Anyone else finding the Renogy 40A MPPT a bit flaky on partial shade days?

Had the same grief with mine last summer. Partial cloud cover and the thing would just... dither. Voltage hunting all over the place instead of settling on a proper MPP. Ended up logging the data and it was genuinely embarrassing how much harvest I was losing on what should've been decent days.

Swapped it out for a Victron SmartSolar 100/30 and the difference was night and day — their perturb-and-observe algorithm is just better tuned for rapidly changing irradiance. Worth the extra outlay honestly.

A few things worth checking before you give up on the Renogy though:

• Firmware — there was a dodgy batch with old firmware that made shade behaviour worse. Worth connecting it up and checking.
• Panel wiring — any loose MC4 connections will amplify the instability massively
• Array voltage — if you're running close to the controller's upper limit, it gets twitchy in partial shade when voltage spikes

My setup in the motorhome is two 200W panels in series so I've got decent Voc headroom on the Victron, which helps it stay stable.

Curious whether others are seeing this on specific roof layouts? I reckon partial rear shading from roof bars is the worst case — hits the string hard. Anyone tried adding a Fogstar battery with better BMS comms to see if that smooths out the acceptance side of things at all?

Would be good to get a few more data points on this — feels like the Renogy might just genuinely struggle with UK weather conditions where you're rarely getting clean full sun anyway.

@WildTinker that voltage hunting on patchy cloud days is a known weak spot with the Renogy units — their MPPT algorithm seems to have a pretty narrow tracking window and just loses the plot when irradiance is shifting every 30 seconds.

I swapped mine out for a Victron SmartSolar 100/30 at the cabin and the difference was immediately obvious. Victron's algorithm re-acquires MPP much faster after a cloud event — you can actually watch it settle in the VRM app in real time, which is satisfying.

Worth noting: panel layout matters too. If your array has any series strings, partial shade hits hard. I rewired mine to parallel strings with individual fusing and that alone reduced the hunting noticeably, even before the controller swap.

Would be curious to see your logged data though — what were you capturing it with?

@WildTinker I've seen identical behaviour on my narrowboat setup — the Renogy 40A really does struggle when irradiance is jumping around every 30 seconds. The tracking algorithm seems to need stable conditions to confidently settle at MPP.

Switched to a Victron SmartSolar 100/30 and the difference was immediately obvious. The adaptive algorithm handles rapid irradiance changes far better — you can actually watch it re-track cleanly in the VictronConnect app rather than hunting back and forth.

Worth noting that if you're running panels in series vs parallel it can also affect how badly the hunting manifests under partial shade — series strings with mismatched irradiance across cells will give the MPPT a harder job regardless of controller quality.

If you've got the data logs already, post them up — would be interesting to see the voltage swing amplitude.

@WildTinker oh brilliant, I recognise this pain. Mine used to do the same thing — I called it the "Renogy Shuffle." Spent about 20 minutes one afternoon genuinely convinced something had gone catastrophically wrong, only to realise it was just a single cloud the size of a transit van drifting overhead.

Ended up swapping

@WildTinker this is really timely for me — I'm just speccing out the solar for my narrowboat and was weighing up the Renogy 40A against a Victron SmartSolar 100/30. The price difference is significant but threads like this are making me think the Victron might be worth the extra outlay.

Quick question for the group — does this "voltage hunting" behaviour actually translate into measurable energy loss, or is it more of an annoyance than a real-world problem? Like, has anyone actually logged the difference in harvest between a Renogy and a Victron unit on the same patchy day?

Also @PennineNomad curious whether you've done anything to mitigate it on your narrowboat setup, or just lived with it? I'd rather know before I commit to anything given how unpredictable British canal-side shade can be with trees and bridges.