Wow, that's a huge system, congrats. Puts my existing 3.5kW system to shame, for sure.
Anyway, I think you're double counting your "savings".
Since you're already paying (let's just say "about") $54k, you're already getting the full 30% solar ITC ($16,000), right?
If you used your PW credits against solar, your ITC would go down $4,950. So I think that's how much more you're actually "saving" by Tesla forcing you to use the PW credit for your M3 instead of solar. (#firstworldproblems, right?
)
16500 on 3 Powerwalls + $7500 federal + $5000 state + $16000 ITC (solar) = $45000
Therefore all other things being equal, I don't think you can say you're "saving" $16000 above, since you're already saving that $16000 by doing nothing different. What you're really "saving" is the additional $4,950 ($16,500*30%) differential between those two scenarios.
And in addition, you'd get the $7500+$5000 state credits on a Model 3 anyway, so again, you're already "saving" those dollars either way just by buying an M3. Those don't change because of the PW2 credits.
So to properly account your actual "savings" (differential) for the all the PW2 awards, I would rephrase that as:
16500 on 3 Powerwalls +
$4,950 ITC ("forced savings") = $ 21,450
If you had zero PW2 awards, everything else would still be the same buying an M3+solar: $7500 federal + $5000 state +
$16000 ITC=$28,500.
Still, a pretty darn good deal, no doubt!