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  • 300v system grid tie help

    So I have in route 40 270w 32.2v? (With 89% life left rated) Pannels. I want to have it grid tied to reduce my electric bill that is about 60 a month. Im planning to have 8 set of 5 pannels. To give me a higher voltage of about 257v or so. But i cant seem to find anything on google that has a step down setup with a MPPT to constant voltage. My input is about 257v at 48 amps i need the output to match my gid of 240v. Some advice, pleare be kind its my first time. Also sorry if this isnt the right section
    P.s. I want a high voltage system

    Panel Data
    Size
    25.23 IN wide
    77In long
    1.8in tall
    Power
    197W
    32.2V
    6.08A
    -------------------------
    Possible Config
    5 sets of 8 Panels
    257V
    1,576W
    48.64A
    Last edited by Woodzykiler; 04-19-2020, 08:44 AM.

  • #2
    There are a few ways to do this, in increasing order of price and performance:
    String Inverters
    String Inverters with optimizers
    Microinverters

    This video gives a good comparison of the three choices:
    https://www.youtube.com/watch?v=H2aeV8d7SJY
    Note: I've heard good things about the vendor that made that video, but haven't used them personally so don't recommend for or against them.

    The best performance will come from Enphase iQ7 microinverters or APsystems QS1 quad microinverters. Enphase is better known. APsystems is quite a bit less money and from my limited experience using them at home, seems to be just as good. You connect each panel to a microinverter (or 4 panels to a quad microinverter) and the microinverter to the house's circuit breaker box through a combiner. Each microinverter puts out 240VAC. It's that simple. OK, you also need to make sure that you have approved wiring, the right connection to your circuit breaker box, a permit, permission from the power company, etc. But the general structure is that simple.

    String inverters and optimizers will be cheaper than Enphase, but roughly comparable to APsystems. The string inverter will not perform quite as well as the microinverter, depending on your exact situation. Strings don't do well if there is any shade on any panel. Optimizers get around that issue, but increase complexity and cost. The video above mentions Enphase, Fronius and SolarEdge. There are other respected brands.

    I'm sure that others here can suggest good string inverter solutions.

    A side benefit of microinverters is that you get the ability to monitor the power coming out of each panel. With string inverters, all panels are in a series string.

    You can check out the websites of Enphase, APsystems, Fronius and SolarEdge for more information on their individual products.

    Are you an electrician or do you know one who can help? You'll be dealing with 12kW of electricity. If you do something wrong, that's enough to quickly set a house fire and/or kill people. Please don't underestimate this. It's a whole different league than wiring a light switch. I don't mean to insult you. I'm just trying to prepare you for the road ahead.

    I hope that this gives you a start. Please keep asking questions. You may want to tell us more about your situation. Do you have a really clear, flat terrain, live in the dense woods, or somewhere in between?
    7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

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    • #3
      Ill check out that video thank you! I couldnt sleep so looked on my pc right fast. There 257v 1576w 48.64A per string of 5 pannels. Each one is 197w 32.2v 6.08A. So 8 strings of 5.
      I got a mobile home and reinforced the roof for this project with 4x4s on the steel trusses. Its a very flat roof with full sun all day... I can fix 3 across with 6in over hang on both sides. I want to have them 8in off the roof to let the summer heat escape better. With the added 4x4 supports it can support the weight now. Where I'm located and that its going ON my mobile home no permits required! Only the external disconnects between pannels and inverters.

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      • #4
        Generally, in the USA, installs that produce over 10kw, require special treatment, because of the power being backfeed into the Grid.

        The electric company has to allow the install, and often city permits are required, but you will know best.

        With panels flat, they will collect debris like a sandbox, and will require regular monthly morning hose down while they are still cold. (cold water + hot panels = broken glass)
        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

        solar: http://tinyurl.com/LMR-Solar
        gen: http://tinyurl.com/LMR-Lister

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        • #5
          The first guy said 12kw your saying over 10kw. Where is this data comming from??? Cause my math shows only 7.8kw (7,880watts). Using the data from the first post. what about my Voltage of 257V? stepdown?

          Question, what is closed and open circurt voltage? there different ratings on my Test pannel i got. help me to understand why there diffrent
          Last edited by Woodzykiler; 04-19-2020, 08:16 AM.

          Comment


          • #6
            Originally posted by Woodzykiler View Post
            The first guy said 12kw your saying over 10kw. Where is this data comming from??? Cause my math shows only 7.8kw (7,880watts). Using the data from the first post
            40 times 270 Watts equals 10,800 Watts
            9 kW solar. Driving EVs since 2012

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            • #7
              I said 12kW as a round number. I wasn't saying that 12kW is the threshold of certain problems. I was trying to say that 12kW is a lot more power than a 100 watt lamp. You'll need heavy wire to carry that much current. Also, if you have a connection that isn't very well done, there could be excessive resistance in the connection. That excessive resistance can heat up when the system is running and could cause the connection to fail and start a fire. It's a much bigger problem at higher power levels.

              An experienced electrician knows what wire to use, what connectors to use, how much bend is allowed in the wire, what conduit is required, how to prepare the wire for the connectors, how to torque the connectors, how to size the circuit breakers, how much current you can safely feed into a specific circuit breaker box, and much more. They may not be smarter than you, but they had to memorize this stuff to pass an exam.

              You say that they are 270 watt panels and you have 40 of them. Simple math comes out 10,800 watts. You also give the number 89%. If that were an accurate number, that would mean 9,612 watts. I'm not sure where 7,880 watts comes from.

              Mike was saying that many power companies in the US have different regulations for systems rated over 10kW than for systems under 10kW. But in either case, if you are in the US and you are doing a grid tie, you need power company approval. In my area, the differences between <10kW and >10kW are not significant. They charge an extra $100 and do a more thorough inspection, but that's it.

              We are guessing that the power company will ask how many panels and the power rating of the panels, not the expected degraded output. From experience, we think that they will put you in the >10kW category. But the only way to know for sure is to look up your power company's website and read their regulations.

              Just as a bit of trivia, a 270 watt panel puts out roughly 270 watts when new, at standard test conditions (STC). Standard test conditions is defined as an amount of light, an amount of air mass and an air temperature. If you lower the temperature or increase the amount of light, those panels can produce more than 270 watts. If the sun is directly overhead, you have less air mass than if the sun comes in at an angle. And about the "roughly" part? When you get panels from the same manufacturer, made at the same time, from the same factory, from the same lot, with the same materials and design, each one will put a different amount of power at STC, perhaps varying +/-5%.

              Here's some more trivia. The panel output is not a fixed voltage. The voltage depends on the operation of the electronics in the inverter. In almost all cases, the inverter is a low-loss voltage converter that can adjust the load on the panel so it produces the most actual output power. Think of it like shifting a car into the right gear for the speed and load on the engine. We use various terms to refer to these functions, including switching regulator, PWM, and MPPT. The key point is: don't fixate on panel or grid voltage. The inverter takes care of that, assuming that you get the right inverter.
              7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

              Comment


              • #8
                Originally posted by Ampster View Post

                40 times 270 Watts equals 10,800 Watts
                my first post said 5 strings of 8 panels, thats no where close to the 10-12kw
                Last edited by Woodzykiler; 04-19-2020, 08:44 AM.

                Comment


                • #9
                  Originally posted by bob-n View Post
                  I said 12kW as a round number. I wasn't saying that 12kW is the threshold of certain problems. I was trying to say that 12kW is a lot more power than a 100 watt lamp. You'll need heavy wire to carry that much current. Also, if you have a connection that isn't very well done, there could be excessive resistance in the connection. That excessive resistance can heat up when the system is running and could cause the connection to fail and start a fire. It's a much bigger problem at higher power levels.......
                  OHHH that makes more since, thank you so much for that! I wasnt aware a panel could output more then there label stated in some conditions Im planning 8 strings of 5 panels to get my 257V. My worrie is that the voltage is to high for any inverters, the best i have seen for grid tie so far is 240V input. so i wonder if my 257V will just melt it. so in perfict ideal tim of day blah blah.. Each pannel could make more then 32.2V and more then 270W. Thats crazy! i need to account for this. Im getting used panels for this, they have 90% life left im told there about 8 years old.

                  Panel Data
                  Size
                  25.23 IN wide
                  77In long
                  1.8in tall
                  Power
                  197W
                  32.2V
                  6.08A
                  -------------------------
                  Possible Config
                  5 sets of 8 Panels
                  257V
                  1,576W
                  48.64A
                  Last edited by Woodzykiler; 04-19-2020, 08:44 AM.

                  Comment


                  • #10
                    Originally posted by Woodzykiler View Post

                    my first post said 5 strings of 8 panels, thats no where close to the 10-12kw
                    8 panels at 270 Watts equals 2160 Watts. Five strings of 2160 Watts equals 10,800 Watts. As a check on my math, 10,800 divided by 40 equals 270 Watts per panel as stated in your your first post.

                    However, you may have the cart before the horse. Which kind of inverter have you decided to use to convert the Direct Current (DC) of the panels to the Alternating Current (AC) which runs your mobile home? The inverter will determine how many strings you need and how many panels should be in each string. For example my inverter requires a minimum of 250 volts and has a maximum voltage of 600 volts. Every inverter is different. You should decide which inverter first before you worry about string size.
                    Last edited by Ampster; 04-19-2020, 09:11 AM.
                    9 kW solar. Driving EVs since 2012

                    Comment


                    • #11
                      Well I havent pick one yet... I been looking around for a good mppt one. That can handle the 257v down to 240v. Or do 7 panels per string if i have to..
                      I thought in string the voltage would rise but keep the same wattage? Cause 8panels in 1 series(string?) Would be the 257v at 270w I thought

                      Comment


                      • #12
                        Originally posted by Woodzykiler View Post
                        Well I havent pick one yet... I been looking around for a good mppt one. That can handle the 257v down to 240v. Or do 7 panels per string if i have to..
                        I thought in string the voltage would rise but keep the same wattage? Cause 8panels in 1 series(string?) Would be the 257v at 270w I thought
                        Read the specs of inverters and you will find out that the string voltages (DC) are often much higher than the output voltage (AC). Are you clear how I calculated 10.8kW?
                        9 kW solar. Driving EVs since 2012

                        Comment


                        • #13
                          In addition, now would be a good time to be thinking about how your electrician is going to connect an inverter to the electrical panel of your mobile home.
                          How many circuit breakers will you need?
                          What size breakers?
                          Is there room in your panel for more breakers?
                          All of that will be a function of your system size. That is why we need to establish a common understanding about your system size.
                          9 kW solar. Driving EVs since 2012

                          Comment


                          • #14
                            Ampster makes many good points. To his point about thinking through the electrical panel (aka: circuit breaker box, load center) connection, at higher power levels, there is also a concern about exceeding the electrical panel bus-bar rating. You may need a line tap or second main panel for that much power. It depends on the electrical panel that you have.
                            7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

                            Comment


                            • #15
                              The house is still undergoing a full remodel ATM. all of the electrical and piping is getting replaced. along with room size changes.
                              I was planning on a 30 breaker 200Amp service panel. as its a tiny 200A one now but is outdated and very old..
                              Im thinking about doing a 8 Series P>P>P>P>P>P>P>P= 256V@ 270W then paralleling 5 of them to keep the 256V but have 1,350W (270Wx5)? That would be 40 panels
                              With a inverter and Power company approve. Also having a 36V 100AH battery backup with a 5000W inverter for basic backup needs (some kind of switch over?) like some lights, Dvd player and tv. Well thats the idea anyhow..
                              The idea is to have my panels per-series output 256V Each
                              Here is a image of my planed layout, subject to changes and advice :P
                              https://ibb.co/7XmgppC
                              Last edited by Woodzykiler; 04-19-2020, 10:24 AM.

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