In Line vs Parallel Solar Panels


TFP Guide
In The Industry
May 14, 2007
New Brunswick Canada
Hello All:

A snowy back yard has gotten me to thinking about solar heating for pool next summer. In the attached file you can see my current set up and my proposed new set up. Will this be more effecient?

What do you all think?





LifeTime Supporter
Oct 5, 2007
Valrico, FL
I believe that you really have to pipe the panels in parellel. A single panel can only handle about 3 to 5 gpm. So connecting them in parellel allows for more flow through the solar array.


TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
Yes, the lower diagram. You want the water entering the panel to be as cold as possible, the larger the temperature difference the more heat is transfered. If the water has already gone through one panel it will be warmer, and thus the second panel in a series hookup will be less efficient. To avoid that you want to have water directly from the pool feed to each panel. This is also good for the reason dschlic1 mentioned, the designed flow rate of the panels is fairly low. You want as much water going through the panels as possible, so every panel should get it's own flow (unless you have a *really* large number of panels).

The panels are intentionally designed to work either way. There are situations where it is impractical to plumb both ends of the panel, so they provide a loopback mode, which makes it possible to make all plumbing connections on one end. That mode is less efficient, but required in rare cases.


TFP Expert
LifeTime Supporter
May 3, 2007
Pleasanton, CA
One modification I would make to diagram 2, make sure you should feed water into the bottom of the panels and not the tops. It makes priming the panels easier and better for heat flow.


TFP Expert
LifeTime Supporter
Apr 8, 2007
Waaay NW MN
I have mine run parallel however, I have each one piped in and out from one main back to one main, but different from yours.

Ours has a main with a simultaneous split to each panel intake and the outles from each one simultaneously enters the single pipe, rather than in sucession as you have it. I don't know if its better or worse or no difference, but each panel gets the same amount of water pressure that way, rather than the last panel on the sucesssion getting less.

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
San Rafael, CA USA
The bottom diagram in the earlier post that showed the parallel panels will also have equalized flow rates in all panels due to the extra loop since the water flows in at one end of panels (top right in the diagram) and out the other end (lower left) so the path length for the water is the same regardless of which panel the water flows through. This ensures that the pressure difference between the top and bottom of each panel is the same for all panels so that makes the flow rates the same which is what is important. The fact that the pressure at the same point in each panel is different is irrelevant. All that matters for the flow rate is the difference in pressure between the top and bottom of each panel (and this difference is equal for all panels).