I run 4 S3s on a solar setup.
For a properly working system you need an MPPT charge controller.
A good one will cost around $200.
Then need solar panels of total 1500W for you to run 2 S3. That will cost another $1000 (Not DIY).
DIY Panels are cheap, but I will not recommend it for professional installations like for mining.
Now Solar Cable, Fuses, MCBs and other Misc. electrical components costs around $200.
Mounting stands for solar panels: $200
Total it will become $2000+ if you are doing it yourself.
Else if you are handing over the solar project to an agency/company it will cost above $5000.
See my Solar Setup Thread: https://bitcointalk.org/index.php?topic=655325.0

Do your ROI now. Solar setup is expensive.