I will probably get a sunny boy sma 5kw.
Get a used one for $600, that makes the 3.6kw portion cost $432.
The sunny boy has 3 inputs so I could do 3 to 3.6 south facing like I was planning then also add on an array of 1 to 2 kw of South east facing panels plus 1 to 2 kw of South west facing.
If I get this inverter I will be looking to have it make close to 5kw from sun up to sun down.
Run the numbers again.
The constants are panel cost, the cost of the mounts and racks for up to 3.6kw of roof top panels, the budget for the inverter. So all I have to do is ground mount more panels.
I will likely make up to a 6kw system on a 5kw inverter.
So let's say $2,500 for 3.3 to 3.6kw of roof top I was planning to do.
Then let's say I add a south west array of 2.4kw, up to 3kw.
(The sunny boy sma likes at least 250vdc on its inputs, 2.4kw puts me at 280 vmp. 2.1kw or 7 panels might work but that puts my vmp at the low end of the recommend vmp.
So the additional 2.4kw to 3kw of panels should only need about $300 to $380 worth of racking and attaching for ground mount (no expensive rack feet).
To add up to 3kw of SW facing ground mounts should run about $1,150. Just panels, unistrut, anchors, wire, no inverter.
I will probably start with the minimum. 3kw of roof top panels and 2.1kw of SW facing panels and just see what happens, then add panels from there.
$3,650 for up to 6.6kw of panels on a 5kw inverter.
Only problem is I really down know what the pay back on the south west facing array will be. I could assume it would be producing around 70% of the south facing arrays production.
Is going to get you.