"Top" missing off generation

Hi Folks,
I thought I'd spotted this a while ago. My setup (Gen1 3.6, 4kWp solar, 3.5 years old) seems to not be generating as much as I expect during the middle of the day. This is the actual vs. prediction from Solcast:

My first thought was clipping but, at 3.2kW, I haven't hit the 3.6kW where I'd expect clipping to start.
It was a glorious day today. Cool, light wind, cloudless, shadowless, not far from midsummer. I expected the panels to perform better. Anyone got any bright ideas why the middle of the day isn't performing as well as I hoped? The panels could be a little grubby, but I'd expect that to be reflected throughout the day. If one panel was faulty, I'd also expect a hit across the board.
What am I missing?
Thanks in advance, all.

Panel temperature. High Panel temps lower efficiency. Also clear days are not as good as you would expect. High haze is better as more useful sunlight gets bounced back to ground rather than straight out to space.

Hmmm. Thanks Chris. I get high panel temp is a bad thing, but it was breezy and cool today. I'm not convinced the panels got that hot. I hear what you say about clear days. Maybe that's it. Still feels odd though...

BobB Optimal panel temp is 25c. I'm going to bet that even with a cool wind your panels were twice that at the top of the day, maybe even more. Mine were at a peak of 67c today.

cluelesscris Mine were at a peak of 67c today

Wow! Well they are black, I suppose. I'm going to bow to your superior knowledge, Chris.

I wish I had a sensor to measure the temp...

Thank you.

It almost looks like you only have one string and you're hitting the 2.8 kW per string limit. How many strings do you have and which directions do they face?

SJB
Oh, you superstar! Look at this!

That's exactly what's happening. I only have one string and it faces almost exactly due south.
If this was a clipping problem I'd start sending DC power to battery to alleviate it. Do you know of any way to work around current limit in a similar way?

Also, your house load comes off what you can export. So with a 3.6kW inverter and a 400W house load you can only export 3.2kW.

Looks like the installer has used panels that are not compatible with a Gen1 inverter. On the panel datasheet, the IM should be less than 11A.
I recommend
Perlight Delta 400W PLM-400OM2B im=9.76A
Trina Vertex 425W TSM-DE09R im=10.08A

What panels do you have?

If your inverter supports fast FW the PV side gets boosted from 11A to 13.5A

BobB I don't know of any way to manage this to get more out of the string. @hoggy's comment is interesting - I wish I could do it unfortunately my Gen1 inverter is too old to take that firmware and if it wasn't I'm too risk averse to do it in the current circumstances.

Rubikcube ...and down the rabbit hole I go!

They're JA Solar 395W PERC Half-Cell Black modules which, according to Google, have an STC Maximum Power Current of 9.76. I've ten of them.

I'm a little reluctant to go all out blaming the installer. It's an easy thing to do but the system does seem to have been screwed together reasonably well. I've not had any significant issues and, with GE going bust, I'll take that over eeking out the last few % generation on spectacular days.

hoggy Well, as the fish said when it bumped it's head into a brick wall: damn!

I do think my Gen 1 is sufficiently "young" to cope with the fast FW and that's a great suggestion, Hoggy.

But given the GE situation, I'm just too chicken to install any new SW. I'm going to live with my clipping.

hoggy Mine tops out at 11A with 191/193 f/w - ie no change from production firmware.

SJB Totally agree and thanks again for the original spot.

I realise now that I've been using the word "clipping" incorrectly. What I have is clipping. My clipping is on the input side. I agree that means there's probably nothing I can do about it (apart from Hoggy's suggestion, I've dealt with that...). If my clipping was on the 3.6kW output side, I could redirect some DC to the battery to maximise solar intake.

In reality, I think there's a balance that installers attempt to optimise. In winter, I'm sure my setup works for me in that I'll get to the necessary current to activate the inverter that little bit sooner.

This has been fun! Thanks to all for engaging.

Vestas Yep. Me too, Vestas. my flatline shown above bounces between 10.9 and 11A. I'd love 13.5, but I'm just too chicken to change anything.

Vestas the numbering is a mess but think it's a later version

hoggy Ah I see. Paul L put 191/193 on mine in April 24 so it won't have that.

I also appear to have made the right decision to stay on BMS 3015.

Where did these firmware notes come from? Never seen these before.

Vestas https://givenergy2025.zohodesk.eu/portal/en/kb/articles/gen-1-a1xx-d1xx-firmware-log

BobB JA Solar 395W PERC Half-Cell Black modules

Those panels are fine. Having 10 isn't great. More than 8 on a string and you won't get full power in summer, less than 6 and you'll get a slower startup in winter. You are right to stick with what you have and just accept it.