difference in energy and roof pitch

I am purchasing a house with a perfect south facing roof. No trees. It has a 6/12 pitch. I am in central Florida. What percentage of energy gain would I get if I built a 3/12 pitch ground base system instead of putting them on the roof?

Comments

  • AguarancherAguarancher Solar Expert Posts: 282 ✭✭✭
    You can try this


  • blueblue Registered Users Posts: 35 ✭✭
    Thanks, I'm puzzled though. It seems a 7/12 pitch is best for central florida. Seems like 3/12 would be best. 
  • EstragonEstragon Registered Users Posts: 3,335 ✭✭✭✭✭
    Ground based may run a bit cooler (more airflow vs roof), giving a bit more potential (assuming mppt type controller).  You could also use adjustable tilt racking for seasonal tilt change, which can add to production vs a comprimise year-round tilt, or even a tracker which follows the east-west path of the sun daily.

    Ground based is generally easier to install, clean, and maintain, but may also be easier to steal if that's a concern.

    3/12 sounds about right to me for fixed tilt in central Florida.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.BB. Super Moderators, Administrators Posts: 28,617 admin
    edited October 2018 #5
    Just to be clear we are talking about the same thing (showing our work):

    3/12 = 0.25
    arcTan 0.25 = 14 degrees
    7/12 = 0.5833333
    arcTan 0.583333 = 30 degrees

    Using a simple solar calculator. Fixed array
    The calculator shows 28 degrees from horizontal (62 degrees from horizontal) is optimum for year round harvest:

    Orlando
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 62° angle from vertical:
    (For best year-round performance)

    JanFebMarAprMayJun
    4.29
     
    4.76
     
    5.36
     
    5.79
     
    5.75
     
    4.99
     
    JulAugSepOctNovDec
    4.96
     
    4.87
     
    4.74
     
    4.89
     
    4.55
     
    4.16
     

    And for summer, 13 degrees from horizontal (77 degrees from vertical):

    Orlando
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 77° angle from vertical:
    (Optimal summer settings)

    JanFebMarAprMayJun
    3.80
     
    4.40
     
    5.21
     
    5.91
     
    6.14
     
    5.39
     
    JulAugSepOctNovDec
    5.32
     
    5.07
     
    4.72
     
    4.60
     
    4.06
     
    3.63
     
    So, if you want optimum power year round, then 28 degrees is not bad... If you want more power during summer (air conditioning), you do get a bit more energy at this time.

    The data is based on actual measured harvest... And if you have summer thunderstorms or a morning/evening marine layer, that will affect the optimum angles for harvest.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • blueblue Registered Users Posts: 35 ✭✭
    Thanks, the link above was great help too. It shows a few degrees off doesn't make much difference. I'm a 50 miles north of Orlando so 30 degrees might be optimum. I was surprised. Glad I don't need to build a ground based system, much better on the roof. Lots cheaper and nice big backyard with lots of flowers and bushes to help absorb co2. Gotta help our poor planet. Thanks
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