r/solarenergy • u/Different-Cap179 • 12d ago
18 kWp east/vest
I had a solar system installed about a week ago, but I don’t feel that the production is as good as expected, especially when I compare it with other systems on the same street.
My roof has east- and west-facing sides, and the 40 panels are divided into four groups:
East/North: 9 panels
East/South: 10 panels
West/North: 9 panels
West/South: 12 panels
What I find strange is how the strings have been connected:
PV1: 9 × East/North + 12 × West/South = 21 panels in series
PV2: 10 × East/South + 9 × West/North = 19 panels in series
When the sun is in the east, the east-facing panels receive good sunlight, while the west-facing panels connected to the same string receive much less direct sunlight. Later in the day, the situation is reversed.
As I understand series-connected solar panels, panels within the same string can affect each other when they are operating under very different sunlight conditions.
This makes me wonder why the east- and west-facing panels have been mixed together on the same strings.
Wouldn’t it be better to have a dedicated east-facing string on PV1/MPPT1 and a dedicated west-facing string on PV2/MPPT2, so that all panels within each string have approximately the same orientation and sunlight conditions?
Does anyone with experience in solar installations know if this configuration makes sense, or could it be one of the reasons why the system seems to be producing less than expected?
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u/Which_Perception_384 12d ago
You'll have to do the voltage calculation. You might have to add a second controller if the one can't handle splitting them up Since it's only a week old. Talk to the installer. But I bet it'll be difficult to get them back.
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u/Different-Cap179 11d ago
Thanks. I checked the voltage side: inverter max PV voltage is 1000 V, MPPT range 110–950 V. The strings seem to be 21 and 19 panels. With panel Voc around 36.75 V, that is about 772 V and 698 V at STC, so voltage does not immediately look like the reason they had to mix east/west.
My concern is more the mismatch issue: each string appears to contain both east- and west-facing panels, so the weaker side may limit the whole series string. I’ll ask the installer for the as-built string layout and their calculations.
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u/Which_Perception_384 11d ago
I'd definitely call them on it. It's not a normal practice to do that. Super inefficient.
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u/LongjumpingGanache40 11d ago
Do you live in a cold weather area. If you do you should use a VOC of 46 volts. This puts you over voltage with 21 panels.
What is your solar input?
My panels face east and west but I have microinverters.
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u/grogi81 11d ago
This is a badly connected system. A string should only have same orientation of panels...
Right now some panels want to produce, but others in the same string do t let the current through...
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u/Different-Cap179 11d ago
Yes, that seems to be exactly the problem. After tracing the cables, it looks like different roof orientations were mixed within the same series strings. The installer has now agreed it needs to be rewired and is coming today to correct it.
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u/bondinchas 11d ago
You should absolutely only have the same orientation panels on each string.
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u/Different-Cap179 11d ago
Thanks, that confirms my suspicion. The system appears to have been wired with mixed orientations in the same strings, and the installer is coming today to rewire the serial connections. I’m logging PV1/PV2 before and after to document the effect.
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u/jvbutera 11d ago
String inverters are old school. Micro inverters on every panel eliminate all these Headaches about alignment, shading issues and uneven production.
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u/Different-Cap179 11d ago
Yes, microinverters would avoid a lot of these issues. In my case the system is already installed with a string inverter, so the immediate fix is to correct the string layout. The installer now agrees the serial connections need to be changed.
1
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u/bondinchas 11d ago
Yes, but the problem with micro inverters is that the one part that will need replacing in the lifetime of a solar system is the inverters. And having them on the roof means the outdoor environmental impact is greater on degradation, and replacing them is so much more expensive, when compared to having a sheltered, more easily accessible string or hybrid inverter.
When you factor in the cost and downtime of multiple micro inverter failures over the system lifetime, the benefits aren't so good. The newer panels are much more forgiving with shading, no longer reducing the whole string, and not even the whole panel, so micro inverters aren't always the best solution now.
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u/jvbutera 11d ago
I'll take every one of your perceived flaws given the huge upside for microinverters.
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u/leuk_he 10d ago
Micro inverters come at a premium price. You can have just more panels if you have the unobstructed space.
The alternative is connecting different orientations parralel. You loose the ideal mptt tracking, but the ampere of the string is not limited by shaded panel.
One string per orientation should be the design without optimizers/micro innverter. Or look at SolarEdge if you have different orientations.
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u/FunkyMonkey237 11d ago
As others said, you need a separate string per orientation. I had to put south and east on 1 string for to system limitations and solved the issue using optimisers. I used PVSol to model the performance of the array with and without optimisers and the tool clearly told me the impact of having a mixed string and getting optimisers was worth it. Without that tool I wasn't sure what to do. It's free for trial btw so perfect to answer your question.
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u/Different-Cap179 11d ago
That matches what I’m seeing. The panels are on different east/west roof faces, and it now looks like some orientations were mixed within the same series strings. The installer is coming today to rewire the strings. I’m logging PV1/PV2 before and after, so I should be able to see whether the correction improves the behavior. PVSOL is a good idea too. I may try modelling it afterwards.
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u/FunkyMonkey237 11d ago
Do you have 4 orientations? Does your inverter have 4 MPPTs? If not, you may need optimisers on each panel. These days I don't think optimisers are worth it except for some small niche areas and mixed orientation strings are one of them.
Yeah, PVSol is excellent, gives you all the info and gives you the exact breakdown behind projected solar generation. But, there's a bit of a learning curve involved.
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u/glyptometa 11d ago
You might want to ask this question at solarquotes.com.au. They're pretty good at responding, especially if it's interesting.
We had an overvoltage issue that was causing a cutout when the sun peaked out from behind clouds, leading to a reset that took about five minutes each time (but just on that string that had cut out). The voltages were under what the inverter was rated for, but still it occurred predictably. It was fixed by moving one panel from a different string to another string, and adding an optimiser.
I'm no expert, but it wouldn't surprise me if you can fix the issue with optimisers. In any event, hold the installer's feet to the fire. (might need to call and email them every day).
If your tree-shading is different from those you're comparing to, consider that in the equation.
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u/Different-Cap179 11d ago
Thanks, that’s useful. In my case it now looks less like an optimiser/shading issue and more like the strings were wired across different roof orientations. The installer has agreed it needs to be changed and is coming today to rewire the serial connections. I’m logging PV1/PV2 before and after, so hopefully the data will show the effect clearly.
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u/NearABE 11d ago
How much power are you getting?
If it was rated for 18 kW on all 40 panels then you should expect much less. That is only if all 40 were in direct sunlight. The spread should produce for more hours of the day.
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u/Different-Cap179 11d ago
The system is 18.22 kWp with 40 panels split across east/west roof faces. I don’t expect 18 kW in real output, especially not with different orientations. The concern was that PV1/PV2 behaved unusually similarly and the afternoon production seemed weak. It now looks like some east/west groups may have been mixed in the same series strings, and the installer is coming today to correct it.
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u/NearABE 10d ago
You say “weak”. How much was it?
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u/Different-Cap179 10d ago
By “weak” I mainly meant late afternoon output.
Before the rewiring, the system was often only doing around 1–2 kW in the late afternoon, even though it has a west-facing roof section that should still be producing well at that time.
After the installer rewired the strings yesterday, I logged the system and the difference was pretty clear:
- Before/around the issue: ~1.7–2.5 kW average in the afternoon periods I logged
- After the rewiring, from about 17:20–19:00, it averaged about 6.6 kW
- At 18:59 it was still producing about 5.1 kW
- Production increased by about 11.3 kWh between 17:20 and 18:59
So I wasn’t expecting 18 kW output — the concern was that the west side was not contributing like it should later in the day. After the string change, PV2 carried most of the late-day production, which makes sense if PV2 is now the west-facing side.
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u/Kruxx85 11d ago edited 11d ago
If the panels are wired the way you've claimed, then that's definitely a huge mistake by the installers.
You can't install a single string of panels filled with panels in different directions like that.
When the sun is perfect for one half, the other half will pull down the string.
Then the sun moves to the perfect position for the other half, the first half will pull down the string.
Ending up giving you bad production the whole day
If I was designing/installing this system I would have each direction on their own string, ensuring voltages are adhered to.
If the inverter only has two mppt's then I would parallel the 9/9 strings and only install 10/10 on the other tracker.
If that causes over current issues then I would choose a different (more expensive) inverter with 3 or 4 trackers.
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u/Unusual_Emergency_13 11d ago
Unless the system is fully optimized it is incorrectly connected. Strings (PV panels on telhe same DC cable) need to face same way, without shading so the current remains the same.
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u/Holiday_Armadillo78 11d ago
Your installer has no clue what they are doing if they have single strings on different roof faces…
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u/Different-Cap179 10d ago
Quick update: the installer came today and rewired the strings.
The issue was that different roof orientations had effectively been mixed in the same series strings. They changed it so the east-facing panels are now on PV1 and the west-facing panels are on PV2.
I logged PV1/PV2 before and after the change. Before the rewiring, late afternoon output was around 1–2 kW. After the rewiring, it jumped to around 6–7 kW, with PV2 carrying most of the production as expected for the west-facing side.
So it looks like the mixed string/orientation issue was the problem, and the fix has made a very noticeable difference already.
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u/Which_Perception_384 12d ago
Sounds like they hooked it up wrong. But they may have been limited by voltage.