When my Solar is on, I am seeing an 8 PSI increase at the filter pressure gauge (from 4 PSI to 12 PSI). I have an Intelliflo VF which is set to run at a constant 25 gpm both with solar on and off. So the PSI increase is entirely down to added TDH from solar (rather than flow rate increase).

My back of the napkin calculations say I should only be seeing a 4 PSI increase, so it seems significantly over pressure.

- All 1.5 inch plumbing

- 50 feet of pipe length (not counting the solar headers)

- 25 by 90 elbows

- 6 by 45 elbows

This gives me a TDH for the plumbing of 2.8 PSI

The highest point on the panels is 12 feet above water line. The panels themselves are split into 2 arrays of 7 (14 panels total). The 2 arrays are connected in serial, so this gives 3.5gpm per panel. According to the manufacturer specs (Heliocol) this gives a TDH of ~ 0.18 feet per panel.

14 panels * 0.18 feet = 2.52 feet = 1.1 PSI

TOTAL PSI = 3.9, which is well below the 8 PSI I see in practice.

Are my calculations wrong, or is there something going on with the system?