Not sure which is the appropriate forum but I'll start here.
Starting to put more focus on getting a solar panel heating setup this summer, the panels in question will be placed on my garage roof, distance from filter to panels (at the closest edge) will be +-25 linear feet of 1.5" pvc, about 10 feet of that will be vertical.

What I'm having difficulty understanding is: each night when the pump goes off part of the downstream section will drain out due to gravity, having a check valve after the filter will prevent the water traveling TO the panels from draining back, but the feed FROM the panel will partially drain when the pump stops. Now, when the pump comes on in the morning won't this mini-priming cause some water hammering? I'm thinking that's not good.

Can someone shed some light for me?

PS, in the pic below I'll be coming from filter to pool edge, follow it a bit and then straight across to the garage wall and then vertically up the wall to the roof.

There should be four valves in a solar system. You mentioned the check valve after the filter but you should also have one on the solar return so the panels do not fill backwards when the solar valve is off. Next is the solar 3-way valve to turn on and off the panels and last is the vaccum release valve. The vacuum release valve near the panels will open when the pump is off and allow air to enter the solar panels so they can drain. You can design a solar system that is not self draining and remains full of water all the time but I would not recommend that.

However, there shouldn't be much if any water hammer since that only occurs when a valve is quickly closed or opened. Check valves can sometimes cause this but only under certain conditions like when the pump is turned off and then back on a few seconds later. Since the panels have not drained completely, the solar return check valve can sometimes slam shut. But water hammer for a pool plumbing system is more annoying than damaging since the water pressure usually doesn't get high enough.

Sounds great, thanks for the help.
I've planned all the valves you mentioned except the one near the solar return, didn't know one was needed there.