative for longer distances, such as different current transformers or metering via a meter?
Are there also length limits for the other ETS cables (1.5 mm² AC-In measurement cable, K1/K2 control via the AUX relay, feedback contacts)?
Has anyone already successfully registered a three-phase 8/10/15 kVA system in either of these configurations, ideally with Westnetz? What did the grid operator require?
I’m no expert on our bureaucracy, but I think it works like this: the “smaller” units are certified for single-phase operation, so there’s an extra note saying that they may also be operated in a three-phase configuration. The larger units aren’t even eligible for single-phase operation because of the phase imbalance limit, so there’s no need to mention possible three-phase operation—it’s effectively mandatory.
That doesn’t make sense: the “small ones” can be distributed across the 3 phase conductors in single-phase operation anyway. I’ve never really understood the whole thing either. The lack of certification for a three-phase configuration of the “larger ones” has also made me wonder.
As I understand it, a configuration via VE.Bus isn’t the same as a three-phase device. I suspect “Switch as Group” was never approved.
I have the same question, as I think a picky grid operator could reject a three-phase configuration (3x10000).
There’s no such thing as “being allowed anyway”. The MP 6k5 has a reduced inverter output in software when operating on the grid, specifically so it could still be certified as a single-phase device.
So, bureaucratically speaking (for inverters), it seems that “three-phase” is the norm, and single-phase units need an additional certification—a sort of proof that they can’t exceed the phase imbalance limit.
But as I said, this isn’t my area of expertise; it’s just a logical deduction. Maybe our @M_Lange is closer to the practical side of things and can give a specific answer.
I don’t really need 30 kW of backup power, but during normal operation I get peak loads that exceed the maximum current rating of the transfer switches on the smaller MP models. For this reason, only the MP models from the 8000 upwards are suitable, but the 8000 doesn’t really offer good value for money compared with the 10000. We don’t have power cuts very often, but I’d still like the option of backup power if possible.
My daily electricity consumption is about 30 kWh. The battery size was chosen to comply with the factor 1 rule and allow the house to be supplied with backup power for at least two days. If you think the battery is too small, I could also plan for a larger one.
The devices causing these load peaks presumably won’t be able to run during a power cut, because they would cause the MultiPlus units to shut down.
If possible, you could connect them to the AC IN side instead, which would allow you to use smaller MultiPlus units.
Anything that isn’t essential during a power cut can be connected to AC IN, or fitted with a changeover switch so that these circuits can be switched to AC Out if needed.
The larger the MultiPlus units, the higher their own power consumption.
With 3 x 10 kVA, you should expect 200–300 W; over 24 hours, that’s 4.8–7.2 kWh.
It would make a lot of sense to connect the “high-power appliances” via ACin… otherwise, if the grid goes down, they’ll drain the battery in no time.
And via ACin, grid consumption is still offset, so very little changes… but you save a lot of money… and when the grid goes down, you shouldn’t be using the big appliances anyway (since you don’t know how long the outage will last).
Nobody will switch on the large loads in the event of a power failure. However, I can’t separate them from the rest of the installation to connect them to AC IN. They’re in different outbuildings, so the wiring would have to be changed everywhere, trenches dug and new supply cables laid. That would involve a great deal of extra work and, consequently, expense. I also can’t completely exclude these outbuildings from the backup power supply, as they contain, for example, our heating system and other equipment that needs to remain powered during a power failure.
For this reason, I’ll probably have to use a MultiPlus whose transfer switch can handle more than 50 A. Is the MP’s 200–300 W self-consumption based on your experience? I checked the datasheet, and it says that a 10,000 MP has a standby consumption of 28 W.
@M_Lange Are the 200–300 W power consumption figures based on real-world experience? That would really be far too much for me. According to the datasheet, it should be only 28 W per device.
I actually wrote the reply last week, but didn’t send it
In my experience, 200–300W is much more realistic than 90W (3 × 28W).
We always tell our customers to expect self-consumption of around 1% of the inverter’s rated power.
I just tested it again with a 5000 MultiPlus-II and a bench power supply. The power fluctuates between about 17 and 27W, so around 22W on average.
If it’s double that for the 10kVA Multi, that would be 44W, or 132W for three units.
So 300W may be a bit of an overestimate after all, but I would expect around 150W.
OK, thanks very much for taking the measurements. But regardless of which MultiPlus I ultimately choose, it would be advantageous for me to use an external transfer switch so that I only have to run one cable to the MultiPlus (in the outbuilding). Is the 20 m between the MultiPlus and the transfer switch a strict limit? Is the certificate no longer valid if I exceed it? Is there any way to place the transfer switch about 65 m away (for example, by using better-shielded measurement cables with a suitably large cross-section)?
The cable length shouldn’t be a problem for the certificate; it’s more the measuring leads for the CTs, as extending them could result in inaccurate measurements.
With a setup like that, you’d be outside the official specifications and therefore essentially no longer covered by official support.
