Auslegung Grenzbereich BlueSolar SmartSolar MPPT Tracker für PV Module mit hoher Modulspannung

Been wrestling with exactly this kind of headache lately for the shepherd's hut build, so figured it's worth opening up the discussion here.

I'm running a string of 400W panels that push Voc up around 49V each — series the pair and you're nudging 98V open-circuit before you even account for cold morning temperatures. In January on a clear frost morning here, I measured genuine -8°C at the panels, which adds another ~5% on top. Suddenly you're flirting with the 100V absolute maximum on a Victron SmartSolar MPPT 100/30, which makes me deeply uncomfortable.

The temptation is obvious — higher string voltage means lower cable losses and you can get away with thinner DC cable runs. But the margin for error on the 100V-rated controllers is genuinely thin once you factor in:

• Temperature coefficient of Voc (typically -0.28%/°C to -0.35%/°C on most panels)
• UK winter lows (Scotland and upland areas especially)
• The fact Victron's specs are absolute limits, not conservative guidelines

I ended up stepping up to the SmartSolar MPPT 150/35 to give myself proper headroom, even though the current output was already fine on the smaller unit. The 150V input rating just removes the anxiety entirely.

Has anyone here pushed panels close to the boundary on a 100V controller and lived to tell the tale? Or gone parallel strings instead to keep Voc down? Curious whether Fogstar or other UK suppliers are seeing customers come back to them with fried controllers from exactly this scenario.

Worth discussing — especially as more people are fitting higher-voltage 400W+ panels to vans and huts where the wiring

Hey @WillReid, the thread title's gone a bit German on us there mate 😄 but I know exactly the headache you're describing!

Key thing with the BlueSolar/SmartSolar MPPTs is that your absolute worst-case Voc needs to account for cold temperature derating - folk often forget that panels can spike well above their STC Voc on a freezing clear morning. Victron's own sizing tool will flag this properly if you plug in your lowest expected ambient temp.

For a shepherd's hut build specifically, are you looking at the 100V or 150V input models? That'll determine whether you need to reconfigure your string arrangement entirely. What's your actual panel count and Vmpp roughly? Happy to run through the numbers with you.

@VanBarry already flagged the title going rogue, so I'll skip past that.

This exact scenario nearly caught me out with my static van setup last winter. Had a string of 410W panels from Renogy and the Voc on a crisp January morning was genuinely alarming — panels love the cold, which is the bit people forget when they're planning in August sunshine.

The rule I'd drum into anyone: take your worst-case Voc (coldest realistic morning in your location), multiply by your string count, then stay comfortably under your controller's absolute maximum. Not at the maximum — under it.

With Victron's SmartSolar range the datasheets are clear enough, but the margin matters. I derate deliberately. A blown MPPT because you pushed the boundary on a frosty February morning is an expensive lesson nobody needs.

Yeah the Voc thing is a proper gotcha if you're not careful. Victron's MPPT range has a hard ceiling — the SmartSolar 150/35 is obviously 150V max input, but people forget that's the absolute limit, not your operating target.

Cold morning temps will push Voc higher than the datasheet STC figure — sometimes 10-15% depending on your panel's temp coefficient. Ran into this myself when spec'ing panels for the van, nearly went over on a frosty January morning.

Use Victron's own MPPT calculator on their site — it factors in temp coefficients properly. Punch in your lowest expected ambient and it'll show you actual worst-case Voc.

For a shepherd's hut in the UK, I'd be budgeting for -10°C minimum tbh, maybe lower depending where you are.

@BurnBen's point about the hard ceiling is the key one — and what people miss is that the cold temperature correction can push you well over it even if your nominal calcs look fine.

Quick rule of thumb I use for my van build: take your string Voc, multiply by 1.25 for a UK winter worst case, and make sure that still sits comfortably under the controller's max input voltage. Victron publish the temp coefficients in the datasheet (usually around -0.29%/°C for monocrystalline) so you can do it properly too.

For a shepherd's hut sitting exposed on a hillside overnight, that cold-morning spike is very real. Fried a BlueSolar on my first build before I learned this the hard way. Now I overspec the controller more than most people think necessary.

Really glad @CoveMick brought up the cold temperature correction because that's where I've seen people come unstuck even after they've done the maths. Worth adding: don't just check your local historical low — Victron themselves recommend using the record low for your region, not the average winter minimum. For most of the UK that's surprisingly cold once you factor in a clear January night with panels exposed to the sky.

On the shepherd's hut specifically @WillReid, are your panels fixed or can you tilt them? Orientation affects how quickly they warm up in the morning, which is precisely when you're hitting that cold Voc peak before the sun does its job. Just another variable worth factoring into your worst-case calculation before you commit to a controller.