10kw solar system. House faces due north, therefore majority of panels will obviously face south.

My question is for any other panels that wont fit on the south facing roof, which other direct is best, east or west?

Thanks in advance.

Day lengths this close to the equator don't vary that much. Bangkok is about an hour's daylight difference (sunrise to sunset) from the shortest to the longest day of the year.
Phuket, being closer to the equator, would have a smaller difference, while Chiang Mai, being a lot farther north would be slightly larger.

Noon (on the clock) rarely equates with the sun being directly overhead and even over the course of the year, it would be a matter of a few minutes.

HOWEVER, the west facing side would be the best as the afternoon sun brings more light than the rising dawn.

We are going through this now in Bangkok, most will be on the South side, but they show 3 or 4 panels on the East side, though not sure if this is for the besy sunlight, or for access and easy installation, orderd in march start mid to end of May, must be a lot of work going on 2 companies could not even do a survey for 2 months

I should have said it also depends on trees shadows etc as to which will have the most sunlight, when they turned up for the survey, i expected them to do it with a drone, but they had used google to show the roof and panel layout

1 hour ago, The Oracle said:

Day lengths this close to the equator don't vary that much. Bangkok is about an hour's daylight difference (sunrise to sunset) from the shortest to the longest day of the year.
Phuket, being closer to the equator, would have a smaller difference, while Chiang Mai, being a lot farther north would be slightly larger.

Noon (on the clock) rarely equates with the sun being directly overhead and even over the course of the year, it would be a matter of a few minutes.

HOWEVER, the west facing side would be the best as the afternoon sun brings more light than the rising dawn.

Thanks, I was thinking west too due to more intensity.

1 hour ago, howerde said:

I should have said it also depends on trees shadows etc as to which will have the most sunlight, when they turned up for the survey, i expected them to do it with a drone, but they had used google to show the roof and panel layout

Yes, my guy used google earth too. I used him some years ago for a few things, called him up the other day and he also is backed up with work.

37 minutes ago, sungod said:

Thanks, I was thinking west too due to more intensity.

From memory, "the best" sun is from between 1000 and 1600. Which, to me, means the afternoon - west - has four hours of "good" sunlight while pre-noon only has two.

Well this install is getting out of control, looked again and it does have 5 panels facing west and 2 facing east with most facing south

Ours face S & W, as prefer to go into the night, as topped up as possible. Especially since in the kitchen using appliances, just prior to sunset.

Contrarian view here:

In the part of Thailand we live, the afternoon is much more likely to have rain then mornings. The afternoon very often brings an onset of cloudy skies around 15:30 to 16:00 hours,even if there is no rain, hence truncating the solar radiance significantly.

Conversely - it is the afternoon and the heat soak that brings on the heaviest AC use, which would mandate more power generation in the afternoon is needed. Still, my installation prioritizes eastern facing (6.5 kW) compared to western (4.4 kW)

As for south facing panels:

I have one string, 10 panels, producing 24 kWh on Jan 1, 2026; producing 21 kWh on April 22, 2026 and will get progressively worse until July 2, not counting the worsening weather. I need a lot less power in January, output is too high, I need to catch every photon I can get this time of the year when it's hot. If I could, I would go north facing with more panels, or flat, like a carport.

YMMV.

4 hours ago, howerde said:

Well this install is getting out of control, looked again and it does have 5 panels facing west and 2 facing east with most facing south

Does your inverter have MPPT for each direction? How do you balance Voltage with such different string panel counts facing different directions?

10 hours ago, The Oracle said:

HOWEVER, the west facing side would be the best as the afternoon sun brings more light than the rising dawn.

Claude/Sonnet 4.6 said:

'2. "The west facing side would be the best as the afternoon sun brings more light than the rising dawn"

This is the most factually wrong claim. Morning and afternoon bring equal total light — the sun's intensity is symmetrical around solar noon. A west-facing panel gets the same solar resource as an east-facing one. South-facing is optimal in the Northern Hemisphere (including all of Thailand), maximising exposure when the sun is highest and strongest around midday.

For solar panels specifically, south-facing beats west-facing significantly in annual energy yield. The claim that afternoon sun is somehow superior to morning sun has no physical basis.