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  • Final Check on 14.22kW System

    Thanks again for all the help in my previous post, I have made the changes suggested and want to make sure I'm making all the right calls before this huge investment.

    -14.22kW System
    -2 SE 7600H Inverters
    -36 LG395N2W-A5 Modules
    -36 P-505 Optimizers
    -25 Year Warranty Parts and Labor
    -Ethernet Hardwired Production Monitoring
    -Ethernet Hardwired Consumption Monitoring (+$1,000)

    Azimuth 268 Degrees, Tilt 50 Degrees, Flush Mounted all on 1 roof plane, Eastern Texas
    0 Shade, my house is 2 stories and both neighbors are 1, no trees within 150ft
    Expected Annual Production: 16,000kWh
    Average Usage: 18,000 kWh

    Gross Cost: $37,683 ($2.65/w*14,220)+$1,000 Hardwired Consumption Monitoring=$38,683 or $2.72/w (with consumption monitoring)
    Net Cost: $38,683-Oncor Rebate ($9,970)-Federal Credit($8,613)=$20,100 $1.42/w

    All look good? Committing the vast majority of the funds and ordering components Monday, Thanks!!



  • #2
    Too bad you have a less than optimal orientation.

    PVWatts suggests about 17,800 kWh/yr. or so for Dallas.

    Vendors often underestimate output by 10 % or so for lots of reasons, not all of them having to do with conservative design.

    How did you get the estimated output ?

    FWIW, and if you already know this forget I brought it up, an optimal orientation would have reduced the proposed array size by 20-25 % and the cost close to the same % age but will produce about the same 17-18,000 kWh/yr. output.

    Do you have net metering and/or TOU billing ?

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    • #3
      No it's "false" net metering as Texas doesn't allow it. Green mountain sells at 12.3c then buys all production at 12.3c "netting" it out. Any other cheaper plan would sell me the 2000kw show the 1,900 I generated then charge me for the full 2,000.

      Estimated output was by what looks like a design program, tilt, dust, average degradation over useful life, several other factors, etc. that the company sent. They said to expect more in earlier years, but they didn't want to over promise.

      For optimal location are you talking azimuth or tilt? Tilt is too high because of flush mounting and that's the roof pitch. Aesthetic decision. Azimuth is that the front of the house is a multi-tier with many shadows and would look poor, that's 180 degrees. Some panels at 90 would be better but it's technically 87 degrees just like the other side is 267. This violates the terms of the 90-270 requirement of Oncor's rebate and would destroy my ROI as they don't prorate they either give it or decline the whole project.

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      • #4
        Originally posted by adam61 View Post
        No it's "false" net metering as Texas doesn't allow it. Green mountain sells at 12.3c then buys all production at 12.3c "netting" it out. Any other cheaper plan would sell me the 2000kw show the 1,900 I generated then charge me for the full 2,000.

        Estimated output was by what looks like a design program, tilt, dust, average degradation over useful life, several other factors, etc. that the company sent. They said to expect more in earlier years, but they didn't want to over promise.

        For optimal location are you talking azimuth or tilt? Tilt is too high because of flush mounting and that's the roof pitch. Aesthetic decision. Azimuth is that the front of the house is a multi-tier with many shadows and would look poor, that's 180 degrees. Some panels at 90 would be better but it's technically 87 degrees just like the other side is 267. This violates the terms of the 90-270 requirement of Oncor's rebate and would destroy my ROI as they don't prorate they either give it or decline the whole project.
        Understood. Thank you.

        In response:

        Most decent design models will, for the same inputs and almost by definition, produce about the same annual output. Most model inputs are adjustable by the user and that's often done - unfortunately sometimes to produce a model output that appears lower to customers usually unfamiliar with such things, but giving such customers confidence while helping vendors sell a bigger system than required with no embarrassing questions from potential customers. An added bonus for the seller, besides overselling with fewer questions, is when the system appears to be overproducing (but probably isn't) and the customer thinks they got a better deal than they actually wound up with.

        PVWatts has been shown to be a decent model for residential PV preliminary design. There are other good models. That PVWatts suggests a long term average annual output that's about 10 % greater than you were told fits in with the often found underestimate of annual output a lot of (but by no means all) vendors use. Sounds (reads) like in mentioning common and expected decline in annual output (which is usually accounted for in a decent model), the seller may be trying to mask the underestimate of production. Nice way to B.S. someone.

        As a design philosophy, some overdesign is probably a good idea, but rolling up and piggybacking conservative design measures isn't the way to do it. A better idea might be to tell (or best of all ask) the potential customer how much overdesign they want while taking the 5 minutes or less it takes to explain the benefits and drawbacks of adding capacity to a design, and letting the customer make an informed decision rather than skunking added size on an ignorant mark. I appreciate that can happen - I was a com mission salesperson for ~ 10 yrs. peddling industrial power and process equipment and took a pay cut when I changed to engineering as a way to make a living, but such practices and others - like hiding overdesign in inputs to a model that will then under-predict output in deceptive ways is B.S.

        On optimal orientation: That includes both tilt and azimuth considerations as well as practical considerations of the rebate situation, and lots of other things as you now mention. I wasn't knocking what you have, it is what it is, and roofs or available array locations aren't usually too adjustable. I get that. As you have not, until now, mentioned any other considerations or reasons or limitations on orientation, I was, then and now, simply asking if you are aware that the orientation you do have is less than optimal from an annual production standpoint considering only the information you've supplied up until your last post.

        Some of the above may or may not have been part of your considerations before you committed.

        Just a response to your question "All look good ?" Take it for what it's worth. Scarp the rest or all,of it.
        Last edited by J.P.M.; 04-20-2019, 12:35 PM.

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        • #5
          May want to check about using LG commercial panels on residential. I tried once and was told it is a no-no according to LG

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          • #6
            The Neon 2 395's seem like consumer options. They have black flashing and wiring and talk about being a great fit for your roof on their product ads. Why are they commercial only?

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            • #7
              This may be a different line, but we had an issue with one of the high output commercial panels that were to be used on commercial only. I'll check the model numbers at the shop tomorrow

              Originally posted by adam61 View Post
              The Neon 2 395's seem like consumer options. They have black flashing and wiring and talk about being a great fit for your roof on their product ads. Why are they commercial only?

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