I have solar mats on the ground which I plan to move to the house roof. The solar lines between the pump and the house will run underground. There will be no way to gravity drain the lines at the pump and I'm concerned about winterization ( NJ ). Can you blow out pipes when there is a air relief in the line? I don't imagine you can, so I'm consider putting a union on each line where they go vertical at the house. Or valve/union combo (hayward sp 723). Valves at the house and at the pump would amount to an extra set of isolation valves, but it would make winterization a bit easier. Open the lines, blow them out at the pump, and watch the geyser. Does this make sense? Or is there a better approach?
On the solar supply line I need a check valve to prevent backflow and backwashing the filter. Do I need one on the solar return? I have an isolation valve there already.
Lastly, I see a lot of installations using 10' or 12' mats run vertically. I'd like to use my 20' mats (3 * 4x20) and run them nearly horizontally (I'll pitch them 5 inches to drain). My ranch roof has room for them. Any reason not to use them?