GPM for Fafco solar panels in parallel


Jul 27, 2021
Chicago area
Hi all. I've read through everything I could find here, but still can't determine what the flow rate should be through solar panels hooked up in parallel.

The panels I'm looking to get are the Fafco "Solar Bear" 4' x 20' panels.

The Fafco specification sheet states that the recommended flow is .1 GPM per sq ft, which for a solar bear (which is 75 sq ft) equals 7.5 GPM.

However, the manual assumes you're hooking it up so that the flow goes down the panel one way, then turns around and comes back. Essentially the water is traveling in a 2 foot wide panel for 40 feet. (see figure 1)

So if I hook mine up with the center valve open, and have it exit out the other side, It's a 4 foot wide path, and I can double the flow rate, right? So each panel can carry 15 GPM? (see figure 2)

Ultimately I would like to hook up 2 panels in parallel, so can I assume that the ideal flow rate for this configuration is 30 GPM? (see figure 3)


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TFP Expert
LifeTime Supporter
May 3, 2007
Pleasanton, CA
Pool Size
Salt Water Generator
0.1 GPM/sq-ft is not unique to those panels and is used by most of the industry as a target. It doesn't matter much if the panels are in series or parallel, manufactures will use the same target.

The ideal flow rate and the maximum flow rate are two different things. The first is just an approximation where the efficiency of the panel starts to level off. By reconfiguring the panels from series to parallel, the ideal flow rate actually goes down, not up because parallel panels are more efficient. They should really derate the target for a series implementation.

But I think you are assuming that number is really a maximum flow rate which it is not. It doesn't mean that you can't have flow rate higher than that, it just means that you won't benefit much by going over that value. So if you want to run at higher flow rates, you can as long as it is within the manufacture limits.
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