Announcement

Collapse
No announcement yet.

solar problems/need guidance

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • #61
    will get back with more info in a couple of days. something always comes up.

    Comment


    • #62
      its been a long couple of days but here is the latest info. turns out all 3 inverters are bad. so now I need to replace them. what I have is 46 panels of sunpower panels. each one is 210w 5 amp 40 v.
      they are wired -- 8 panels in series and 2 strings ties together. except the last string has only 7 panels. so being a positive ground what would be the best replacement inverters? I can change the strings around if needed. I seen the sma sunyboy inverters. maybe 2 5000, or can I just change to 1 inverter? any suggestions?

      Comment


      • #63
        Originally posted by tim a View Post
        its been a long couple of days but here is the latest info. turns out all 3 inverters are bad. so now I need to replace them. what I have is 46 panels of sunpower panels. each one is 210w 5 amp 40 v.
        they are wired -- 8 panels in series and 2 strings ties together. except the last string has only 7 panels. so being a positive ground what would be the best replacement inverters? I can change the strings around if needed. I seen the sma sunyboy inverters. maybe 2 5000, or can I just change to 1 inverter? any suggestions?
        Do they all face the same direction and do you have any shading? SMA SB as well as many other modern inverters expect ungrounded panels meaning neither '+' nor '-' DC is connected to the ground but the frames, etc are of course connected.

        SMA SB have max input voltage of 600V which allows for longer strings (up to 12/string). 210W x 46 = 9,660 rated power. If you can live with some clipping single SB 7.7 inverter clips at 7,950W. It has 3 independent MPPT inputs 10A each. You can connect your 46 panels in 4 strings and connect them as: 12 + 12 + 11||11 panel strings to its 3 inputs. 2x 11-panel strings will be connected in parallel. If your panels face different directions this would complicate things as while inverter can support up to 3 directions we need to know how many panels are in each direction as only those in the same direction could be connected in the same string.

        Comment


        • #64
          all face same directions, no shade

          Comment


          • #65
            this is the layout
            Attached Files

            Comment


            • #66
              Those panels really require an inverter that will make sure they operate at negative voltage (positive grounding). Here is a paper explaining what is going on.

              TL;dr - If the panel voltage is above ground potential, 203 W output would (reversibly) degrade to 140 W.

              I don't know how those panels would perform with a transformerless inverter, but I doubt it will work well.

              The SBxxxxUS series of inverters are transformer based, and field configurable for positive ground. Renvu still has the 3000 W, 4000 W, and 6000 W models available on their specials page. They don't have AFCI, or ground fault protection on both conductors, so they are difficult to put into a new installation and be compliant with code.
              CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

              Comment


              • #67
                Originally posted by sensij View Post
                Those panels really require an inverter that will make sure they operate at negative voltage (positive grounding). Here is a paper explaining what is going on.

                TL;dr - If the panel voltage is above ground potential, 203 W output would (reversibly) degrade to 140 W.

                I don't know how those panels would perform with a transformerless inverter, but I doubt it will work well.

                The SBxxxxUS series of inverters are transformer based, and field configurable for positive ground. Renvu still has the 3000 W, 4000 W, and 6000 W models available on their specials page. They don't have AFCI, or ground fault protection on both conductors, so they are difficult to put into a new installation and be compliant with code.
                how those panels worked in the OP strings to begin with as being connected in series inevitably puts panels at the ever increasing potential to the ground towards the end of the strings?

                the article sounds fishy to me, they might have just washed the panels by providing 'water film' over cells front surface. Sounds all too similar to statement JPM made once that "any research will confirm what the client pays for" or something to that point. At the end they also state that SP is going to put conductive layer on the cells themselves (under the glass I presume) to mitigate this effect so from the outside their panels would have the same interface anyway.

                New transformerless inverters should be then even better in this regard as they are constantly switching strings around ground potential. I wouldn't let SP semi- marketing article drive my decision as their panels were not performing any better than of any other reputable manufacturer based on multiple member's posts here.

                Comment


                • #68
                  Originally posted by max2k View Post

                  how those panels worked in the OP strings to begin with as being connected in series inevitably puts panels at the ever increasing potential to the ground towards the end of the strings?
                  No. If you put a panel at -40 V in series with another panel at -40 V, you get -80 volts. That is what positive grounding does. The OP's strings, as installed with those SPR3200 inverters, were entirely below ground potential, avoiding the effect described in the paper.

                  Sunpower *did* in fact eventually change the construction of their panels, so that positive grounding was no longer required. The thrust of the paper was not that Sunpower panels outperform, but that the reason they *underperformed* with conventional negative grounding was because of charge accumulation. By applying -1000 V, the accumulated charge was eliminated and the panels restored back to expected output.

                  Newer transformerless inverters will not keep the entire array below ground potential, and therefore increase the risk that the OP's panels will suffer from the degradation described.

                  CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                  Comment


                  • #69
                    Originally posted by max2k
                    New transformerless inverters should be then even better in this regard as they are constantly switching strings around ground potential.
                    Could you please elaborate on "switching strings around ground potential"? thanks, Bruce Roe

                    Comment


                    • #70
                      Originally posted by sensij View Post
                      Those panels really require an inverter that will make sure they operate at
                      negative voltage (positive grounding). Here is a paper *** explaining what is going on.

                      TL;dr - If the panel voltage is above ground potential, 203 W output would (reversibly) degrade to 140 W.
                      If that were a notable effect in the field, I would expect to see the panels near the positive
                      end of a high voltage string put out 5% less power than those near the ground end. No
                      such effect has been observed here, or seen reported. My inverters are neg gnd. Bruce Roe

                      Comment


                      • #71
                        Originally posted by bcroe View Post

                        If that were a notable effect in the field, I would expect to see the panels near the positive
                        end of a high voltage string put out 5% less power than those near the ground end. No
                        such effect has been observed here, or seen reported. My inverters are neg gnd. Bruce Roe
                        You are using Sunpower panels? Which model? The positive grounding was only required for the designs Sunpower (and only Sunpower) produced 10 years ago or so.

                        Also, for what it is worth, the problem is with *accumulation*. If the string is negative grounded, the high voltage end will degrade faster, but ultimately, they would all degrade. (See Figure 6 in the paper, showing the same degradation after 100 min of +1000 V, but after 1000 min of +100 V)
                        Last edited by sensij; 10-12-2017, 07:41 PM.
                        CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                        Comment


                        • #72
                          Originally posted by bcroe View Post

                          Could you please elaborate on "switching strings around ground potential"? thanks, Bruce Roe
                          Actually- no, it's more of a guess as I haven't connected scope there. I guessed this by looking at overall topology: http://www.elp.com/articles/powergri...ar-design.html option 3. The '-' end of the string there seems to be half DC voltage below Neutral and '+' end half DC voltage above. OTOH SMA states their inverters start producing full power from 125V DC for 240V AC so they could be switching full string voltage between AC L1 & L2 when DC is less than 240V or may be they just used option 4 and put some step up converter in front of the inverting switches.

                          Comment


                          • #73
                            will this inverter work with a positive ground?
                            Attached Files

                            Comment


                            • #74
                              Originally posted by sensij View Post

                              You are using Sunpower panels? Which model? The positive grounding was only required for the designs Sunpower (and only Sunpower) produced 10 years ago or so.

                              Also, for what it is worth, the problem is with *accumulation*. If the string is negative grounded, the high voltage end will degrade faster, but ultimately, they would all degrade. (See Figure 6 in the paper, showing the same degradation after 100 min of +1000 V, but after 1000 min of +100 V)
                              Sharp ND-250HAT panels, 5 years old, in service here. If the affected panels haven't been
                              made for a decade, I can see why. Bruce Roe

                              Comment


                              • #75
                                Originally posted by tim a View Post
                                will this inverter work with a positive ground?
                                No. SB6000US(-10) or SB6000US-12, if you want to use SMA.
                                CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                                Comment

                                Working...
                                X