11.2 kWp, 2 strings, cold climate — Victron architecture & MPPT advice

DIY
,
1

Hi all (since english is not my main language - difficult to write; easy to read - i decide to get chatgpt help to translate),

After reviewing several turnkey PV quotes, I decided to move forward with a self-procurement approach: sourcing all equipment directly and having a certified electrician complete and sign off the installation (mandatory in Portugal for grid connection).

The cost difference remains significant—equipment savings in the €4k–€7k range—so I’m now locking down the final system architecture and would really value feedback from experienced Victron users.

:house: System overview (final design)

Location: inland Portugal (cold winters, frequent frost → high Voc risk)

Roof:

  • Type: 4-pitch roof

  • Base tilt: 15°

  • PV mounting tilt: 35° (elevated structure)

Orientations used:

  • South (primary)

  • East (secondary, winter morning boost)

Design goal:

  • Maximize winter production (Nov–Feb)

  • Maintain strong annual self-consumption

  • Summer surplus is expected and accepted

:battery: PV configuration

Module: TWMNH-66HD 620 W
Total modules: 18
Installed capacity: ~11.2 kWp

:blue_circle: MPPT 1 — South array

  • 10 panels (6 + 4 layout)

  • 1 string (series)

  • ~6.2 kWp

:orange_circle: MPPT 2 — East array

  • 8 panels (5 + 3 layout)

  • 1 string (series)

  • ~5.0 kWp

:high_voltage: Electrical architecture

  • 2 independent MPPTs

  • 2 strings total (no parallel strings)

  • No combiner boxes

  • Low mismatch risk

  • Clean, simple topology

This is intentionally designed for robustness and simplicity over maximum density.

:thermometer: Key technical constraint: cold-weather Voc

Given frost conditions, I’m particularly concerned about:

  • String Voc at low temperatures

  • Staying safely below inverter max PV input voltage

  • Avoiding edge-case shutdowns or long-term stress

This is especially relevant for:

  • 10-module South string

  • High-efficiency large-format modules (620 W class)

:gear: Victron system approach

I’m currently evaluating:

  • Parallel setup with 2× Victron MultiPlus-II (to achieve ~6 kW AC output), + external MPPTs
    vs

  • 1× Victron Multi RS Solar (integrated MPPT)

:warning: Important design constraint

  • No future PV expansion planned (roof is fully utilized)

  • Only possible upgrade path: battery capacity expansion

So the system should be right-sized from day one, not modular for PV growth.

:red_question_mark: Key questions for Victron users

1. MPPT / voltage strategy

For this exact type of setup (2 strings, ~8–10 modules each):

  • Would you stay within ≤450 V MPPT systems (e.g., SmartSolar range),
    or go directly to high-voltage MPPT (Multi RS Solar)?

  • How much real-world safety margin do you apply for cold Voc?

2. Multi RS Solar vs MultiPlus-II + SmartSolar

Given:

  • ~11.2 kWp PV

  • ~6 kW AC target

  • No PV expansion

What would you choose in practice?

Multi RS Solar:

  • Cleaner integration

  • Higher PV voltage capability

  • Simpler system

MultiPlus-II + MPPTs:

  • More flexible

  • Potentially more robust under load

  • Better scalability on battery side

3. High-voltage string experience

  • Anyone running ~8–10 modules in series in cold climates?

  • Any issues with:

    • MPPT clipping at high voltage?

    • Cold-start behavior?

    • Reliability over time?

4. DIY + Victron ecosystem

Plan:

  • DIY mounting + DC wiring + equipment installation

  • Certified electrician for AC, protections, and grid connection

From experience:

  • Any common mistakes in Victron-based DIY systems?

  • Anything you would avoid doing yourself?

  • Any “must-have” components often overlooked?

:brain: Final design philosophy

  • Prioritize winter performance over annual peak yield

  • Keep electrical design simple and robust

  • Avoid unnecessary parallelization

  • Accept summer surplus as a non-issue

Appreciate any feedback—especially from those running Victron systems in cold climates with similar string voltages.

Thanks!

P.S.: :counterclockwise_arrows_button: Alternative (non-Victron) option under consideration

As a reference point, I’m also considering a more conventional all-in-one string inverter:

  • Solis S6-EH3P8K-H (8 kW hybrid inverter)

This would simplify the system significantly (integrated inverter + MPPT + battery management in one unit).

However, my main concern is that I would lose much of the flexibility and intelligence of a Victron-based system, particularly:

  • Advanced energy management via a GX device (e.g. Cerbo GX)

  • Fine control of loads such as:

    • EV / PHEV charging

    • High-temperature heat pump operation

  • More granular automation and system logic (ESS behavior, scheduling, prioritization, etc.)

:warning: Important note on consumption assumptions

I’m intentionally not including current consumption data in this project, because it does not reflect future usage, namely:

  • Planned addition of an electric or plug-in hybrid vehicle

  • Planned installation of a high-temperature heat pump

So the system is being designed based on expected future loads, not current consumption patterns.

:brain: Strategic consideration

This essentially comes down to:

  • Solis approach:

    • Simpler, cheaper, all-in-one

    • Less configurable / less “smart”

vs

  • Victron ecosystem:

    • More complex and modular

    • Significantly more powerful in terms of control, integration, and long-term flexibility

If anyone has experience comparing a Victron ESS setup vs something like the Solis S6 hybrid series in real-world use (especially with EV + heat pump loads), I’d really appreciate your insights.

2

I don’t think you can do 10x 620W panels in series and staying under 450V Voc.

Have you checked: mppt.victronenergy.com?

3

Given the High Voc of the module, (52.5V @-10C), I would definately move to 2 strings per array - as in 2 x 5 modules per string. This reduces the constraint on the PV isolator switch, as well as the MPPT.
your question " How much real-world safety margin do you apply for cold Voc?" The answer is given in the data sheet for the solar module: {https://invercel.solar/wp-content/uploads/2024/02/TW-600-620w.pdf}

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For the MPPT unit: The RS 450/200 could do the job, given the different azimuth of the two sub arrays. You may find that the output would limit at 200A for part of the day, when the theoretical possible current would be 240A@50V for 12kW. as you have 20 x 620W module, kWp is 12.4kW, but that is within the capability of that charger. There are also 4 mppts which matches nicely with the 4x5 module layout (263 Max Voc).
Victron mppt’s don’t “clip” at high input voltage, a protection FET is turned on to short the input, this gives an error condition, which is cleared by a reset.(after removal of the high voltage).
Any “must-have” components often overlooked? usually fusing, isolation and lightning protection. Given your array size and operating voltage, earth leakage detection for the pv may also be a mandatory requirement.
Hope this helps.

4

will you use more power through the battery or directly?

Did you think about Micro-Inverters like Hoymiles HMS Series?

I use many of them, so each panel is directly connected

Is has the pro: directly used energy is converted at a higher efficiency

con: Enerfy to the Battery is stored with lower efficency

I live in germany, cold, dark winters, and have a heat pump

although we have 25kWp - often the heat pump takes that much that almost nothing is over for battery

In summer, when there is enough sun, i don´t worry about efficency

5

@Zarb

Do you have a 1-phase or a 3-phase grid?
Depending on the grid type and local regulations, you might be forced to go with 3x MP2 if you want to charge AC-PV into battery.

I would mix 20-30% AC-PV to cover direct usage and 70-80% DC-PV (MPPT) to Charge battery efficient.

Portugal‘s ration between December and June is 2, e.g. while produng 1kWh/day in June you get only 0,5 kWh-“/day in December.

If you want to maximize for Winter, consider a PV fence or vertical panels a the wall. For those micro grid inverters might be greate.

6

That’s a problem with Victron… smart solar is limited do 250v (4 panels over 600w each) as see it..
Or i can put 10 panels with 4 string… but the i will have a increase of cost with solar cables and also, more MPPT…
With Solis S6 i can put 9 panels.

7

but a MPPT RS 450/200 is over 2000 euros… only for a MTTP.
That is going to be dificult to get over a Solis S6, with 2+2 MPPT and inverter in one machine that is under 1500 euros…

8

But i will need a Hoymiles HMS Series for each 4 panels… to 16 panels (minimum), i would have to get 4 Hoymiles HMS Series. So is about 350 euros each…

To expensive to get a real return on investment. Like if i go to Victron RS 450/200

9

I have 1-phase.

The problem with fence is that the only part of by home that as not shade, is the roof. I live inside a florest, so even in my backyard and my walls i have a lot of shade for the trees around.
And also, micro grid inverters are a efficient way with Victron system?

10

And if i divided the 16 panels in 4 string and get two SmartSolar MPPT RS 450/100-MC4? Could it do the job?
Also, what more equipment i should get?
The panels and the battery are almost chosen: panels TW 620W and Sunwoda Atrix Max 16 kwh.

11

@Zarb
I see no advantage using 2x RS450/100 over one RS/450.
Maybe buy the equipment in Germany. The RS450/200 is 1,350 w/o tax or 1,600 EUR inkl tax.

Another source might be NKON in Netherlands. There the RS450/200 is 1,600 EUR for PT. They supply good batteries NKON ESS Pro 16 or 32kWh. You could order all together and get it shipped to Portugal.

https://www.nkon.nl/pt/victron-energy-scc145120510-smartsolar-mppt-rs450-200-mc4-solar-laadregelaar.html

I would go for:
1x RS450/200
1x MP2 6k5 or bigger depending on regulations in Portugal
2x Lynx Distributor
1x Cerbo mk2
16 or 32kWh battery
1x Victron EVCS, this can charge 32A/7,2kW single phase.

Add the fence with 2x HMS-2000-4T on AC_out later. Then you can use full 7.2 kW EV charging with a MP2 6k5.

12

I think I finally understand the architecture better now, but I want to check if my reasoning makes sense.

My panels are around 49–51 Voc each, and because winters here can get cold, I don’t think I can safely put 8–10 modules in series on a Victron RS450 without risking exceeding the 450V limit in cold conditions.

I wasn’t understand

So what I’m currently considering is:

- Orientation 1: azimuth 200°

  • 5 modules on tracker 1

  • 5 modules on tracker 2

- Orientation 2: azimuth 110°

  • 6 modules on tracker 3

- Tracker 4 left free for future expansion (possibly another orientation later with maybe 5–7 modules).

My understanding is:

- each tracker is independent,

- I should keep one orientation per tracker,

- and this would allow me to stay within both voltage and current limits without needing parallel strings.

Does this seem like a technically correct architecture for a single SmartSolar RS450/200, considering the azimuths and module Voc values?

Or am I still missing something important that would force me into multiple RS450 units?

13

Good evening,

Why not buy 2 Fronius single small Mppt PV inverters and put these on the output of your Victron inverter (free pf correction as well and so more efficient), and only 1 dc/dc Mppt from Victron…or…“as Bjorn days”, a big RS and (my advice on top of that) a single Victron dc/dc Mppt, this that batteries being charged with the install in service…or not working…that’s called fail safe…instead one thing what does it all…see my point…

Hi, @BjoernK, all ok?, do you agree?, I think it’s best for this install?

Regards, Jeroen.

14

@Zarb

Yes each tracker is independent and should have panels with same direction, orientation and same (no) shading. On RS450 a single tracker can charge 80A, whereas the average charge capacity of all trackers is 50A per tracker. You can “over panel” and “over tracker” your RS450 if you have the trackers for different orientations.

Please check Victron MPPT calculculator.
The link shows your custom panels on STC (1000W/m2), though save for tempertur -10C to +60C.

You can put up to 8 panels in series on one tracker, which will give up to 80A, which is the clipping point for a single tracker in the RS450. Minumum is 2 panels in series for start voltage of MPPT (RS).
Though you are free to chouse between 2 und 8 panels per tracker on a RS450.
5-6 panels per tracker seem to be the optimium as it is not clipping the single tracker on cold temperatur. 6 gives 68-80A, 5 gives 57-67A per tracker.
Considering different directions of your trackers, you can paln more than 50A per tracker.

Victrons MPPT calculator does not mind elevation and direction of panels. Though you might have some extra margin.

According redundancy mentioned by @Jeroen2

If your system is grid connectd, I would not do much consideration about redundancy.
Though for a grid connected system I would got with:
1x RS450/200 (4 trackers) and later add some micro grid inverters for vertical fence or wall PV that get light some time over the day and can gather reflections from snow.

Jeroen is right, a mixture of DC-PV (RS/MPPT) and AC-PV (Fronius) is most efficient as AC loads are supplied by the AC-PV with 98% efficiency, while converting from DC via MP2 takes some 10%. On the other hand the DC-PV is needed for black start and is more efficeint to charge batteries.
If you find some partly shaded places later to use during winter, you need the MP2’S converting capacity (factor 1:1 rule) for micro grid inverters. A MP2 6k5 can have 6,5kWp AC-PC on AC_out. Though starting with a RS450/200 is “save” in this case, while not optimal from conversion perspective.

If your system is critical, than I would consider some redundency.
Either a generator or spliting the MPPT e.g. 2x RS450/100 or some other mix with Fronius AC-PV. I would consider micro grid inverters as a add on as they might not restart properly. I have some firmwares with defective grid code. The restart frequency is 502Hz (comma is missing), though after SOC 100% (e.g. frequency shifting to 53Hz), they need to be power cycled, which happens during night. Works, but not optimal for off grid and mission critical.

15

I am also using AC PV (Fronius) and DC PV MPPT, up to now is the perfect match.

As already posted, AC PV is perfect for daytime consumption, Victron having great time with Fronius inverters !

16

Good evening,

Don’t forget solar flares, almost nobody calculates this, a flare can last 5-10 minutes or so, 1200-1400W/M2 (pending country), so, read your inverter spec to cope with that as well, thanks @BjoernK for your always attendance in general…

Regards, Jeroen.

17

sorry, never heard about that - where did you get that rumour?

If a flare would affect PV panels that much, humans would also feel it

18

Good evening,

Sorry, don’t your government tells, specially at the beach, your inverters go hi-wire that time?

Then another thing, did you ever hear about black solar spots?

This year there are a lot, and so in the whole world we have less solar radiation (sea level measurements of course), this year about 15-20% less then a top year when there are way less, the cycle is about 10-11 years, already taken and measured in the 17 century-isch years…yep…

Yep, you go solar, but many have no clue what this sun does, isn’t it?

Always regards, Jeroen.

19

@Zarb

I checked the Fronius single-phase inverter series “Primo”.
With your high current panels your need to select at least the Fronius Primo 6.0-1, which allows 18A DC input. The smaller ones are limited to 12A DC input.

Fronius Primo 6.0-1
2 MPPTS
18A DC input
240-800V MPPT input
→ 6-10 panels of your type

Option 1 “Fronius”:

  • MP2 6k5
  • Fronius Primo 6.0-1 for the south array with 10 paneles in series, leaving second MPPT free
  • Victron RS450/100 with 5 panels on each tracker

Option 1 provides::

  • 20 panels / 12,4kWp PV , 12,5 kW combined AC (Fronius + MP2)
  • extension by 3kWp (15,4kWp) at the free tracker on Fronius but with different high voltage panels
  • max extension
    • 12,5 kW AC
    • 15,4 kWp PV
  • Build:
    • slighly more complex start
    • higher AC on start
    • less extension
    • less complex extension

You cannot add micro grid inverters as the factor 1:1 rules is satisfied by the Fronius (6kW AC) allready.

Option “extendable”:

  • MP2 6k5
  • RS450/200
    • tracker 1: south 5 panels
    • tracker 2: south 5 panels
    • tracker 3: east 6-8 panels (with 8 panels the tracker will be saturated at any temperature, but is ok)
    • tracker 4: free fo extension

Option 2 provides:

  • 11.16kWp PV, 6,5kW AC
    EV can be charged less than 7,2 kW but most EV might support only 16A single phase (3,6kW) either.
  • High efficient battery charging. Wihtout heat pump and EV, normal load is ~300-500W. Though this setup is more efficient.
  • extension 1: add 6kW AC-PV with 7.44 kWp PV for winter opration
    combined AC of 12,5 kW AC like option 1
  • extension 2: add 5-8 panels (5kWp) to the free tracker #4 on RS450 for winter operation
  • max extension
    • 12,5 kW AC (like option 1)
    • 23,6 kWp PV compared to oared for winter oporations
  • build:
    • simplier start
    • less AC on start
    • with extension significant more PV, which stronger shadow management and winter operation
    • with extension more complex

You choise: simple and more static or more extendable wiht higher winter performance and higher complexity

Please mind, per 1 kWp PV you will need 3kW battery to absorb the energy. This translates to 32-64 kWh battery depending on setup/extension.

I would not consider the Victron MPPTs as:

  • you need 5V above battery voltage → min 2 panels in series
  • you need to use either MPPT 150 with 2 panels or MPPT 250 with 4 panels
  • each (short) string add costs for generator box with surge protection and disconnect switch

Use long strings for cost efficency → Fronius, RS450
Use short strings (1 panel) for extrem shadow management → micro grid inverter

With Victron you can combine all this and later extend.

20

i know what solar flares are and that they happen

But this has absolutely nothing to do with PV inverters

Even if i take the smallest inverter , regardles if victron or not - i could also wire 100+ PV cells in parallel, nothing will happen

I still have because of german laws some PV cells doing max of about 800W connected to an inverter capable max of 500W

Voltage is given, current is drawn, that is a big difference

your shaver also won´t take 2000W simply because the fuse allows it