So, we look back on online shops In my country, I can buy Cheap Solar Kit Panel 20 Watt with
only cost $50 - $60,
and when I look in amazon store, I only spend about
about $37.
It's not enough and probably dangerous due to the subpar quality specially that PWM generic charger controller which doesn't have proper protections.
Here's what I can say about each parts:
Set: The kit doesn't even come with a power inverter so you'll have to make use of the battery and/or charger controller's 12v output.
Solar panel: As others have mentioned, the power output is just too low.
In comparison, my 320W (
160W+160W parallel) panels can only produce about 180W~200W at noon and 60W~120W of power in early morning and afternoon until 3 or 4PM. (
sunny weather)
Not to mention, it usually drops extremely low if it's too cloudy, you'll likely get 1W on cloudy weather.
BTW, I installed them two years ago for a "
test" and still working today (
BOSCA Brand).
Battery: You can only safely drain that kind of "
SLA battery" down to 50% or it'll end up broken within months.
It's based from self-experience since I've once busted a 100Ah SLA battery in just 4months by directly connecting 2pc 12v LED lights that are running about 18hrs/day
(
even until the voltage drops below 11.6v)
Your very small battery can only provide you 3.5Ah x 12v which is about 42Wh of stored power (
more if you'll push it to 30%).
So after "
daylight", you'll only have 42Wh before your battery drain down to critical levels.
Overall, If you want to solar power your RPi node, buy at least 120W solar panel, MPPT solar charger controller and bigger LiFePO4 battery enough to run the load when there's no sunlight.
Because it's not just the output of the panels but also the capacity of the battery and the panel's capability to top it up while being used/bad weather.