Do I need to put a drain at the top of the panel?
A solar thermal installation can be filled by means of a station that during the filling operation compresses and expels a large part of the air from the installation.
Drains placed on the roof are not necessary in this case.
Instead, a central air separator is installed in the machine room. This removes the residual air bubbles in the fluid flowing between the tank and the exchanger during the operation of the installation.
The advantage of this solution is that filling and draining are carried out in a single step.