Is it safe to wash solar panels with cold water while they are hot? Could the panels crack?" Posted by Frank Molina, Stellavolta on Aug 30th 2018 No, it is not safe to wash hot solar panels with cold water. Yes, they could crack. The best time to clean them is in the morning after they have cooled overnight. Mr. Long Arm Mr Long Arm solar panel cleaner solar panel 1009 1008 1005 1001 ProCurve Solar solar panel cleaning