[Kirby64]

Unless your Macbook negotiates USB-PD, or USB-C standard 5V mode, it won't charge. There's a USB-PD controller in front of all the USB ports, so they will not pass any current in unless it gets the right signaling.

If you just try to trick it, there's over- and under-voltage protections built-in, so it should shut off if you just let the voltage float around.

Stick with something in-between to handle the solar.