Some claim COPs of 3 or 4 depending on the temperature of the air it’s sitting in, but don’t forget, if you are using electricity, even if it’s electricity from your own PVs, that’s electricity which could be put to use doing something else! And there are better ways to heat hot water! Like the sun! And it would be just as good to use a simple propane or natural gas hot water heater directly, since the efficiency of electric power plants is about 33%. Let’s compare.
$500 propane hot water heater
$2800 heat pump hot water heater (like the Stiebel Eltron ACCELERA 300 which I’ve heard is well received)
And nothing’s keeping you from having just as many PVs. Maybe you’ll have some electricity left over for your neighbors, or for charging your electric car.
I mean, if you were me… and trying to decide how to heat your hot water… what would you do?
I mean… solar yes. But in MA they** say you can only get to a 60% solar fraction. Should I believe them? I say no. Gary at builditsolar.com gets 95%+ in MT. OK, so how does one do that! Most people claim you shouldn’t do drainback, but I’ve been reading, and Tom Lane’s excellent guide to solar hot water systems says they are actually the way to go. So that’s that. We’re doing it. (Now to find someone to actually do it.)
**they as in… Google around, and you will find it’s quite typical. But I think this is partially because people 1) use non-drainback systems and 2) design such systems to provide ~60% (undersized, not a steep angle for keeping up in the winter and reducing temps in the summer, etc).