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  • Grid Tied System - Design

    Hi All,

    In VA there are a few limits to residential solar and in general it hasn't been a big market. Power here is cheap (right now), there are not additional incentives and it isn't like AZ sun (and we have lots of trees probably doesn't help either). For more background on my project you can see the intro post (https://www.solarpaneltalk.com/forum...-from-virginia) I am allowed (for now) to participated in net metering but the main limiting factor in my design are the archaic rules put in place essentially by Dominion to limit the use of solar outside of their own solar farms (ironic right). Anyway we can discuss politics elsewhere I am just a little guy and have to follow the rules as written. My home is not efficient and is totally on electric so we have historical demand to allow up to the 20 kW max system size permitted (you can only install based on historical usage) BUT after 10 kW (AC side) of production Dominion (Local power) starts charging a monthly stand-by fee (of "Standby Charge of $2.79 per kW of demand") Which seems to vary month to month based on news stories but it does say per kW not kWh and could be $60 or more per month. So this system is meant to produce a MAX of 9.95 kW AC. I don't have any specific questions but let me know if there are known issues with any of the components or other ways you all might think about it.

    Location: Barn roof (not yet built) 24 x 60 ft of south facing standing seam roof
    Panels: Likely SolarWorld 290W (17.3% efficiency) or Canadian Solar CS6k-300Ms (18.33%)
    Total Panels: 36 (3 strings of 12 panels) Total kW DC will (obviously) depend on final panel decision but these are both similar in around 10.5 kW with string voltage around 390 and amps around 9.15.
    Inverter: Fronius Primo 10.0-1 plus Quattro rapid shutdown for a combiner
    Lightning Protection: TBD but using Midnite's products to protect the strings and inverter
    Wiring Size: TBD, Maybe 1 AWG for the long run

    I plan on installing the panels on the roof with S-5 connectors and iron ridge XR100 rails in two rows that are two panels tall (so from the eve there would be two panels, a gap then two more panels). It will be about a 2' gap between rows, on a 4/12 slope which I hope is enough to allow access later if needed. The Quattro will be installed on the roof near the array, combine two strings, and run in conduit two DC wires and a communication wire to the Fronius Primo. The inverter will be installed in the barn directly below the south facing roof so run length should be around 25'. The inverter would then output to the long run back to the house in buried conduit, around 170', to a disconnect then the new breaker in one of the existing load panels.

    Anything else I should think about?

    Thanks,
    Bill









  • #2
    If the limit is AC then you might be better off with an inverter like skaredge SE10000h that can be over paneled a lot and build the barn with east west roof puttin 7ke east and 7kw west. The inverter would limit you to 10kw and you would have a lot longer production resulting in more kWh. Also cheaper rapid shutdown and better monitoring. It could be done with string inverter as well though.
    OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

    Comment


    • #3
      You will be way ahead on efficiency to run the 390VDC over the long 170' run (like I do), then put
      the inverters fairly close to your meter. 1 AWG not required. And I second the idea of more hours
      of production without a bigger inverter, with over paneled E and W facing. Just how much this can
      be pushed depends some on the angle of the roof, steeper gives less peak power overlap at midday.
      Bruce Roe

      Comment


      • #4
        Great ideas. I can see the dominion form review team looking at the submission and being like 'Who is the idiot that put 14 kW on a 10kW inverter' haha look who's laughing now! What I haven't mentioned yet is that I plan on adding another 10 kW of panels on the south facing roof for a separate offgrid system as a 'work around' to the limit. I was trying to avoid information overload on a single post but it is relevant regarding other creative work arounds. I will save the details for another thread as it is amazing how much easier grid tied really is!

        If I stick with the string inverter then I will seriously look into moving it next to the panel and comparing the wire specs. 1 AWG is probably overkill for the AC as well. I need to do the cost comparison on wire price vs voltage drop loss.

        Back to the solaredge inverter though, that was my original plan (- the overpanels) with micro inverters but when I priced it out the cost was about the same as the TL string inverters. I don't actually need (per my reading of code i will find out later!) rapid shut down and used the Quattro piece because it was not that expensive and easier than wiring a combiner. My thinking on the picking between the two was that I discounted the shading, as I expect minimal shading, and monitoring single panels was interesting but I didn't give it much value (and will probably be proved wrong but that is just Murphy) and the Fronius seemed simpler (less pieces to break) at the same price point. As I am not the worlds best shopper did I miss something on the price side of things or is it only an advantage for the over paneled case?

        Comment


        • #5
          Micro inverters make it a lot more difficult to optimize the E-W idea, because you must take a pair
          of panels (on opposite sides) and connect them in parallel to EACH micro inverter. That sets your
          over panel ratio at 200% of inverter capacity. With strings, things can be adjusted more finely.

          In addition micros force you to run the much less efficient AC all the way to the panels. And
          you need a big AC bus at the array to plug all that into. With DC strings the wiring becomes so
          much simpler, a few wires go to a combiner and a pair of relatively smaller wires run to the inverter.
          Sketch it out and see. Bruce Roe

          Comment


          • #6
            BillSunGen, as you are new, welcome! Also,while there may be installers or sales or designers or enthusiasts (like me) or ... here, Bruce knows his stuff from having a huge (by my definition) array and every day, feet-on-the-ground working knowledge. You would be wise to heed his advice.

            I have to bring this up as the monitoring of SE data was mentioned. I really dislike SE monitoring as it is all cloud based. They pretty much make it mandatory that access of MY data has to go through them. While I don't sit on my array and only check the status ~2-3 times per week (not counting my automated data pulls), there have been more than a few times recently that the SE site has been down. Without a lot of hook and crook and wedge and shimmy, there is no way to directly get real time, granular data locally from the inverter. If monitoring is going to be important then you may do some looking into the SE monitoring/reporting strategy before making a decision.

            Comment


            • #7
              I think you are confusing optimizers like Solaredge and micro inverters like Enphase. An east west over panel system will not work well with micro inverters but will work great with solaredge optimizers. You have to look at how much you can over panel the inverters without breaking th warranty.
              As for the simplicity, solaredge optimizers are very regular without film based capacitors and he inverter is much simpler than the fronius due to the distributed MPPT to the optimizers. It has film caps as well which are much more rugged and is one of the highest efficient inverter systems available.
              That all said others tend to disagree and and recommend the less component method. I will say that we have not had that great of luck with fronius, SMA would be a better brand in my opinion of string inverter.

              as for the off grid system, that will never have any return on investment and you still will need to pull permits and inspections on it.

              You can run some models in pvwatts with the two azimuths. And see your production curve.
              OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

              Comment


              • #8
                Originally posted by DrLumen View Post
                I have to bring this up as the monitoring of SE data was mentioned. I really dislike SE monitoring as it is all cloud based. They pretty much make it mandatory that access of MY data has to go through them. While I don't sit on my array and only check the status ~2-3 times per week (not counting my automated data pulls), there have been more than a few times recently that the SE site has been down. Without a lot of hook and crook and wedge and shimmy, there is no way to directly get real time, granular data locally from the inverter. If monitoring is going to be important then you may do some looking into the SE monitoring/reporting strategy before making a decision.
                Nearly all grid tie inverter monitoring solutions are cloud based. A few have some limited local access these are mostly in older models and are going away.
                solaredges monitoring is just about the best monitoring of any of the systems available though.
                OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

                Comment


                • #9
                  Case in point... I have ~492 square feet of solar panels and still need a photocell to control the outdoor lights.

                  Comment


                  • #10
                    Originally posted by DrLumen View Post
                    Case in point... I have ~492 square feet of solar panels and still need a photocell to control the outdoor lights.
                    You could just as easily control the lights with cloud based pv monitoring if you wanted to, Or any of the weather/time based rules from IFTTT or other such services.
                    OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

                    Comment


                    • #11
                      Originally posted by DrLumen View Post
                      Case in point... I have ~492 square feet of solar panels and still need a photocell to control the outdoor lights.
                      I suppose outdoor lights are there for the convenience of the owners, and to discourage those who
                      should not be there. I found motion triggered lights do both much better. The average power is so
                      low, I can have a lot more of them, than all night lights. You can circle my place, and never be in
                      the dark. Bruce Roe

                      Comment


                      • #12
                        Originally posted by bcroe View Post

                        I suppose outdoor lights are there for the convenience of the owners, and to discourage those who
                        should not be there. I found motion triggered lights do both much better. The average power is so
                        low, I can have a lot more of them, than all night lights. You can circle my place, and never be in
                        the dark. Bruce Roe
                        I prefer motion lights for the same reason.
                        OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

                        Comment


                        • #13
                          ButchDeal you are correct I was confusing the optimizers and the micro inverters. I know i started with the optimizers but i guess looking into the enphase systems I just lumped them all together at some point in my head. Good to know on experience with the Fronius, I am a bit sensitive on 'capacitor' issues. I had two fairly expensive motherboards fail due to what is now apparently known as the Capacitor Plague according to Wikipedia (https://en.wikipedia.org/wiki/Capacitor_plague). For SMA I speced out a Sunny Boy 5, Sunny Boy 6 combination but that would have required a combiner box as well and (in theory) was getting close on the 10 kW limit but would probably have been fine after loss adjustments. The Fronius seemed simpler so was leaning that way. Is there anyone here who is a fan of the Fronius systems?

                          On the permit side, I plan on doing both (of whatever the final design is) at the same time and will be fully permitted and by the book. As I read it Dominion can't write the rules if it isn't connected to 'their' grid. But yes, I understand it is a whole different cost/benefit set of decisions on that one.

                          On monitoring, any system that allows direct access to the data is a plus for me. My internet connection is through 3g/4g on a cell phone and most 'smart' devices are EXTREMELY chatty with their network traffic. My guess is that most internet of things developers are on fiber or just plain stupid when it comes to caring about network efficiency (To name specific ones I am looking at Samsung as the worst in my house). So the geek side of me loves the data and the cool interfaces, reporting, and management but if it can't be done locally it probably isn't for me.

                          Comment


                          • #14
                            Originally posted by BillSunGen View Post
                            On the permit side, I plan on doing both (of whatever the final design is) at the same time and will be fully permitted and by the book. As I read it Dominion can't write the rules if it isn't connected to 'their' grid. But yes, I understand it is a whole different cost/benefit set of decisions on that one.
                            the power company does not write the requirements for the permit, the AHJ does and you still have to meet the code requirements on or off grid
                            the off grid will have zero return on investment. Your cost benefit analysis for the off grid side is easy.

                            Originally posted by BillSunGen View Post
                            On monitoring, any system that allows direct access to the data is a plus for me. My internet connection is through 3g/4g on a cell phone and most 'smart' devices are EXTREMELY chatty with their network traffic. My guess is that most internet of things developers are on fiber or just plain stupid when it comes to caring about network efficiency (To name specific ones I am looking at Samsung as the worst in my house). So the geek side of me loves the data and the cool interfaces, reporting, and management but if it can't be done locally it probably isn't for me.
                            Some like SolarEdge have a cell modem option for monitoring.
                            OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

                            Comment


                            • #15
                              I have been running a pair of Fronius IG Plus string inverters here for 5 years, no failures. They are
                              over paneled quite a bit. Of course no individual panel monitoring. No hands on experience with
                              optimizers here. Bruce Roe

                              Comment

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