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Slar panel mounting

  • 1.  Slar panel mounting

    Posted 09-02-2024 10:14 AM
      |   view attached

    I recently had 39 405 watt q-cell panels installed on my roof with IQ8 inverters.  There are 10 panels on the south facing slope of my roof and 29 facing north.  The panels facing south have consistently produced twice as much as those on the north slope - primarily I suppose due to the angle sloping away from the sun.  I was wondering if there is an easy or recommended way to angle the north facing panels toward the sun without having to spend $50-$100 plus per panel.   It seems most adjustable solutions Ive found online are geared towards RV type setups.   The company that installed the panels did a great job all around but actively expressed no interest when I asked them about this.   Perhaps it would be cheaper to just add more panels, but the difference in production of power between the north and south facing panels does seem quite high to me, as a south facing panel may produce 1.92 kWh in a day while a north facing one only produces 855wh.   That is a comparison from yesterday via my Emphase app.



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    MICHAEL MILLER
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  • 2.  RE: Slar panel mounting

    ASES Life Member
    Posted 09-03-2024 11:30 AM
       A more detailed description of your system will be needed to correct the poor situation, which a good installer would have anticipated.  If you are in the northern hemisphere you can expect close to zero production from the north facing photovoltaic modules from September 21 until March 21 each year.  Most likely it cost more than $100 per module to have better production, while meeting wind load requirements.  
       It will help to know how the production with the existing configuration compares to your load.





  • 3.  RE: Slar panel mounting

    Posted 09-03-2024 11:31 AM
    I can't believe that you put the modules on the northside, but I remember back when I wouldn't install them on the East or West side roofs.  The economics made the 80% output become cost effective after many material price drops.  The economics for mounting north-facing arrays isn't great, as in your example with a 50% decrease in generation compared to your better performing orientation.
    Adding large sails (sloped rail system) to you nothfacing roof will create all kinds of neissues.  Rain & snow drainage issues as well as the huge wind load increases, not to mention the general butt-ugliness of this poor performing design concept, along with all of the additional material and labor expenses.  Your installer should have modeled your generation potential before selling you this design. But if you get 50% less generation, as is, on the wrong sloped roof, you just might find the do nothing option is the most prudent option.





  • 4.  RE: Slar panel mounting

    ASES Life Member
    Posted 09-03-2024 01:41 PM

    This array faces south but is supported by Unirac high-profile tilt legs on the north side of my hip roof.  I use them to seasonally adjust tilt angle.  I don't think they are really the right solution for you but it may give you some ideas.



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    Mike Curran
    Retired EE
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  • 5.  RE: Slar panel mounting

    Posted 09-04-2024 07:50 AM

    thanks for the screenshot - very helpful.



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    MICHAEL MILLER
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  • 6.  RE: Slar panel mounting

    Posted 09-04-2024 09:21 AM
    Edited by Ken Nadsady 09-04-2024 09:21 AM

    @Mike Curran:

    Just curious, what is the ASCE wind speed in your location, and was the racking with those tilt legs at that high angle assessed structurally to withstand it?



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    Ken Nadsady
    AviSun Renewable Energy
    Hudson OH
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  • 7.  RE: Slar panel mounting

    ASES Life Member
    Posted 09-05-2024 07:08 PM
      |   view attached

    Don't  know, and no structural assessment done.  House is pretty well surrounded by trees, and that array has been up since 2007.  Last August (2023) we had a large live cherry tree fall on our barn during a windstorm.  That occurred with the house array panels/struts in their summer position, fairly flat (~25° IIRC).



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    Mike Curran
    Retired EE
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  • 8.  RE: Slar panel mounting

    Silver
    Contributor
    Posted 09-06-2024 12:10 PM
    Edited by william fitch 09-09-2024 01:51 PM

    I am sure they will be standing for another 20 years. When you have allot of trees like that, it really cuts down the wind.... Ground arrays out in the open is a different story regarding wind......



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    william fitch
    Owner
    www.WeAreSolar.com
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  • 9.  RE: Slar panel mounting

    Silver
    Contributor
    Posted 09-03-2024 01:44 PM

    Without knowing were you are (Unless I missed it), a comment would be futile for the most part.

    North side panel installation was not even a "thing", until they got so cheap it began to make sense, depending on the exact circumstances of the site. Low roof angles are pretty much required and generally you should be happy you get much of anything at all, given a true north install.

    Latitudes under 20deg can fair not too badly. North of that gets progressively worse. North of 40, Winter will be in the toilet.

    I would be happy and leave it alone, with a quality install. If its not broken, don't fix it.



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    william fitch
    Owner
    www.WeAreSolar.com
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  • 10.  RE: Slar panel mounting

    ASES Life Member
    Posted 09-03-2024 02:32 PM

    Hello Michael

    I also was shocked when about 8 years ago I saw the first residential system in my neigborhood with both south and north facing modules. (I Live in Delaware). Then I thought about it. (I teach a class on solar technology applications). The cost breakdown for a residential system nowadays has the price of modules at less than 30% of the total installed price. So adding modules on the north makes sense since they incrementally add a small amount to  the rest of the fixed costs.  Adding 10% more cost but getting 60% more energy (see below) makes sense! As others have said, this new strategy was only possible due to the dramatic decrease in module pricing. And remember that rear facing modules see all the same diffuse hazy light that front modules see whcih is about 20-30% of the total over a year.

    To verify this, I went to the NREL PVWatts calculator https://pvwatts.nrel.gov/pvwatts.php. I assumed a 1 kW ssytem facing S (180 deg azimuth) or N (0 deg azimuth). I assumed a slope of 30 degrees and calculated the output for a N and S facing systems in Dallas or Chicago. Results are:

    Dallas: N- 1516 kWh, S-905 kWh or 40% less energy for the N facing array.

    Chicago: N-1329 kWh, S-729 kWh or 45% less energy for N facing. This is expected since the farther N you are the less light on the rear. 

    If your slope is less than 30 degrees it gets much better especially the farther N you are. So that is why it is cost effective to put modules on the N.

     I will say I am a little surprised that you ahve THREE times as many modules facing N than S. That is very unusual in my experience and in my opinion not a good deal for you given that 66% of your modules are getting much less energy than the remaining 33%. Which skews the payback against you. 

    Steve 



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    Steven Hegedus
    Professor and Senior Scientist
    University of Delaware
    Newark Delaware
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  • 11.  RE: Slar panel mounting

    Posted 09-04-2024 01:03 PM
    I too taught a solar in solar design, 45 years ago, was the state energy engineer and designed my near net zero home and office.  When you add PVs to the north-facing side of the building, in the northern hemisphere, it's much cooler doing the installation than when you mount them on a proper side.  But you still need to add the racking system, inverters and wiring.  Where the vast majority of the PVs are mounted on the North-facing roof surface, so this project should have been like one of almost 50% of existing roofs that must be walked away from.  This project screams that the install was quite clueless and damaging to the industry.





  • 12.  RE: Slar panel mounting

    Posted 09-04-2024 07:59 AM

    Thanks everyone for your replies and comments!  They were all quite helpful.  With this old farm house, the majority of the panels being on the north side of the house ended up being inevitable, hence the 39 panels for a 14KW system.  I like the "If it ain't broke, don't fix it" quote - as that seems applicable in my situation here in central KY.  My original goal was to ensure as close to 100% electrical cost being covered by the panels, and that has been the case so far.  I had the panels installed in July, and so far they are producing twice the power we use, so I can't complain too much.  I think I'll forego modifications to the angle of the panels on the north side, since they are sitting on the roof of a 150 year old house that was definitely not designed with solar in mind.  If over time I find more production is needed, I always have the option to put panels on the adjacent garage once I have a new roof put on it.  I did end up with the majority of my panels on the north facing roof, due to the area of roof I had available to work with, so with all things considered, I suppose it was cheaper to add more panels there for incremental increases in production over none at all.  Again,  thanks everyone.



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    MICHAEL MILLER
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  • 13.  RE: Slar panel mounting

    Posted 09-04-2024 09:21 AM
    Edited by Ken Nadsady 09-04-2024 09:22 AM

    @Michael Miller

    I think that is a sound decision.



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    Ken Nadsady
    AviSun Renewable Energy
    Hudson OH
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