[madaxe_again]

Indeed - I saw the title and thought “because convection” - I actually reinstalled my PV array last year with exactly this in mind, as while it was at an optimal angle for insolation, I was finding that yield was being hampered by them getting devilishly hot - the summer before last, when we hit 47C air, really underlined the issue, as the panels were getting up to over 85C.

The increase in yield from going near vertical (80 degrees was the best I could achieve using existing mounting gear), has been about 20% - I say about as I haven’t done a scientific study of it, just looking at year on year comparisons for cloudless days, and the panels are 60 C cooler, which is far better than I had hoped for.

[schiffern]

Yes my first thoughts too.

"Oh, it's convection."

"Hey, I wonder what the best in-between angle is, balancing both temperature and cosine loss."

[myself248]

So, a lot of the recent attention is on bifacial east-west arrays because they produce a complementary duck curve throughout the day. In that case, pure vertical makes sense, and production just takes a dip at local solar noon and recovers soon after.

But for traditional south-facing panels, I'd argue that straight vertical is still optimal, at least for higher latitudes. Vertical panels are extremely good at shedding snow. They produce more in winter when you need every watt you can get, and less in summer when the sun is high in the sky and you don't need all that extra power anyway. As soon as you tilt the panels to minimize cosine loss, you open yourself up to snow buildup which can dwarf any cosine gains.

[schiffern]

I'm also a fan of vertical panels in snowy regions, but at the same time it kinda dodges the question.

In a non-snow region (which is most of the country, a fraction which is only increasing decade by decade), what is the optimal tilt angle? 70°? 80°? More? This is quite important for large solar panel farms in the hot and sunny South/Southwest.

The cosine loss is easy to model, so to answer the question what we need is a curve that describes how the convection cooling effect varies with angle.

[beAbU]

Did you factor in possibly improving the incident angle of the sunlight? Solar benefits massively the more perpendicular the incoming sunlight is.

[madaxe_again]

The incident angle was previously optimised for insolation over the course of a year - so halfway between winter solar apogee and summer solar apogee.