I wonder how much the efficiency loss from a laptop car charger would compare to just using something like a NUC -- IIRC some of their models have really wide input voltage ranges (12v-20v or something like that, depends on the model). The laptop is really just bringing a battery, compared to a NUC, for this application, and they are going panel->regulator->battery->converter anyway so the laptop battery seems redundant.
Odroid H1/H2 iirc can run from like 10-22VDC, the issue is finding a solar panel that has an open circuit voltage less than 22V. I found a buck-boost that works with my old laptop and a "car charger" with my admittedly oddball solar panels, so this is possibly, but takes time shopping and reading specifications.
So, the voltage of the panel shouldn't really matter too much, I think (I mean, you size the regulator input range as appropriate). OTOH, solar panels are a little magical from my point of view, so maybe that regulator ought to be replaced by some solarpanel specific thing, which might be more constricting.
It isn’t a regulator, it’s a charger - depending on the design, you can get even higher voltage spikes. 12V batteries charge at 13-14V, but most chargers design for lead acid can get away with reallly really noisy voltage transients due to the way lead acid works. It’s a pretty insensitive chemistry and dampens them normally.
Some chargers with ‘equalize’ or even worse ‘desulphation’ can intentionally go even higher in voltage than normal charging voltages.
So basically ‘if you just assume it wouldn’t kill your laptop to directly connect it, you’re playing Russian roulette with your laptop’.
With a decent spec sheet (and oscilloscope) to verify nothing too crazy that the charger is doing, some decent power filtering capacitors, and good DC-DC power supply you’d be fine though.
That's not a way to get good power out of the PV panel, though. An MPPT tracker (https://en.m.wikipedia.org/wiki/Maximum_power_point_tracking) is needed to get the best results, and the room for improvement is indeed substantial. There are good and cheap chinese ones available, such as Epever brand.
