What puzzles me, though, is the low power consumption - about a fifth of what it had originally (~70 W).
So yes - I will not get rich with it. But it fits my needs and is fun to use.
If it's using 1/5th the amount of electricity, surely you're seeing a decrease in hashing rates. I use solar as well and I can say that I think sending the overproduced energy to your electric company in order to receive a credit has to be better than just burning the electricity. You could probably pay to run your actual heater with the saved funds and be more comfortable and have more money. Not trying to discourage you, but for $0.04 a day you're probably better off solo mining with that thing and hoping to hit the lottery. That at least has the possibility of getting you a return. I think everyone else would agree though, you're better off just turning that thing off unless you need heat and your heater is broken or something.