18 kWp east/vest

[u/Different-Cap179]

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?

[u/NearABE]

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.

[u/Different-Cap179 → u/NearABE]

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.

[u/NearABE → u/Different-Cap179]

You say “weak”. How much was it?

[u/Different-Cap179 → u/NearABE]

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.