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First Month Results - Easily Beat PVWatts Estimates

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  • First Month Results - Easily Beat PVWatts Estimates

    Hi all. I'm pretty happy with my first month results. I used a 10.5% loss factor in PVWatts to compute my estimated output for my 5.88 kW system. For November I was estimated to create 458 kWh. With a loss factor of zero it estimated 513 kWh. I actually produced 602 kWh, beating the the estimated by 131% and maximum by 117%. Hopefully this will keep up!


    ScreenHunter_428 Dec. 01 09.08.jpg

  • #2
    That will help cover months that fall short.
    But, congratulations, and remember PV watts is a average guide, not a strict rule
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister

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    • #3
      Steve, are those numbers coming from a revenue grade meter device? Lots of inverters software overstate their production.......some have greater variance than others......just saying.....

      Reconcile with your Utility bill to get a feel. If still not satisfied, then an second independent measurement might be necessary.

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      • #4
        Good question Dan. I'll compare these numbers which are generated by SolarEdge with my utility provided PV revenue grade meter. Should be interesting to see the difference. Or sad if it is really far off. And I just fired up my electrically heated spa so I'm going to need that extra juice. I'll report back later today.

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        • #5
          PVWatts is a modeling program, not a short term performance predictor. Actual months will be different, sometimes by a lot. Read the help/info screens for a good explanation why it's not a good idea to think every month will be the same as, or even close to the model.

          For the last 4 Novembers my output has been, 553, 631, 662 and 628 kWh, using what I believe to be reasonably accurate usage and system generation numbers. Those #'s pretty much match what to expect from the irradiance and temperature data recorded by the pyranometer/weather station located about 4 ft. north of the array.

          PVWatts with 10 % system losses models 579 kWh for November.

          While it may seem good to be that much in excess of PVWatts, and while possible, I wonder if something is amiss in your reporting system or the inputs to PVWatts. Kind of like buying a Toyota Camry and getting 60 MPG.

          A little more output than PVWatts models is probably to be expected, particularly with a new array. But with a 31 % overage - I'd check my #'s and see what Dec. brings.

          What's your zip and orientation ?

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          • #6
            Hello. I looked this morning at my revenue grade meter and my lifetime production is 695 kWh. SolarEdge indicates 714 kWh. So about a 3% difference. Pretty close. So subtracting that difference I'm still doing better, 128% over the expected 10.5% loss and 114% better than zero loss.

            My zip is 95670 and orientation is pretty much due south. 5.88, standard panels, roof mount, 20 degree tilt.

            I'm just happy that it is up and running and performing better than expected. I'm still going to lose money during these winter months though. SMUD's winter costs are .1068 per kWh, so I need to produce 750 kWh to break-even on my solar payment. Hopefully I'll get lucky and in the summer months production will continue to perform better and help me make up for the winter.

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            • #7
              Originally posted by steveholtam View Post
              Hello. I looked this morning at my revenue grade meter and my lifetime production is 695 kWh. SolarEdge indicates 714 kWh. So about a 3% difference. Pretty close. So subtracting that difference I'm still doing better, 128% over the expected 10.5% loss and 114% better than zero loss.

              My zip is 95670 and orientation is pretty much due south. 5.88, standard panels, roof mount, 20 degree tilt.

              I'm just happy that it is up and running and performing better than expected. I'm still going to lose money during these winter months though. SMUD's winter costs are .1068 per kWh, so I need to produce 750 kWh to break-even on my solar payment. Hopefully I'll get lucky and in the summer months production will continue to perform better and help me make up for the winter.
              For most applications summer production exceeds winter production. That's the type of information where PVWatts is useful. Whatever your annual production turns out to be, looks like ~ 2/3 of it will be April 1- Sept.30, Summer's are generally pretty sunny in Sacramento.

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              • #8
                Here in Indiana when solar production far exceeds PVWatts projections for a few months it means DROUGHT!

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                • #9
                  Yeah, I can see how a drought would help production. I guess we just need for it to rain at night. These last two days have been cold with perfectly blue skies, perfect solar weather.

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