I will chime in since I just installed a 7.65 kW system mostly to offset my electric bill from mining, however, it is completely a grid-tie system. I paid $.65/watt including shipping (bought from a wholesaler on eBay), $2800 for 2 inverters, installation was $1.10/watt (1 inverter would have worked if I went with SolarEdge w/optimizers). I had to take a break from mining when my Edison bill hit $900 last November for running about 8 TH. Not entirely sure if this system will help in ROI for running S7s, on the other hand, Edison buys back extra power @ $0.9/kW $0.09/kW..
so you spent around $15,000 for 7.65kW and no battery packs?
IIUC, that means you should get ~7kw*12h = 84kwh/day (~$8), and it will take roughly 2000 days, or 6-7yrs, to pay back the system cost assuming no surprises
as i understand, thats not too bad since solar insallations are typically advertised as around 10yrs to break even, at which point you might need to install $4000 of new panels to keep running another 10+yrs
I adjusted the math. you need to find your sun hour zone to calculate annual average daily sun hours. I am in Florida and receive just over 4.5 hours on average.
~7kw*( average daily sun hours) = X kwh/day (~$ Z)
~4.5kW (4.5h) = 20.25kWh/day
At current difficulty and my averaged mining efficiency of .33W/GH, 1kW will run ~ 3Th of gear and will result in ~$.25 in BTC being generated per hour. So my solar setup, on average and at current BTC price and difficulty, earns 20.25kWh($.25) = ~$5/day.
or something like that...