Yes, two Intex pumps can be plumbed in series, and it will double your head. I am using two 2100 GPH pumps with eight solar collectors (2'x20" panels). I pump up two stories.
I've been messing with solar heat a lot over the last five years with lots of iterations, pump combinations etc. The thread is here:
Solar Swimming Pool Heat DIY with SmartThings Automation
I'm happy to answer questions. Aim for the same area of heaters as your pool. You just need a 3 way valve, check valve, and a vacuum breaker. The GAME 50mm to 1.5" adapter are super handy so you can just plumb everything with 1.5" PVC or ABS.
The solar collectors are just plumbed into your system so they are fed water after the filter...and the 3 way valve lets you send water to the panels or not. How you plumb the collectors is also important. Aim for four panels, and make sure they are plumbed paralell so all of the water goes in one end, and returns out the other. If you try to use cross flow collectors, they likely won't work due to the high pressure/loss you see with that setup.
For a pool in shade, like ours (18ft round x 52" high) it pretty much took 320 square feet of panels to get temps into the 80s. Nights are cool (often 50 F) and trees limit sun exposure to the roof panels more or less 11pm to 5:30pm.
So for a 14" pool, start with 154 square feet, or more. Four 2'x20' panels would get you 160 square/feet
View attachment 446623
With
one pump and 4 panels, the numbers looked like this: (the system at the time was just four panels on the first story...I added the upper four panels on the 2nd story roof after)
1. Pool Pump - Intex SF80110-1 , 0.2 amps , 1600 GPH.
2. Actual (measured) system flow with sand filter and solar array in use: 1028 GPH
3. Max measured BTU = 1028 x 8.33 x 6F = 51 379 BTU/hour
5. System head (max lift height to peak of roof) : 17ft
In the pics below, two pumps (.24 hp, Intex SF80110-1 and Intex SF80110-2) are plumbed in series, 1 before the sand filter, the other after. They flow 1800 GPH through the system including eight 2'x20' solar collectors...about 3.75 GPM through each panel. Your target for a 2'x20' panel is 4 GPM. The eight panel system generates a max of 105K BTU (about 30 000 watts of heat) but will typically average about 75K BTU for 4-5 hours during a sunny day at 75 F ambient temps.
View attachment 446624
This image snapshot can be clicked on to take you live data from the system..I'm using some simple automation bits with Smarthings to control power to the pump shed setup. If temps on the roof are 5F over the pool water temps, it turns on...and off if less.
