Is it necessary to have an expansion tank with a DualSun SPRING installation?

Yes, but only for installations larger than 12 panels. 

The expansion tank is not mandatory according to the regulations but widely used for installations with conventional solar thermal panels.

DualSun SPRING panels are hybrid panels, very different in design to thermal solar panels (see more explanation here). In fact, the heat exchanger located on the rear face of the panel, in polypropylene, makes it possible to dispense with the expansion tank for the installations of less than 12 panels. 

In this case, we consider that the panel heat exchanger is enough to cope with pressure variations.

On an installation of less than 12 hybrid panels an expansion tank is not useful because :

• It cannot maintain the filling pressure in the solar circuit;
• It doesn't absorb the expansion of the liquid if it is set to P = P0 + H/10 with P0 = 0.5 bar;
• It absorbs the expansion of the liquid if set to P = P0 + H/10 if P0 is significantly lower than 0.5 bar;
• There is no risk of vaporization of the heat transfer fluid. 

> To find out more: How to dimension the expansion tank for a DualSun installation?