Conductor ampacity rating for line side tap

[voynar]

I am new to solar, and have a novice amount of electrical experience. Recently I've been thinking of a PV (solar) system at my detached structure that will feed back to my MSP, and the grid. It gets great exposure - my home, however does not.
MSP is QO 225A bus, 200A main, 4/O SEU. A 60A 240V circuit feeds the barn with #6 CU and is ~165' away. The barn feed is sent thru 1" PVC, and lands in a QO 100A MLO sub panel.
I want a system that will warrant a 7.6k inverter (32 x 1.25 = 40A of OCP) and backfeed on the existing #6. I've searched for a while now - the 2017 NEC code is a daunting, long-winded, exhaustive, yet informative, piece of literature that has effectively confused the sh** out of me. That's why I'm here.
I am speculating that I will need to pull #4 CU (the largest 4-wire gauge that will fit the 1" PVC) through the trench), upgrade the sub panel or lock down a branch-fed main, or derate something.
I'm wondering what part of the code I need to refer to and the exact calculations I need before determining the wire ampacity rating for backfeeding solar, and possibly line-side tapping.
Thanks!

 

[Dennis Alwon]

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