Question: Risk of rain leakage on flat-roof installation

I am currently undergoing a loft extension on a semi-detached house and we are planning to install solar panels. Our street-facing pitched roof is north-facing so we decided to install solar panels on the flat roof with mounts to angle them south. The solar panel installation company we contacted are planning to use a Renusol console flat mounting system.

Our builders that are working on the loft extension, who admit they are not knowlegable about solar panel systems, have expressed concerns that installing solar panels on the flat roof can cause leakage and damp. Their argument is two-fold: Firstly, the solar panel mounts would need to drilled into the roof and rainwater could leak through these drill holes and, secondly, that water could collect around the mounts causing damp and long-term structural issues. They recommend us to install solar panels on the pitched roof (which we are reluctant to do as it is north-facing).

Are our builders' concerns valid and if so then what is done to mitigate these risks? If these concerns are not valid, then could someone explain why?

Thanks