declining power production

dawgster
dawgster Registered Users Posts: 3
in General Solar Power Topics #1
Hi,
I have a 5kw grid tied system, 22 Schoot panels, a 5k SMA inverter in the Tucson area, installed 2 years ago.
my issue is that the system seems to be producing 10-20% less power per day than last spring. Today was a perfectly sunny day , cool (around 75 degress) and it produced 19.7kwh. seems in the past it should be around 24kwh for this time of year. I don't have the data stored off of my Sunny Boy monitoring device but I'm fairly certain that the system is degrading rapidly.
Is this normal? if not, what could be the issue? a panel? I've covered each panel 1 by 1 to see if the power produced drops but I can't find an offending panel. could the inverter be the problem? I had a external fuse on the output side blow this summer. I replaced it myself.
appreciate any insight!

dawgster
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: declining power production

    Take a look at the Vmp-array and Imp-array (do you remember the initial values?).

    A 3% fall the first year is not unusual (I think)... Add a bit of dirt too (unless you are keeping the panels very clean--I have not done that for a few years on my second story array).

    More or less, I have seen a pretty big fall off in my system--But I don't know if it is the array or the GT inverter (I had an inverter fail and the replacement did not every work quite as well as the previous one--as I remember).

    If you have a bad solar array or panel--You may see the power output fall to 1/2 in a few weeks of sunny weather (failing joints start overheating worse and worse)--F that is the problem (that is what happened with my first array).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Re: declining power production

    maybe you should contact your installer to verify if there could be a problem as it always helps to have a professional opinion to confront on warranty repairs, if that is the case. 10-20% is allot.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #4
    Re: declining power production

    A quick check of pvwatts for Tuscon on a 5 Kw array tilted at 22.5 degrees pointed due south shows for Nov. 593 kWh. Divide that by 30 days and you are right on track. I notice production is down a bit this last week from the high clouds around.
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  • Lee Dodge
    Lee Dodge Solar Expert Posts: 112 ✭✭
    #5
    Re: declining power production

    We are approaching the shortest day of the year on (about) Dec. 21, so daily output should certainly be dropping this time of year, even if it is sunny. In my part of Colorado, there are a few more clouds this time of year than in the spring. I plot my monthly output versus PVWatts Version 2 predictions as shown at http://www.residentialenergylaboratory.com/rel_energy_use_pv.html to make sure that it is performing as expected. I have not seen a large drop off in power with age over the first 2 1/2 years for my system, but I do put an aging factor of 0.65% per year into the PVWatts predictions. Notice that the average daily power output for my 3.15 kW DC rated system drops from about 18.4 kWh in June to 14.3 kWh in November.
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  • Ian S
    Ian S Solar Expert Posts: 35 ✭✭
    #6
    Re: declining power production
    dawgster wrote: »
    Hi,
    I have a 5kw grid tied system, 22 Schoot panels, a 5k SMA inverter in the Tucson area, installed 2 years ago.
    my issue is that the system seems to be producing 10-20% less power per day than last spring. Today was a perfectly sunny day , cool (around 75 degress) and it produced 19.7kwh. seems in the past it should be around 24kwh for this time of year. I don't have the data stored off of my Sunny Boy monitoring device but I'm fairly certain that the system is degrading rapidly.
    Is this normal? if not, what could be the issue? a panel? I've covered each panel 1 by 1 to see if the power produced drops but I can't find an offending panel. could the inverter be the problem? I had a external fuse on the output side blow this summer. I replaced it myself.
    appreciate any insight!

    dawgster
    I'm in Phoenix and I have a 6.9 kW Sunpower system installed in May. My production on November 30 was 24.3 kWh. My array faces due south with a 15 deg tilt on a flat roof. It's producing better than 10% more than predicted by PV Watts. Sounds like you're doing OK depending on your array orientation. You should not compare output to last spring rather compare it to last January.
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  • GreenPowerManiac
    GreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    #7
    Re: declining power production

    Lee is correct. December is the worst month for PV rays due to the angle of the sun. It'll get slightly worse until winter solstice, then improve a bit per day. The amount of daylight and its quality in winter has never produced much on my end in the 8 hours of possible daylight, and at 26% efficiency max, be lucky to have 4 hours of decent light from it.
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