For solar thermal panels, manufacturers’ recommendations often call for a minimum inclination (e.g. 15°). This is sometimes a constraint on a flat roof or a roof with a small angle of inclination. It is important to abide by this requirement because otherwise condensation in the cells drains off poorly. The glass eventually gets dirty and the efficiency drops. The panels will then produce much less hot water.
Because of their construction DualSun panels are not affected by this problem. They can be placed at 10° or 5° like photovoltaic panels. They can also be laid horizontally to optimize the roof area, but regular cleaning must then be ensured.
Finally the inclination will have an impact on the production - thermal and also photovoltaic, so it is a matter of choosing between the different constraints (optimum production per panel, for the roof overall, budget, aesthetics).
For more information see: What Is the optimal orientation and tilt angle for solar panels?