So is the minirig, at jally power draws, a minirig needs 9KW of power each. It's a portable fire starter and neighborhood light dimmer, and the power bill will each up a vast amount of profit.
the average household only can pull 3kw tops if you run everything you have all at once.
You are right about the issues with running a minirig off of household power, but it is ridiculous to assert that the power costs of a 9kW 1.5Th/s rig would "eat up a vast amount of profit". At current difficulty, price, and the average US electricity price ($0.12), power costs would be 0.29% of revenue. At 76x the current difficulty, it would be 22%, similar to the efficiency of a dual 5970 rig today.