Roof rack angle?

Arkansasoffgrid
Arkansasoffgrid Solar Expert Posts: 117 ✭✭
With a fixed position roof mounted array, what is the optimal angle with a latitude of 34.3779, longitude -93.2405 ? This is a south facing roof, with absolutely no shading.
8-420AH US Battery L-16s, Midnite Classic 150cc, Whiz Bang Jr, Magnum MS4448PAE inverter/charger,  4590w Canadian Solar panels. Honda EU2000i generator.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Roof rack angle?

    What is your load profile?

    If you use AC during the summer and not too much power during winter, then flattening the array to ~(34 degrees - 15 degress=) ~20 degrees from horizontal.

    In theory, ~34 degrees from horizontal will collect the most energy over a 1-year period.

    Use PV Watts and "play" with the numbers to see what is best for your location/needs (PV Watts takes "average" weather into account). You can also play with facing array South East vs South vs South West--Morning fog vs afternoon thunderstorms, Cooler mornings (Vmp is higher, more power) vs afternoon A/C (use afternoon power to run AC instead of batteries)... Using 0.52 system eff for off grid vs 0.77 default:
    "Station Identification"
    "City:","Little_Rock"
    "State:","Arkansas"
    "Lat (deg N):", 34.73
    "Long (deg W):", 92.23
    "Elev (m): ", 81
    "PV System Specifications"
    "DC Rating:"," 4.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 2.1 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 34.8"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 7.4 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 3.78, 237, 17.54
    2, 4.38, 244, 18.06
    3, 5.19, 312, 23.09
    4, 5.67, 318, 23.53
    5, 5.89, 331, 24.49
    6, 5.81, 309, 22.87
    7, 5.93, 320, 23.68
    8, 6.08, 332, 24.57
    9, 5.41, 291, 21.53
    10, 5.16, 299, 22.13
    11, 3.69, 213, 15.76
    12, 3.56, 218, 16.13
    "Year", 5.05, 3422, 253.23
    "Station Identification"
    "City:","Little_Rock"
    "State:","Arkansas"
    "Lat (deg N):", 34.73
    "Long (deg W):", 92.23
    "Elev (m): ", 81
    "PV System Specifications"
    "DC Rating:"," 4.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 2.1 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 20.0"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 7.4 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 3.33, 207, 15.32
    2, 4.04, 224, 16.58
    3, 5.04, 303, 22.42
    4, 5.80, 326, 24.12
    5, 6.26, 355, 26.27
    6, 6.31, 338, 25.01
    7, 6.36, 346, 25.60
    8, 6.29, 344, 25.46
    9, 5.34, 287, 21.24
    10, 4.81, 278, 20.57
    11, 3.32, 189, 13.99
    12, 3.10, 186, 13.76
    "Year", 5.01, 3383, 250.34
    "Station Identification"
    "City:","Little_Rock"
    "State:","Arkansas"
    "Lat (deg N):", 34.73
    "Long (deg W):", 92.23
    "Elev (m): ", 81
    "PV System Specifications"
    "DC Rating:"," 4.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 2.1 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 50.0"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 7.4 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 4.02, 253, 18.72
    2, 4.48, 250, 18.50
    3, 5.06, 303, 22.42
    4, 5.23, 292, 21.61
    5, 5.20, 291, 21.53
    6, 5.01, 263, 19.46
    7, 5.18, 275, 20.35
    8, 5.54, 300, 22.20
    9, 5.19, 278, 20.57
    10, 5.23, 303, 22.42
    11, 3.87, 224, 16.58
    12, 3.82, 236, 17.46
    "Year", 4.82, 3268, 241.83

    Don't get too wrapped up in the calculations--Real life will interfere and limit your accuracy to around 10% (year to year average variations). If you think you will need more power (don't plan on using 100% of predicted power daily, perhaps ~66% to 75% daily power, plus optional wash day/more A/C when plenty of sun, cut back in bad weather, run genset).

    You can generate lots of data doing this. But it will give you a good feeling about how much you can affect your harvest with changes to your array installation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Roof rack angle?

    A good explanation of what's involved: http://www.solarpaneltilt.com/
  • Arkansasoffgrid
    Arkansasoffgrid Solar Expert Posts: 117 ✭✭
    Re: Roof rack angle?

    Using the above link, at location of Hot Springs Arkansas my summer panel angle should be 10.62°, and winter angle should be 49°. Does that sound about right?
    8-420AH US Battery L-16s, Midnite Classic 150cc, Whiz Bang Jr, Magnum MS4448PAE inverter/charger,  4590w Canadian Solar panels. Honda EU2000i generator.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Roof rack angle?

    One question, which time of the year will you need the most power, Summer , Winter or Fall/Spring? that determines your optimal angle... in my case it is winter, Summer I have no worries of meeting needs...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Arkansasoffgrid
    Arkansasoffgrid Solar Expert Posts: 117 ✭✭
    Re: Roof rack angle?

    Definitely summer, trying to keep house cool. Winter we'll have wood heater.
    8-420AH US Battery L-16s, Midnite Classic 150cc, Whiz Bang Jr, Magnum MS4448PAE inverter/charger,  4590w Canadian Solar panels. Honda EU2000i generator.
  • dalekir
    dalekir Registered Users Posts: 1
    Re: Roof rack angle?

    Arkansasoffgrid says your a not so new guy. can I ask you a question?
  • Arkansasoffgrid
    Arkansasoffgrid Solar Expert Posts: 117 ✭✭
    Re: Roof rack angle?

    Sure, but that status must have gotten changed due to the amount of questions I've asked, not the amount of experience I have.
    8-420AH US Battery L-16s, Midnite Classic 150cc, Whiz Bang Jr, Magnum MS4448PAE inverter/charger,  4590w Canadian Solar panels. Honda EU2000i generator.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Roof rack angle?
    Sure, but that status must have gotten changed due to the amount of questions I've asked, not the amount of experience I have.

    Yes, that's how it works; more posts automatically move you up the ladder. :roll:
  • verdigo
    verdigo Solar Expert Posts: 428 ✭✭
    Re: Roof rack angle?

    I would set mine to noob if I could until I don't have to ask as many questions. I may not live that long though.