Victron MPPT Sizing Calculator
Enter your panel specs and string layout. We do the cold-weather voltage maths.
The most-Googled question in DIY solar: "which MPPT do I need?" This calculator takes your panel specs and string layout, adjusts Voc for cold UK mornings, and picks the smallest Victron SmartSolar model that safely handles your array. Every recommendation links to the exact model on Amazon UK.
Your Array
Enter the specs from your panel datasheet and your planned string configuration.
⚡ Why cold weather matters
Solar panel voltage goes UP as temperature goes DOWN. A typical panel with -0.34%/°C temperature coefficient gains about +10% voltage at -5°C compared to 25°C. That's why you never run your array Voc right up against the MPPT's max - a cold January morning can push you past the limit and fry the controller.
UK rule of thumb: keep your temperature-adjusted array Voc at least 5-10% below the MPPT max. The calculator uses -0.3%/°C as a default temp coefficient, which covers most panels (JA Solar, Longi, Jinko and similar).
Victron SmartSolar MPPT Reference Table
Click column headers to sort. Highlighted rows are recommended picks. All models linked to Amazon UK.
| Model | Max Voc (V) | Max Isc (A) | 12V (W) | 24V (W) | 48V (W) | Connection | Typical use |
|---|---|---|---|---|---|---|---|
| 75 | 15 | 220 | 440 | -- | VE.Direct | One small panel, van or shed | |
| 100 | 20 | 290 | 580 | 1,160 | VE.Direct | Two panels, 12V or 24V | |
| 100 | 30 | 440 | 880 | -- | VE.Direct | Two to four 100W panels | |
| 100 | 50 | 700 | 1,400 | -- | VE.Direct | Four panels on 12V/24V | |
| 150 | 35 | 500 | 1,000 | 2,000 | VE.Direct | Popular all-rounder, 48V systems | |
| 150 | 45 | 650 | 1,300 | 2,600 | VE.Direct | 3-4kWp on 48V | |
| 150 | 60 | 860 | 1,720 | 3,440 | VE.Direct | High-power 12V/24V and 48V | |
| 150 | 70 | 1,000 | 2,000 | 4,000 | VE.Direct | Large 48V arrays | |
| 150 | 85 | 1,200 | 2,400 | 4,900 | VE.Direct | Up to 5kWp on 48V | |
| 150 | 100 | 1,450 | 2,900 | 5,800 | VE.Direct | Up to 6kWp on 48V | |
| 250 | 60 | -- | 1,720 | 3,440 | VE.Can | Long series strings on 48V | |
| 250 | 70 | -- | 2,000 | 4,000 | VE.Can | Long strings, high power | |
| 250 | 85 | -- | 2,400 | 4,900 | VE.Can | Up to 5kWp on 48V | |
| 250 | 100 | -- | 2,900 | 5,800 | VE.Can | The big boy, up to 6kWp |
Note: 250V models require 24V or 48V battery (not 12V). The 450/100 and 450/200 models are for very large commercial arrays. All prices approximate, check Amazon for current stock. As an Amazon Associate, DIY Solar UK earns from qualifying purchases.
Common Questions
What does 150/35 actually mean?
The first number (150) is the maximum PV open-circuit voltage the controller can handle. The second number (35) is the maximum charge current in amps it delivers to the battery. So a 150/35 handles up to 150V from your panels and charges at up to 35A. Simple once you know it.
Can I over-panel a Victron MPPT?
Yes, within reason. Victron MPPTs current-limit at their rated output and won't be damaged by excess PV power - as long as you NEVER exceed the max Voc rating. Over-panelling by 30-50% is standard practice in the UK to get decent winter output. The MPPT simply caps at its rated maximum on sunny days.
Do I need the 250V models or are 150V ones enough?
Most UK residential installs use the 150V range. With modern 400W panels (Voc around 37-41V), you can fit 3-4 in series on a 150V controller - enough for a single string. You only need the 250V range if you want 6-8 panels in one long series string (typically to minimise cabling on a detached garage or outbuilding). Two 150V MPPTs on separate strings often works better than one 250V unit if you have split roof orientations.
VE.Direct vs VE.Can - what's the difference?
VE.Direct is a simple serial connection used on MPPTs up to 150/100. It connects to a Cerbo GX or Raspberry Pi via a VE.Direct to USB cable (around £25 each). VE.Can is CAN bus networking on the 250V models - faster, supports daisy-chaining, and uses standard RJ45 ethernet cables. For a home system with one or two MPPTs, VE.Direct is perfectly fine.