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Problem with PVWatts calculation for Big Island

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  • Problem with PVWatts calculation for Big Island

    I put solar on my home on the north west side of the Big Island. I calculated my estimated production using PVWatts and it was amazing close to my actual production for my first 6 months of monitored output. However, I recall that there were different weather data sets (TMY2, TMY3, etc.) on the PVWatts map that I could choose at that time.

    I am building a new home about 13 miles away. Now when I use PVWatts, there are no other data sets for the Big Island. My only choice is the default NREL NSRDB grid cell for my location (Lat, Lon: 20.05, -155.86). To test the accuracy of this dataset, I moved the red pin to Hilo. When I repeated the calculations, the estimated output for my home's location was very similar if not identical to Hilo's location, 63 miles away. However, the weather is dramatically different in Hilo than at my home's location of the sunny, dry NW coast of the Big Island! Hilo has many more clouds and much more rain than we do! Has PVWatts changed so that now I don't have good estimated irradiance and weather data for my location? Getting the same results as a location in Hilo is next to worthless.

  • #2
    At the opening page, typing in Hilo goes to :
    NSRDB Weather Data
    Location: Lat, Lon: 19.73, -155.1
    Lat/Lng: 19.730, -155.100
    Elevation: 130 m

    Sometimes dragging map pins around does not work well
    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A



    • #3
      There is an option in PVWatts to use legacy data sites. I am on my phone and couldn't explore that option to see if one of those is closer to your longitude.
      Last edited by Ampster; 06-20-2019, 02:55 PM.
      9 kW solar. Driving EVs since 2012


      • #4
        Mike90250 was correct. Dragging the red pin to new location did not change the location being evaluated. Furthermore, I didn't get the blue box around my red point in Chrome but did see it with MS Edge.
        Now I have trust again in the numbers being generated for different azimuths!


        • #5
          From what I understand about HECO rates solar makes economic sense just about anywhere on the Islands. My brother just installed solar plus a Tesla Powerwall on his place in Lahaina.
          9 kW solar. Driving EVs since 2012