Personally, I wouldn't. An external battery is cheap; Macbook Air logic board replacements are actually free if you have AppleCare+, but then you lose your laptop for days while it's being repaired. I'd just have the solar panel just charge a (small, portable) battery and use that battery to charge the laptop, with bonus points for not having to have your laptop tethered to the solar panel if you want to use it while the sun is out.

As far as the Macbook air goes, the official chargers will do 5V, 9V, 15V and 20V output, so yeah, no probably; it supports those.