I have a strong opinion not to solar mine as a whole unless you are a home miner and recognize that the capital outlays for the specific purpose of getting "free energy" to offset mining costs is a fallacy.
But, I am green and I have roof panels to run my entire household and am under the firm conclusion that I will ROI in about 9 years and feel better about my carbon foot print as it pertains to my household.
My mining is at locations where local power is predominately wind.
This device is probably nowhere near as efficient as roof based panels, but worthy of a discussion.
The problem with your 9 year ROI is that by that time the panels will lose a percentage of their efficiency, so with each year you'll be able to produce less and less.
I still think solar panels are not worth the trouble at current prices. They're only a viable option if you're in a remote area with no electricity or with frequent power outages.
I've been interested in wall mounted solar heating panels for quite some time and they can be quite efficient when placed properly. During Winter the sun is low, so it shines right on the panels. You have to take that into account because your electric panels will lose some of their efficiency as the Sun gets higher. Also glass in your windows will reflect some of the light. I don't think these will be efficient enough to be worth it.