Assuming the pump can initiall lift the water the height really does not come into play as you are pumping up but the falling water acts like a siphon pulling down on the pump. If you draw a box around the entire system you are only raising water from the skimmer level and injecting it back at the surface for a net rise of about a foot or less. You do have the friction loss in the added piping but it should not be that big a factor. I put in 1.5" pipe for my two panels, way overkill but causes almost no head loss.