In my previous post "How To Choose A Rooftop Solar PV System", I mentioned that the orientation of solar panels might significantly affect the power output of the whole solar PV system with a centralized string inverter.
Besides, solar panels facing west seem to produce more energy compared to solar panels facing south, which contradicts the fact that south-facing is the best orientation for an area located north of the equator.
Anyway, I'm not an expert in this field. I'll just share my layman observation here.
Firstly, even though my house is facing south, it's not 100% south, it's actually about 10-20 degrees to the south west direction.
The west facing roof is thus slightly tilted toward the northwest direction.
I guesstimate that the roof angle is about 45 degrees which is almost the same for all directions.
I installed 10 solar panels with 3 microinverters:
- 4 panels with 1 microinverter facing south
- 3 panels with 1 microinverter facing west
- 3 panels with 1 microinverter facing west
There are fewer panels facing south because of space limitation on the south-facing roof.
There is a DTU (Data Transfer Unit) that transfers the data from the inverters to the app in my phone. From here I can check the energy & power output of each solar panels and the overall electricity generated in a day.
The DTU is connected to Wi-Fi and turned on 24/7.
The best day for solar PV system would be a hot sunny day without clouds. If the day is cloudy, the energy output will certainly drop. A long rainy day will be the worst.
On a good day, my 6.40kWp solar PV system can generate up to 34kWh of energy a day. On a bad day, it can drop to below 10kWh.
The picture below demonstrates how the power output looks like throughout a day in different kinds of weather.
For the day with "FULL SUN" above on 29-6-2025 with almost perfect sunshine without obstruction, the TOTAL daily energy generated for each panels is as shown below.
As mentioned earlier, all the panels are divided into 3 groups with one microinverter each, one group facing south and 2 groups facing west.
With full sunshine without obstruction from the morning until the evening, the panels facing west (~3.5kWh each) seems to outperform panels facing south (~2.7kWh each).
There was another day (12-8-2025) when the total electricity output was higher. The overall energy generated by each panel is as shown below.
Similar to the previous one on 29-6-2025, the panels facing west (~3.4kWh each) still outperformed panels facing south ~(3.1kWh each) by almost 10%.
Not only these 2 days, I notice that in almost all the days without rain from June to August, panels facing west consistently generate more electricity than panels facing south.
Nevertheless, starting from mid September up to now in mid October, panels facing south seems to slowly overtake panels facing west.
This should be due to the apparent change in the sun position throughout a year. Thus, I can't conclude that panels facing west will always be better than facing south throughout a year.
If we include the whole year performance, I think solar panels facing south should be the best base on science.
In the morning when the sun rises in the east, solar panels facing the east will definitely perform the best compared to other directions.
In my case, I can't expect the panels facing west to generate more energy than panels facing south in the morning hours.
The picture below shows power generation at one point of time in the morning.
At 9:45am, solar panels facing south generated about 173W of power each compared to panels facing west at about 152W each. There was about 12% of difference between the two.
At the peak output of the solar PV system at 2:30pm, panels facing west (520W each) worked significantly better than panels facing south (400W each). There difference in power output widened to 30%.
In the evening 6:00pm, panels facing south generated merely 85W of power each while panels facing west could still generate 280W of power each which was a huge 3x difference.
All these examples show that even without any obstruction or shade, there is significant difference in the power output between panels facing different directions.
If I use the string inverter, does it mean that my whole solar PV system will have its energy output reduced to the level of worst performing panel?
If it really is, then the string inverter seems to lose out significantly to microinverters even with just difference in the orientation of the solar panels.
In fact, it's a known fact that one of the cons of string inverter is that it is less efficient in condition with varying panel orientation.
The question is how much difference there is, and does the difference warrant the extra cost to consider microinverters?
From what I see as a layman, the difference seems to be rather significant but I don't know the real difference in real situation because I don't have the data from solar PV system with string inverter.
When I got the quotation to install solar PV system, one quotation with microinverters is almost the same price as other quotation with string inverter.
The choice is obvious for me.
Why is that so? It's because some solar companies give extra discount on group purchase.
So, try to ask for it and find as many people as possible who wish to install residential solar PV system to negotiate a good price that benefits both parties.
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