If you can install a small panel outdoors, then this is actually very easy and inexpensive. The efficiency of the charging and MPPT (Maximum Power Point Tracking) systems are not as critical. Cheap boards/panels from eBay/Amazon can be used. I currently have a solar system running my outdoor temperature logger project using low cost materials. This wakes on a timer every minute, connects to WiFi, and logs temperature to a Corlysis. After running for a few months, the 4.2V lithium cell has not ever dipped below 4V. A wake interval of 1 minute is pretty demanding, so this is quite impressive.
I recommend a pretty decent battery for this, just to guarantee the system can ride through the night and cloudy/rainy days. I use a beefy 18650 style battery like this:
All materials arrived:
You’ll notice that the solar panel has a barrel jack, so cut that off and install a JST connector as was supplied with the MPPT board:
This is how it all looks wired up:
This is an example how I have my weather station installed, but this has been running smoothly for a couple months. Panel is just taped up on a gutter:
All boards just mounted in random enclosures I have - note this is under an awning to give some weather protection:
Then all buttoned up:
And with the temperature logger project you can see the daily charging/discharging of the battery - pretty cool!!
Coming soon! Still under test!