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Since a week or two ago we have had sunny weather every day here in western france. It's not that hot, 20 - 25C but I have noticed a 1kw drop in max production (from 4.4kw nominal power installation).
Is this normal due to higher panel temperatures or should I be looking for a problem somewhere?
One more question: should I expect even lower production as the summer heats up?
In our warm climate it becomes noticeable around 37C.
Chargers and inverters will also derate then, depending how hard you push them.
Usually hot weather causes a drop in PV production . But 20 - 25 celsius is not so hot and a drop in the production of 1 Kw seems unusual. Have you noticed if the panels are maybe dirty . Last week we had sandy rain and the panels were dirty and the production dropped of about 30%.
My experience is that the Panel temperature can be quite a bit higher than the air temperature (measured in the shade). Especially on bright sunny days the panels can be to hot to touch even if it's not too hot outside.
Is in your installation enough space between the panels and the roof to allow airflow underneath the panels?
.not normal at that rate....but maybe intended?
Some installations are capped, like 70% nominal....in some installations, the DSO can control the output remotely in steps (like 0, 30, 60, 90 %).
...is this a new installation or are you having a history knowledge with it from last year?
Are you referring/basing this on nominal power or on observed power, like from yesterday,
Fo the latter, such a big, constant drop, suddenly occurring is not normal (besides clouds/shading which could cause huge but temporary drops, of course)
Edit: I suggest to fetch a forecast and compare that to the real vales.
This will help to identfy a technical problem or dirt causing a deviation from the expected values.
like that (which is running fine, although fairly dirty ATM - waiting for rain, as many do) 
Installation was only done in January so I have nothing to compare to for June but we could regularly get 4.5kw at peak times in April even 5kw momentarily I suppose when a gust of cool wind happened in full sunshine.
Maybe the recent lack of rain means the panels are dirty. I will give them a hose-down this evening and check back tomorrow.
Not enough details.
Could be just because the loads are lower (longer days, so the battery gets charged earlier).
You're asking the same question as before.
Battery, even grid when necessary: supplies more power.
Production: the same
I can't be any clearer on that now.
You're asking the same question as before.
Battery, even grid when necessary: supplies more power.
First time you answered that question.
When the grid has to supplement the power for an increased load, the limit is coming from the inverter, not from the PV panels / MPPT.
What mppt do you have?
RS 450/100
I'm noticing the string voltages look lower than "usual". Does that point to dirty panels?
I promise I will wash them tomorrow even though it's not their birthday or anything. ;)
@usernamepasswordbs given you posts when designing the system, how is the shade looking now?
I'm noticing the string voltages look lower than "usual" could be higher temps, could be panels by-passing.
Does that point to dirty panels? dust will have a minimal impact on output.
Dust can form a layer of mud on panels with a low tilt, less self cleaning.
Shade comes into play around 5.30pm and the chimney affects in a different way than I predicted so I am going to rearrange the strings.
Anyway, the pitch of the roof is quite shallow and we are at the time of year where there is dust and pollen in the air so the dirt could be a factor.
Same behavior here. Panels are covered with pollen and dust, no rain for the past 3 weeks. Panels are more matte, than bright. Wp went down from 5kWp to 3kWp. It's time for a nice rainy day to clean up the panels.
I have seen the same issues. Less production max points, but more generation overall due to longer days.
I have the same charge controllers (2x both showing the same issues) I thought it VRM issues because it seem to hit the same time as these problems. My install is also very new.
Peak PV was 6.2kw now lucky to get 5.2kw.
It could be a firmware issue too, given the fact someone else is seeing the same odd behaviour.
My equipment temp is around 20c.
I too installed in January
What i have seen with my x3 RS450/100 is when the day's where shorter the MPPT,s would pull 10 to 15kwh when required but now the day's are longer they don't get anywhere near that as its now spread over the longer day.
Now the MPPT,s will only pull that power if i put a heavy load on so to me this seems normal - yes i have cleaned my panels :)
They still produce the same total power over a day and this is usually 2 to 3kwh more than i have used by the time the sun goes down.
Hi, it may look silly, but where are you located & what angle is used on your PV arrays ? Mine are using an optimized angle for winter, so even if I get more power on summer, it is not as much as I could get, but this is normal regarding my design.
I'm in western France, my roof is fairly low pitch maybe 30 degrees so I think that should favour summer.
High load does not change production for me, just means I pull more from the batteries or grid but I already switch on extra loads when production is high as I know when the batteries reach 90-95% then the charging will reduce so it's not a case of "throttling back".
I gave the panels a quick hose-down today. I saw on the graphs afterwards an short-lived increase in voltage probably from the cooling effect, but no lasting increase in production. Still 1kw down on middle-of-the-day production from last month so if it doesn't rain in the next few days I will give them a good clean and see what that does.
So it's the temperature that is causing it?
You still have x11 405w panels?
According to the data sheet, there is a loss of 25% just from the panel itself... The 405Wp are given in labs controlled conditions... So it make sense to get such numbers. Being in Spain, Catalonia, my panels are at 65 degrees, so I can have an optimized production in fall - winter, even if I get around 17-18kWh / day in summer.
I had to extend my setup, as I wasn't producing enough on my basic installation. I have 4 arrays south orientated, and added 2 arrays west orientated, so I can get much more power in the afternoon.
You may consider such kind of possibility.
Michel.
I thought that summer production would be much higher than winter production but it looks like that won't be the case especially with these panels. Are these panels really bad or just a bit worse than average?
I also thought adding more panels would be overkill in the summer but maybe not.
I've looked at some other panels out of curiosity and they seem to be about the same 25% difference between the two test scenarios so I suppose it's normal.
We had a couple of heavy rain showers over the last two days and max. production is back up to 4.5kw when the sun is out. With the change in the weather there is also a reduction in ambient temperatures so it's still unclear exactly what caused the drop in production, the heat or the dirt.
I will keep an eye on things and see what happens.
@usernamepasswordbs higher array temps will reduce the panel Vmp / peak array output.
This is offset by longer sun hours in summer. Higher daily total kWh.
Look at the daily totals.
I am concerned with how low the production will get if we have some 40 degree days this summer....
Ok so today we are back up to 26 degrees today and the production is maxing out at 3.7kw with 4kw now and again momentarily. That is higher than last week when we had the same temperatures but lower than last month.
I think the temperature and the dirt are both factors then.
