Announcement

Collapse
No announcement yet.

Please comment on this off-grid design with gen backup

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #31
    Originally posted by Living Large View Post
    OK, more great information. I could also go with 4AWG wire, lose about 1%, and that would fit the 60A breaker terminal, I believe. Could I fit five 4AWG in the standard conduit? Incidentally - silly question, are these five wires the 4 power conductors + a ground conductor?
    Wire is derated when ran in conduit and all conduit ran underground is considered a wet environment according to code, so buy the proper wet rated wire. You need to let the electrician figure this out, all you need for your cost estimate is the length/ga of wire and the conduit.

    Your questions are beginning to make me think you plan to do this yourself, so at this point, I can not answer anymore of your electrical questions. All of your answeres can be found in the NEC which is free to download.
    1150W, Midnite Classic 200, Cotek PSW, 8 T-605s

    Comment


    • #32
      Conduit fill

      http://www.prioritywire.com/techdocs/conduitfill.pdf (Thank you Google!)
      Solar Queen
      altE Store

      Comment


      • #33
        Originally posted by thastinger View Post
        Wire is derated when ran in conduit and all conduit ran underground is considered a wet environment according to code, so buy the proper wet rated wire. You need to let the electrician figure this out, all you need for your cost estimate is the length/ga of wire and the conduit.

        Your questions are beginning to make me think you plan to do this yourself, so at this point, I can not answer anymore of your electrical questions. All of your answeres can be found in the NEC which is free to download.
        Nope - I do not plan to do this myself. Scout's honor, mother's grave, all that. I am a detail oriented person, and I love to design things. I wired my entire current house AC and ran a 100A service to another building and installed a load center, but I have no DC experience and I am not going to experiment on my house and newly built garage. Amy brought up things that bear on the matter, so I asked more questions. It sounds like she has faced the issue of five 2AWG in a conduit, but she couldn't answer 4AWG. That's fine. I am satisfied with what I have learned, and knowing something about the issues that will come up is helpful. In that conversation I learned more about acceptable voltage drops, where a breaker can serve as a disconnect and I won't have to buy an extra box, etc.

        I am concerned with finding an installer that will do a good install, and use good practices. Picking up all this information will also assist me in screening the one I choose. I've asked a couple questions of one or two already I didn't really like the answers to. So, finding an installer I can work with will be important. I'd hope that if the client says "I'd like my panels attached to the roof this way, which I have heard is best practices" that could be accommodated. I had one say they use wood 4x4s, so naturally I am hoping to be able to have a detailed discussion about the design from end to end.

        Today, I'm very happy to be honing in closer to a design. Amy really helped me start to see a solution on the PV/MPPT side. But I do pledge I'm not going to do this job myself. I can see why you may think that based on my interest in little details like terminations. But my interest comes from the possibility of connecting part A to B, not being able to order that connector so I can do it myself.

        As an example of something I know nothing about, and won't be asking about, but would be if I were doing this, is how exactly how grounding is handled. I did ask about the 5th wire, because I was sitting here thinking 4. But how it is terminated I don't need to know.

        I'll be moving on to questions about battery selection and back to generators, and I hope you will continue to contribute if you see something you can offer. I do see at some point I need to bite the bullet and choose an option, but I'm not there yet on those two. Thanks for the help you have offered.

        Comment


        • #34
          Originally posted by Amy@altE View Post
          Hey, look at that. Thank you. If you read the lengthy reply I wrote to thastinger, your will see that I am very interested in details including this one. However, I won't be pulling out the battery operated drills and screwdrivers and assembling this thing myself. I would be excavating for an underground propane tank and conduit, which I could do since I have a backhoe. But I have had a design and install fee in my budget.

          On that topic, I'd be interested if there are any guidelines for design and install costs. I know they could vary quite a bit, maybe each of these. I'd have a roof-mounted array of 18 panels, a load center with two MPPTs and the inverter, and connection to a generator. I don't want to reveal the amount I have been using, for fear I may be low and insult someone. The ditch would be dug, but everything else I think I would need done except constructing the battery storage area, including ventilation.

          Comment


          • #35
            Understood.

            Grounding can vary place to place. My inspector wanted 6Ga copper even though my largest conductor was 10ga. Luckily I had already run 6ga with 3 grounding rods due to me defaulting to the stricter side of code. My NEC notes are up at the vacation property but IIRC it states that all grounds must terminate at the same location. It also specifies a min resistance when measured to Earth, I was able to get that (can't recall the value) with 3 grounding rods but the inspector said he doesn't make people do more than 2 ground rods. I guess that is one of those "gray areas".
            You might want to talk to your local building inspector ahead of time. Mine was very helpful on specific things he prefers relative to the gray areas. I.E. he wanted every AC outlet to be a GFCI outlet, after some discussion and me quoting the NEC, he relented to letting the first in the home run be a gfci and protect the other outlets on the string, NEC does not say how many is too many either.
            1150W, Midnite Classic 200, Cotek PSW, 8 T-605s

            Comment


            • #36
              Originally posted by thastinger View Post
              Understood.

              {snip} he wanted every AC outlet to be a GFCI outlet, after some discussion and me quoting the NEC, he relented to letting the first in the home run be a gfci and protect the other outlets on the string, NEC does not say how many is too many either.
              Has the NEC changed, or is this specifically for off-grid systems? GFCI on every branch circuit with outlets? Now, I have to admit, I haven't looked at it in 20 years.

              Comment


              • #37
                Shout out to Amy@altE store

                The wire sizing video on YouTube, and the application of the NEC requirements is amazing. Thanks for helping us beginners out. I can see now why earlier today you asked if I had seen it.

                I also learned that panels can be attached to standing seam roofs with clamps and no penetrations, which is a simple concept but I didn't know.

                Comment


                • #38
                  Originally posted by Living Large View Post
                  Has the NEC changed, or is this specifically for off-grid systems? GFCI on every branch circuit with outlets? Now, I have to admit, I haven't looked at it in 20 years.
                  My off grid building is a garage. GFCI outlets are now required in garages in addition to kitchens and bathrooms.
                  1150W, Midnite Classic 200, Cotek PSW, 8 T-605s

                  Comment


                  • #39
                    Originally posted by thastinger View Post
                    My off grid building is a garage. GFCI outlets are now required in garages in addition to kitchens and bathrooms.
                    Ah. Didn't think of that. I never wired my garage past the load center and one outlet. The kitchen and bath requirement was there in 1994. Good suggestion by the way, to speak with a code official. Thanks. When my service drop and load center were installed, they had trouble putting a ground rod into my shale. I watched it being done, and I was not impressed. They ended up with two on an angle of 30 degrees as I recall.

                    Comment


                    • #40
                      The guidelines I learned strive toward less than 3% loss in the wires.

                      This link below, is for a very comprehensive voltage drop calculator spreadsheet. Panel voltage, distance, expected tempatures, it does NOT cover conduit size or fill. It's smart enough to know the difference of amps from input and output of charge controllers.

                      http://www.solar-guppy.com/download/...calculator.zip

                      Another option, is to use aluminum wire, you use approved Cu/Al fittings w/oxide goop, and go up 2 sizes, so a #8 copper could be served by #6 aluminum which is much lower in price. I did that on a 1,000 foot run, and the aluminum wire is much softer and bendy for pulling than copper is.
                      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

                      Comment


                      • #41
                        A footnote to Amy's comments on the 2AWG wire I was told I needed by the Schneider tool earlier in the thread (for less than 1% drop), and the consideration that 6AWG would cause a possibly acceptable voltage drop (less than 2%).

                        When I looked at the altE Store YouTube video on wire sizing and selection, they came up with 6AWG needed for 2 strings in parallel of a panel similar to mine. The NEC derating due to heat and conduit fill are quite large. I don't believe I will come anywhere close to being able to use 6AWG for three strings in parallel.

                        It was quite a day, but there is more to learn.

                        Comment


                        • #42
                          OK, I ran the NEC procedures that the altE Store procedure walks you through on 3 strings paralleled.

                          My Iscc = 9.58
                          The corrected current in the wire to the combiner is 3 * (1.56* 9.58) = 44.7 A

                          Using THWN-2 wire and assuming a roof mount with conduit 1/2 off roof and a 38 deg ambient,

                          I divide by 0.8 to correct for fill (5 wires)
                          44.7/.8 = 55.9 A

                          Then correct for temperature
                          Adder is 22 deg C from 310.15(B)(3)(c), for 38 + 22 = 60 deg C
                          --> divide by 0.58
                          55.9/.58 = 96.4 A

                          From 310.15(B)(3)(16), 2AWG can handle 115 A, 4AWG 85 A

                          The conduit fill (2 circuits) and temperature corrections shot me into 2AWG.

                          Combiner can handle 1-1/4" conduit, 2AWG wire. Looks like I can either go 2AWG with 3 in a string or switch to 4 panels in string and go to 6AWG - my option.
                          Last edited by Living Large; 12-19-2014, 02:24 PM. Reason: Answered own question

                          Comment


                          • #43
                            But did you also do the dance of joy as instructed when completing the calculations? Hmmm, so maybe I should retract my comment about the Germans being to picky, sounds like my instructions led you to the same answer they gave. I guess those Germans know what they are talking about!
                            Solar Queen
                            altE Store

                            Comment


                            • #44
                              Originally posted by Amy@altE View Post
                              But did you also do the dance of joy as instructed when completing the calculations? Hmmm, so maybe I should retract my comment about the Germans being to picky, sounds like my instructions led you to the same answer they gave. I guess those Germans know what they are talking about!
                              The "dance of joy" was fricking hilarious, and you said it with such seriousness. You have a perfect voice and tempo for doing instructional videos.

                              Yup, I arrived at the same answer and that didn't go unnoticed. While I chuckled at the dance of joy, I was also moaning over the thought of having to run 2AWG conductors.

                              Comment

                              Working...
                              X