I soldered a 2x 3″ 5.0V (make certain you use a 5.0V solar panel- on eBay/ Amazon) solar panel to a TP 4056 ( on eBay) lithium ion battery charging board. The output is soldered to a 18560 battery cradle (holder). No need for a diode- the motherboard will shut down at 4.2V which is considered a fully-charged cell. Good project for a young person interested in STEM or an adult at home. I have my students carry this project out in my ‘intro. to fuels’ lab course .
Post time: Jul-13-2017