I just looked into this. Harbor Freight has a system that sells for around $200 or something. That got me interested. So, my son and I went through the calculations. Under very good conditions it would take 7 years to pay for itself (as I remember).
Very disapointing. I wanted to see if I could run my computers durring the day by solar. It would take thousands of dollars to set up and would never pay for itself.
Bummer
.