Welcome to Winter (Solstice)

Just a stab in the “dark”: dibs on the two 23.5 degrees off the equator.

 

Felt somewhat of the trendsetter with panels still being quite expensive in the 2000s . Our system was commissioned january 2008. Rated at 8kW AC.



(always thought DC ratings were a marketing gimmick as that's not what your system ultimately needs to output). Charging 2 Cars + home electricity - it paid for itself in just over 6 years (as feds picked up ⅓ of the cost). Our electric bill was usually a couple hundred dollars a month average (So Cal) prior to 2008 - having some of the highest rates in the nation. The utility rates just kept going up & up, & PV kept zeroing out.
Now, we're living up north and are considering bifacial panels - which run 15%-30% more efficient:



Ideally aligned from North to south, they convert sunlight on both sides, & in snowy conditions especially - light capturing can include reflection off snow. Our roof in the NW is horrible for locating PV on any south facing directions - but we have a good amount of land - which will make this weird verticle install more practical. Plus, way way easier to keep Montana snow off - compared to flat / relatively flat roof mounts.

 

Now that others have had some time to chime in, here is the solution I'm leaning towards, at least so far. It uses astronomical equations very similar to what I located and put on my old unix workstation back before they migrated us to WinDoze:

https://oikofuge.com/which-place-gets-the-most-daylight/


Shortest total daylight at the South Pole with 4388 hours, longest on Arctic Circle with 4649 hours, a difference of 261 hours. Go mountain climbing, and get 5052 hours atop Mount Forel in Greenland. Denali and a few other peaks in Alaska and Siberia exceed 5000 hours, but still fall more than a day short of Forel.

Other charts show the work path towards this final chart. He also mentions some additional complications not factored in.

I've long accounted for the solar disc not being a point, and for atmospheric refraction, but for some reason had never considered the north-south difference caused by Earth's elliptical orbit. This non-circular orbit effectively lengthens the North's summer a bit when Earth is farther away from the Sun and moving slower, while shortening the South's summer when closer and moving faster. Perihelion (closest point to Sun) is in early January, aphelion (farthest point) in early July.

= = = =

This has a significant discrepancy between its Arctic Circle and your 80 degrees latitude. The discrepancy deserves some exploration.