Updated: May 4
Panels just to the East of north, giving the sun the best chance to heat the water throughout the whole day.
A small amount of dirt or dust on the panels is ok, this dirt or tree sap layer would be stopping the panel from collecting heat. It would be acting like constant shade on the panels so affecting the amount of hot water this panel can make.
Cleaning of your panels once a year, around April is a really good idea.
We will always help you remember this when part of the Sears Solar Community by sending you a reminder to give them a clean.