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  • My System

    Well guys its finally up and running and I will never allow a contractor near one of my houses again after all the stuff up I had to fix.
    Its only been 1 week and two days and haven't I learnt a lot about this Solar PV stuff.

    Single String
    Like I have said before I have 12 X 170 Watt PV Panels connected to an Sunny Boy SB 2500 inverter in conjunction with a sunny beam monitor and the SDC computer program.
    So let me see if I am right here I have 12 X 170 Watt= 2040 Watts in total.
    Off load the 12 panels deliver 460Volts, On load they deliver (depending how hot and cold the days are) 400 Volts so here are my calculations for expansion.
    If I add another three panels in series (total 15 panels) I will have in total 2550 Watts (SB 2500 is rated at 2500W) but the biggest concern is the open circuit voltages and they would be with 15 panels 575 Volts and that could increase on a very cold morning and on load voltages would be 500 Volts and the both are too close to the magic number of 600 Volts for over voltage on one string.

    Now 2 strings set Up.
    If I connected the 12 panels using two strings I would have 6 X 170Watts = 1020W X two strings of the same equaling 2040Watts but the differences would be in the open/closed circuit Voltages.
    string one and two would have 6 X 38.3V Open Circuit Voltage= 230Volts, and in closed it would be 6 X 33.8 Volts= 202.8 Volts with is too low to fire up the inverter so I cannot use two strings.
    Now If I buy 4 more panels I cannot put them in series as the voltages would go through the roof (Above 600VDC) so I would go back to the two string system that I could not use before because of under Voltage.
    So now I would have 8 Panels x 170 Watts x 2 strings = 2720 Watts in total that's 220 watts over the limit, The open circuit voltages would be now 306 Volts, On load closed circuit voltages would now be 270 volts and this would be sweet.
    The thing that gets to me is that all inverters have a sweet spot where they like to keep the voltages at a certain point and for mine its 320-340 volts.
    To achieve this I would have to increase more panels in series in both strings and by doing this I would dramatically increase the wattage outside the operating window so I have come to the conclusion in one week as a week ago I knew nothing about this stuff that I was supplied the wrong panels for this inverter.
    Now If I had a Sunny Boy SB 3000 this is what I would have and I would ask for.
    2 Strings of 9 panels.
    string one 9 x 170 Watts= 1530Watts x 2 strings = 3060 watts and that's only 60 watts over the rating of the SB 3000 Inverter.
    Open Circuit 9 x 38.3 Volts = 344.7 Volts and closed volts would be 9 x 33.8 Volts = 304 Volts which is as close as you are going to get to the Magic 320- 340 volts as if you increase the system by another 2 panels you will be spot on with the close circuit on load voltages but over with the wattage's allowed to the inverter.
    Now are you all confused?
    By the way as my system stands today I have no trouble in the middle of winter generating over 10Kw a day.

    http://i400.photobucket.com/albums/p...y/100_4259.jpg
    Attached Files
    Last edited by Blackman; 07-04-2009, 01:33 AM. Reason: Trying to add the bigger picture.

  • #2
    Poke around on the SB site, and in your manuals, see if you can find an "efficiency" chart. You need to see what input voltage runs the SB inverter at the highest efficiency. As long as you are "tuning" your system, tune for highest efficiency. I believe with xantrax inverters, 300VDC was a very good spot, which gave me good efficiency.
    http://www.mike-burgess.org/images/GT_Screen_Save.png

    You are right, to NOT exceed the max input voltage on cold mornings.

    Overwattage.
    When your panels are running, how much of their "rated" wattage, are they actually producing. It's fair to use actual produced wattage, not STC, to size array to inverter.
    Most grid-tie inverters, if fed too much power, just throttle back a bit, to stay within spec. Your system may only reach peak power 3 or 4 times a year, and if your inverter is of the type that gracefully throttles back, you would be fine.
    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

    Comment


    • #3
      Originally posted by Blackman View Post
      . . . By the way as my system stands today I have no trouble in the middle of winter generating over 10Kw a day.
      Yep, we get ~5kw/day here with our 1.05kw system. I do have a tree over the road that casts a shadow on the panels at around 3:30pm, but we don't lose too much as we've had the 6 hours from 9 til 3 anyways.

      Glad that you've got your system fixed, and a kick in the bum to your solar PV company who botched the job.

      Comment


      • #4
        Originally posted by Mike90250 View Post
        Poke around on the SB site, and in your manuals, see if you can find an "efficiency" chart.
        For the SB 2500 the Efficiency spot is 330Volts DC but this is hard to achieve as you have a very limited range of panels available here in Australia to play with.

        Originally posted by Mike90250 View Post
        Overwattage.
        When your panels are running, how much of their "rated" wattage, are they actually producing.
        My panels add to 2040watts. The most I have pumped out of them only once in the last week or so since I've had them is a short burst of 1.8Kw.
        Most of the time around 11 AM to 1PM (best time, clear sky cool day, 19 Deg C, That's cool for Brisbane) the Sunny Beam monitor and the SDC in the computer tell me I am generating around 1550 Watts.
        By this you can see Its hard to generate the rating of the panels

        Comment


        • #5
          BoB, The funny thing is Eco Kenitics won't sell me the extra panels seperate. I have to have one of their expert technicians install them for me for a price.

          Comment


          • #6
            Guys i'm thinking of adding 4 more panels to my above system to load it up correctly and the question I would like to ask is if you look at the above picture of two staggered sets of 6 panels where would you put the extra 4 so the look good.
            I'm thinking od adding two to the bottom left row to make it eight with two left overs on a new row (third row) one on each side, what do you think.

            Comment


            • #7
              2 panels to the left 2nd row would look nice and neat.

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              • #8
                Well guys I now have 16 panels up and running. 2up the top, 6 in the middle and 8 on the bottom row. All looks good, (How can I post a full size pic? or is this only for mods only).

                Comment


                • #9
                  Originally posted by Blackman View Post
                  Well guys I now have 16 panels up and running. 2up the top, 6 in the middle and 8 on the bottom row. All looks good
                  Great stuff.

                  What's your average output per day with the extra panels?
                  . . . How can I post a full size pic? or is this only for mods only.
                  Include the pic as an attachment through the "Manage Attachments" link when you make a post.

                  Comment


                  • #10
                    Today will be the first full day.
                    WoW its 8.45 AM and i've already pushed out 1.51Kw

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                    • #11
                      Its 10.28AM and the PV system has pushed out 4.2 Kw.

                      Comment


                      • #12
                        Originally posted by Blackman View Post
                        Its 10.28AM and the PV system has pushed out 4.2 Kw.
                        Excellent!! You should push an easy 10kw/day there.

                        I take it you have a feed in tarrif with your energy provider there? I get AUS$0.44/kwh feed in here. Even with our basic 1.05kw system, we knocked around $200.00 off the last power bill, down to $240.00. I plan on adding another 2kw up there, so that will knock all future power bills down to nothing, given the feed in credit of AUS$0.44/kwh and the cost of usage of AUS$0.16/kwh.

                        During the day we power the house from the panels, mostly, and draw from the grid at night.
                        Last edited by Aussie Bob; 07-19-2009, 09:00 PM.

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                        • #13
                          I think 16 panels will do. but I do have room for more
                          Attached Files

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                          • #14
                            Picture is limited to 97kb?

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                            • #15
                              Originally posted by Blackman View Post
                              I think 16 panels will do. but I do have room for more
                              Looks great!! But you need 4 more under there, to balance it out.

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