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New 9.6kW solar install in Northern VA

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  • New 9.6kW solar install in Northern VA

    Hello,

    I'm in the final stages of designing my DIY home grid-tie solar system and just wanted to run it by you guys to see if I'm missing anything. The basics are as follows: 35x 275W (CS6K-275M) for a total of 9.625kW. SolarEdge SE7600A-US inverter with 35 P300 SolarEdge optimizers. Twenty-nine (29) of the panels are facing South (170°) the remaining six (6) are facing West (260°). Two strings divided equally 18/17. String 1 will run at max 4,950-5,040W @350V --> 14.4A. String 2: max 4,675W-4,760W --> 13.6A. Existing electrical panel rated at 200A/240V. All wiring will be running in conduit inside the attic all the way to the attached garage (less than 60'). For the racking, I'm planning on using IronRidge XR100 rails on QuickMount Flashing E-mounts, although I'm open to other options. I'd prefer to be no more than 3" off the roofing surface. My main south roof is 33° pitch and the west side roof is 45°. The roof material is asphalt shingle. My next step is drafting up some diagrams/plans and applying for building and electrical permits. Already have applied for my local power company (Dominion Power) Solar Purchase program and have local HOA/town approvals. Hoping to start construction end of September with switch on date October 1st. Any other suggestions or advice?

  • #2
    That is a little more than I would put on a 7600.
    I would consider the Ironridge Flashfeet instead of the quickmounts
    What are you using for an external AC disconnect?
    OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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    • #3
      Keeping the cart before the horse before design details, did you do a load analysis to figure out what array size might offset how much of your electric bill in the most cost effective or whatever way your priorities take you ?

      One other preliminary design decision: Are you aware that a 6" standoff vs. the 3" will probably allow the array to run cooler and thus have a higher probability of a somewhat greater annual output ?

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      • #4
        Originally posted by ButchDeal View Post
        That is a little more than I would put on a 7600.
        I would consider the Ironridge Flashfeet instead of the quickmounts
        What are you using for an external AC disconnect?
        Thank you, I'll look into Flashfeet. As far as the AC disconnect, if I were to install the SolarEdge inverter outside my garage, would that eliminate the need for additional external AC disconnect? The 7600A-US includes RapidShutdown switch that deenergizes the system within 10s. (in compliance with NEC 2014 Rapid Shutdown code 690.12) Any pros/cons of keeping it inside vs. outside?

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        • #5
          Originally posted by Ne0eN View Post
          Thank you, I'll look into Flashfeet. As far as the AC disconnect, if I were to install the SolarEdge inverter outside my garage, would that eliminate the need for additional external AC disconnect? The 7600A-US includes RapidShutdown switch that deenergizes the system within 10s. (in compliance with NEC 2014 Rapid Shutdown code 690.12) Any pros/cons of keeping it inside vs. outside?

          The SE7600 does not come with an AC disconnect. It has a DC disconnect built in. Check your local code for requirments of locking AC disconnect.
          OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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          • #6
            Originally posted by J.P.M. View Post
            Keeping the cart before the horse before design details, did you do a load analysis to figure out what array size might offset how much of your electric bill in the most cost effective or whatever way your priorities take you ?

            One other preliminary design decision: Are you aware that a 6" standoff vs. the 3" will probably allow the array to run cooler and thus have a higher probability of a somewhat greater annual output ?
            Yes... My average annual electrical load is 17,440 kWh based on the last 5 yr data at my current 3,600 sq.ft. house. This system should produce 13,376 kWh based on PVWatts calculation. So this should cover 75% of my current usage. I did upgrade one of my HVAC systems from 10 seer to 16 SEER this year, so that should make some impact on my annual usage. I'm also in the process of replacing all of my 75W recessed lights with LED bulbs (there are around 50 of them). My design criteria/priority was to use the largest possible inverter without making too many changes to my existing electrical system, as well as utilizing as much of my southern roof area as possible. I would love to eventually lower my electrical load but at the same time I may look into an electrical car couple of years from now.

            As far as the roof standoff, my HOA approved my design with the stipulation that the panels have a "low profile, mounted flat on the roof"

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            • #7
              Wait, you're doing the Dominion power selling program? They give you $.15/kWh for everything you produce...but they send you a check for it and you have to pay tax on it. So, it's like you're getting 11-12 cents per kWh. Dominion does support net metering, that's what we did, you can simply request that a smart meter be installed with net metering enabled. No additional income to claim on your taxes, just less kWhs to be billed for.

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              • #8
                Originally posted by nevetsyad View Post
                Wait, you're doing the Dominion power selling program? They give you $.15/kWh for everything you produce...but they send you a check for it and you have to pay tax on it. So, it's like you're getting 11-12 cents per kWh. Dominion does support net metering, that's what we did, you can simply request that a smart meter be installed with net metering enabled. No additional income to claim on your taxes, just less kWhs to be billed for.
                Yes, but they don't actually send you the check, but credit the amount on the bill. I think either way it's a wash, and I can always change to net-metering. Btw, the system has been up since mid-December and is producing power nicely. Should be hitting 1MWh of total production in the next few days.

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