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  • Alternate proposals - thoughts?

    Hi All,

    Going through the process of obtaining proposals from local companies that are rated highly.

    Just sent a note to all three asking that they propose to the same components - 34 340W Hanwha panels, IQ 7+ inverters. This keeps me in Tier 1 category with Gulf Power and meets my baseline of last year’s power needs.

    One had previously proposed this config, and the other two had proposed Aptos 330W and REC 385W solutions - all with Enphase IQ 7+inverters.

    I’ve got room for more panels, but more puts me into Tier 2 with higher insurance. and Gulf Power pays only 16% or so of the rate I pay them, so no real reason there, and 34 at 340W maxes me out with GP on an annual basis.

    I can’t see a reason to spend more on higher power, but would it make more sense to do end more on panels with slightly better thermal performance or better degradation percentage at End Of Life/End Of Warranty?
    Last edited by NWFPat; 03-28-2021, 10:57 PM.

  • #2
    Originally posted by NWFPat View Post
    Hi All,


    I’ve got room for more panels, but more puts me into Tier 2 with higher insurance. and Gulf Power pays only 16% or so of the rate I pay them, so no real reason there, and 34 at 340W maxes me out with GP on an annual basis.
    ......
    Is the Gulf Power limit based on panel capacity (DC) or inverter capacity (AC)?
    Did any of the proposals give you an estimate or garantee of production in kWhs for a year? You have a common denominator of the same number and same model of inverter.
    I would focus on the issue of total production in kWhs and not worry about specific panels unless the constraint by Gulf Power is based on DC capacity.
    9 kW solar. Driving EVs since 2012

    Comment


    • #3
      How much shading do you have at the proposed site ? If not much, why are you proposing to use micros ?

      Comment


      • #4
        Capacity is AC per Gulf Power, but, given my usage from last year, I need to nearly max out that Tier 1 of 10 kW, and if I build in a few percent for thermal (Florida), and degradation at end of life/warranty, I need every Watt possible.

        So, basic math is: panel output in Watts DC x number of panels x DC to AC conversion (0.85) = total Watts AC. Does the conversion factor change from system to system or is just the factor used for IQ 7+?

        In theory, then, with my usage rate I need to get as close to 10 kW AC, so I could play with panel output to maximize?

        No shading issues now, but trees grow fast here, and a neighbor to the south does have a couple.

        Comment


        • #5
          Originally posted by NWFPat View Post
          Hi All,

          Going through the process of obtaining proposals from local companies that are rated highly.

          Just sent a note to all three asking that they propose to the same components - 34 340W Hanwha panels, IQ 7+ inverters. This keeps me in Tier 1 category with Gulf Power and meets my baseline of last year’s power needs.

          One had previously proposed this config, and the other two had proposed Aptos 330W and REC 385W solutions - all with Enphase IQ 7+inverters.

          I’ve got room for more panels, but more puts me into Tier 2 with higher insurance. and Gulf Power pays only 16% or so of the rate I pay them, so no real reason there, and 34 at 340W maxes me out with GP on an annual basis.

          I can’t see a reason to spend more on higher power, but would it make more sense to do end more on panels with slightly better thermal performance or better degradation percentage at End Of Life/End Of Warranty?
          To your last question, it depends to some degree on what, if any, other goals you have besides staying below a 10STC kW system size.
          But as long as your stuck in the microinverter box w/IQ7+'s, and depending on how much clipping is incurred with any panel to micro match, and what that clipping loss translated to in terms of the lost production billing offset, that would be something I'd be looking at.

          The biggest reason I asked about shading was because while micros may be a partial solution for an application that has shade, for application without much shade micros add a lot of complexity to a design than tends to violate the kiss principle for little production gain while increasing the probability of more maint. and more down time for what's probably more upfront $$ vs. the choice of using string inverters .

          FWIW, an EQ7+ and 330 or 340 STC W panels probably won't result in too much clipping. The match of 385 STC W panels with a micro that clips at 295 W will probably produce more clipping than the smaller wattage panels. Whatever the reason(s) for staying below 10 STC kW, using the 385 W panels with the 295 W micros will produce less annual output than 10 STC kW comprised of 330 or 340 W panels geared with 295 W micros because the clipping will be less with the lower wattage panels.

          Or, seeing as how you don't want to spend more on higher power, you might spend less money and get a cleaner, less service prone system by having a lot fewer electronics (that don't like heat BTW), sitting on a hot FL roof in places mostly inaccessible once they're installed by using a properly sized string inverter. You'll also wind up with little or no clipping, or at least be able to minimize it more easily.

          BTW, how much electricity do you use in an average year ? As a real SWAG, an optimal (for annual production) and unshaded 10 STC kW system in FL will produce something like 15,000 to maybe 17,000 kWh/yr. +/- ~ 10 % or so based on weather.

          In the meantime, your postings reads to me like you need some more information/education. Get and read a copy of "Solar Power Your Home for Dummies". A slightly dated version is a free PDF download, with revised a version available for ~ $25 at Amazon or bookstores. Read it, then, and after the read, download a PV modeling program called PVWatts from NREL, found at @ pvwtts.org. Just read ALL the help screens a couple of times, get the inputs as close to what the preliminary design is, and use 10 % for system losses rather than the 14 % default the model uses. If nothing else, fooling around with the model will give you a better idea of what a 10 STC kW system will produce for you as a long term average as well as seeing what other sizes/orientations might be expected to produce +/- ~ 10 /yr. or so with most of the annual variation based on weather. Doing so will also serve as a check on how the vendor's production estimates - who never lost a job for underestimating annual output - compare to what an unbiased model will produce.

          Take what you want of the above. Scrap the rest.

          Comment


          • #6
            JPM,

            I ran quite a few model scenarios on PVWATTS - great site. Will likely improve quite a bit as the model improves to the point of being able to add specific panels and inverters - probably won't be till after I have decided on my system

            I understand the clipping issue - I think I understand it may be better to have more, lower power panels with lower cost micro inverters, than fewer higher power panels that drive one to more expensive IQ 7A micro inverters. It also seems reasonable that a lower cost can be obtained with an inverter per linear row of panels - as long as I can get suitable service when a panel or inverter fails.

            Annual usage was 15,934 (just reached the 12th month in the house). Our available sunlight is a bit less than southern Florida with greater cloud cover.

            Have 2 of the 3 bids now:
            Uni - 11.56 DC and 16,491/yr (Qcell 340 and IQ7+ inverters - different software calculating total?)
            SunF - 11.56 DC and 15.958/yr (Qcell 340 and IQ7+ inverters - different software calculating total?)
            Comp - 12.05 DC and 16,272yr/ (REC 380 and IQ7+ inverters - more power per panel and better thermal and less degradation, but 40%! more expensive is a non-starter - waiting on their matching proposal)

            Comment


            • #7
              Originally posted by NWFPat View Post
              Capacity is AC per Gulf Power, but, given my usage from last year, I need to nearly max out that Tier 1 of 10 kW, and if I build in a few percent for thermal (Florida), and degradation at end of life/warranty, I need every Watt possible.
              ..........

              In theory, then, with my usage rate I need to get as close to 10 kW AC, so I could play with panel output to maximize?

              No shading issues now, but trees grow fast here, and a neighbor to the south does have a couple.
              AC capacity is simply the AC capacity of the inverter. In the case of an IQ7+ its continuos output is 295 Watts. You would have to confirm that assumption with Gulf Power or find out what number they use..The math be simple; and it coincidentally is 34 IQ7+ inverters which would give you 9860 Watts.
              To meet your long term goal you are correct that you would have to play with panel output. I have attached the spec sheet for the IQ7 series. Instead of asking each vendor to propose the same panels I would ask them to propose maxing out the panel size and have them give you an estimate or better yet a gaurantee of annual production..
              Increasing the DC capacity will result in a higher DC to AC ratio and you do not want to exceed the manufacturers specs. If I had to choose one of your proposals I would pick the one with 385 Watt panels. That is a DC capacity of 13 kWs and a DC to AC ratio of 1.3 to 1. I consider that conservative but you will experience some clipping. My DC to AC ratio is 1.5 to 1 and I get some clipping. I believe my inverter size may have been constrained by my service panel size or my power provider but the installer designed a system based on maximizing the output of that inverter.

              The catch here is that the metric often used to evaluate system cost is DC capacity. The vendors love to propose more DC capacity with smaller inverters because their costs are less than if they use a larger inverter. In your case there is a market constraint and your goal is to maximize kWh output in the long term.

              Last edited by Ampster; 03-30-2021, 12:23 PM.
              9 kW solar. Driving EVs since 2012

              Comment


              • #8
                Whoops - forgot to mention, duh - I have orientations for 250 and 160 to work with - largest area of roof is at 250 - each of the companies arranged panels a bit differently I their proposals, which likely explains some of the differential in annual output. I think roof is 4/12.

                Comment


                • #9
                  That is a further reason to be aggressive on the DC to AC ratio. You can check their output estimates against the PV Watts model. There are many discusions here on how to do that.

                  With multiple orientations the benefits of string inverters come into play. The two negatives are shade and that the size may not come as cliose to 9860 Watts like multiple small inverters. However @bcroe subsequently makes a good argument about leveraging multiple orientations with string inverters.
                  Last edited by Ampster; 03-30-2021, 01:28 PM. Reason: Add comment from Bruce.
                  9 kW solar. Driving EVs since 2012

                  Comment


                  • #10
                    Seems to me, the size panels was badly (over)matched to the size micro inverters.
                    As mentioned a string inverter can be used to advantage in multi orientation, in
                    avoiding this sort of mis match, and allowing a higher DC:AC ratio and more energy
                    collection for a given total inverter (and AC rating) size. Panel strings with different
                    orientations can be connected to the same string inverter, allowing a far higher
                    DC:AC WITHOUT CLIPPING, collecting more energy. Alternately here, I adjust
                    both the number and orientation of panel strings, to just touch clipping level,
                    while the increased panels ALSO boost collection under clouds.

                    Take that, no brainer micros. Bruce Roe

                    Comment


                    • #11
                      Originally posted by NWFPat View Post
                      Whoops - forgot to mention, duh - I have orientations for 250 and 160 to work with - largest area of roof is at 250 - each of the companies arranged panels a bit differently I their proposals, which likely explains some of the differential in annual output. I think roof is 4/12.
                      Well, that does change things a bit. What are the available roof areas for each orientation, are there any building/fire code restrictions on array placement, which roof area will get more shade, any time of use rate considerations, and what's your zip ?

                      Comment


                      • #12
                        brcoe and Ampster - thank you both for your thoughts - and help.

                        I had two basic different proposals - two had 330-340W panels, and the other 385W panels - all proposals used IQ 7+ inverters.

                        If ones starts with theoretical 340W panels (real word maybe lose 10% for dirt, shading, etc, so figure 306W) and then puts on 295W inverters, that's about 4% over the 295W output rating ... is this how you would do the math?

                        The other panel, on the other hand, at 385W minus 10% nets 346.5W, so 17% over the inverter's rating. This solution was 40% more expensive than the 340W panel solution, but had better thermal and lower degradation (92% at EOW)

                        I'm trying to approach this from a raw financial perspective, so looking for the most power for the least dollars - and, since I'm trying to stay at the max level for Tier 1, and they rate by AC output, it still seems like more lower power/lower cost panels is more advantageous and that this also means lower cost inverters.

                        I'm probably not getting some of the points you are both trying to make ...

                        Comment


                        • #13
                          JPM,

                          Zip is 32526, both 250 and 160 orientations were used in all the proposals, but I can fit 34 panels on the 250 facing (28 in one large area, and another 6 in a smaller area). The 160 orientation does not provide enough space for all the panels, and has some limited chance of tree shading in the far future.

                          Here's the time of use rate program from GP - we are not currently enrolled. https://www.gulfpower.com/content/da...elect-Rate.pdf

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                          • #14
                            The below shows one of the proposals - the sidewalk to the front is pretty close to 250 degrees.

                            Screen Shot 2021-03-30 at 5.40.05 PM.png

                            Comment


                            • #15
                              Originally posted by NWFPat View Post
                              JPM,

                              Zip is 32526, both 250 and 160 orientations were used in all the proposals, but I can fit 34 panels on the 250 facing (28 in one large area, and another 6 in a smaller area). The 160 orientation does not provide enough space for all the panels, and has some limited chance of tree shading in the far future.

                              Here's the time of use rate program from GP - we are not currently enrolled. https://www.gulfpower.com/content/da...elect-Rate.pdf
                              Thank you. Any building or fire code restrictions on panel placement ?

                              Hard to tell, but from the photo you provided it looks like some NW portions of the large array location may come under some shading from the roof in the winter in the late afternoon, but as a SWAG, the penalty may well be small enough to ignore.

                              I'd also note that your T.O.U. daily times and seasons are very similar to mine and also those of the big 3 CA I.O.U.'s, although your rates are a lot lower. You sure this is going to be cost effective ?

                              Do you have access through your POCO of your prior use by hour or smaller increment ? If so, and if you're truly interested in getting a fair estimate of an annual (residual) electric bill or better yet, the yearly value of the generated electricity to offset any annual electric bill (provided the system offsets less than 100% of an annual load), using PVWatts hourly output spreadsheet and the hourly draw data from your POCO you'll be able to do that to a pretty good approximation.

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