For Solar, I believe the margin should be reasonable, you need a good engineer to sign and finalize the setup with the proper equipment, a small mistake in installation or post installation failure can cause early failures later, or even worse a fire destroying properties. even more on large 10kW, 15kW + , that is lot more labor intensive. The margin should depend the engineers and staff salary at a minimum, and return of investment. I can share my own second solar purchase, I got quotation that for 10kW top of the line setup, that will produce 9.6kw at peak hours. I got a really decent price, and I think a decent but not huge margin for the seller, I managed to get a great discount because, first I will install on the new garage roof, only 4m high, very easy to access, ready to hold the panels. I made it super easy for the installation for them, no need to drill anything, in my single-story metal sheet garage, it will be roughly 2x to 3x faster than on a two-story ceramic tile roof. After my discount, Gemini calculated the contractor profit to be 50,000-100,000 baht for 350,000 baht setup. 50K using prices from Dec 2025. 100K if sourcing everything myself from Lazada with coupons. But they offer 3-Year Full Support Guarantee, I have experienced really terrible support in my 5kW Bangkok solar setup, I even got fined 2,200 baht by MEA because the company made mistake to enable sending back to the grid before approval. This company seem to have good reviews and photo of their setup looks good. TIP: if you want to get the best out of a bifacial solar panels installed on metal sheet roofs, paint the metal sheet with White TOA G222 2in1 paint, it will give you an extra 20% of albedo light that can break-even in just one year alone the paint cost.
