Yesss, in theory, because then it only has to outperform the 11c FIT we would otherwise get for the unused solar. But in the evening when I am using the PC anyway I tend to have NiceHash running on the GPUs. The additional power load isn't much, and with the high value of BTC at the moment it's easy to justify. I power it down overnight when I'm not using it. But compared to the load of the fishtanks, heated towel rails and the day-to-day power usage of a 4-person household having one PC mining away is pretty insignificant.