As it's easy to adjust the voltage from the PPK2 it almost stands in as a dummy solar panel, although you can't current limit the output.
I'm now absolutely set on using the ESP32-S2 for this project but I'll run this prototype off the panels for a few days and see how it behaves.
Update: I can't continue using the PAM2301 buck regulator I had intended to, testing showed it 'trips out' when panel voltage is ~6v. Which is fair enough given that's what's in the data sheet, but my expectation was charging load would keep voltage on a 5.5v panel below that, even though no-load voltage can be quite high. This is not true.