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Finished self-install in phoenix- 11.7kw dc.

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  • Finished self-install in phoenix- 11.7kw dc.

    Started the talks a couple months back just wanted to post that the install is finished. Have inspection scheduled. Had the system on for most of the day Saturday to ensure all micros came online, updated, and produced as expected. Now shut off waiting PTO.

    I'll try to list some reasoning and explanations in case anyone has questions or is wondering why I did a couple things that go against the norm.

    34x Silfab 345SLGM
    34x Enphase IQ6+
    1x Enphase combiner box w/ envoy-s
    50 x Quickmount PV S Tile Replacement
    Ironridge XR100

    A little electrical system background:
    400 amp ses with two mains, 200A and 100A. The 200A feeds a 200A bus panel, the 100A feeds a 125A bus panel. Thus, I could either do 40A backfeeding to main, 50A backbeeding to the secondary, or a combination of both (however not technically possible as the power company wants a single Kwh meter between the solar and service panel.

    So the options were
    A) Line side tap (electrical engineering \ permit signoff required.)
    B) Derate main breaker (electrical engineering \ permit signoff required, plus load calaculations)
    C) Feed max of 50A ocpd to second panel.
    D) Feed max of 40A ocpd to main panel.
    E) Upgrade 125A panel to larger panel.(additional permit required, plus load calaculations + engineering since it is derating the breaker, even though it already existed derated)

    So to avoid paying an electrician to sign off on load calcs and stamp their name on my permit, which i'm not sure one would even do without being hired for the job, I opted to keep it under 50A OCPD backfeed.

    First datapoint, is I don't have an ideal roof for solar. The majority of the non interrupted roof points about 290 degrees WNW. I have a couple small hips that face ideal, around 200 degrees, but they arent very large in size. This means that I'll have a sizable difference in DC KW to AC KW output for much of the year. I could have scattered some facing around 110 degrees, but a panel here and there is kinda ugly.

    Micros chosen for a few reasons;
    1- I liked the idea of zero conduit on the roof given my layout and SES location. And popping a conduit body into a jbox under the panels and running romex to the garage saves quite a bit in materials and labor.
    2- Also helps keep the aesthetics up- no conduit over the roof. And bending conduit in an attic, not fun.
    3- Minor shading in AM, but not a big deal.
    4- The fear of electronics dying on the roof doesn't concern me, and I'm aware reliability has improved drastically on their newer gear. And given the quantity i have, I probably wouldn't even file warranty claim until at least 2 or 3 die and swap them all at once. losing 1/34 is only 3%, a few bucks a month, so no micro fear here..

    There was also the fact that micros were a little easier to max out my electric design. For instance, I debated between solaredge. but would have wanted two 5000h's. 21A output each. = 42A In fact, every combination close to my DC size (11.7kwh) to get a decent ratio was all A/C over 50A of OCPD. The only way I could have stayed under 50A was with a 6000 and a 3000, for a total of 37.A continuous output. So, I opted for 34 IQ6 micro inverters, at 1.17A each for 39.78A continuous, or 49.275A of OCPD. This allows my maximum to stay under the 50A OCPD limit, while still maximizing the power i produce to get to 50A. SE would have been 8.88KW AC vs IQ 9.57KW AC.

    To get the most raw power for my AC kw rating, I oversized the panels with Silfab SLG345M 72 cells modules. I wanted to keep the total panel count low, so opted for 72 cell. (more panels = more mounts = more inverters = more cost). I understood clipping would be an issue for the 8 panels that face 200 degrees, by having a 1.18 ratio of 345W panel to 290W max inverter. This was already obvious as they hit 290w by 11am and stayed there until 2pm. Should be less when it heats up, now is about the perfect solar producing weather here. Be lying if i said it wasnt sad to see them cap at 290w.

    The electric plan will be APS's 3-8PM peak, no demand, with about $.24 peak and $.11 offpeak, and a grid connection charge of something around $12. Est production 18,000kwh into a consumption of last year around 21,000kwh.

    Attached images
    1 - is production during testing- didn't turn the system on until 1030 (another day of testing showed it starts produces as early as 730). but still hit 48kwh for the day which is very close to PVwatts estimate. Still making fair power at 3pm once the peak time starts.
    2- Shows the general layout with that test day of kwh.

    Looking forward to the good production into the late afternoon as the sun gets higher! And being able to run A/C all day and not sweat out the afternoon waiting for off peak.

    Could I have achieved more power at a cheaper cost? Absolutely. I could have gone string, saved on micros and paid an electrician with the difference to modify my service to accommodate a higher AC kw. Could have used cheaper railing. But, this wasn't necessarily about the cheapest cost. It was a good blend of aesthetics, self-install 100%, total output, output during afternoon, me being able to sleep at night, and a good ROI all said and done.

    About $1.05 / kwh installed after credits, including a few costly mistakes Could have been $1/kwh. For my usage, it should take about 5-1/2 years to get the investment back.

    All in all, fun project, and now at the mercy of the AHJ.
    Attached Files

  • #2
    Congrats! It's fun to watch the numbers and see it all work out.

    I'm in Gilbert with SRP on the Basic plan so no TOU for us. We actually became even more energy efficient after going solar when the pool pump got replaced. Last year we generated 12,000 kWh but only used 9500. We cashed out the balance at wholesale and the account credit pays the connection fee for 4 months. In 2017 we paid just under $100 to SRP.
    Dave W. Gilbert AZ
    6.63kW grid-tie owner

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    • #3
      $100 a year is a good utility bill!! It would have been nice to not have time of use but those days are gone in APS land...they're fighting to put everyone on demand charges too, because they know thats where they stick it to solar users in the evening. The new demand charge essentially says if you want to turn on your ac pay us $50 just to do that.. plus energy. Criminal.

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