2 panel solar bank - same side feed/return or opposite

hwy17

Well-known member
Mar 17, 2021
176
Northern California
So I'm adding a DIY solar setup to my AGP this year:

2x 4x20' Fafco Solar Bear in a parallel bank on a 10ft 4/12 rooftop close to the pool, 1.5" plumbing.

The only remaining design choice I'm hung up on is whether to locate the panel bank inlet on the same side or opposite side of the bank as the return.

I understand perfectly well in theory why opposite side is usually recommended to balance pressure across the array, but I question how much of a difference it really makes. And I'm trying to weigh the benefit against the detriment of having an 8' longer feed line with 2 extra 90's to locate the inlet on the far side of the bank.

What do you guys think?
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
14,826
Pleasanton, CA
Pool Size
20000
Surface
Plaster
Chlorine
Salt Water Generator
It won't matter very much. With only two panels, the head loss from the header is insignificant. What matters more is that they are in parallel rather than series.
 
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hwy17

Well-known member
Mar 17, 2021
176
Northern California
Thank you. I hadn't thought of it in terms of head loss across the header but it makes logical sense that way and lines up with my intuitive assumptions.

Brings me back to another design choice I thought I'd settled on: 1.5" plumbing since my equipment and the panels have 1.5" threaded fittings. Didn't seem significant since the rooftop is feet away from the equipment and this started out as a just a slap together project but when I add up the runs it quickly reaches a total of ~50ft of pipe.
 

hwy17

Well-known member
Mar 17, 2021
176
Northern California
Thank you for the consideration.

It's going to be manual bypass though and my plan is to leave it running through the solar except when vacuuming. So I'm hoping for a higher flow rate than that for filtration.

Conceivably I could adjust the diverter valve to allow partial bypass, providing adequate flow to the solar as well as a greater amount of total throughtput for filtration, but I'm not sure about that idea. I can't quite wrap my head around whether it will provide adequate pressure to prevent VRV trouble.

This will be powered by my main 1HP single speed Hayward Powerflo Matrix pump. I'm aware that it's not a high head pump and it's possible that it will disagree with the application. If that turns out to be true my plan is to consider replacing it with something like a 3/4HP high pressure Pentair Challenger.

I've just redrawn the system with 2" and the additional reducer bushings, couplers, and pipe cost all amounts to under $40.
 
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mas985

TFP Expert
LifeTime Supporter
May 3, 2007
14,826
Pleasanton, CA
Pool Size
20000
Surface
Plaster
Chlorine
Salt Water Generator
Conceivably I could adjust the diverter valve to allow partial bypass, providing adequate flow to the solar as well as a greater amount of total throughtput for filtration, but I'm not sure about that idea. I can't quite wrap my head around whether it will provide adequate pressure to prevent VRV trouble.
That is what I was suggesting as it is a normal procedure for solar. You should be able to adjust the solar flow rate such the VRV stays closed but still not at 100% solar flow. 10' high panels requires only about 5 PSI at the filter to keep the VRV closed.

This will be powered by my main 1HP single speed Hayward Powerflo Matrix pump. I'm aware that it's not a high head pump and it's possible that it will disagree with the application. If that turns out to be true my plan is to consider replacing it with something like a 3/4HP high pressure Pentair Challenger.
The Matrix should work just fine. Solar doesn't require a high head pump. I ran solar on a two story house for many years with just a 1/2 HP med head pump. It also worked fine with my current pump which is a med head VS pump. You can also cheat a little by placing the VRV closer to the pump so it closes with lower flow rates.
 

Teald024

TFP Guide
Ah, ok then, thank you for all that. I didn't know partial bypass was a common operating mode.
Yes, partial (or most) bypass is common. You want to adjust the flow through the panels to get a degree or two rise across them. This is the most efficient mode. Then the remaining flow bypasses and goes to the return directly.

This was my install. Not perfect, but it worked for my setup.
 

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