Static head is related to the height of the water only (i.e. weight of the water). It doesn't require a sealed system (i.e. closed VRV). However, if the VRV does open, the pressure at the VRV becomes 0 PSI and the return side column of water will drain out at a faster rate than the supplied water replaces it.
But I would not be concerned with the above. The primary reason for a VRV is so the panels become self draining to prevent freeze damage. It is also useful if solar is turned off during the heat of the day. I would definitely plan on having a VRV. However, the placement of the VRV can be critical depending on the total plumbing design.
Thanks. Yes I'll plan to get that VRV installed soon.
The 75% of return head for 1.5" suction and 1.5" return pipe is pretty much spot on.
I have a 3 meter rise to the solar panels.
My gauge measures about 1.45 psi more when they are switched on. This equates to about 3.3 feet or 1 meter loss only. (including friction due to the extra piping)