How are my panels doing for output?

CVN-71
CVN-71 Solar Expert Posts: 54 ✭✭
in Off Grid Solar & Battery Systems #1
Now that my system is running, I'm curious how the experts think my panels are producing. I have 1200w at 24v mounted on the roof facing south, in the northeast (using Concord NH Isolation data of 4.9 for July). On a typical end of day, the charge controller is reporting 5kw. I don't get full sun on the panels till 9:30 am due to some trees. With derating, does this seem about right? Would it be beneficial to cut down some of the trees, change tilt, add more panels? Any thoughts appreciated.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: How are my panels doing for output?

    generally speaking that 4.9 is full sun hours. so 1200w x 4.9 is 5880wh. the trouble is 2 fold here as pvs rarely put out their stc ratings and there are losses from wiring (minimally from wire resistance with high voltage strings) and maybe about 10% or so from inverter operations for gt inverters. ptc is about 10% less than stc and adding the 10% inverter loss comes to 5880 x 80% = 4704wh. now this could mean the pvs are outputting a bit more than i anticipate or that the inverter's efficiency as well as other losses are better than i anticipated. it seems inline though unless you have more specifics to correct my generalizations.
    pv ptc ratings times 4.9hrs equals base power in watt hours per day. from there multiply by the inverter efficiency to get your net power and see how well it matches what you are getting. i'm betting it is in the ballpark of what you are getting.
    clearing any shadowing from pvs will only help them and will be up to you if the effort is worth the gain.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Re: How are my panels doing for output?

    With PVWatts, you can also output "typical" hourly output data... For Concord and 1.2 kW of panels with 0.77 output derating:
    1981, 8, 16, 07:00, 4
    1981, 8, 16, 08:00, 140
    1981, 8, 16, 09:00, 217
    1981, 8, 16, 10:00, 392
    1981, 8, 16, 11:00, 273
    1981, 8, 16, 12:00, 419
    1981, 8, 16, 13:00, 256
    1981, 8, 16, 14:00, 462
    1981, 8, 16, 15:00, 467
    1981, 8, 16, 16:00, 399
    1981, 8, 16, 17:00, 153
    1981, 8, 16, 18:00, 13
    ...
    1981, 8, 17, 07:00, 53
    1981, 8, 17, 08:00, 320
    1981, 8, 17, 09:00, 546
    1981, 8, 17, 10:00, 314
    1981, 8, 17, 11:00, 639
    1981, 8, 17, 12:00, 545
    1981, 8, 17, 13:00, 533
    1981, 8, 17, 14:00, 464
    1981, 8, 17, 15:00, 444
    1981, 8, 17, 16:00, 250
    1981, 8, 17, 17:00, 111
    1981, 8, 17, 18:00, 3

    For those two days, it looks like you would gain between 400 and 1,000 Watt*Hours if you removed the shade (assuming you get near zero production until 9:30am...

    Otherwise, also look at the shading during winter. Depending on the angle of the sun and trees--you may be missing out more time when the sun is low in the sky.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • jcgee88
    jcgee88 Solar Expert Posts: 154 ✭✭
    #4
    Re: How are my panels doing for output?
    CVN-71 wrote: »
    I have 1200w at 24v mounted on the roof facing south, in the northeast (using Concord NH Isolation data of 4.9 for July). On a typical end of day, the charge controller is reporting 5kw. Would it be beneficial to cut down some of the trees, change tilt, add more panels?

    Cutting down trees and/or trimming them annually is usually
    not a good strategy. Assuming that you have a professional
    do it (which I highly recommend, it's dangerous up there!),
    trimming will cost $300-500 per tree, and it could cost $1000
    or more to cut down a large tree. To put the trimming in
    perspective, if I had to do that for my site, the cost would
    have negated the entire annual savings I get from my 3kW
    system. Your 1.2kW system would be hard pressed to ever
    show a profit.

    By the way, I almost subjected myself to annual tree trimming,
    but after figuring out the trimming costs, I instead placed the
    PV panels in a different location on my roof.

    As to tilt angle and more panels, BB has already suggested
    that you evaluate those options using PV-Watts. I would
    second that recommendation.

    John
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #5
    Re: How are my panels doing for output?

    I assume that since this is in the off grid section, you have a battery based system.

    Given that, remember that a derate factor of ~.55 is pretty standard for a battery based system. Add to that, it is rare that the charge controller/batteries go to float just as the sun goes down, so there is some more built in "waste" or lost power due to the batteries being full or near full that isn't reported in the harvest data.

    I like to use the rule of 50%. Take the name plate rating of the PV divide in half to account for all system loses, multiply that number by 4 and that gives a pretty good average of what one might expect to harvest on average over time.

    That said, I would not consider pruning trees, (cutting them down maybe!) as pruning trees leads to more pruning, which in turn leads to more pruning. Most trees, (conifers in specific) tend to create multiple growing tips when the leaders are pruned, causing them to grow a whole lot of new leaders that can actually make shading worse.

    Tony
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  • CVN-71
    CVN-71 Solar Expert Posts: 54 ✭✭
    #6
    Re: How are my panels doing for output?

    Thanks everyone. Using PV watts, my summer tilt should be 27 degrees and 67.5 in winter. Right now they are at 24 degrees, the pitch of my roof. I do plan on upgrading to adjustable mounts in the fall, so I can get better winter sun.

    As for trees, I have two guys who take my trees down for free, in exchange for taking the nice oak for firewood. :-) It's worked well for me, have had a dozen trees removed for free. I do have sun before 9:30, but shaded. If I removed two more, I could certainly get some more early morning sun.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
    Re: How are my panels doing for output?
    CVN-71 wrote: »
    Thanks everyone. Using PV watts, my summer tilt should be 27 degrees and 67.5 in winter. Right now they are at 24 degrees, the pitch of my roof. I do plan on upgrading to adjustable mounts in the fall, so I can get better winter sun.

    As for trees, I have two guys who take my trees down for free, in exchange for taking the nice oak for firewood. :-) It's worked well for me, have had a dozen trees removed for free. I do have sun before 9:30, but shaded. If I removed two more, I could certainly get some more early morning sun.

    consider yourself lucky to get this done for free. too bad you aren't closer to me as i'd get him to take away quite a few black locust trees around me. it is a hard wood and many of these trees aren't accessible from the road and they tower around 120ft. they scare the you know what out of me at times and i know they will come down one day on their own. i have the costs working against me and the fact that it would leave the steep hillside with little to keep it in place. i'd figure out the 2nd one if i had the first one done.;)
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  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    #8
    Re: How are my panels doing for output?
    I do have sun before 9:30, but shaded. If I removed two more, I could certainly get some more early morning sun.

    Hi CVN71 (I served a short time on the CVA64) due to low sun angle at 9 am trimming a few trees will probably help very little. Your maximum output is probably between about 10 am and 4 pm and if this is a clear shot you are doing well without a tracker. I think your harvest is OK with 1200 watts of panels if this is a battery system. Today I generated about 6 kw with a 1480 watt pv battery system and there was periodic cloud cover. I have pulled three of my panels from my system which is on a trailer for irrigation purposes. We are in a drought.
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  • CVN-71
    CVN-71 Solar Expert Posts: 54 ✭✭
    #9
    Re: How are my panels doing for output?

    MikeO, the Connie was a good ship!

    Yea, even though I can have the trees cut down, I didn't see much extra power I would get out of it. I think the best bang right now would be to change the mounts so I can adjust tilt in winter. Yes, I have 8 L16 Lifetime AGMs. I may add another 400 watts of panels as well. Prices are low an my state give $3 per watt rebate which makes it even better.

    Niel, ask around your power company for the names of the guys who trim/cut their trees. Many of these guys do side work. 2 yrs ago, I had one of them cut down 8 oaks, 3 maples and a few pines for only $1100. He even chipped all the branches. Lots of folks are doing it for free in exchange for the wood.

    Cheers,
    Bob

    6 (205W) Evergreens
    FM80
    Midnite MS4024 Inverter/Power Panel
    8 Lifeline L16 AGM's.
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