The AirTap cycle time is pretty short and won't occur too many times a day,
unless it's wash day.
Too bad they cranked up their price last summer. I think they may have had some hurricane damage.
Years ago (early 70s) when I had 3 Novan hotwater panels on the roof,
we had 84 gallons of preheated water to feed into the domestic coil on the boiler.
In the summer, the tank would get up around 180, and keep the boiler
from using any oil when we turned on the hotwater tap.
In the winter, it would get up to about 120, which was still a help.
After about 18-20 years, the heat exchanger died (due to bad water),
but I think those old collectors are still at work on a roof somewhere in New Hampshire.
(Wish I had kept them). I still have a couple of little brass Taco circulating pumps.
-----
I guess an AC element is about the cheapest way to go, if you need to dump some power.
If I ever get to that point, I'll have to keep that in mind.
I've read about guys using AC element space heaters in their DIY EV cars
and running them on 120-130 VDC.. Just have to change the fans.