neither this nor the trapezoid accounts for atmospheric attenuation
https://duckduckgo.com/?q=solar+panel+daily+energy+curve
not sure what kind of curve the more realistic results here are, but it would be easy enough to imitate and fun! with the slight trailing edge of production!

True, I actually did look at some real curves just for reference and saw the trailing bit too. You could definitely add it, with the technique I "invented" here you could substitute any function you'd like really. But the cosine is a lot simpler I think you'll agree, and does model a static panel without an atmosphere, hahaha.

I made the function to be hopefully more realistic. More importantly, the length of day and night are equal - this is realism.
https://mods.factorio.com/mod/realistic-solar-graph