My knowledge is limited, but how long do your PV panels last? I read at one point you need to replace them after about 15 years, maybe sooner, because they go down to about 40% efficiency, or something like that, after that time.
At that point, if break even is 10 years, and you have to replace it in 15, I'm not too sure it's worth the hastle. Sure you get 5 years worth before replacing, but the efficiency drops.
I'm more interested in a "build as you go" system. It's much easier to put $1-2k a year into a system (one or two new panels a year, new battery, ect.) for 10 years than it is to put $20k upfront. At least for me.