Q:

How important is it that the PV panels face due South?

A:

The performance of PV panels is more sensitive to direction than solar thermal collecors are. Every attempt should be made to face the PV panels as close to South as possible.

Also - PV panels are very sensitive to shading! A very small amount of shade on any part of a group of PV panels will dramatically reduce the output of the panels and reduce the performance of the pump. Ideally the PV panels will not see any shading between 8am and 6pm.