How much of a PSI increase with solar panel?

[cleancloths]

I don't understand why everyone seems to be hooking these things up to make pressure drop an issue. I run the panel of a side stream and only run a portion of the water through them, thus pressure does not come into play.

[tphaggerty]

Panels are rated to withstand much higher pressures than that. The increase you see at the filter is going to be higher (don't know by how much) than the pressure in the panels due to the backflow pressure of all of the extra piping & fittings as well. At a minimum, you are forcing the water to go through 4 90 degree fittings, most likely much more.

My panel set causes about an 8 to 10 psi increase at high speed. If you have a diverter, you can come close to optimizing your system by fully closing the diverter while the panels are on, noting the pressure increase, then slowly opening the diverter until the point where the pressure just starts to drop (assuming that the increase is "reasonable" to begin with, say less than 12psi). At this point, you should be getting close to maximum flow through the panels.

[mas985]

The more flow through the panel the more pressure rise you will see and flow through solar panels is a good thing. Panels transfer more heat to the water, the faster the water moves through the panels.

So if you are bypassing too much water around the panels, they will not work very well. With solar panels, if the flow drops too low, your efficiency will drop and you won't be heating the pool as quickly. There is usually a minimum flow spec depending on the types of panels. My spec is 10 GPM/sq-ft of panel which means that I should not drop the flow rate below 48 GPM.

So while a high PSI does mean you are increasing the time to turn over the pool, it may be a bad idea to try and reduce that too much. My PSI rise is about 7 PSI although I too have a bypass so I can lower it to 4 PSI but I have done the head calcs to make sure I do not drop the flow rates below optimum.

[tphaggerty]

Totally agree, MAS985! 8 to 10 psi seems to be a reasonable target for most (though I'm not sure if there is a difference between "permanent" and the more flexible "above ground" panels) solar installations. Maximum flow through the panels without exceeding there designed pressure limits is best.

What I was trying to make clear, but maybe didn't, is that you can use the diverter to hit that sweet spot - and then no more - even if your pump is capable of over driving your panels. If the pressure drops immediately when you start to open the diverter, your pump isn't "overdriving" the panels at all (sounds like this is happening in your case) and you can just leave the diverter completely closed.

Maybe a better way is to start with the diverter fully open and close it down until you see a 7 to 10 psi increase (or until the diverter is fully closed). Closing it any further at that point would lead to more pressure, but no real flow increase.