solar plumbing pipe diameter design. Flow efficiency. 2inch pipe into 1.5 inch solar header

[AGP noob]

So i have been doing my homework before i build my solar system and am curious why i have not come across this.
2 inch piping is much "better" than 1.5 inch, but in the situation you have multiple solar panels hooked up, and these panels have 1.5 inch diameter headers, then this would be a major innefficiency in the water flow. Therefore, instead of hooking up two solar panels together and having one 2 inch pipe connect to the 1.5 inch header of the first solar panel (out of two panels). Why not have the 2 inch pipe flow to EACH 1.5inch solar panel separately. See diagram below. I just have not seen this done or in the solar instructions but maybe i missed it.
Flow rate should also be slower I think with this design

thanks!

 

[mas985]

The transition from 1.5" to 2" does not add much head loss at all. I don't think you would see much of a difference between the two designs.

 

[AGP noob]

Thanks Mas
Just to clarify, are you saying not much head loss at all to have a 1.5" for the entire system or just for that one transition if going from 2" to 1.5" solar header then back to 2"?
Correct me if Im wrong but it seems the 1.5 vs 2 in has significant head loss for the whole system?

Thank you!

Swimming Pool Feet of Head Calculations

Learn how to calculate your pool plumbing system's feet of head, so you can accurately select the proper pump size!

blog.intheswim.com

The chart shows the feet of head per 100 feet of pipe according to the pipe diameter

GPM	1-1/2" PVC	2" PVC
40	9.43	2.75
50	14.3	4.16
60	20	5.84
70	28.6	7.76
80	36.7	9.94

 

[mas985]

The diagram you were showing and your description appeared to be only about the way the panels were fed. Parallel header vs serial header and in that case, the difference is minimal. But yes, for the entire system it does matter.