Introduction and first questions about Multiplus 2

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1

Hello,

I signed up here because we’re currently renovating an older building for our own use, and an energy-efficiency retrofit is also planned. I was looking for a system that would give me the greatest possible flexibility in choosing components as the work progresses, while still offering all the other conveniences of what I might call all-in-one systems with storage.

The project will take several years, and there are still many uncertainties, including how the roof areas will be used, so I already need that flexibility at this stage. Feeding electricity into the public grid is neither planned nor desired; I prefer a storage solution that simply saves any surplus energy that isn’t needed for periods of low generation. The system also needs to be modular, meaning the PV inverter and storage must not be combined in a single device, in line with the requirements above.

To put it briefly, I’ve been looking into this for a while and, in terms of its features, the Victron MultiPlus and related products—namely the Quattro and whatever else there is—are essentially the storage solution that comes closest to what I’m looking for. The UPS functionality is also a very pleasant bonus.

Since I know our usage patterns and therefore our energy consumption fairly well, the 5 kVA MultiPlus would probably be my choice. The system will be designed for single-phase operation, which also provides the reserves for three-phase operation. In principle, the 3 kVA would already be sufficient, and for reasons of redundancy I’d like to operate two of them in parallel. However, that would exceed the permitted phase imbalance, so it presumably won’t be allowed.

The next question regarding the system design concerns the PV inverters: what happens when the battery is full? Despite having export limitation configured, would the Victron then try to feed that amount of energy into the grid? I can imagine that it might.

Best regards,

Mario

2

and what do you want to know now? what exactly is the question?

3

Roughly where is the construction located?

If you need to get through the dark, long Swedish winters or live in a snowier part of Germany, you’ll also need a backup such as a combined heat and power (CHP) unit.

4

Hello,

@Karl Heinz, postcode area 07xxx, but we do get some fairly severe winters here too. That’s why there’s also a smaller diesel generator with a manual start in cold standby, which can also be run on heating oil.

Basically, I’m trying to fill the roofs to the absolute maximum, but the only aim is to generate as much as possible during the low-yield period. Hence my question about what the Victron does with surplus power that won’t fit into the batteries or can’t otherwise be consumed on-site. It probably feeds it into the grid, which I don’t want, and yes, I don’t mind if I then simply don’t use that amount—it is what it is.

Because of the solar thermal system installed at the other property—and the new old house is getting one too—you have to be aware that nothing is produced for four weeks before and after Christmas. The PV system is somewhat less affected by this, but it still isn’t really capable of guaranteeing energy self-sufficiency. If it were, you could build an off-grid system.

Cheers,
Mario

5

It’s best to find an experienced Victron dealer/installer who can support you with the planning and implementation (if you also buy the components from them). That way, you’ll also have someone to contact who knows your system if anything goes wrong.

Victron has a map for this on its website, or you can take a look at my profile :).

Victron MPPTs can be regulated down to zero export, and this is also possible with some PV inverters (Fronius).
“Dumb” PV inverters would feed excess power into the grid, and there’s nothing the Victron system can do about that.

Yes, that wouldn’t be permitted in Germany.
But you wouldn’t automatically have redundancy either.
If multiple VE.Bus devices are configured together as a system, whether in parallel, in a two-phase or three-phase configuration, they all switch off if one device shuts down.
You then first have to reconfigure the system manually.

If the grid is available, as appears to be the case here, there’s no need to worry about that—unless you’re expecting power cuts lasting several days in winter.

6

Hello,
and thank you for your reply.
First of all, the situation with the grid in Germany, the way electricity is generated and where it comes from — that quickly becomes political, so please let’s not discuss it in this thread. For some people, the stuff simply comes out of the socket.
Suffice it to say that I have compelling reasons for wanting to look into this at all. The location of the property is also a factor; the grid isn’t 100% stable everywhere.
The inverter’s grid-parallel operation already means that, by law, I need an authorised installer for the Victron system and the PV installation, so I’m happy to discuss it with one.
If they can also supply the equipment at fair prices, then all the better — they have to make a living too, after all.
If I weren’t looking for possible approaches and solutions, I wouldn’t be here either.
Here in my area, I’ve had both encounters of the third kind with “advisers” and encounters with very sensible, properly qualified installers who, unfortunately, were not particularly familiar with the Victron solution.
I’m looking for the optimum solution for me/us and don’t want something that merely looks right because it’s the way we’ve always done it. Nor am I the kind of enthusiast who spends years tinkering with their configuration and chasing every pointless update. Set it up and forget it; minor issues can remain as they are, provided they don’t jeopardise stable operation.
The question of what to do with the surplus power has already been answered, so thank you for that too. I’ll have to see how I can make it work. I don’t want any dangerous voltages on the roof, which already severely limits the choice of inverters; once you add power regulation and affordability, the options will probably become very limited.
As for redundancy, I’m already aware that the system might shut down completely in the event of a single fault, or switch to bypass operation. I can live with that; after all, the term redundancy covers different levels, two of which are cold and hot redundancy, although they aren’t quite the right fit here.
If one of them fails, I would still have the option of maintaining at least limited operation with the other one.

Regards
Mario

7

Morning, morning… I can already sense how this is going to get out of hand in a little while. Four years ago, I was in a similar situation to you and I understand your argument 100%. Matthias’s tip is of course a good one. Unfortunately, I didn’t have much luck finding an installer at the time. In the end, as a layman back then, I built most of it myself, but I did have a long-established electrical contractor who was happy to take care of the registration and AC connection on an hourly basis. In hindsight, I’m very glad things worked out that way; today, I know exactly what runs when and how in my house.

As for your statement, “I know my consumption very precisely”: yep, I phrased it exactly the same way, and things turned out just as everyone said they would — my system is actually at the lower end.

At the time, I built a three-phase system with 3000s, which together only produce a maximum of 7200 kVA, and even that only under optimum conditions (temperature). Today, I would always go for 5000s, and definitely three-phase. This core system, including a GX module, an EM 530 meter or similar, and a solid DC distribution busbar, should be the minimum starting point. In principle, you can build everything else on top of that later: however much storage, however many charge controllers or Fronius inverters you want.

Please bear in mind that a system like this is supposed to last 15–20–30 years, and NO ONE can tell you today what developments in e-mobility (whatever you may think of it) or heat pumps (the same applies) are still to come. I would strongly recommend going three-phase and not choosing too low a kVA rating. I let myself be persuaded to do so at the time, at least, and today I’m very, very grateful for it.

8

Well . whether you need 3-phase, single-phase .. a 3000 or 5000 model .. depends primarily on the household’s electricity consumption.. and he hasn’t mentioned that yet ;O)))

And of course it also needs to match a planned solar installation…

so some information is quite important .. otherwise you can “hardly” give any advice..

9

Then you should read the above more carefully; some of the details you asked for are already there.

10

He did write that he knows the system’s output, but he didn’t specify it… and there’s no indication anywhere of how large the solar installation should or can be either..

And that he’s thinking of a 3000-watt one… but the rest has to be suitable for that…

11

With an AC-coupled system, yes. With a DC-coupled system, it hardly matters at all. There, only the demand is decisive. And since no feed-in is wanted, I would assume it’s a DC-coupled system. The emphasis was explicitly on storage, too.

I knew it

12

Hello,

@Sarowe, good point and definitely something to bear in mind. That statement made me realise something else.

@all, as I’ve already written above: whatever can go on the roof will go on it, and whatever can’t, won’t. If there’s too much power, I’m fine with it going unused. The only potential issue will be throttling the inverters. That will also reduce the strain on them.

I don’t want to go into detail about my consumption either; suffice it to say that I have a workshop with a lathe, a gantry milling machine, two welding machines, each around 4 kVA, a large pillar drill, etc. This equipment, like the rest of the workshop, is already single-phase, with variable-frequency drives for the three-phase motors. My wife’s toy, the carding machine, which is also around 3 kVA, is single-phase too, and will be added to the mix.

The Victron doesn’t need to cover that: these aren’t base loads, nor are they essential. The electrical installation will be designed accordingly. Heating and lighting, IT, the wastewater treatment plant, and smaller consumers are the important things; their power requirements are known and manageable. The CNC would be nice to have—perhaps that’s the reason for the 5 kVA. The tools and ruined workpieces might help offset the cost somewhat.

The two remaining 5 kVA units for three-phase operation would provide a planned power reserve in case the demand does end up increasing. Although, if I’m interpreting this correctly, you can also operate two 3 kVA units, one on each mains phase. That would then give one phase for the house and one backed-up phase in the workshop, exclusively for the CNC. I’ll have to think about that some more.

Best regards,
Mario

13

Why does it always have to be single-phase?

14

@mariob
Hi Mario,

think about how long your strings could be, and what maximum voltage you want.
If you have a lot of shade, different orientations or tilt angles, you’re heading towards a string length of 1, or microinverters. In that case, you need to be able to charge the entire AC-coupled PV system into the battery via the MP2/Multi RS.
A string length of around 4–6 panels, depending on the panel, with the 250 V MPPTs would be better, but then you’ll need a lot of surge protection.
There’s less cabling (and surge protection) with the RS 450s. Even fewer cables, but then AC-coupled PV again, is a Fronius system with 800 V PV.

With the MP2s, you need to take inverter efficiency into account. Their maximum efficiency is at around 25% load.
So a larger one can be more efficient than a smaller one.

The Multi RS units are probably more efficient and quieter, but may not be able to handle as much starting current from motors or welding equipment.

The MP2s switch off if one unit is missing from the cluster. The Multi RS units can continue running, regardless of whether they’re configured in parallel or as a two- or three-phase system.
That means you could also have one of the Multi RS units switched off and „on standby“.

As soon as you have PV, your consumption will increase.
Partly because of the MP2s and batteries, and partly because it’s free.
I use excess electricity to heat water, use an infrared heater, and now have an air conditioner.
Consumption has risen from 4,500 kWh to 6,500 kWh—but only when the PV system is producing power.

A Victron system isn’t something you simply install once and then forget about.
You need to study it in depth if you want to configure it, but in return you can connect almost anything via the interfaces.

You can estimate your PV yield with the „Victron MPPT Calculator“ or PVGIS24.
In Germany, the difference between summer and winter is 7–10. In early summer, I get up to 900 kWh per month; in December, sometimes only 50. In that case, I switch off the MP2s because they consume more than the roof produces.

The more information you give us, the more suitable advice we can offer.

Feel free to take a look at my system presentation in my profile. It gives you a few impressions.

Good luck!

15

Do you simply not want to feed power into the grid, or are you not allowed to?

If you are allowed to, why not include the EVG?

If you are not allowed to, it gets relatively complicated

You write about a relatively large amount of machinery — this will probably mainly be used during the day, when the sun is shining, right? Then I would not use MPPTs, but convert directly to AC, as the efficiency is considerably better

Am I understanding this correctly — you essentially also want a UPS for the machinery?

An MP2-5000 is hardly more expensive than a 3000, but it is not quite as easy to connect

The 3000 only needs 16 A circuit protection

Three-phase is currently a hype — I see more disadvantages than advantages

  • high standby consumption
  • if one part breaks, everything shuts down, which means a lot of work again with a transfer switch and so on

My house is deliberately not connected to the MP2’s AC output; there is only an emergency power outlet

You must also not forget — if you connect the house to the AC output, then do a firmware update or something similar, click-clack, the isolation relay trips — and then you have to reset the clocks on the cooker and so on

v

16

Hello,

@sarowe, single-phase is sufficient for me given my usage profile and plans; it simply means having more time to live, and I don’t believe in reincarnation :slight_smile: .

@all Otherwise, I’ll look into the matter of the RS to see whether I’m allowed to feed power into the grid or not. I tend to take the path of least resistance and try not to find out in the first place. According to a local company, this will apparently be over from next year anyway.

And to be clear once again, the workshop equipment is connected directly to the mains; I certainly wouldn’t put that on the Victron. The only possible exception is the CNC. When the mains is down, it’s time for other activities, watering ice flowers or something :slight_smile: .

Best regards

Mario

17

But it does make things considerably easier if you’re allowed to feed electricity into the grid.

We had a case here involving someone we know where this wasn’t allowed because the grid was overloaded — that made the system considerably more complicated.

We asked the grid operator about fluctuations caused by the control system, and whether those would at least be acceptable — they then agreed to that.

Interestingly, a 10 kWp system is now allowed to feed less electricity into the grid than a balcony solar system.

18

If the local distribution transformer has no more capacity, you won’t get approval!

Newly ordered transformers often have lead times of several years.

Being able to run your installation in island mode has its advantages when the power isn’t coming from the mains.

19

Why are you writing that with an exclamation mark now?

It’s ridiculous: the village transformer can’t handle any more, yet feed-in is still allowed on a netted basis.

20

Actually, I had intended to hold back a little. But there are some things you simply can’t leave unchallenged like that. I actually agree with your philosophical approach to single-phase systems. But that has little to do with the technology. There are many reasons why our predecessors introduced three-phase distribution, quite apart from star-delta circuits. I just don’t understand the approach. In the “generation” stage, you squeeze everything onto a single phase, only to split it apart again in the “workshop” using some kind of technology. Even in domestic installations, I keep running into conflicts, whether it’s an electric cooker, a future EV charger, a heat pump or something else. Especially since regulatory requirements regarding phase imbalance also stand in the way. For a BKW or a small flat, single-phase systems may make sense, partly because of their efficiency. For entire houses, with a workshop and the option of expanding, single-phase setups make no sense to me.

The next point: “I’m not going to put the workshop through my Victron system.” I think there are one or two fundamental misunderstandings here. Are you planning a grid-connected system? In that case, any consumption exceeding the system’s generation capacity will always be drawn from the grid. Even if the workshop’s load is too high, I would always try to use the portion that the system can cover. Since you don’t want to export electricity to the grid (nor do I), you will reach the point of having a surplus in summer. You want to leave that on the roof, but have the workshop draw its power from the grid. That makes absolutely no sense.

I get the impression that, aside from topics such as the microinverters, string lengths and the like mentioned above, you should take another look at the fundamentals.

This really is meant as friendly advice. Some things in your descriptions are fundamentally contradictory.