Hugely inefficient if you only want heat, maybe. But the trick here is you want the PV first and foremost to produce electricity. The heat pile is just to make use of the excess.
Also, be careful about assuming that PV is in fact inefficient... Under the right circumstances I'm sure electricity to move heat is cheaper than pipes with fluids in them.
Ah. I get it, the electricity that would be waste is converted into heat. Free heat. I had the idea a while ago that solar thermal would be a good constant source of energy for bitcoin mining, because the heat is stored at 600degrees in solar salts and could be converted to electricity at night when there was no sun. Hence 24hour up time. But I'm not an engineer so haven't talked about this with others.
