if you have 2kwatts per hour 24/7/365   you can run 2 s-7's  clocked down to 4000gh esach total of 8000 gh

2 kwatts per hour is 8000 btus of heat and the gear is loud


but if you have free the free power of 2 kawtts a day and buy two s-7's my guess is in a year you could 2x the money invested.

that is a guess not a certainty.