One array, two locations?

SolarMusherSolarMusher Solar Expert Posts: 172 ✭✭✭
I have a 2.1kw array off-grid on roof mounted, 4 strings of three 175W mono panels, 107VMP, 45° tilt angle. I plan to add 2 more strings (1.1kw) on pole because not enough place on roof, it would be a fixed pole mount array at a 20 feet distance max from the first one. Both arrays would feed a 250V Midnite PV12 combiner to a Classic 200 CC.
Do you think the different operating temperatures could be a problem?
I could have a good deal on 175W poly panels, could mono and poly panels be mixed (parrallel) if spec are very closed? Or am I better to keep on growing this array with mono only?
Any advice would be appreciated.
Erik

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: One array, two locations?

    Welcome to the forum.

    From my point of view I don't think there will be much difference in operating temperatures. Provided the arrays are facing in the same direction at the same angle and have the same Vmp there should be no trouble in paralleling them. The types of panel shouldn't affect it either.

    Others may have differing opinions.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: One array, two locations?

    hi erik,
    in my opinion the temp difference would create a voltage difference. now we generally say to keep it within 5% (me) or 10% (bb.) and i don't think it would exceed either requirement, but you should check on that for the pvs involved and the min/max temps. midnite has a little calculator you might try and see what it says running each string separately. determining the actual roof temperatures at different times of the year may be a challenge though. you will need detailed specs for the pvs involved to enter this into the calculator.

    as to mono vs poly there may be differences here too and although very minor they could add to the differences already to be seen on the different locations.

    http://midnitesolar.com/smf_forum/index.php?topic=556.15

    without going through all of this, my gut feel is that if you aim both arrays exactly as the other then it most likely will be fine to combine the 2 arrays.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: One array, two locations?

    Welcome to the forum. Its nice to see you over here (I've seen your posts over at Midnite).
    I agree with Niel & Marc (Cariboocoot). After you wire up the new array you can always flip off the breakers (at combiner) for one array, and then the other, and see what the Classic reports for Vmp. If its too far different you can then add a new combiner & controller.
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • SolarMusherSolarMusher Solar Expert Posts: 172 ✭✭✭
    Re: One array, two locations?

    Thanks Vt, Niel and Coot
    My shingle roof could be very hot in summer (as everyone :D), have a 6/12 slope and the array was flush mounted but it was too hot and so I tried to tilt this array to 45° to see if it could run cooler and have a better output in summer. There's not a great amps output difference for these two angles. I was thinking that if this array was tilted to 45°, it could match closer +- to the temp of this pole mount array with a same tilt angle. I will try first to connect these two arrays on the Classic 200 as it could handle all these watts without problem.
    Do you think I could use the same ground for both array or am I better to use a secondary rod for the pole and connect these two ground together?
    Thanks a lot for sharing your knwoledges,
    Erik
  • SolarMusherSolarMusher Solar Expert Posts: 172 ✭✭✭
    Re: One array, two locations?

    Vt,
    If its too far different you can then add a new combiner & controller.
    From your experience, what would be for you a VMP difference that could work? Buying a new Classic was not part of my projects :cry:
    Niel,
    midnite has a little calculator you might try and see what it says running each string separately
    Have already tried it, but I trust more in your experience in real world and real datas over the different periods of the year.
    as to mono vs poly there may be differences here too and although very minor they could add to the differences already to be seen on the different locations.
    If you had to choose, would you Niel prefer to expand this mono array with others mono panels (very close spec 5/10%) or it doesn't really matter?
    Thanks
    Erik
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: One array, two locations?

    i can't say for sure for your case as you will need to see the differences from your roof to what ambient is. roofs can get quite a bit hotter than ambient with summer being obvious with the more intense sunshine and even in winter with the house leaking heat ever so slightly. an infrared thermometer could give you a better idea of how much higher it may actually go. the temp difference would probably need converted to degrees c, but you can figure out the voltage difference for the pvs by the pv's temp coefficient. once found for a single pv then multiply that by the number of pvs in series for the total voltage fluctuation.

    if you can get the same pvs it would be preferred, but sometimes other pvs have specs that would be nearly identical that you could use. pay close attention to not only the voltages like vmp and voc, but the temp coefficient as well.

    like i said the odds are you could do it if you determine if the end result would put your within the % of your choice. i don't believe it would be all that critical. keep in mind that the ones on the pole being colder will have a bit more voltage for identical pvs aimed exactly like the other array.
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