I mine using an inverter, and I haven't mined directly from the charge controller to the rig motherboard yet. I learned about mining from a charge controller from the guy in this video. But I'd like to try mining direct from a charge controller because, like you said, it's more power efficient. I do mostly mine from sun generated power though. Right now my wife and I have two 250 watt panels. Money in the form of light is raining from the sky every day! It's fun using systems to catch that sunlight, convert it into electricity, then sell that electricity for whatever crap coin is profitable and the get paid in Bitcoin.