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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
    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


    • #3
      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


      • #4
        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


        • #5
          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


          • #6
            Case in point... I have ~492 square feet of solar panels and still need a photocell to control the outdoor lights.

            Comment


            • #7
              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


              • #8
                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


                • #9
                  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


                  • #10
                    Originally posted by bcroe
                    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 have some motion lights as well but I have a flag that, per flag etiquette, should be lit if flying at night. I also want the front porch light on all night. Plus, I want the photocell signal for some HA functions.

                    Originally posted by BillSunGen
                    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.
                    Is that a Samsung Smarthings hub? My Frontier internet was down for a few days and the smartthings hub was completely useless. I quickly got away from that and only use it for a few inconsequential things now.

                    Originally posted by ButchDeal
                    Some like SolarEdge have a cell modem option for monitoring.
                    Those only report every four hours. Unfortunately, that is what my installer put on mine.
                    Last edited by DrLumen; 06-11-2018, 02:32 AM.

                    Comment


                    • #11
                      One item you haven't mentioned is surge/lightning protection. Barns seem to attract a fair share of hits as they are usually tall without a lot of trees around them. Nothing is guaranteed if there is direct strike but its definitely worth spending the bucks to try to get protection in place. I am impressed with the specs on the Midnight Solar SPDs and the construction seems to be step above others I have seen. If it was my system I would have one on at the combiner box on the roof and another, between the inverter and the subpanel in the barn. For good measure I also suggest one on the main panel but that is not as much PV related as general good practice to keep utility surges out of your panel.

                      Also look around for the recommendation on how to ground the wiring on the property. Sunking and others are the pros and have opinions on what is code and what is right and suggest you do some searching on older threads to get the latest and greatest. I think it involves putting in ground rod at the barn connected to the main house ground point via #4 copper laid in the conduit trench but as I said its worth doing the searching.

                      Comment


                      • #12
                        Originally posted by DrLumen View Post
                        I have some motion lights as well but I have a flag that, per flag etiquette, should be lit if
                        flying at night. I also want the front porch light on all night. Plus, I want the photocell signal for some HA functions.
                        I have a photocell light control for the 3 W LED light in my phone booth. A similar size might work for a
                        porch light, I switch on a bulb for reading. Bruce Roe

                        Comment


                        • #13
                          Originally posted by DrLumen View Post
                          Is that a Samsung Smarthings hub? My Frontier internet was down for a few days and the smartthings hub was completely useless. I quickly got away from that and only use it for a few inconsequential things now.
                          That is the crazy thing. It is just a TV, a 'Smart' TV but I don't have anything setup on it. Just how it came out of the box. I had to connect it to the internet to get it to turn on but then blocked it at the router the next day as all my other devices were operating at a crawl. It is amazing how many of the new devices have to have an internet connection to do something local. You want your doorbell to ring? Needs internet. Want to view your security camera? Needs internet. Want to read your newspaper? Needs internet (oh wait I still get the paper so that one works...) Same with the home automation stuff. It is neat, takes a lot more time than I have to setup, but all breaks if the internet isn't available. Makes it a bit fragile. Being able to configure something on a local subnet just isn't something that comes up in regular marketing materials but it is probably out there somewhere.

                          Comment


                          • #14
                            Originally posted by peakbagger View Post
                            One item you haven't mentioned is surge/lightning protection. Barns seem to attract a fair share of hits as they are usually tall without a lot of trees around them. Nothing is guaranteed if there is direct strike but its definitely worth spending the bucks to try to get protection in place. I am impressed with the specs on the Midnight Solar SPDs and the construction seems to be step above others I have seen. If it was my system I would have one on at the combiner box on the roof and another, between the inverter and the subpanel in the barn. For good measure I also suggest one on the main panel but that is not as much PV related as general good practice to keep utility surges out of your panel.

                            Also look around for the recommendation on how to ground the wiring on the property. Sunking and others are the pros and have opinions on what is code and what is right and suggest you do some searching on older threads to get the latest and greatest. I think it involves putting in ground rod at the barn connected to the main house ground point via #4 copper laid in the conduit trench but as I said its worth doing the searching.
                            I will be including lighting protection. We do have lots of tall trees around too but that seems like the opposite of protection! The plan will be to use the midnite products, they have sold me with the comparison tests and seem legit. I don't understand the sizing but am sure I can figure it out from the internet or old posts. I was really surprised that it seemed like each combined array (set of strings?) required protection plus all the inputs downstream. My house actually has a full lightning protection system built in with rods through the eves and grounding wires presumably buried appropriately deep. We haven't had any issues but the owners before us (per stories from the neighbors) lost a lot of electronics to lightning. (They also stored chlorine in the unconditioned (read damp) basement like space that houses the electric panels and guess what, they rusted! so one of the first things we did was to replace those panels and inspect the house wiring and we added surge protection to each panel at that point as well. The lights are still on so i guess it is doing its job. And there is no more oxidizers stored there and it is now de-humidified too!) My concern is with the lightning system on the house has always been that it would attract the lightning to the house by giving it an easier path to ground.

                            Reading through the recent post on grounding I think this is the relevant point:
                            Originally posted by Sunking View Post
                            So what I am telling you is treat the panels as Air Terminals and take the Down Conductor directly to the GES bypassing everything. A straight dire route to EARTH good ole dirt. If you drive a rod to accomplish that, then it must be bonded to all other electrodes so as to make a common GES. It can also be routed to the GEC and bonded below the Meter Can just above or below grade. It comes down to how everything is laid out. A good layout will bring the Lightning Down Conductor straight down to the AC Meter Box so you do not have to drive another rod and go that extra expense and trouble.
                            Since I am adding an outbuilding, the barn, from a grounding standpoint I will probably need to treat the panels like lightning rods and connect them all directly to a new driven rod at that location. BUT like you said it will be important that I tie the barn grounding to my existing lightning and meter grounding at the house too.

                            Comment


                            • #15
                              Originally posted by BillSunGen View Post
                              That is the crazy thing. It is just a TV, a 'Smart' TV but I don't have anything setup on it. Just how it came out of the box. I had to connect it to the internet to get it to turn on but then blocked it at the router the next day as all my other devices were operating at a crawl. It is amazing how many of the new devices have to have an internet connection to do something local. You want your doorbell to ring? Needs internet. Want to view your security camera? Needs internet. Want to read your newspaper? Needs internet (oh wait I still get the paper so that one works...) Same with the home automation stuff. It is neat, takes a lot more time than I have to setup, but all breaks if the internet isn't available. Makes it a bit fragile. Being able to configure something on a local subnet just isn't something that comes up in regular marketing materials but it is probably out there somewhere.
                              Right. It's crazy huh? My TV's phone home to check for software updates. My ST hub still phones home or gets commands down from the internet. If Samsung wants to know when the cat water bowl pump gets triggered or I raise and lower my garage door, they will have that info in spades!

                              Comment

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