dickon wrote: ↑
Wed Sep 11, 2019 10:13 pm
FWIW, I have a 120Ah 12V deep-cycle leisure battery and a 80W panel in southern England, oriented south, with a solar charge controller and a cheapish <24V->5V converter, and I get almost a full year on a Pi 1B. It fails for about a month of nights, and misty days, in the middle of winter. It would probably be fine on a Zero.
I have made the same experience in Germany.
You need a huge battery able of powering your equipment for about a month without any relevant solar contribution in the rainy/foggy/snowy winter days.
0,25 A * 24h * 30 days = 240 A/h @ a 12V battery is a good start.
Of course, a day with few hours sun may
change the deal, but a full month without direct sunshine is plausible.
Additionally you need to protect your battery from freezing.
Off grid solar power 24/24/365 is not easy.
Must it be a 4B?
The first thing with off-grid stuff is to be greedy on power.
I moved to Arduinos to get the data acquisition and data compacting, then LoRa radio to transmit the values to a location where grid power is available and a 'Pi can take over. And remember: an "always-on" 'Pi 4 will require about 50 KWh/year. In three years, you will have paid more for electricity than for the hardware.