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

[Zarb]

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.

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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

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PV configuration

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

MPPT 1 — South array

• 10 panels (6 + 4 layout)

• 1 string (series)

• ~6.2 kWp

MPPT 2 — East array

• 8 panels (5 + 3 layout)

• 1 string (series)

• ~5.0 kWp

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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.

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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)

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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)

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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.

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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?

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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

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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?

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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?

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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

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

Thanks!

P.S.: 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.)

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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.

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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

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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.

[Skipper]

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

Have you checked: mppt.victronenergy.com?

[MikeD (Mike)]

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}

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.

[kr0815]

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

[BjoernK (Björn Kellermann)]

@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.