Sounds like a fun project and I can sure understand wanting the pool warmer!
You need to be aware that this system won't drain fully when it's shut off. It may drain enough to stand the freezing in the black poly pipe, maybe not, or you can blow it out with compressed air for winter. If you want to blow it out, provide for that in your plumbing.
You want to target a minimum of 2/3 of your pool's surface area in collector area for the project to be worthwhile. A 1:1 ratio would be better.
The simplest way to plumb it, assuming manual control of your system, is to plumb in a three way valve with one outlet going straight to the pool, and the other outlet going to solar. This valve is your manual on/off and can also be adjusted to get the right amount of water flowing to the solar. You're going to want to automate it later, and a pool valve can have an actuator added.
Then a tee, downstream from the three-way on the line going to the pool, for the heated water to re-join the flow.
Both of these should be after your filter, but before your main heater or chlorinator (if present).
When the system is shut off, there will be suction on it from the weight of the water, so you need to add a vacuum breaker at the highest point in the system. You will need to have enough pressure at the top to keep this valve closed when the system is running, because the pull of water coming back down when it's running may suck air if there's not enough pressure. If this happens and your pump is already flat-out, you'll need a throttling valve on the return line coming down.
Check valves depend on pool height and equipment pad height, and I suppose in your case where the system doesn't drain, you may be able to just close it off and leave the water in the "to solar" side. The easiest way to suggest check valves is for you to describe where any check valves are now, and pool height vs. equipment pad, and then you'll get an answer. The key is that you don't want water coming back down and going backward through your filter when the pump shuts off. The drain water needs to go to the pool.
On the two lines ("to solar" and "from solar") you want tees joined by pipe with a ball valve between the two tees. The ball valve is left slightly open so the "to solar" side can drain into return line when the pump is shut off. This can be very small pipe, e.g. 1/2 inch.
Be aware of wind loading which can be extremely high during storms. One of our neighbors had their "professionally" installed system rip clean off the roof. Thankfully they and their children were not in the yard. This is critically important. The system needs to be tied down adequately.
This link is to the installation manual for my system. Page 33 has the schematic, and you can also find wind loading information (albeit Australian) starting on page 30. These won't help for your location, but will explain the importance.
http://www.ecoonline.com.au/content/manuals/oku_solar_pool_heating_install_manual.pdf
You'll notice little tubing for draining. I preferred a properly plumbed drain line between the two sides of the system, not the little tubing shown in the manual. These plug up and drip and just aren't worth the savings.
Professional installers here use black PVC pressure pipe, and that's a great way to go. I got free pipe from my builder and painted it black. If you leave it white, light gets in and algae can grow in it during the off-season.
I can't do drawings and parts lists and post them here, but maybe after you dig into it a bit deeper, you can draw something up and post it. Experts here will point you in the right direction.
