Can Someone check my math?

Great site by the way!!!
I live in Alaska and we have a 3hour solar window here at this location. I want to make sure I'm estimating my array output correctly.

I have 20 Kyocera 210 GX LPU's grid tied for a total array wattage of 4200watts.

4200X 3(hours in solar window)= 12,600watts or 12.6Kwh generated per day on average. 12.6X30 days in the month = 378Kwh per month on average?

Is this correct?




  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Can Someone check my math?

    Here is the PV Watts website that you can use for calculating your solar generation...

    However, it is not working right now for me. :confused: Maybe it will be up by Monday.

    As a rough estimate, you also need a derating factor... For the typical Grid Tied system, that derating factor is 0.77 times the factory/marketing number for the solar panel wattage.

    For an off-grid system using flooded cell batteries and a 120 VAC inverter, the derating factor goes down to ~0.52 ...

    The amount of solar radiation varies by season and local weather patterns. The PV Watts program has ~20 years of data for each location and can give you a good average result (by month, by year, or even hour by hour).

    I hate to give any numbers at the moment when the PV Watts program is down. There are other solar power calculators out there, but I do not know how accurate they are (and some only cover 1 state worth of data--such as those for California).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Can Someone check my math?

    You could use the Nasa SSE dataset to find out how many full sun hours you have in a given day for a given month:
  • PhotowhitPhotowhit Solar Expert Posts: 5,653 ✭✭✭✭✭
    Re: Can Someone check my math?

    Since BB linked to a gov web site, for your IP address, Anchorage Alaska;

    "Station Identification"
    "Lat (deg N):", 61.17
    "Long (deg W):", 150.02
    "Elev (m): ", 35
    "PV System Specifications"
    "DC Rating:"," 4.2 kW"
    "DC to AC Derate Factor:"," 0.770"
    "AC Rating:"," 3.2 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 61.2"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:","12.4 cents/kWh"

    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 0.83, 76, 9.42
    2, 2.16, 198, 24.55
    3, 3.77, 382, 47.37
    4, 4.35, 411, 50.96
    5, 4.88, 462, 57.29
    6, 4.74, 414, 51.34
    7, 4.50, 401, 49.72
    8, 3.77, 338, 41.91
    9, 3.28, 293, 36.33
    10, 1.88, 175, 21.70
    11, 1.39, 132, 16.37
    12, 0.61, 53, 6.57
    "Year", 3.02, 3335, 413.54
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former, 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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