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Please help me understand my production rate vs my system size.....???? Confused...

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  • #46
    ok I just reread and saw where you said you were kidding about that. Phew

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    • #47
      I'm hoping I could open this thread again as I found it very useful. I understand the original posting and the following replies but I'd like to propose a slightly different angle that I've been fighting for some time now. I have 20 Canadian panels 230w with an ABB inverter (installed Jan '19) that is rated at 3.6kw (stated by Tesla(solarcity). For every sunny day I've encountered the inverter shows production shoot up to 2971kw then flattens there. Occasionally it'll drop due to clouds and of course there's a ramp up in the morning and ramp down in the afternoon as the sun moves across the sky but for a few hours mid day it's plateau's.

      When I called Tesla, their support team was surprised to hear that. They indicated it should only produce at any one time a maximum of 3.6kw but felt the inverter had some head room (clearly I spoke with a level 1 person). My question is less what it's capable of producing in a day or in a month, I think I'm clearing seeing the inverter limiting what my panels can produce at any one point. I'm aware that they won't each procude 230 in reality on a roof but the graph really shows a flat ______ roof limit.

      I think they undersized my inverter but half say yes, most say it was purposeful to not over utilize the panels (what??!) I'm wondering what this community thinks and how you think I should approach Tesla. I may be only seeing a gap of 20watts per panel but no way of me knowing what's above that plateau. They won't even look at my graphs ...from THEIR dashboard...

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      • #48
        Originally posted by Homer View Post
        I'm hoping I could open this thread again as I found it very useful. I understand the original posting and the following replies but I'd like to propose a slightly different angle that I've been fighting for some time now. I have 20 Canadian panels 230w with an ABB inverter (installed Jan '19) that is rated at 3.6kw (stated by Tesla(solarcity). For every sunny day I've encountered the inverter shows production shoot up to 2971kw then flattens there. Occasionally it'll drop due to clouds and of course there's a ramp up in the morning and ramp down in the afternoon as the sun moves across the sky but for a few hours mid day it's plateau's.

        When I called Tesla, their support team was surprised to hear that. They indicated it should only produce at any one time a maximum of 3.6kw but felt the inverter had some head room (clearly I spoke with a level 1 person). My question is less what it's capable of producing in a day or in a month, I think I'm clearing seeing the inverter limiting what my panels can produce at any one point. I'm aware that they won't each procude 230 in reality on a roof but the graph really shows a flat ______ roof limit.

        I think they undersized my inverter but half say yes, most say it was purposeful to not over utilize the panels (what??!) I'm wondering what this community thinks and how you think I should approach Tesla. I may be only seeing a gap of 20watts per panel but no way of me knowing what's above that plateau. They won't even look at my graphs ...from THEIR dashboard...
        1.) Run PVWatts for your location and array orientation w/a 10 % system loose factor rather than the 14 % default value.
        2.) Then, get the hourly output option. Then find the max. hourly output. That will give you some ballpark # for likely max. hourly output.
        3.) If you have a production curve with a very flat top on (some) sunny days, that usually, but not always indicates a condition called "clipping". That is, the panels are putting out more power than the inverter can take in. If your output is flat @ 2,971 W ( not kW BTW) for a period of time > say, ~ .5 hour or more, chances are the inverter is clipping.

        For how long, under what conditions and about what time(s) of day and/or seasons of the year does the output flatten out ?

        4.) I'd guess, without knowing your location, array orientation or shading that a reasonably oriented (that is generally equator facing and at some tilt to the horizontal) 4.6 kW array that's mostly shade free ought to have a max. output maybe a bit less than 4 kW or so. Without being there, and only going by what you've written, I wouldn't be surprised if you have a 3 kW inverter that's clipping in sunny weather and at times when the solar incidence angle on the array is small (that is, the angle between the sun vector and the array normal).

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        • #49
          If your output under good sun goes up and then flattens to a straight line for any
          significant time, your inverter is clipping. You could prove this by checking string
          output voltage to the inverter. Voltage will be around 80% of open circuit rating,
          then begin to rise as the curve flattens, maybe to 85 or 90% of open circuit. Same
          thing in reverse later.

          I would expect 3KW is a pretty poor best peak for a 4.3KW system.

          My inverters clip at about 101% of inverter rating, you should see a similar thing.
          Bruce Roe

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          • #50
            I read this thread and I have a similar question.I'm in the process of getting a system and just had the sire survey last week.
            It's a 320watt 21 panel with optimizers 6.7kw system. They have me down for a Solaredge SE6000H-US sine wave inverter.
            The designer said it pulls 25 amps. I was not sure if that was large enough. When I had an inverter before with my electric powered food truck, I went with a larger inverter so it ran cooler and would last longer. I asked for the 7.6 inverter and they can do it but for a $300 charge. I would have thought they'd use that in the first place so it runs more efficiently than running at peak during the sunny times. I also have zero shade on my flat roof and in Arizona so there's plenty of sun. Doesn't the SE7600H-US make more sense.
            Also, I inquired about installing the meter/inverter in the garage and keeping the disconnect out by the panel and they said no problem, but for $500. I would just think that if it were in the garage, it wouldn't get as hot in the summertime and it would last longer and also not have to worry about vandalism. The panel is on the opposite side of the garage, so I wouldn't think I'd get quoted $500.
            Is that something I shouldn't even worry about ?

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            • #51
              Originally posted by Jasper7821 View Post
              I read this thread and I have a similar question.I'm in the process of getting a system and just had the sire survey last week.
              It's a 320watt 21 panel with optimizers 6.7kw system. They have me down for a Solaredge SE6000H-US sine wave inverter.
              The designer said it pulls 25 amps. I was not sure if that was large enough. When I had an inverter before with my electric powered food truck, I went with a larger inverter so it ran cooler and would last longer. I asked for the 7.6 inverter and they can do it but for a $300 charge. I would have thought they'd use that in the first place so it runs more efficiently than running at peak during the sunny times. I also have zero shade on my flat roof and in Arizona so there's plenty of sun. Doesn't the SE7600H-US make more sense.
              Also, I inquired about installing the meter/inverter in the garage and keeping the disconnect out by the panel and they said no problem, but for $500. I would just think that if it were in the garage, it wouldn't get as hot in the summertime and it would last longer and also not have to worry about vandalism. The panel is on the opposite side of the garage, so I wouldn't think I'd get quoted $500.
              Is that something I shouldn't even worry about ?
              As a first approx., an inverter ought to put out close to or slightly more than the max. likely instantaneous output of the array it's attached to. After that, if it'll cost $300 more for an inverter that eliminates 20-30 kWh/yr. of clipping, it might make more economic sense to use the smaller and $300 less expensive inverter.

              The key is to have some idea of how much the average annual system output will perhaps be over many years and how much of that will be lost to clipping with any inverter. If it's going to cost $300 more to knock $5.00/yr. off your bill, the larger inverter might not be as cost effective and tolerating a bit of clipping might be the more cost effective choice.

              Run PVWatts w/correct array orientation and location and model the system w/10 % system losses. Get the hourly output option and sort by max. hourly output. Then size up an inverter and see how much loss of output, or output reduction results for each inverter.
              Last edited by J.P.M.; 04-15-2019, 09:21 AM.

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              • #52
                I do not know how bad your angle/shade situation is, but 30KWH a year is so far down
                in the dirt it might as well be zero. On the face of it, the number is ridiculous. Bruce Roe

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                • #53
                  East-West or SE-SW situation ?

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