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Assistance to see if the system I'm getting would give me the kilowatts quoted

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  • Assistance to see if the system I'm getting would give me the kilowatts quoted

    Looking for some guidance, from reading other posts it seems solar panels get 80-90% of what they're rated for. These panels are Silfab SLA-M 320Wp
    My total kW usage last calendar year was 11,794kw. The system they created states it will produce 11,721kw
    They have 21 panels at 320 watts each which is 6,720 watts. An AZM of 182 degrees, tilt 15 degrees, and system loss of 14.08 to equal 11,721kW. That averages to 32.11kW a day produced.
    From rough calculations of calculating a summer day and windy day it doesn't seem like that would produce that much power.
    How they divided it for my area and historic weather conditions it came out to this.
    Monthly production:
    Jan 774
    Feb 802
    March 1079
    April 1167
    May 1241
    June 1172
    July 1042
    Aug 1017
    Sept 974
    Oct 939
    Nov 796
    Dec 717
    Even taking the best month and the amount of daylight hours, is this realistic.
    I guess I shouldn't be too concerned as after the sit survey, they'll give me exact numbers (but should be about the same) and there's a production guarantee.
    They said if the system didn't produce 11,721kW (minus .06% max degradation per year) they would add panels at no charge.
    I have a flat roof and there's nothing to shade the panels except for the parapet walls, but how it will be positioned on the roof, the shade from it shouldn't get to the panels.
    Any insight would be great.
    Thanks

  • Jasper7821
    replied
    Thanks, I just trying to calculate what my electric bill will be annually with the solar since I already know (if same as last year) what it will be. And I know the production will be different daily.
    Im trying to see what my electric bill will be with solar added so I can justify spending the 13k after credits.
    I think it's worthwhile, plus I like to help the environment when possible. I have a plug in Hybrid so i save there too.

    And thanks for the clarity on KW and KWH.
    Still learning all this stuff.

    as far as production warranty, I'll read it thoroughly and see what I think.
    And with the SolarEdge app, wouldn
    Last edited by Jasper7821; 04-03-2019, 01:01 PM.

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  • J.P.M.
    replied
    Originally posted by Jasper7821 View Post
    Thanks, the zip is 85712 Tucson AZ.
    That number includes their calculated 14.08% loss and they got 11,721kW production for the year.
    Stil have to look at that link but it didn't seem like an actual number.
    and as far as shopping around, I did a little and was happy with my sales rep so we'll see what happens. The site survey is tomorrow and should have an exact production of kilowatts per year. As long as it has the production guarantee, I guess I'm happy.
    You will never get an "exact production of kilowatts per year".

    First off, annual output is measured in kWh/yr., not kilowatts per year.

    Second, you will not see the same output for any consecutive 365 day period any more than you will see the same weather for any consecutive 365 day period.

    Third, and partly due to the second point above, read the fine print on any production warranty. They are full of holes and pretty much useless. Also, you or most any residential user, even if they read the production warranty, will neither understand the terms or have the equipment or record keeping necessary to verify conditions for a warranty claim.

    Lastly, production warranties are strictly a marketing tool. they mean nothing in any real measure.

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  • Jasper7821
    replied
    I used the calculator and it's pretty cool. I changed form 15 degrees to 20 and it bumped up the production 219kW to total 11,994kW. That was the number that was the default number in there. And 14.08 was the default so I left that.
    soni guess my system will generate that then ?

    Leave a comment:


  • Jasper7821
    replied
    Thanks, the zip is 85712 Tucson AZ.
    That number includes their calculated 14.08% loss and they got 11,721kW production for the year.
    Stil have to look at that link but it didn't seem like an actual number.
    and as far as shopping around, I did a little and was happy with my sales rep so we'll see what happens. The site survey is tomorrow and should have an exact production of kilowatts per year. As long as it has the production guarantee, I guess I'm happy.

    Leave a comment:


  • J.P.M.
    replied
    What's your zip ? As Mike suggests, run PVWatts yourself and confirm the output. Looks like from that system loss of 14.08 (I'm assuming %) you write of, someone may have already ran PVWatts.

    When you rerun to verify, use 10 % system losses. Many folks find that # is a better fit for actual performance, at least in the early years of a system's life.

    If you live in a vey sunny, and moderately cool climate, you may have a shot at 1,744 kWh/yr. per installed STC kW, but that's close to about as high as it gets. Example: I'm in zip 92026 and w/out shade loss I've averaged 1,805 kWh/yr. per installed STC kW.


    ~ $3.00/STC W seems about the going rate. I'd get a couple more quotes and spend as much time looking at vendor quality as low initial price. Buy cheap, buy twice. Once to buy, once to fix things not done right the first time.

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  • Jasper7821
    replied
    Thanks for the reply, it's going to be a purchased system for 20k before Federal/State credits. It includes 30yr warranty on the entire system and 15yr warranty on the roof.
    Its going to be a rack system that they have just over 4K but that cost is included in the 20k It comes out to $3 a kilowatt and that seems to be the norm.
    as far as roof maintenance (resealing every 5yrs or so) I need to check on that. Maybe like the other stuff up there now and just seal up to whatever is sticking into the roof.
    Thank you for the link, I'll check that out.
    Last edited by Jasper7821; 04-03-2019, 11:09 AM.

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  • Mike90250
    replied
    Is this a purchase or a lease system ?

    You can do 95% of this yourself, with PV watts https://pvwatts.nrel.gov/pvwatts.php put in your data, and it gives you a monthly/yearly estimate.

    The big question , is how will the panels be affixed to the flat roof, anchors and sealant, or ballast racks ? Who do you call when it leaks ? who pays for roof repair, and when roof needs maintenance, who removes/replaces the solar ?

    Leave a comment:

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