Yup, assuming the solar panels will be in the wind, potentially at highway speeds, absolutely do not rely on TPU threads for that. Threads rely on stiff material to transmit the forces from the angled faces of the thread into linear forces. Anything flexible will rip out very easily. It's shocking how fast a rubber material - even a firm rubber - gives up when real force is put onto it. It's like it's not even there.

The through bolt idea is pretty good. It should be easy enough to make a spool shape out of the TPU that will work as a shock absorber. Honestly even then I'd keep an eye on it to make sure it's not getting ripped up.

EDIT: I was curious how to quantify the difference, so I found this datasheet which shows the difference between the stiffness of rubbers, particularly polyurethane, which is what TPU is, and steel:

https://www.ansys.com/content/dam/amp/2021/august/webpage-requests/education-resources-dam-upload-batch-2/material-property-data-for-eng-materials-BOKENGEN21.pdf

You're looking for Young's modulus, which is 1.3 - 2.1 GPa for polyurethane, and 190-220 GPa for the various steels. Steel is hundreds of times stiffer. And for the threads to fail, they don't need to be damaged, just shift out of the way enough to slip past each other.