X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    Originally posted by thejq View Post
    Not sure where you got the 1% from. Just for kicks, I looked at my outputs today (first sunny day of March). For my 16x300W panels (http://pvoutput.org/intraday.jsp?id=...88&dt=20150303), if I had gotten M250 micro-inverter, anything above 4KW will be clipped (in fact, since not all panels reaches 250W at the same time, the actual clipping point is slightly less, but that's beside the point). So today, I would have clipped from 11:30 to 1:30 for 0.353 KWh which's 1.2% of my total production today. According to PVWatt, during June/July/Aug the production should be 50% higher than today. For simplicity and be pessimistic, I'm going to assume the production curve is a triangle (in stead of bell curve). After a few geometric manipulations, increasing the total production by 50% would result in about 3.74% clipping in those 3 months. Since I'm expecting to produce 1000KWh / month, I'd be losing 112 KWh (or *$.49 = $55) in just those 3 months. If again pessimistically assume the rest of the year altogether, I loose 1/2 that due to clipping, then for the year I would have lost $83. Of course there're lots of hand waving here, but since I've been pretty pessimistic in my logic, that number is likely the lower bound for me. I guess I'll know more precise numbers as the summer rolls around.
    The lack of agreement between your PVOutput.org page and your SolarEdge page is interesting. PVOutput shows 4153 W at 13:00 on 3/3, while the SolarEdge public portal shows 4032 W. Any idea why that is? There is a consistent 3% disagreement across all the data that I've just checked.

    Assuming the inflated values are correct, I ran a simulation in SAM and scaled the output to match the clear day peak power this time of year to what your system is actually reporting. When production is higher in the summer, most of that extra generation is in the width of the bell curve, not the height of the peak. It would not be surprising if your peak power in June is the same or slightly less than your peak power in March, around 4.4-4.5 kW based on your PVOutput data, because June tends to be warmer. By August, the peak height is even more likely to be lower.

    The degree to which scaling was required suggests the 3% inflation is not real, but I am clearly not able to say for sure what is accurate. Even with the inflated output, the difference between clipped and unclipped power annually came out to 136 kWh (<1.5% of annual production), or $67 if all of that occurs during TOU peak... which is unlikely to be true for very many years as SDG&E is proposing to shift the peak times to later in the day when output would have dropped below the 4 kW clipping level.

    If the SolarEdge portal values are correct, the clipped energy in this simulation drops to 79 kWh annually (<1% of annual production), or $38. There is reason to doubt that even the SolarEdge portal calibration is correct, so without a revenue grade meter attached on the inverter, it is hard to say exactly what is being produced.

    Also keep in mind that the panels will degrade over time... the warranty allows 2% in the first year and 0.7% after that, so you may figure that after at most 5 years, and probably fewer, whatever clipping you would have been seeing now will be gone anyway. 5*38 = $190, which means if the M250's were more than $200 less than the SolarEdge system, either one would be worth the same (all other things being equal, which is probably not true). If the 3% higher vales are correct, the total value clipped may max out at more like $300-$400, but probably less.

    None of this is intended to say that I think designing a system with clipping is a good thing. All I'm saying is that if avoiding clipping is going to be a design decision, the cost-benefit of that decision can be estimated. I believe that spending several hundred $$ to avoid clipping is rarely supported when the panels are only 1.2X the inverter capacity, as they are with 300 W on a 250 W microinverter. If there is no difference in cost, then sure, avoid clipping if you can. If you buy into the idea that operating the inverter at its rating for an hour or two a day for part of the year will shorten its life, and spending more money upfront on a larger inverter will prolong the life of the system, I won't argue with that either, but only point out that I have found no evidence that it is true.

    Please do not to take this as an argument in favor of microinverters over SolarEdge. They each have their place, but in general, I would avoid microinverters for reasons that have nothing to do with clipping.

    In the grand scheme of things, a few hundred dollars either way is pretty insignificant, so as long as a system is not grossly mis-sized, my interest and arguments are more weighted towards the decision making process, not so much the outcome. The outcomes are all essentially the same.

    None of this is intended to suggest I can see the future. However, I continue to believe that modeling expected outcomes, informed by current data, is a reasonable way to make decisions about how I would choose to spend my money, or advise others on how to spend theirs (when asked).
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

    Comment


    • #17
      Originally posted by sensij View Post
      The lack of agreement between your PVOutput.org page and your SolarEdge page is interesting. PVOutput shows 4153 W at 13:00 on 3/3, while the SolarEdge public portal shows 4032 W. Any idea why that is? There is a consistent 3% disagreement across all the data that I've just checked.

      https://getsatisfaction.com/pvoutput...osely-how-come


      there may also be some net delay introduced in Pvoutput for m more accurate net calculations.
      [I][url]http://pvoutput.org/list.jsp?userid=27957[/url][/I]

      Comment


      • #18
        Originally posted by logdin View Post
        https://getsatisfaction.com/pvoutput...osely-how-come


        there may also be some net delay introduced in Pvoutput for m more accurate net calculations.
        Glad to see the problem isn't isolated. If it was just a timing issue, I would kind of expect the sign of the error to change between when the sun is coming up and when it is going down. The nice thing is that PVOutput.org includes the ability to apply a correction factor, so taking that extra 3% out to make the data match the monitoring portal would be easy enough to do, should he want to do it.

        The only meter that really matters is the poco's, so getting a good calibration against that probably affects the financial projections more than any other value, to the extent that possible error matters. Especially with a meter monitoring device like the Rainforest Eagle, but maybe if the inverter and meter are close by, a way to pin down the calibration would be to let the PV system run until its peak production during the day (when the curve is flattest), and then flip the breaker to shut it off. By watching the meter before and after the flip, it should be possible to scale the reported power to the measured power. Do it a couple of times or on a couple of days to average out any transients, and hope that the offset is proportional and constant.
        CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

        Comment


        • #19
          Originally posted by sensij View Post
          Glad to see the problem isn't isolated. If it was just a timing issue, I would kind of expect the sign of the error to change between when the sun is coming up and when it is going down. The nice thing is that PVOutput.org includes the ability to apply a correction factor, so taking that extra 3% out to make the data match the monitoring portal would be easy enough to do, should he want to do it.

          The only meter that really matters is the poco's, so getting a good calibration against that probably affects the financial projections more than any other value, to the extent that possible error matters. Especially with a meter monitoring device like the Rainforest Eagle, but maybe if the inverter and meter are close by, a way to pin down the calibration would be to let the PV system run until its peak production during the day (when the curve is flattest), and then flip the breaker to shut it off. By watching the meter before and after the flip, it should be possible to scale the reported power to the measured power. Do it a couple of times or on a couple of days to average out any transients, and hope that the offset is proportional and constant.
          How are you getting the data to PVOutput? if pulling directly from SolarEdge, then solarEdge only support poling every 15 minutes. This means that the data is being averaged on a 15 minute level and sent to pvoutput.org. This tends to clip off the peaks and smooth out the graph.
          OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

          Comment


          • #20
            Originally posted by ButchDeal View Post
            How are you getting the data to PVOutput? if pulling directly from SolarEdge, then solarEdge only support poling every 15 minutes. This means that the data is being averaged on a 15 minute level and sent to pvoutput.org. This tends to clip off the peaks and smooth out the graph.
            Yes, the discussion in logdin's link addresses that, but determines that sampling / averaging error wasn't contributing to that person's mismatch. In this case, if it was an averaging issue, then the error would tend to follow the slope of the curve, with more error when the generation rate was changing quickly and less when it was flat. The mismatch here is a constant 3%... no way that is just a timing thing.
            CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

            Comment


            • #21
              Originally posted by logdin View Post
              https://getsatisfaction.com/pvoutput...osely-how-come


              there may also be some net delay introduced in Pvoutput for m more accurate net calculations.
              Yes because of this discrepancy I had the pvoutput scaled to match solaredge's total output. So now they match almost spot on at the end of the day.
              16xLG300N1C+SE6000[url]http://tiny.cc/ojmxyx[/url]

              Comment


              • #22
                Originally posted by sensij View Post
                Yes, the discussion in logdin's link addresses that, but determines that sampling / averaging error wasn't contributing to that person's mismatch. In this case, if it was an averaging issue, then the error would tend to follow the slope of the curve, with more error when the generation rate was changing quickly and less when it was flat. The mismatch here is a constant 3%... no way that is just a timing thing.
                The 3% is the scaling factor I put in to match pvoutput against solaredge's end of day output and inverter LCD display which I think is the most accurate.
                16xLG300N1C+SE6000[url]http://tiny.cc/ojmxyx[/url]

                Comment


                • #23
                  Originally posted by thejq View Post
                  The 3% is the scaling factor I put in to match pvoutput against solaredge's end of day output and inverter LCD display which I think is the most accurate.
                  Most accurate because it is the highest? Um, ok. This is among the reasons why PVOutput.org data isn't totally reliable.

                  Edit:
                  You might want to check this thread to see that the SolarEdge end of day energy number could be inflated by several percent relative to more trustworthy data sources.
                  Last edited by sensij; 03-04-2015, 04:51 PM. Reason: Sorry for the snark. SolarEdge's portal site was down.
                  CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                  Comment


                  • #24
                    Originally posted by sensij View Post
                    Most accurate because it is the highest? Um, ok. This is among the reasons why PVOutput.org data isn't totally reliable. Shutting off the SolarEdge public site is classy, too.

                    Edit:
                    You might want to check this thread to see that the SolarEdge end of day energy number could be inflated by several percent relative to more trustworthy data sources.
                    No, because that's where current is inverted, and the place from where all the data is originated. I trust the source than any sub-sampled, over-sampled, interpolated or extrapolated data from pvoutput, TED or POCO's readings (esp. the last two where transmission lost, heat and usage fluctuation come in play).

                    But I think we are digressing a little bit, I think we're in agreement that purely basing ones' choice on clipping alone without weighting cost is not smart. When costs are comparable, the effect of clipping (or running at full capacity) is very much dependent on individual situation and personal preference.

                    Edit: just checked, my SolarEdge public site is still working, did they shut down yours?
                    16xLG300N1C+SE6000[url]http://tiny.cc/ojmxyx[/url]

                    Comment


                    • #25
                      This is a good read on oversizing.......may help your decision process:

                      http://www.civicsolar.com/resource/s...ray-oversizing

                      Comment


                      • #26
                        How far is your array from your house?

                        Originally posted by Poway View Post
                        Looking comments on the following configurations... And PM of recommended installers (thejq any recommendations?)

                        Ground Mount. Perfect conditions (point south or slightly west... any elevation... no obstructions)

                        11.95 kW DC
                        28x SunPower 427W Panels
                        Solar Edge P400 Optimizers
                        SE11400 inverter (is this to small for the 11.95 DC if so could drop to 26 panels 11.1KW?)

                        10.8 KW DC
                        36x LG 300W Panels
                        Solar Edge P300 Optimizers (or should I still use P400 optimizers?)
                        SE11400 inverter

                        10.8 KW DC
                        36x LG 300W Panels
                        Enphase M250 (will these clip ... do I need to use lower wattage panels given ideal pointing of array?)


                        Thanks
                        I too am working up the design for a 7.2 KW ground-mount array, and am comparing the advantages of a 24 panel LG300 array plus optimizers and a string inverter, with 24 LGA1C-B3 AC panels. My design site is about 140' from my service panel, so I tend to favor the AC panel approach with #6 AWG cables to the panel, to avoid long heavy DC cables. How far from your house is your ground site? Also, what mounting frame is being proposed by your installers? Since I am figuring on doing 80% DIY, I am basing my design on the Ironridge ground-mount system.

                        Comment


                        • #27
                          Originally posted by Hillsider View Post
                          I too am working up the design for a 7.2 KW ground-mount array, and am comparing the advantages of a 24 panel LG300 array plus optimizers and a string inverter, with 24 LGA1C-B3 AC panels. My design site is about 140' from my service panel, so I tend to favor the AC panel approach with #6 AWG cables to the panel, to avoid long heavy DC cables. How far from your house is your ground site? Also, what mounting frame is being proposed by your installers? Since I am figuring on doing 80% DIY, I am basing my design on the Ironridge ground-mount system.
                          Whoooooo.....high voltage DC does not require "long heavy DC cables". Your confusing low voltage battery cables with high voltage home run cabling from combiners at the array.

                          Do a little more homework on the design.

                          Comment


                          • #28
                            Originally posted by Hillsider View Post
                            I too am working up the design for a 7.2 KW ground-mount array, and am comparing the advantages of a 24 panel LG300 array plus optimizers and a string inverter, with 24 LGA1C-B3 AC panels. My design site is about 140' from my service panel, so I tend to favor the AC panel approach with #6 AWG cables to the panel, to avoid long heavy DC cables. How far from your house is your ground site? Also, what mounting frame is being proposed by your installers? Since I am figuring on doing 80% DIY, I am basing my design on the Ironridge ground-mount system.

                            The calculator I like the best
                            http://www.calculator.net/voltage-drop-calculator.html
                            computes a 1.4% loss for #6 wire at 140ft
                            this drops to 0.9% loss for #4 wire (which is cheaper by the foot than #6 at both home depot and lowes now [$0.79/ft * 140 ft * 4 wires = $442 for AC from panel to main]

                            But what DanS26 said is correct. If you do this with DC (and have the inverter at the house) the voltage would be approx twice as high and with 4 wires could bring back two strings so (so 1/4th the curr in each of the 4 wires) bottom line is small #10 wire could be used

                            One last thing to consider though is if you bring back DC then you will have to use metal conduit approx $1/ft and mark it every 10 feet i think. And this approach is not compatible with Micro inverters ... but does work with optimizers

                            Good luck

                            Comment


                            • #29
                              Originally posted by Poway
                              One last thing to consider though is if you bring back DC then you will have to use metal conduit approx $1/ft and mark it every 10 feet i think. And this approach is not compatible with Micro inverters ... but does work with optimizers. Good luck
                              Here in the Wild West DC underground conduit isn't metal; 260' of it. Bringing back wires
                              from each string may allow using the inverter internal combiner function, instead of a
                              separate combiner box. Bruce Roe

                              Comment


                              • #30
                                Originally posted by Hillsider View Post
                                I too am working up the design for a 7.2 KW ground-mount array, and am comparing the advantages of a 24 panel LG300 array plus optimizers and a string inverter, with 24 LGA1C-B3 AC panels. My design site is about 140' from my service panel, so I tend to favor the AC panel approach with #6 AWG cables to the panel, to avoid long heavy DC cables. How far from your house is your ground site? Also, what mounting frame is being proposed by your installers? Since I am figuring on doing 80% DIY, I am basing my design on the Ironridge ground-mount system.
                                Hi Hillsider,

                                I have read this thread with interest as we just installed 24LG 300 panels, 24 SE 300 Optimizers, and the SE6000 Inverter system - vendor said it would handle the load but didn't say it would not convert it!

                                My understanding about DC overrating was incorrect, as the SE6000 inverter will accept up to 7500WDC, but MAX AC output for this unit is 6000W AC.

                                So we are loosing 4-5 KW a day or roughly 100KW month due to clipping. Now the interesting thing is every other SE Inverter than the SE6000 has a 10-15% over the rated AC output capability.

                                For instance the SE7600 max AC output is 8450 W AC and the SE11400 is max AC output is 12000 W AC - its like Solar Edge and the SE6000 was at the top of the design limit. So with your 7200 W output you will be fine with the SE7600 if you go that route.

                                By the way, I learned that the SE6000 when over current, it "shuts down" or limits the current input to the inverter keeping it at the max 6000 W AC output so as not to convert the excess to heat at the inverter, it lets the heat out at the panel level. In any case, as I have learned buyer beware!

                                I intend to build another house with 6KW system in the coming years, so will swap inverters at that time.


                                Carl

                                Comment

                                Working...
                                X