Solar heats Small tank - recirculation pump over to regular tank

I was doing more thinking about the logistics of the small electric tank acting as a heat exchanger pumping in PV power for a larger gas powered tank.   The one with the recirc pump.  

The ideal scenario is to have both the electric and gas tank cold at the start of the day so its ready to accept the PV power from the array. 

Electric tank has a thermostat and ECO. 

Recirculation pump turns on when the electric thermostat reaches satisfied set point.   Turns off when cools off.  This effect transfers heat from the small electric heater to the gas tank away from the electric tanks element.

Gas tank has thermostat+ECO mod to top of the tank so it turns the entire system off (PV array disconnect using high amp DC relay) when that thermostat is satisfied. 

Not sure at this point if gas heater upper thermo satified should override the recirc pump and turn it off.  Im thinking NO at this point.

If either ECO trip it disconnects the PV array via the DC relay.
ECO trip means something has gone wrong. So it goes into the failsafe condition and stays there until manual intervention with ECOs reset.

Gas "timer" / control valve also needed to let the user to fire up the gas heat manually.   The manual over ride timer ability goes along way for user acceptability.  Warm water is fine for washing hands, pots & pans, feed to dishwasher, cloths washer, etc.   ....

.....   Its the cold/cool/luke warm shower part that is not going to be popular/dangerous with Legonella.    With temperature awareness of what is going on in the gas heater (Like I have with my water heater) its easy for the user to determine if they should fire up the gas for 15min, 30min or an hour before they have their shower.

But like I said the idea thing is to minimize gas use and let the PV do its job.  Also low temp in tank minimizes standby loss when heated with gas.  Its like tankless efficiency (with respect to standby loss) but not using a tankless (of course).

Mixing valves are a big plus in any PV solar system.