New Off-Grid Install - So Far, So Good

mjp24cohomjp24coho Posts: 104Solar Expert ✭✭✭
I had a busy last week, finally installing my big solar upgrade at my offgrid cabin. So far, everything seems to be working OK, but I've got a long ways to go to get it dialed-in (and remote monitored). That will have to wait until the next trip back. I added 8 Kyocera 215W panels (4 wired in series, 2 strings in parallel) on top of the cabin roof. I then run that 120' into my detached garage (6 awg THHN in conduit) where all my components are. In there I have a Midnite pre-wired Epanel with a Magnasine 4000W inverter and a Classic 200 charge controller. The backbone behind the system is a 800 AH 24V forklift battery, placed in a resin deck box (so I can add Styrofoam in the winter to help insulate it), with a Honda 5000W generator for backup or charging batteries when needed. I've attached a few of the pictures of the install. The hardest part was mounting the panels on the roof (using Unirac rails) - it was pretty steep, and a bit much for just me and my 8-yr old son to do on our own. But we managed, and succeeded withno injuries. After double and triple-checking all the wiring, it was a white-knuckled moment when I wired up the battery and finally flipped the switch - but everything worked (there were plenty of high-fives between my son and I). I can't thank everyone enough on this forum for all the advice and learnings over the years. I'm definitely solar-addicted, and look forward to getting it dialed in and learning more about my system.

One thing I noted that seemed a bit odd: the panels are wired 4 in a series at 26.6 VMP, that should be 106.4V. With the 6 awg THHN wire, I wasn't calculating anything more than 2.5% voltage drop over the 120' (240' roundtrip). But the incoming volt reading on the Classic was 94.6V. Why would that be so low? That last reading was in the early evening (5 PM), but wouldn't the lower sun production only impact wattage production (only showed 800W, instead of 1720)?

Comments

  • NorthGuyNorthGuy Posts: 1,925Solar Expert ✭✭
    Re: New Off-Grid Install - So Far, So Good
    mjp24coho wrote: »
    One thing I noted that seemed a bit odd: the panels are wired 4 in a series at 26.6 VMP, that should be 106.4V. With the 6 awg THHN wire, I wasn't calculating anything more than 2.5% voltage drop over the 120' (240' roundtrip). But the incoming volt reading on the Classic was 94.6V. Why would that be so low? That last reading was in the early evening (5 PM), but wouldn't the lower sun production only impact wattage production (only showed 800W, instead of 1720)?

    The Vmp will decrease with the temperature, and also will decrease a little bit with lower insolation. It might be 95V at your conditions.

    However, at 5pm when batteries are on float, the controller needs to dial down the production. It can do so by moving away from MPPT. Mine goes up, so I may see, say, 105V while my Vmp is 95V. Classic may have a different mechanism though. Anyway, I would only look at PV voltage during bulk.

    BTW: Your pictureas are very small. I hardly can see anything. Bigger pictures would be much better.
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: New Off-Grid Install - So Far, So Good
    NorthGuy wrote: »
    BTW: Your pictureas are very small. I hardly can see anything. Bigger pictures would be much better.

    You're seeing thumbnails, try clicking on them --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: New Off-Grid Install - So Far, So Good
    mjp24coho wrote: »
    One thing I noted that seemed a bit odd: the panels are wired 4 in a series at 26.6 VMP, that should be 106.4V. With the 6 awg THHN wire, I wasn't calculating anything more than 2.5% voltage drop over the 120' (240' roundtrip). But the incoming volt reading on the Classic was 94.6V. Why would that be so low? That last reading was in the early evening (5 PM), but wouldn't the lower sun production only impact wattage production (only showed 800W, instead of 1720)?

    The magic of MPPT. The "T" stands for tracking. If Vmp were constant you wouldn't need to track it. Your Classic decided (at that time) that you could get more power by loading down your panels to 94.6 volts.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • NorthGuyNorthGuy Posts: 1,925Solar Expert ✭✭
    Re: New Off-Grid Install - So Far, So Good
    vtmaps wrote: »
    You're seeing thumbnails, try clicking on them --vtMaps

    That's because he changed them! LOL! :D
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: New Off-Grid Install - So Far, So Good
    NorthGuy wrote: »
    That's because he changed them! LOL! :D

    Actually the forum software does this: you start out with a big picture that fills a lot of screen and the next thing you know it's thumbnails. :confused: I don't know why; I just see it a lot. :D
  • YehoshuaAgapaoYehoshuaAgapao Posts: 280Solar Expert ✭✭
    Re: New Off-Grid Install - So Far, So Good

    Looks like you have a shading nasty affecting your early AM production, probably a tree. If you are northern latitude (as many people seem to be) a flush mount on a roof often won't be at optimal tilt. That would be less insolation and a lower Vmp. If you compare STC (1000W/M^3) and PTC/NOCT (800W/M^3) stats on solar panels, the VMP is lower in PTC/NOCT stats, generally 10% lower Vmp with 20% less insolation though a higher operating temperature is in this stat also. Heat lowers panel voltage (cold raises it) more than less insolation does.
  • inetdoginetdog Posts: 3,123Solar Expert ✭✭✭✭
    Re: New Off-Grid Install - So Far, So Good
    ... a flush mount on a roof often won't be at optimal tilt. That would be less insolation and a lower Vmp.

    Nothing about the insolation has a significant effect on Vmp, just on Imp. Unless you are talking about partial shading, in which case the string Vmp will drop a fixed amount for each totally shaded panel while Imp stays about the same.
    SMA SB 3000, old BP panels.
  • mjp24cohomjp24coho Posts: 104Solar Expert ✭✭✭
    Re: New Off-Grid Install - So Far, So Good

    Yes - ther is some early morning shading. The picture was taken early - around 7 am. By 8:30 shading is a non-event. The roof mount wasn't ideal (about 15 degrees off due south), but my only option.
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