HI

I have 9 x 425w panels (garage roof) and 8 x 545w panels (house roof) installed = 8185w. They are north facing at +-25deg Tilt. Currently I am only getting +-3.4kw max at midday, 2400w on PV1 and 1000w on PV2. This is far below the installed 8.1kw and there is big difference between the two strings.

What should I be expecting installed vs output?

How do I check whether all panels are still working?

Thanks

5 hours ago, Francois Taljaard said:

HI

I have 9 x 425w panels (garage roof) and 8 x 545w panels (house roof) installed = 8185w. They are north facing at +-25deg Tilt. Currently I am only getting +-3.4kw max at midday, 2400w on PV1 and 1000w on PV2. This is far below the installed 8.1kw and there is big difference between the two strings.

What should I be expecting installed vs output?

How do I check whether all panels are still working?

Thanks

It’s Sun angle and how your panels are oriented. I’m barely going over 2.5kW in clear sunny skies but in summer I’m hitting 4kW on one and a bit over 500W on the charge controller.

Come summer you’ll be back to generating close to your peak.

Winter solstice was just 3 days ago, so ja, poor power generation is still basically the worst right now that it will be all year. But the 1000W on a panel set of 4360W sounds like too little. What's the Voltage and Current on PV2? Around 250V and 4A? Do you generate any more on PV2 if the PV1 string is disconnected? Do you have any problems with shade being cast over that 2nd string?

Edited June 24Jun 24 by GreenFields

If you can DIY....

UNI-T UT673PV Solar MPPT Meter

UT673PV Solar MPPT Meter,Miscellaneou,Environmental Testers

Isolate all PV from your system and disconnect each panel for testing early morning before voltages of panels rise.

Just remember, this tester is for testing ONE panel at a time.

7 hours ago, Francois Taljaard said:

I have 9 x 425w panels (garage roof) and 8 x 545w panels (house roof) installed = 8185w. They are north facing at +-25deg Tilt. Currently I am only getting +-3.4kw max at midday, 2400w on PV1 and 1000w on PV2. This is far below the installed 8.1kw and there is big difference between the two strings.

What should I be expecting installed vs output?

Hi Francois,

It will help us to advise you if you can supply more information:

• Where are you (or should I say the house) located - the Cape has much less PV production at this time of the year than (say) Prieska...

• Are the panels facing exactly to true north, or are they offset a bit to the east or west? Without knowing this one can not make an accurate estimation.

• Can you confirm if the 9x425W panels are on one string (connected to one MPPT), and the 8x545W panels on a second string (second MPPT)? Are all panels in a string connected in series?

• Do you have any shade on any of the panels during the day? Even just a fraction of one panel shaded can drastically reduce the production for the whole string.

• Are you actually trying to pull more load than what is being produced? PV panels will only produce the amount of power being demanded from them, and if e.g. you are only demanding 2kW from the panels at (say) 13:00 on a clear sunny day, then the panels will only produce 2kW of power...

• Lastly, it will help to know what make/model of inverter you have, and what brand(s) of solar panels.

In Gauteng my install of just over 6000kWp is at a 26 degree angle, and about 5 degrees off true North, and I have noticed quite a drop-off this winter, possibly due to poor air quality. That is over and above the cloudy weather that we have experienced in Gauteng.

It is confirmed by my weather station, which measures W/square meter, here is the graph for the year to date (1 Jan 2026 to 24 June 2026):

In January I was regularly getting peaks of over 1000W/sqm (even 1171 in February), this has now dropped to my best peak in June at 576W/sqm.

Here is a graph of the last 12 months (25 June 2025 to 24 June 2026):

So yes, it's is quite a significant drop-off from Summer to Winter.

Here are my Port Elizabeth weather station's graphs, for the year to date (1 Jan 2026 to 24 June 2026):

Ignoring the dip in March/ April and the spike in May (due to various comms issues), you can clearly see peaks of well over 1000W/sqm in January vs barely over 500W/sqm in June.

Here is a graph of the last 12 months (25 June 2025 to 24 June 2026):

So in my experience, with both coastal and inland installations, it is generally a drop of around 50%.

Those figures do seem a bit low. I'm consistently hitting 60% of installed capacity at midday on my three arrays. Admittedly I'm in Northern KZN so a fair bit further North than most but I'd expect at least 50% of installed.

5 hours ago, Yellow Measure said:

So in my experience, with both coastal and inland installations, it is generally a drop of around 50%.

Interesting - here in Bloemfontein my average solar harvest for 1-24 June is only 21.7% below my average for April (best performing month for this year...) My panels are facing true north, and at a slope of 27 degrees.

1 hour ago, HennieL said:

Interesting - here in Bloemfontein my average solar harvest for 1-24 June is only 21.7% below my average for April (best performing month for this year...) My panels are facing true north, and at a slope of 27 degrees.

Indeed, but now we are comparing two totally different metrics 🙂 and yours has a whole lot more variables.

My best month this year was May, then again I have been off grid since December. But I also upgraded my battery bank in March, and started deeper cycling (and evening usage) in May.

3 hours ago, Yellow Measure said:

Indeed, but now we are comparing two totally different metrics 🙂 and yours has a whole lot more variables.

I concur - there's just too many variables to be able to compare one system with another - even in the same town... I generally only use about 50% - 60% of my system's capacity, and that alone will skew my PV harvest, as my (lack of) consumption would limit what the panels can produce... Still, nice to compare figures as long as it's not taken too seriously 😉

1 hour ago, HennieL said:

just too many variables

So true,
Also running an off grid system. My winter production is always higher than summer. If I were to max out the potential in summer with a constant load, then the summer numbers would be higher too.
The week between 15 to 22Jun was particularly low due to the cloud cover mostly, with last Sunday being my lowest ever for one day at just over 4kW from the panels for the whole day.
This is what my last 12months looked like.




and the sudden drop in production from 15 to 22Jun is clearly visible in the "last 30 days" graph.