Anyone else finding their Victron MPPT wildly optimistic about daily yield estimates?

My Victron SmartSolar 100/30 reckons I should be pulling around 18Ah on a cloudy day but I'm lucky to scrape 6Ah from my two 175W Renogy panels when there's proper British "sun" doing its thing.

Checked all the wiring, connections are solid, panels are tilted at 35° facing south — by the book. Running into a Fogstar 200Ah LiFePO4 so the battery side seems fine. The app just sits there looking smug showing me a yield graph that bears zero resemblance to reality.

Is this a settings thing, a physics thing, or just Victron having a laugh at my expense?

Hey @BC_Boats, yeah the yield estimates on the Victron app are based on panel rated capacity rather than actual conditions, so they're always going to look rosy compared to what UK weather actually delivers!

A few things worth checking though - what angle are your panels mounted at? On a boat I'm guessing fairly flat, which will kill your output on low winter sun angles. Also worth checking for any partial shading, even a bit of rigging shadow across one cell can drag the whole string down surprisingly badly.

6Ah on a genuinely overcast day from 350W of panels doesn't sound catastrophically wrong to be honest - I've seen worse! The History tab in VictorConnect is your friend for spotting patterns over time rather than chasing daily figures. What's your actual consumption looking like versus what you're generating? That's the number that really matters.

Yeah, @BC_Boats, totally feel your pain on this one! Worth checking what irradiance figure Victron is basing those estimates on — it's typically assuming something like 4-5 peak sun hours, which is frankly laughable for most of the UK, especially autumn through spring.

What I'd suggest is logging a few weeks of actual yield data and working out your real average peak sun hours for your location. Then you can set more realistic expectations rather than chasing figures the app throws at you.

Also worth double-checking your panel orientation and any shading losses — even a chimney shadow catching a corner of a panel can hammer your output disproportionately with series-wired strings. 6Ah on a proper overcast day from 350W of panels actually sounds about right to me honestly!

@BC_Boats my Fogstar-packed shepherds hut system laughs in the face of Victron's optimism every single grey Norfolk morning — 18Ah is what my panels dream about while weeping into the overcast sky.

@BC_Boats totally normal mate, don't panic! The thing worth checking is your panel orientation and any shading losses — even a slight shadow across one corner of a panel can absolutely tank your output with standard series wiring. 6Ah on a properly overcast UK day from 350W of panels is actually fairly reasonable if your irradiance is sitting around 100-150 W/m² (which is pretty common here in winter or heavy cloud).

If you're not already, have a look at the VictronConnect history graphs — the actual peak wattage figures will tell you a lot about whether you've got a wiring or shading issue versus just the weather being grim. Also worth double-checking your panel connections are solid; loose MC4s can cause all sorts of grief that looks like a yield problem.

@BC_Boats totally get this frustration! Worth knowing that Victron's yield estimates are typically based on a default irradiance figure of around 1000 W/m² (peak sunshine hours), which bears absolutely no resemblance to a proper overcast British day where you might only be seeing 100-200 W/m².

What I'd suggest is having a look in the VictronConnect app under your MPPT history — compare the "maximum power" figure against your panel's rated Voc and Isc. That'll tell you whether the panels themselves are underperforming or whether Victron's baseline assumption is just wildly unrealistic for your location.

Also, 6Ah from 350W of panels on a genuinely cloudy day isn't actually terrible depending on how long the "usable" daylight window was. Don't be too disheartened — the estimates are basically best-case marketing fluff rather than UK reality! 😄