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

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  • #16
    Originally posted by sharpd1 View Post
    Thanks guys. I understand that i would only get 80-90% efficiency...that's why i used the word 'ideal'. i never said i expected it....I was trying to understand it at the 'ideal level'.
    With that said, I'm not sure i've gotten a yes or no to this yet....so let me phrase the question again:

    under IDEAL (lab/never attainable/whatever we want to call it) conditions, is this correct?

    305Wh is the maximum amount of energy that can be produced by one panel in an hour under ideal conditions. 33 x 305Wh equals ~10,000 Wh (ie. 10kW) of energy that can be produced under ideal conditions in an hour.


    Also, i'm still trying to understand why the max that i'm showing as producing is 8kW....Why doesn't it show as generating above 8.0kW on the App? is it capped by the inverter? is that normal? Anything I should/can do to make that more?


    ps. i generated 55.7 kwhs yesterday super happy and excited!
    305 W/panel is the output under S.T.C. conditions.

    There are no "ideal" conditions.

    Some operating conditions produce more array output than others.

    Suit yourself, but you may have an easier time understanding what everyone is telling you if you disabuse yourself of that idea and that term "ideal" with respect to PV.

    Under most real operating conditions a 305 W panel will produce less than 305 W. Provided your reporting system is operating nominally as it should, real operating conditions are most likely the reason for the 8.0 kW output you write of.

    FWIW, that 8.0 kW for max. power produced and the 55.7 kWh for a daily energy output sounds about right under sunny skies. Reread my post and others for explanations.

    Bottom line: At most times and under most operating conditions your array's actual power output will be less than 100% of your array's S.T.C. power output.

    On some other (and probably few) occasions or conditions, the 305 W/panel S.T.C. power output may be exceeded. At such times and under such conditions your array's actual power output will be greater than 100 % of your array's S.T.C. power output.

    As for increasing output, either power or energy: Besides keeping the array reasonably clean and free of shadows to the greatest extent practical, after design, construction and commissioning, there isn't a whole lot to be done to increase array output. It pretty much is what it is and pretty much at the mercy of the weather and the elements.

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    • #17
      Let me rephrase my question....perhaps it'll help me understand better.

      Given the information i've provided (33 305W pannels and let's say facing directly south, what is the MAXIMUM energy i should be able to produce in 1 HOUR on a sunny day with zero shade?

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      • #18
        Originally posted by sharpd1 View Post
        Let me rephrase my question....perhaps it'll help me understand better.

        Given the information i've provided (33 305W pannels and let's say facing directly south, what is the MAXIMUM energy i should be able to produce in 1 HOUR on a sunny day with zero shade?

        not really something to look at there. Solar is generally done on averages over longer times like day/week/month/ and year.
        An hour and peak generation is a really odd one to look at and most of the systems do not work on that.
        Now I think what you are getting at is what is the peak kW it can generate at any time but I would suggest that you ignore that as well and look at daily / weekly/ monthly averages.
        Your conditions are unlikely to EVERY be constant for an hour ( of course the Earth rotation is the biggest non-constant for your figure but weather and temperature are also).


        If you are concerned that your inverter is undersized and clipping then check the model of the inverter before going forward.

        You can run the system through PVwatts.nrel and see that such a system could theoretically get to almost 9kWh
        But as noted your system is NOT south facing, and is NOT without shadows. Further you are not even sure what inverter you have (though I suspect it is the SE10000h)
        OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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        • #19
          Originally posted by ButchDeal View Post


          not really something to look at there. Solar is generally done on averages over longer times like day/week/month/ and year.
          An hour and peak generation is a really odd one to look at and most of the systems do not work on that.
          Now I think what you are getting at is what is the peak kW it can generate at any time but I would suggest that you ignore that as well and look at daily / weekly/ monthly averages.
          Your conditions are unlikely to EVERY be constant for an hour ( of course the Earth rotation is the biggest non-constant for your figure but weather and temperature are also).


          If you are concerned that your inverter is undersized and clipping then check the model of the inverter before going forward.

          You can run the system through PVwatts.nrel and see that such a system could theoretically get to almost 9kWh
          But as noted your system is NOT south facing, and is NOT without shadows. Further you are not even sure what inverter you have (though I suspect it is the SE10000h)
          Inverter Model Attached.
          Attached Files

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          • #20
            Originally posted by sharpd1 View Post

            Inverter Model Attached.
            oh wow, you have an older model SE7600A (not the HDWave version). This makes your readings of 8kW very suspect. It can spit out slightly more than 7.6kw but only for a few seconds and only if the AC voltage is higher. You are not going to get 8kWh in any given hour from it. That said I doubt you are doing all that much clipping here due to the roof layout and shadows.

            https://www.solaredge.com/sites/defa...-datasheet.pdf
            OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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            • #21
              Originally posted by ButchDeal View Post

              oh wow, you have an older model SE7600A (not the HDWave version). This makes your readings of 8kW very suspect. It can spit out slightly more than 7.6kw but only for a few seconds and only if the AC voltage is higher. You are not going to get 8kWh in any given hour from it. That said I doubt you are doing all that much clipping here due to the roof layout and shadows.

              https://www.solaredge.com/sites/defa...-datasheet.pdf
              So, is that a sh*t inverter?

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              • #22
                Originally posted by sharpd1 View Post

                So, is that a sh*t inverter?
                ah no. The SolarEdge inverters are the most efficient in the industry. That is just the previous generation of the SE7600. The current version which came out early last year is the SE7600H and is the HDWave model. I expect SolarCity had a lot of these older inverters sitting around.
                OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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                • #23
                  Does the production rate decrease slightly when the air temperatures are higher?
                  Reason i ask is that we have had sunny days in the 50s where my 'current production' rate is stuck on 8.0 on my App for close to 1 or two hours......and then a few days ago, had a fully sunny day where the same rate was going between 7.4 and 7.8....never saw it go past that. temperature was around 85

                  There didn't seem to be any clouds whatsoever during the hot sunny day i mentioned above...so it made me think about the other factor that seemed to be different: temp.

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                  • #24
                    Originally posted by sharpd1 View Post
                    Does the production rate decrease slightly when the air temperatures are higher?
                    Yup, there should be a coefficient that tells you by how much. Panels are rated at 25 degrees Celsius and can have a coefficient of -0.5%/degree Celsius. That mean if it is 35 degrees Celsius you will see a 5% decrease in efficiency. If it is 15 degrees Celsius you see a 5% increase in efficiency. BTW, on a sunny day the temperature of the panels will be well above the air temperature.

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                    • #25
                      Originally posted by sharpd1 View Post
                      Does the production rate decrease slightly when the air temperatures are higher?
                      Reason i ask is that we have had sunny days in the 50s where my 'current production' rate is stuck on 8.0 on my App for close to 1 or two hours......and then a few days ago, had a fully sunny day where the same rate was going between 7.4 and 7.8....never saw it go past that. temperature was around 85

                      There didn't seem to be any clouds whatsoever during the hot sunny day i mentioned above...so it made me think about the other factor that seemed to be different: temp.
                      Somewhat technical bottom line is mostly yes. Array temp. is influenced mostly by three things, two of them easy to understand: The two easy ones are "Plane of Array" (P.O.A) irradiance and wind vector. More irradiance increases array temp. like a black object sitting in the sun gets hot. More wind decreases array temp. by increasing convective heat transfer sort of like cooling a piece of hot food by blowing on it. That convective (wind) heat transfer rate is mostly dependent on the wind velocity and (here's were the air temp. comes in) the difference between the air temp. and the array temp.

                      That third method of heat transfer I mention is thermal radiation. Everything radiates thermal energy similar to what you feel when you sit in front of a campfire. An operating solar array in the sun will radiate thermal energy to its surroundings - and the sky - that are cooler than the array in a relatively complicated fashion. Depending on the array's and surroundings' temps., an array operating at, say, 50 deg.C. while the surroundings (and note, not the necessarily the air temp.) are at, say, 20 deg. C., may lose about 30 % of all the solar energy rejected (that is, the 80-85 % of the incident solar that is not turned into electricity) by thermal radiation to the surroundings.

                      Practical bottom line:

                      Your array's efficiency (output) will decrease approx. 0.5% for every 1 deg. C. increase in array temp. as measured from a S.T.C. temp. of 25 C. Finding/estimating an array temp. is complicated by influencing effects that interact with one another. Under clear skies and moderate wind (whatever that means - maybe 2-3 m/sec or so), my array's average measured temp. runs roughly between 24 and 28 deg. C. above the ambient air temp. on my roof which runs about 3-5 C above the amb. air temp. closer to the ground. Yours and others' arrays probably have a somewhat similar temp. behavior and profile.

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                      • #26
                        Originally posted by J.P.M. View Post
                        Somewhat technical bottom line is mostly yes. Array temp. is influenced mostly by three things, two of them easy to understand: The two easy ones are "Plane of Array" (P.O.A) irradiance and wind vector. More irradiance increases array temp. like a black object sitting in the sun gets hot. More wind decreases array temp. by increasing convective heat transfer sort of like cooling a piece of hot food by blowing on it. That convective (wind) heat transfer rate is mostly dependent on the wind velocity and (here's were the air temp. comes in) the difference between the air temp. and the array temp.
                        For extremely hot climates, like Arizona, has anyone come up with an air cooling system for PV's? Even a simple fan system to increase air flow around panels might be beneficial.

                        Comment


                        • #27
                          Originally posted by discodanman45 View Post

                          For extremely hot climates, like Arizona, has anyone come up with an air cooling system for PV's? Even a simple fan system to increase air flow around panels might be beneficial.
                          Not anything that's practical and workable much less cost effective. For many reasons, fans will be effectively useless and in workable.

                          Be VERY aware of scams and ignore the crackpot crap on idiot's bible Screw-Tube.

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                          • #28
                            Originally posted by discodanman45 View Post

                            For extremely hot climates, like Arizona, has anyone come up with an air cooling system for PV's? Even a simple fan system to increase air flow around panels might be beneficial.
                            How about a thick tarp or a roof type structure on top of the solar panels to be used to provide full shade during sunny days? The structure and/or tarp can be removed at night to allow for maximum energy production.

                            just a thought.

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                            • #29
                              Originally posted by sharpd1 View Post
                              How about a thick tarp or a roof type structure on top of the solar panels to be used to provide full shade during sunny days? The structure and/or tarp can be removed at night to allow for maximum energy production.
                              "Surely you can't be serious!"

                              Comment


                              • #30
                                Originally posted by discodanman45 View Post

                                For extremely hot climates, like Arizona, has anyone come up with an air cooling system for PV's? Even a simple fan system to increase air flow around panels might be beneficial.
                                Wind , we get quite a bit of wind and usually have a breeze most of the time.
                                9.36 grid tied, Phoenix Arizona

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