PV panel temps

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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #32
    Re: PV panel temps

    Jim, et al.

    All this has me dreaming of getting a mppt controller. My summer average daytime temp is ~+15c average winter is ~-15c, although we can go weeks at ~-35c.

    Question is, is there a linear relationship between temp and out put, and is there a chart/graph somewhere for a "generic" pv set up.

    As I said I am rebuilding my system and have bought 2 more sieman 55 watts that will bring the total to 210wts. I am on the cusp of buying a mppt controller, but I would like to do some calcs over an average year to see what the true benefits would be for me in my situation.

    As I said previously, I don't use all the amp/hours I generate now, but you know how the loads increase over time. I've just added 12vdc water pumping, along with 12vdc heat tape for the 6 month freeze season. (no more carrying water in buckets,,,bo hoo)!

    Icarus

    PS I have learned more in 6 months reading this forum, than in 10 years of trial and error. Where we are, net accesss is new and we have had no source for info except annual catalogues that are years out of date. Now I can learn more in a day than I could in a year. Thanks for this forum, as well as NAWS (and the web). Were not as far in the sticks as we think sometimes. Double edged sword however.

    T
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #33
    Re: PV panel temps

    Tony,

    The relationships between power, voltage, current and PV cell temperature are “linear enough”, in my view, for our applications. For example, a typical temperature coefficient of power might be expressed as “-0.5%/degree C (or K)”. That’s a straight line with a negative slope.

    Check the graphs in the linked Mitsubishi cut sheet; they’re pretty telling. See: http://lib.store.yahoo.net/lib/wind-sun/Mitsubishi-125.pdf

    The application key is to adjust cell operating temperature for ambient conditions. Specifically, cell operating temperature of a well-aligned PV module under full insolation can be ~34 C above ambient, depending on wind conditions. So, at 15 C (59 F) ambient, cell temp could well be 49 C (120 F), or 24 K (43 R) above the STC reference of 25 C (77 F). At -35 C (-31 F; brrrrr!), cell temperature could be ~-1 C (30 F), or 26 K (47 R) below STC ref.

    Radio Shack sells an inexpensive IR thermometer that you might find useful. ;)

    Finally, note that very low ambient temperature dramatically increases both STC Voc and Vmp. In fact, the standard US National Electrical Code (NEC) temperature correction factor for PV Voc in a -35 C environment is 125%. But, this is where the MPPT benefit can really shine!

    This is a great site, isn’t it? I find it wonderful that so many people are able to usefully exchange and debate technical information, and almost always with the intent of finding practical solutions. A few of us go off on tangents on occasion, but I do believe it’s invariably with the best of intentions.

    As a result, we’ve collectively created a technically competent site with virtually no flaming, political messages, or spam. I gather that’s a rarity, and I’m therefore glad to be a part of this community.

    Best of luck with your calculations!

    Regards,
    Jim / crewzer
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #34
    Re: PV panel temps

    Jim,

    Thanks for the info.

    As for the panel temps increasing by ~35c. It would be interesting to do a series of tests at various temps to see if this holds true for "really" cold temps (~-20c 0f). My intution is that the temp difference becomes much less dramatic as the O.A.Temp goes down. I have nothing to back this up, but I will try to do a test this winter. (I am spending the first part of the winter away, so I can't do it until sometime in Feb).

    It would seem if a panel had some air undernieth it it wouldn't warm as much as 35C at very cold temps, as the surrounding mass is so cold, it would tend to draw that absorbed heat away quite quickly. In the same way that thermal mass gets warmer on a warm day.

    I'm hoping Santa will bring me a MPPT controler, either a MX60 or a BlueSky 50. Any opinions on one over the other?

    Icarus
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #35
    Re: PV panel temps

    Tony, OK OK OK enough of the snow bird stuff....;)

    maybe by the time you get back north of the 49 th, the Classic will be out, here's hoping...

    (No smilie for envy)
    Cheers

    Eric
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #36
    Re: PV panel temps

    Eric,

    You should hope for -40. Get rid a a few pine bark beatles!

    Really not snow birding however, as we're in the lower mainland!

    Going to the Arizona and N.MEX in Jan however.

    Tony
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #37
    Re: PV panel temps

    Tony,

    I suspect the module performance won’t stray far from prediction at -20 C. That may be a cold temperature for humans, but it’s not that bad in the physical world. Besides, one of the Mitsubishi graphs reaches down to almost -25 C cell temp. I would suspect the real problems with comparing performance vs. temperature will likely be Sun angle and wind.

    Regarding opinions on charge controllers, I’d recommend the MX60 over the SB50. The MX60 is more flexible and costs less than the SB50DL (from NAWS).

    HTH, and travel safe!

    Jim / crewzer
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