Solar Elevation Data for Rev. Tilt rows on a pitched roof

mtautoken
mtautoken Registered Users Posts: 7 ✭
in Advanced Solar Electric Technical Forum #1
I am trying to get two reverse tilt rows of landscape mounted modules on a 30 degree roof in Southern CA. The city will not allow more than a two foot rise off the roof plane for modules. Which would give me an 8.2 degree southern tilt. I have found a website http://www.esrl.noaa.gov/gmd/grad/solcalc/azel.html that will give me Solar Elevation data for any location on any given day and time.

My problem is figuring out an average to use. I know there is a rule of thumb that 2.5 times the height of the rows should be the setback for a flat mounted array in my area. But I have not been able to find any info that relates to reverse tilt roof mount setback.

I did this once before by using a solmetric suneye and having someone stand up an obstacle to simulate a row of panels and fudged the shade in manually. I just moved the second row far enough away to get a comfortable percentage of solar irradiance. But in this case I am consulting for a friends home that is 5 hours away from me.

Thank you in advance for anyone that can send me the right direction.

Ken
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Comments

  • pechan
    pechan Solar Expert Posts: 92 ✭✭
    #2
    Re: Solar Elevation Data for Rev. Tilt rows on a pitched roof

    Add a couple of extra panels to make up for lost production and call it good.
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #3
    Re: Solar Elevation Data for Rev. Tilt rows on a pitched roof

    mta..,

    It is not clear just what "average" that you are needing, BUT,

    Have you tried playing around with the NREL PV Watts Calculator(?):
    http://pvwatts.nrel.gov/pvwatts.php

    FWIW, Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    #4
    Re: Solar Elevation Data for Rev. Tilt rows on a pitched roof

    The sun angle in December for your latitude is less than 30deg above the horizon, so the second set of panels will be totally shaded during the winter on your reverse sloped 30deg roof. Another words, your set back is infinite and you really can't do more than one row of panels on that part of the roof. Plus it looks horrible and gives solar a black eye to have panels sticking up like that. Even here, with the typical 4/12 pitch roofs (18 deg), we don't do multiple back rows.
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