Well, the installers returned this morning and found the fault in our Solar PV system. They had reversed the polarity on one of the modules! I consider that a basic error and for me it has thrown into question the quality of the installation as a whole. I am going to have to review my options regarding getting the install checked out by an independent installation company (if that is at all possible).
In the meantime, it seems to be working and so the coming few weeks will see just how much the system will generate.