Solar Panel Cooling

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christian09
christian09 Registered Users Posts: 22 ✭
in Solar Beginners Corner #1
Hi,
Last May, we (in Florida), had a big cool spell, where the daytime temps were in the 60's. :D Furthermore the wind was going at about 15-20mph vs. a norm of around 5. I noticed my maximum output from my panels went from 18-20 kwh to 30+ kwh per day.
I am sure it is the cooler temps of the panels.
I measured my panel undersides yesterday(88 F ambient) and the lower panels were 140 F and the panels at the roof peak at 148 F. Since Florida is about 90 F May-Oct, and in the 80's for the rest of the year, it only makes sense for me to cool down my panels somehow. I have been thinking about installing a couple solar powered fans and direct the flow them from the bottom of the array up to the peak of the roof, or putting the fans on top and "suck" out the hot air.

Does anyone have thoughts on this, or another idea...I cannot add any more solar panels.
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  • SkiDoo55
    SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    #2
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    Re: Solar Panel Cooling

    What is the spacing of your panels to the roof? A lot of trouble to go back and remount if essentially flush mounted. Recommended is 6 in or greater.

    On running fans to cool would have to determine what the net gain would be if any by consuming power for the fans vs; not running them? Would take a large volume of air to be effective.
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,461 admin
    #3
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    Re: Solar Panel Cooling

    In general, I don't think your 50% increase in power was due to just cooling of the array--You may have had less haze/humidity which will also increase output (sometimes diffusion from high clouds can help too).

    I cannot find a simple chart--But mounting the panels >6" above the roof is about the best you can do without active cooling (i.e., circulating water behind panels, etc.). I think a 0" mount is something like a 10-20% hit worst case...

    You can estimate the panel output based on cell temperature... For example say you can cool from 140F to 90F or ~50F or 28C... The power output loss of a typical panel is around -0.43% per degree C:

    -0.0043 * 28C Cooling = 0.12 = 12% increase in power output.
    20 kWH * 1.12 = 22.4 kWH output if panels are cooled by 28C

    To get an increase from 18 kWH to 30 kWH per day, the panels would have to cool by:

    30kWH * 1/18kWH = 1.67 increase
    0.67 / 0.0043 = 156 degree C "cooling" (or 280F cooling)

    So--There appears to be other reasons for the change in performance for your system.

    There are companies that have sold solar panels with water cooling jackets on the rear of the panels (for solar thermal hot water systems). They seemed to be more costly/complex of install than was really worth it. If you have no more room for panels on your roof and want solar hot water, it is a possible option.

    We have discussed cooling of solar panels before many times--Here is one thread:

    Possible hybrid PV/hot water panel product?

    Sun Drum is one company that has such a product...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • christian09
    christian09 Registered Users Posts: 22 ✭
    #4
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    Re: Solar Panel Cooling

    Thank you for the reply. The spacing is 4". I would love to make it 6 or greater, but looking at the mounting L brackets, as they are on their max level. I was trying to find the manufacturer of my racks, but not even the installer knows..aye! Here is a pic., maybe you know? The pic is an old pick, as I had the installer move it up to 4" from 3".
    Attachment not found.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #5
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    Re: Solar Panel Cooling

    Unirac L brackets are meant to sit on Stand-offs with different heights ( 3,4,5,6 inch ) with a cone shaped flashing. The base is bolted to the rafters. You can use different lengths front and rear to change the pitch angle. Screwing them down to the roof is the cheap, down and dirty way to do it, guaranteed to leak overtime.

    Roof Penetrations are made on every 2nd, 3rd or 4th rafter depending on the calculated load ( Snow & Wind ). A penetration costs about $50 each with labor, made on top and bottom per row.


    Attachment not found. Attachment not found.

    Attachment not found.

    .
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #6
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    Re: Solar Panel Cooling

    not a very good installer imo.
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  • peakbagger
    peakbagger Solar Expert Posts: 341 ✭✭✭
    #7
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    Re: Solar Panel Cooling

    One thing to check if you increase the spacing is wind load. I know that when I designed my racking for a high wind area that going more than 4" would result in the racking selection being inadequate. When I called the manufacturer it was obvious that tech support didn't write the program so they couldn't tall me why the calculation busted at 6" while they worked at 4".
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
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    Re: Solar Panel Cooling

    My panels are about 4" off the roof - at the bottom. More like 18" at the top.
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