Wire size for additional sub-panel;
What type/size aluminum wire would I use to run 400 ft to add a 100amp sub-panel in pvc underground?
Thanks

If your goal is to deliver 100 amps to a terminal point 400 feet away, then you will need to use 300 kcmil conductors.

You might want to reconsider the load (amperage) needed at the destination. 400' is a massive distance. Is there no way the power company can put a transformer closer than that or have you considered using solar power?

For 80A load I come up with 4/0AL.
For the full 100A (which is almost certainly not necessary) I come up with 250mcm.