New user expectations

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System
System Posts: 2,511 admin
in Solar Beginners Corner #1
We recently purchased a 1.8 Kw pole mount solar unit. We have 8- 235 watt Schott panels mounted on a Zomeworks tracker. How much does the temperature affect the performance of a typical unit this size ? At first we were getting over 17 Kwh per day, now its down to 15 kwh. The temperature was 81 when it was installed, now it hovers around 100. My wattage output went from over 1900 down to around 1500, is this normal ? I'm located just north of El Paso Tx. Thanks.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: New user expectations

    Welcome to the forum.

    Temperature is murder on panels. Remember that the temperature inside the panels is much higher than ambient. The higher the air temp, the less heat can be dissipated from the panels.

    Time of year will make a difference as well. PV Watts http://www.nrel.gov/rredc/pvwatts/ can give you some idea what to expect, but it does not give temperature compensation. The panel manufacturer should have data regarding the effect of temperature on the panels.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #3
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    Re: New user expectations

    Sounds about correct. My system will peak at about 10K watts in the Spring and now it is lucky to make 8500 watts midday peak in the 106+ heat of AZ.
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  • SkiDoo55
    SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    #4
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    Re: New user expectations

    Same here in N. Calif. we are 90° to 102°F and my 4600 watts of panels are only peaking at @3500 w output. Give me 70-80°F temps and I will see the GT 3.8 start limiting output to 3875watts. Mine are roof mounted but the back of the panel frame is @9 inches from the roof surface. Plenty of room for air movement. Summer time I could add in at least 2 more 230 w panels to get me close to spring / fall outputs due to temperatures. String voltages are down from @300 VDC tracking to 260 VDC and it's still warming up currently only 86°F at 12:17 pm PDT.

    Sounds like it is working as to be expected for temp increase. Can look at a solar sizing calculator and input the system and temps and it will show you the approximate output expected.
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
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  • System2
    System2 Posts: 6,290 admin
    #5
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    Re: New user expectations

    Ok, I thought the drop in output was rather drastic at first but now I understand how temperature does reduce the efficiency of the panels. Thanks for the responses.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #6
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    Re: New user expectations

    on the bright side (pun intended) wait until the cooler temps of winter come. not sure if you get much in the way of snow, but reflections off of that add even more to the output.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #7
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    Re: New user expectations
    niel wrote: »
    on the bright side (pun intended) wait until the cooler temps of winter come. not sure if you get much in the way of snow, but reflections off of that add even more to the output.

    Where I live that sure works. For me, in Winter, the best overall production is with the the panels mounted vertically. Snow will not build up, or stay on panels, so no running back and forth trying to keep them clean, and with the winter sun low in the sky, plus the suns reflection off the snow, I get the most production ever.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #8
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    Re: New user expectations
    waynefromnscanada wrote: »
    Where I live that sure works. For me, in Winter, the best overall production is with the the panels mounted vertically. Snow will not build up, or stay on panels, so no running back and forth trying to keep them clean, and with the winter sun low in the sky, plus the suns reflection off the snow, I get the most production ever.

    yes, but you missed my point that in winter the colder temps will reverse the effect on the voltage and power from the pv. only drawback is we get less sun both time-wise and intensity, but those reflections do help tremendously when those clouds go away.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #9
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    Re: New user expectations
    DRC59 wrote: »
    We recently purchased a 1.8 Kw pole mount solar unit. We have 8- 235 watt Schott panels mounted on a Zomeworks tracker. How much does the temperature affect the performance of a typical unit this size ? At first we were getting over 17 Kwh per day, now its down to 15 kwh. The temperature was 81 when it was installed, now it hovers around 100. My wattage output went from over 1900 down to around 1500, is this normal ? I'm located just north of El Paso Tx. Thanks.
    To get an idea of what you should consider reasonable, look at the specs for your modules. There will be a coefficient for voltage depression for temperature rise, usually given in % per degree C. For a pole mount system, add about 20-25 degrees C to the ambient temp and subtract 25 degrees to get the difference between your cell temperature and standard test conditions (STC). The temperature dependence of current is much smaller than that of voltage, so for approximations you can just apply the voltage coefficient to STC power, which is the nameplate power for your system.

    If the coefficient is given in percent per degree C, just multiply it times the difference between the cell temperature and STC to get the approximate percentage drop in power that you should be seeing on hot days.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #10
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    Re: New user expectations
    niel wrote: »
    yes, but you missed my point that in winter the colder temps will reverse the effect on the voltage and power from the pv. only drawback is we get less sun both time-wise and intensity, but those reflections do help tremendously when those clouds go away.

    Haha Assuming you mean that PV output is higher when the panels are cold, no Niel, I didn't miss it, however I neglected to mention it, because sometimes I forget that not everyone is aware of that fact and was referring only to winter angle where I live. :D
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