electric hot water heater with added heat exchange loop?

[wwu123]

I currently have a solar hot water setup. (Should never have done it since the in winter, at best, it only gets to 75 degrees)
I have one exchange loop in the tank solar that goes to the spa. Does nothing worth while in the winter. And it does take way too long
unless the tank is at like 150 degrees like it is in the summer.

So, I only think about fast heat when I change the water and want to use that night.
Otherwise, a slow, constant heat with an exchange loop is fine. It is a nice small pump running.
So, if I added another tank, with loop, and it can be heater like a water heater, it just gives me another option
to heat the spa in the winter I would be hoping via the two exchange loops in series. If the solar is colder, I guess the
water going it might even back heat that tank.

Got it, makes sense to me - my vote is a heat pump water heater, used on your spa loop as opposed to your potable water supply, with the 2-3X efficiency (i.e. additional heat). You could even set it hotter than you would an electric tank heater, the additional efficiency more than offset the standby losses of a higher set temp. It's merely an air-to-water heat exchange loop, just with a compressor cycle...

Bonus points if your spa is situated that you could run a passive gravity loop, and not even need a small pump, gravity would constant replenish the cooling water from the spa with hotter water from the tank...

 

[shs1]

My ground source heat pump (pond loop) generates 5 kW of heat for every kW of electricity used, so 5 time more efficient than resistance heating. That said, the problem that needs solving here, in my experience, is when the grid is down and the Powerwall batteries are full but the solar still has some potential output, where can you put that solar output rather than letting the Powerwalls shut down the solar via frequency shifts, which by themselves are annoying. Charging a electric car battery is one very good option and my Model 3 handles this well, only charging when the Powerwalls are at more than 95% (settable) SOC. (Our >10 year old Model S is not that smart.) Dumping excess solar power into a resistance hot water heater is the other good thing to do with excess solar energy as that can also be turned on and off quickly. The advantage of charging a modern Tesla is that it automatically varies the charge rate to just use the excess solar energy and not discharge the battery below the set point.