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Thread: Measuring flow to solar panels

  1. Back To Top    #1

    Join Date
    Jun 2009
    Vero Beach, FL

    Measuring flow to solar panels

    I'm going to add some solar panels as soon as my pool is completed. I'm even having the builder put in the 3 way manual valve but can have the handle replaced and adapted to an actuator. I figure I'll try to operate it manually this first winter and see what happens and what kind of pain it is.

    Anyway, I know the panels have a recommended flow for optimal efficiency. Using the 3 way valve, I can divert a portion of the flow to the panels. But how do you know what is optimal? How can I measure flow just through the panel without an expensive flow meter? And if I hook up a solar controller to move the actuator, can those be adjusted so they are partially open and mix the flow, or are they limited to 90 degree rotations of the valve only?

    25' x 13' Roman, 12000 gal IGP, Plaster, with 500 gal Spa
    SWG, 1 HP Max Flo Pump, C-900 cartridge filter
    Solar heat

  2. Back To Top    #2
    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Measuring flow to solar panels

    The usual rule of thumb is that you want to set the valve so that your filter pressure goes up by 1 psi. In most cases that will give you about the right flow rate to the panels.

    The valve actuator can be adjusted to stop in the correct position to get what ever mix you want. Some of them are a little more difficult to setup than others, but all of them are adjustable that way.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  3. Back To Top    #3

    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Measuring flow to solar panels

    Every solar system is different, but mine on the roof with 12 panels (I think it was at 4.5 GPM each so 54 GPM total) and very long runs of 2" pipe used to raise the PSI on the filter using my single-speed pump by around 12 PSI from 15 to 27. Admittedly unusual, but a 1 PSI rise may not be enough unless you are talking about a single large panel (say, for an above-ground pool) with a short pipe run. You can roughly estimate the flow rate in your system if you know your pump curve, PSI at the filter, and factor in suction head of say 20% of the PSI at the filter. However, this won't work for a partially diverted flow which is what you are talking about.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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