When is it necessary to control the auxiliary heating with Dualsun solar controller?

Case 1: 

Boiler exchanger loop at the top of the tank: no direct conflict between the heating layers. 

⇒ Non-justified back-up control

Case 2: 

The electric resistance works in the middle-top of the tank: no direct conflict between the heating layers. 

⇒ Non-justified back-up control

Case 3: 

Boiler exchanger loop in the middle of the tank: direct conflict between the heating layers. 

⇒ Control of the back-up necessary or installation of a preheating tank dedicated to solar

Note: Monobloc thermodynamic water heating tanks often have the solar and auxiliary thermodynamic heat exchangers stacked on top of each other.

Case 4: 

The electrical heater is slightly above the solar exchanger and the S2 probe is placed at the same level as the electrical heater. Heating the electric resistance may affect the value of the S2 probe and stop the solar pump. 

⇒ Control of the back-up necessary or installation of a preheating tank dedicated to solar