There is a significant difference in thermal expansion between the thermal heat exchanger made of polypropylene and the photovoltaic laminate: with variations in temperature, the heat exchanger will expand considerably, while the glass has a low thermal expansion and will expand much less.

The thermal heat exchanger is thus fixed to the photovoltaic laminate by a "SPRING" system which allows the exchanger to expand freely without any mechanical constraint. In the same way, for the inter-panel connectors, a hose internal to the panel assures the possibility for movement between the panel frame (which is fixed) and the heat exchanger (which expands with temperature).

This design is specific to Dualsun and protected by international patents.

The aluminum heat exchanger of the SPRING4 is subject to negligible dilatation so that it is not subject to any calculation. 

To go further : What is the expansion volume of the heat exchanger of the SPRING panel and the DualQuickFit hose?