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March 20, 2017
News - Simple Solar Power
about 3 years ago
I wish things were as simple as shown in the above diagrams. But they are not - far from it.
If you connect any kind of arduino directly to a solar panel, you will have a system that may boot one time but fail to another time. If conditions are just a bit less than perfect, the panel will not provide enough current for the arduino, and as a result the system will end up in a malfunctioning state that it cannot recover from.
So put a capacitor across the panels, you say. No, that won't work. The capacitor will carge up to the point where the arduino can just begin to boot, and it will end up in the same malfunctioning state.
So use a SparkFun Energy Harvester board with that capacitor, you say. This MIGHT work. The caps will charge up to when the Energy Harvester board's UVLO disengages, and provide just enough for the output to run while the cap discharges from 4-5v down to 3.3v, which is very quickly unless you use a very large supercap. Also, the Energy Harvester output is rated at 100ma which I haven't ever been able to draw from it.
There seems to be no really good solution to powering electronics with solar panels and supercaps. Ideally you want to run your panel at its Vmp, and indeed there are buck converters available that feature this sort of functionality, but they are all without exception intended for battery charging. Which means the unit will try to "trickle charge" your Arduino at the configured Vout. Even with a cap on the output it won't work, because as the cap charges, it will once again reach that state where the Arduino can just enter that malfunctioning state that it cannot recover from.
I've been at this for a long, long time now and I still haven't found a good way to reliably power an Arduino with a solar panel. We need something that will charge a cap at the panels Vmp, and when the cap has reached a specific voltage, and ONLY THEN, it will provide power from that cap to your device - and keep doing this until the cap voltage drops below another specific voltage.
It's amazing how difficult this "simple" problem really is.
No public wish lists :(