Loss of pressure when adding basic solar heater

[PoolDoc]

Add to what Mark said, the fact that most "1500 gph" pumps are low pressure devices with very little reserve capability.

You may need a standard AG pool pump, to drive the water through the panels.

[Watermom]

I don't send all of my water through my solar panels. I usually only open the valve maybe half-way.

[BigDave]

My two cents, sorry to be contrary:
If you find flow is inadequate for filtration with the solar panels on and you'd like to get maximum heating from the panels, plumb a bypass around the panels and run all the water the pump can move through the panels when the sun shines and bypass the panels - pumping only through the filter when it's dark.

[mas985]

Higher flow rates do equate to higher thermal transfer efficiency but only up to a point. Most manufactures recommend 0.1 GPM/sq-ft of panel to obtain maximum efficiency and forcing more water than that through the panels won't get much more heat into the pool but it will lower the electrical efficiency of the pump. For most panel setups, optimum efficiency is achieved at a point that is 3-5 PSI above the operating point without the solar panels.

[BigDave]

Agreed, but, in this case the OP has a low volume, low pressure pump that is unlikely to overwhelm the capacity of the panel. The observation of warmer water returning from the panel demonstrates this. Flow rates approaching the panel's capacity would be less noticeably warmer.

[mas985]

It depends on the size of the panels but typical AG panels are 2'x20' or 40 sq-ft and I got the impression there is only one which would require only 4 GPM. So most of the flow rate can probably bypass the panels and still provide pretty good heat transfer. But once the OP posts back, perhaps he can tell us the size of the panel.

[CarlD]

sometimes it's simpler. I re-routed soft panels when I had them so the water went in one corner and out the other, and ALL the return water passed through them. The efficiency of heating was amazing that way.
It's fundamental to thermodynamics that the faster the water flows through the panels without cavitating, the more heat is transferred. Usually, the limiting factors are a loss in pressure, or more pressure than the panels can tolerate before they start to fail and leak.

I successfully ran a 4'x10' (same as a 2x20) with a little tiny Intex cartridge pump this way, and was able to heat my parents' 13k AG with only 6 hours of direct sun a day. For both, I did it by re-routing the panels so water went in one corner and out the furthest.