Solar Panel plumbing and flow rate

[mas985]

You can usually go by pressure rise. A 2-4 PSI rise is typical but it depends on the type of panels you have. If these are the kind of panels that have both the supply and return on the same side of the panels, they have a lot more head loss so a PSI rise of 5 may be more appropriate.

But the method that swimdaddy outlined will not give you a very accurate flow rate measurement. You are changing the plumbing which changes the head loss and flow rate.