Hi everyone
I figured I make a quick post on how easily you can just dimension a buck converter using this page here:
http://schmidt-walter-schaltnetzteile.de/smps/smps.html
It’s really easy… just choose a frequency over the audible frequency (something like 100kHz)
I’m right now working on a project where this is really awesome:

Update on how I wire the solar panel to the lead accumulator follows soon ^^