OP here. Thank you for all the responses.
It sounds like the decision comes down to using large enough cable to minimize voltage drop and give good results without being so large that the cable is unnecessarily hard to work with or a waste of money.
100 amps over 6 feet with these sizes has a voltage drop of:
size, voltage drop, voltage drop %
1 AWG, .18, 1.5%
1/0, .15, 1.25%
2/0, .12, 1.0%
Where I am not clear is how much voltage drop I should choose that will give good results.
One more factor I forgot to say. The FW will also have a 200W solar panel factory installed (by Cedar Creek), which I am trying to have increased to 400W. Does that make a difference in choosing the cable size?
