In Raleigh, N.C., the lowest low in the last 3 years was:
Oct. 2021 +42F
Nov. 2021 +25F
Dec. 2021 +28F
Jan. 2022 +17F
Feb. 2022 +27F
Mar. 2022 +27
Oct. 2020 +48F
Nov. 2020 +29F
Dec. 2020 +24F
Jan. 2021 +25F
Feb. 2021 +23F
Mar. 2021 +25
Oct. 2019 +40F
Nov. 2019 +24F
Dec. 2019 +27F
Jan. 2020 +27F
Feb. 2020 +23F
Mar. 2020 +25F
Yeah, it could hit -5 degrees once every 36 years (that was the all-time low), but how rare is that? Honestly, I'd be comfortable planning for +15F and putting some kind of thermostat to shut down the DC current coming from the panels when it hits 20F, if there is such a thing. It makes zero sense to me to skimp on the number of solar panels to plan on a 36-year event to occur every year or very low lows that only occur every dozen years for one or two days a winter. Why not add the additional panels and put some kind of safety thermostat switch on the PV strings?