Getting about 1/2 expected output

heynow999
heynow999 Solar Expert Posts: 80 ✭✭✭✭
in Advanced Solar Electric Technical Forum #1
I have a grid connected pv system. I sell everything to the utility under a program where they pay .42 cents a KH. I have 16 x 160 watt Evergreen panels and Froniuos 3000 inverter. They are in two strings of eight. They are at a crappy angle (13 degrees) as I had to compromise to make it work as an awning.

I have been hooked up to the grid since Nov 26th, 2008 which is one month now. Using "pvwatts" I should expect 75 kwhr's from my system for December for Toronto. I have gotten about 40 according to the inverter and between 30 and 40 according to my "sold" meter that measures real output. It is closer to 30Kwhr, but it is a 10x meter and does not show the first digit.

The higest output I have seen on the inverter is 1100 watts in full sun on a clear day. I haven't figured out how to see the highest output, I might not even be able to, as the inverter is outside and I haven't played with it alot.

What little troubleshooting I did is I undid one wire from one string. The output dropped by 1/2, so this tells me that both strings are at least working.

Things I suspect may be wrong are the wire going from the panels to the inverter is only #10. Beyond that I am not sure.

Any help would be appreciated.


Edit

I went out and played with the inverter and I found that my highest output during the month was 1860 watt. I have a total of 2540 watts of panels. So the two strings are working. I am suprised that I haven't had a higher peak output as I thought that panels are more efficient in the cold?
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  • Moe
    Moe Solar Expert Posts: 60 ✭✭
    #2
    Re: Getting about 1/2 expected output

    Let me take a shot at this and have the gurus critique it. At this time of the year (winter solstice), it seems to me perfect tilt for Toronto should be latitude (44º) plus 23º = 67º. Subtract your 13º to get 54º off perpendicular, take the cosine of that, and it appears you should be getting about 59%.
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  • heynow999
    heynow999 Solar Expert Posts: 80 ✭✭✭✭
    #3
    Re: Getting about 1/2 expected output

    Thanks Moe

    I know the panels are at a bad winter angle, but when I run "pvwatts", it allows you to input the angle of the panels, so all the math is done for you

    here is a cut and paste of the page


    Station Identification
    City: Toronto
    Country/Province: ON
    Latitude: 43.67° N
    Longitude: 79.63° W
    Elevation: 173 m
    Weather Data: CWEC
    PV System Specifications
    DC Rating: 2.54 kW
    DC to AC Derate Factor: 0.770
    AC Rating: 1.96 kW
    Array Type: Fixed Tilt
    Array Tilt: 13.0°
    Array Azimuth: 220.0°
    Energy Specifications
    Energy Cost: 0.4200 Can$/kWh

    Results

    Month
    Solar Radiation
    (kWh/m2/day) AC
    Energy
    (kWh) Energy
    Value
    (Can$)
    1 1.83 109 45.78
    2 2.67 148 62.16
    3 3.44 209 87.78
    4 4.57 261 109.62
    5 5.62 321 134.82
    6 6.15 328 137.76
    7 6.07 326 136.92
    8 5.32 288 120.96
    9 4.40 237 99.54
    10 2.91 167 70.14
    11 1.51 77 32.34
    12 1.33 75 31.50
    Year 3.82 2548 1070.16

    Funny thing about angles, my panels at 13 degrees are only about %5 less efficient than the optimum 45 degrees
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #4
    Re: Getting about 1/2 expected output

    If you used this site:

    http://rredc.nrel.gov/solar/codes_algs/PVWATTS/version1/

    and on the result page, push the hourly output button--you will get a file of "typical days" output--and it is about what you have reported (using your numbers)...

    From my experience--a across a continent and much farther south--I found that my winter production is highly variable--based on local weather conditions.

    For my GT system (3.5 kW of panels):
    December 2005 134kWhr
    December 2006 213kWhr
    December 2007 258kWhr

    Predicted:
    December typical 246kWhr

    Sounds like your system is probably running normally.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #5
    Re: Getting about 1/2 expected output
    heynow999 wrote: »

    I went out and played with the inverter and I found that my highest output during the month was 1860 watt. I have a total of 2540 watts of panels.

    Now that's about 73% which is about right. Do you see ANY partial shading at ALL ?? Maybe at first, there wasn't any shading but now there is ???
    ANY shading can significantly hurt production. Also, the angle, if not high enough will also hurt production some.

    One more thing. It doesn't look like there is much spacing between the array and the roof. You need some space for panel cooling. The cooler, the better. (air flow)

    boB
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #6
    Re: Getting about 1/2 expected output

    Also, although low output "hurts" during the winter--notice that most of your power (and for me, my utility's $/kWhr pay back) is much higher in the summer--so agonizing over a reduction in "small" amount of power available in winter, does not cost that much...

    Lastly, your panels are clear of snow, leaves, etc. too... I am sure.

    -Bill

    PS: You might have to move the satellite dish when summer rolls around...
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #7
    Re: Getting about 1/2 expected output

    Another question... your photograph appears to show lots of shading on the panels in the late afternoon... If the shading starts early (3pm or earlier)--you would lose lots of power over the day...

    Use the link and get the hourly results--you can compare those with yours and see how much power you lose due to shading and such.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #8
    Re: Getting about 1/2 expected output

    How far is the inverter from the array? I always use #8 (or #6) if needed from the "J" Box to the inverter.

    I would check the V of each array and make sure your somewhere in the neighborhood of where you should be. Its easy to verify and if it adds up then start looking into shading issues.

    Hope this helps
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #9
    Re: Getting about 1/2 expected output

    it seems to me that snow may account for the rest of the losses not due to solar angles. it takes time for snow to melt, especially when the angles aren't steepened for allowing the better solar exposure.
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  • WisJim
    WisJim Solar Expert Posts: 59 ✭✭✭
    #10
    Re: Getting about 1/2 expected output

    Did you have a site assessment done before installing the system--one using a Solar Pathfinder or similar instrument to estimate the annual output taking into account shade, etc.? A little shade can make a big difference, and it is hard to really account for things that might shade a site without photos and something like a Solar Pathfinder. Looking at the photo, I would guess that you are getting more shade on a panel or panels than you think.
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