How to deal with inconvenient string sizes? (Post Mount)

SystemSystem Posts: 2,511 admin
Can anyone point me to information on how to deal with inconvenient string sizes when using post mounted arrays?
In my current 10kW central inverter project, I have 3 identical post mounts planned, with 16 panels on each array. The problem I am encountering is that the desired string size (2 arrays of 8 PV modules each per pole) will result in a Vmp (hot days) that is only a few volts above the turn off threshold of the inverter (Solectria PVI 10KW, 3phase, 600V). The best scenario seems to be dropping the PV count per pole to 15, and using 5 strings of 9 panels each. Alternative more costly approach is to use a larger pole mount allowing 18 PV per pole (and thus 2 strings of 9 panels per pole)

My question: Since endless $$ are not available, how would one wire the 15 PV per pole option, as the strings will end up being on multiple poles? Are there any technical documents or trade references that would explain what others have done in these cases? Any help would be much appreciated.

Comments

  • solarvicsolarvic Solar Expert Posts: 1,049 ✭✭✭
    Re: How to deal with inconvenient string sizes? (Post Mount)

    It would be easier to give you an answer if you posted the solar panels you are going to use. On my system of pole mounts I had to use 2 different inverter,s as I had 2 different brands of solar panels with different specs. Originally I have 3 4 place panel mounts and 2 8 place panel mounts. I used 14 of the one string of panels on 2 8 place top of pole panel mounts on one inverter leaving 2 empty places on them racks. I had 3 4 place top of pole mounts with 12 panels mounted on them with the 2 extra panels needed for the string of 14 panels on the space left on the 8 place top of pole mount. So 14 of my panels are on 4 separate racks and works well and the inspecter I had approved it.
    Idea # 1 IS strings of 12 panels too high a voltage? If it isn,t you could have 4 strings of 12 panels and go with your 3 16 panel racks.
    Idea #2 Maybe you could do 5 strings of 10 panels. Get your 3 16 panel mounts and get a 2 place panel mount for the extra 2 panels. :Dsolarvic:D
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: How to deal with inconvenient string sizes? (Post Mount)

    Easy, go to a distributed type inverter system like SolarEdge that lets you do anywhere between 8 and 25 modules in a string. Doesn't matter what kind of module (less than 250W and 60Voc) or even if they are even different kinds or brands or sizes. Mix and match all you want and you still get better efficiency than with a central inverter cause you are invidually optimizing each panel. Costs a bit more but then it has built in web interface too.
    String sizing with large modules on central inverters is getting untenable.
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