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Grid-Tie+Battery Hybrid System Install Done, Inspected, and Producing Power

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  • Grid-Tie+Battery Hybrid System Install Done, Inspected, and Producing Power

    After looking everything over from PV solar panels to AC power panels, my inspector applied the coveted green sticker and said, "Nice work." What do you do for a living, he wondered. I replied that I'm an electrical engineer. His reaction was, Oh, now I get it. IMG_2564.jpg

    Two strings, each occupying two rows of REC TwinPeak 290W panels. IronRidge mounting with 45 degree elevation.

    The series connection of each string starts from the lower right panel and goes to the left where it returns via the upper row of panels. Late afternoon spring and fall shading courtesy of a big beautiful larch I can't quite bear to cut down. Yet. At least it loses its needles in winter.

    IMG_2703.jpg

    Custom built equipment shed, with PV conductors coming in from the trench at the right and AC conductors going out via the EMT attached to the fence. The smaller EMT is for Ethernet cable and control wires for a solid-state relay.

    There are four PV circuits coming through that conduit (1 1/4" IMC transitioning just above grade to EMT), through a 10x9 tray cable, i.e., 10 AWG with 9 conductors. By using IMC conduit, I was able to get away with a shallow trench just 6" deep, thus minimizing root damage to the trees around the path from shed to panels.

    IMG_2415.jpg

    The wires (600V rating) are all wrapped in two protective jackets (a clear crinkly inner jacket then some heavy black rubbery stuff), and the cable is listed for direct burial. The photo above was taken inside the junction box by the PV array before I got the PV wires attached. You can see how each wire of the tray cable attaches to the bottom of a Euro style feedthrough connector. The PV wires of each string attached to the top: String 1, + to red, - to blue. String 2, + to orange, - to black. I have two more strings planned for an array that will point straight up in front of the tilted array to collect photons from our often grey Washington skies during cloudy weather, and those will go to the other tray cable wires. The spare yellow wire I phase-taped with green stripes (not yet shown) and used as an EGC in addition to the EGC provided by the metal conduit.

    With high voltage and modest current and no NEC fusing requirements, this is a highly efficient way of transmitting 6 kW over 150 feet. I'm really happy with how it turned out.

    IMG_2706.jpg

    Front view of the equipment shed. EMP resistant (about 20 dB of Faraday cage signal attenuation at 2.4 GHz), waterproof, and--best of all--exempting me from all the NEC's new rapid shutdown and arc fault BS. Air intake vent on the left, and outlet vents above the doors. Next to the inlet vent is a 30A generator inlet.

    IMG_2704.jpg
    IMG_2705.jpg


    I got pretty handy with my two conduit benders. (There's a lot more conduit inside the house, with a total of around 120 feet and some 900 degrees of total bend from equipment shed to the AC power panels.)

    IMG_2726.jpg

    I built the equipment shed to just meet the NEC requirements for working space, which was actually a bit of a challenge. The studs along the back are 2x6, cut down to 2x4 below the oak plywood board. That was so the batteries could go back a bit further and stick out less than 6" in front of the equipment fronts, an NEC requirement. It does make for a comfortable work environment.

    There is a Morningstar ground fault protection device for each TS-MPPT-600-48 charge controller. I added a 600V surge protection device inside each GFPD, mounted on the DIN rail it includes for whatever you want to put there. The wiring from the CCs to the Outback rat's nest, aka "load center," is 6 AWG with an 8 AWG EGC. If it were inside conduit, it would have been too small to meet code for the 60A maximum that travels through it, given the summertime temperatures of around 110 degrees F expected inside this shed.

    I have no problem leaving 48 V wires exposed inside a locked shed, but did want the 600 V stuff wrapped up inside metal all the way.

    IMG_2723.jpg

    My custom-built combination combiner and switch box, all nicely NEC-labeled to advise the many different personnel who will be looking inside it. (Um, actually there will be just one, the guy who freaking designed and built the whole thing. But I digress...) The box, DIN rail, and ferrite cores were from Digi-Key, and the disconnect switches from some outfit I found online. Very reasonably priced, and they disconnect both positive and negative as required by NEC (and common sense).

    The ferrite cores are part of my indulging an apocalyptic fantasy about surviving an EMP attack. (Don't judge...) Between the 150+ feet of ferrous metal conduit, which represents a waveguide below cutoff at EMP E1 pulse frequencies, the very lossy RF transmission line represented by the tray cable, the 150 Ohms or so of RF impedance from the ferrites, and my surge protection devices, I feel pretty confident that my PV array will not act as an antenna to fry my equipment from outside my big ugly Faraday cage.

    IMG_2728.jpg

    The MATE3 showing that the thing can produce power, along with an Ethernet switch and home-built Raspberry Pi computer. Those latter items are powered via 12 V stepped down from the big battery with a DC-DC power supply (all parts from DigiKey). Of course there is a properly sized fuse protecting the wiring to the DC-DC supply.

    The two charge controllers, the MATE3, and my computer are accessible to me via TCP/IP.

    The terminal strip is currently just attached to one control circuit feeding a solid-state relay that feeds my chest freezer. It's a load that can be turned off at night if I wind up off-grid for any length of time--essentially a thermal battery. The relay control comes from the Outback Radian's AUX output in "load shed" mode.

    IMG_2719.jpg

    The Outback GSLC is a rather cozy little space to do wiring in. But it does provide everything you need, and lots of knockouts wherever you might need them. I wound up having to remove all the stock wiring and starting over, using the wire segments Outback provided where I could. I didn't use their ground-fault breaker assembly at all, but it cost no more to order the fully loaded GSLC than to buy a bare one along with the parts I did need. Note the HUB mounted on the left, and a Midnite AC surge protector on the AC grid input.

    Also note the insulating bushings at various important places. The insulation would be a dangerous mess without them. The NEC actually makes a lot of sense sometimes. I couldn't have done all this without my well-thumbed NEC 2017 paperback edition.

    (Due to image attachment limits, continued in a comment below, which hopefully will get approved soon.)
    Last edited by BackwoodsEE; 11-12-2017, 11:58 PM.

  • #2
    (Continued from main post due to image attachment limits...)



    The battery cables are 4/0, plenty big enough. Conductor surfaces prepared with a Scotch-Brite pad (thanks, Sunking) and wiped clean with microfiber cloth, then torqued and later re-torqued to 10 N*m per manufacturer (Rolls-Surrette) specs. Because these are AGM batteries, they can be in the same enclosure with the rest of the equipment. And no messing around with sulphuric acid for me. I'll pay extra for that.




    This sub-panel also served as a pull box on the way to the critical loads panel and main panel, and as an AC disconnect for the critical loads wiring. The AC grid input wires just pass through. The solid-state relay is on the upper right. There's a spare two-pole breaker for a planned mini-split heat pump.

    The wires are 4 AWG, which was expensive, a challenge to pull, and overall a bit crazy. I could have gotten away with 6 AWG per code, though just barely. But you know what? The lights fed by my critical loads panel, which make a 240 ft. round trip from the service entrance to the Radian inverter and back again to the critical loads panel, do not flicker at all when someone turns the microwave oven on. I like low voltage drop.



    A pull box on my long and meandering way to the critical loads panel and service entrance. NEC requires 8" for 4 AWG wire, and you know what? It wouldn't work with anything smaller. The small wires are for the planned heat pump branching off from the previous sub-panel.



    At last, the critical loads sub-panel. Note the AC grid input conductors all nicely wrapped up in a plastic sleeve and feeding through this from the main panel (boring and not shown). Also note that my branch circuit EGCs are separated from neutral because this is a sub-panel.

    One more thing: The guy who built my house went crazy with his branch circuit wiring, dedicating 20A breakers and 12 AWG conductors to every little thing. (I seriously have an entire branch circuit and breaker for a light over my kitchen sink.) The blue connectors are a UL-listed way to combine two branch circuits onto one breaker.

    Because the big wires are 4 AWG, I didn't need them to be colored white for the neutrals. (Two hots and a neutral each for the AC grid in and AC inverter out.) Electrical tape took care of my color coding for me--white for the neutral of the AC grid in and grey (also NEC acceptable) for the neutral of the AC inverter out.

    Obligatory disclaimer: Although I know my way around electricity, I'm not a licensed electrician. I'm not giving you advice here about how to comply with applicable building codes or safety practices. But you knew that already.

    Comment


    • #3
      Nice job on this complex system. Although it looks to be afternoon from the first picture a little chainsaw work seems to be in order.
      2.2kw Suntech mono, Classic 200, NEW Trace SW4024

      Comment


      • #4
        Very nice build. It looks like it will be around long after we are all gone.

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        • #5
          How long have you been working on this?

          Comment


          • #6
            An what is the rought cost?

            Comment


            • #7
              Very nice.

              What brought you to decide on REC TwinPeaks?
              285Wx9 / MNClassic 150 / CSW4024 / TrojanL16H-ACx4

              Comment


              • #8
                Originally posted by Higher Voltage View Post
                How long have you been working on this?
                I started in the spring researching the various options and worked on it all summer long. Got it finished, inspected, and tied into the grid just in time for months of WA wintertime with its darkness and grey skies!

                Comment


                • #9
                  Well then you will be very happy in spring and summer. Big difference in power making. Looks great by the way.

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                  • #10
                    Do you have a moniton inside the house?

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                    • #11
                      Originally posted by SunEagle View Post
                      Very nice build.
                      Thanks!

                      Originally posted by SunEagle View Post
                      It looks like it will be around long after we are all gone.
                      Well, except that the battery will be an inert lump, and the electrolytic capacitors inside the charge controllers and inverter will all be shot. I've thought about trying to find out what kinds of caps are used and buying some spares to keep in a cool place somewhere, sealed inside plastic bags to keep the electrolyte from evaporating. That would probably make them last 20 years or more, and their capacity could be restored by reforming the dielectric with a controlled leakage current before usage. Just got done reading somebody's academic paper where he tested out spare electrolytic caps that had been stored at power plants for 19 years and they worked fine after a bit of dielectric reforming.

                      Comment


                      • #12
                        Originally posted by Matrix View Post
                        Very nice.

                        What brought you to decide on REC TwinPeaks?
                        It is a split-rail design, basically made up of two smaller PV panels connected in parallel. This gives you somewhat better shade tolerance.

                        If one half of the panel is shaded, you can still get half the rated current through the PV cells of the other half. It's not a cure-all for shading, but with a good MPPT charge controller, the split-rail design sometimes lets you produce half your rated current at full string voltage when you would otherwise be stuck with bypassing a bunch of half-shaded panels entirely (thus obtaining much lower overall voltage) or settling for the much lower current produced from shaded PV cells.

                        Comment


                        • #13
                          Originally posted by BackwoodsEE View Post

                          Thanks!



                          Well, except that the battery will be an inert lump, and the electrolytic capacitors inside the charge controllers and inverter will all be shot. I've thought about trying to find out what kinds of caps are used and buying some spares to keep in a cool place somewhere, sealed inside plastic bags to keep the electrolyte from evaporating. That would probably make them last 20 years or more, and their capacity could be restored by reforming the dielectric with a controlled leakage current before usage. Just got done reading somebody's academic paper where he tested out spare electrolytic caps that had been stored at power plants for 19 years and they worked fine after a bit of dielectric reforming.
                          There is always new technology or processes on the horizon that might result in a better energy storage solution.

                          Comment


                          • #14
                            Originally posted by BackwoodsEE View Post

                            It is a split-rail design, basically made up of two smaller PV panels connected in parallel. This gives you somewhat better shade tolerance.

                            If one half of the panel is shaded, you can still get half the rated current through the PV cells of the other half. It's not a cure-all for shading, but with a good MPPT charge controller, the split-rail design sometimes lets you produce half your rated current at full string voltage when you would otherwise be stuck with bypassing a bunch of half-shaded panels entirely (thus obtaining much lower overall voltage) or settling for the much lower current produced from shaded PV cells.
                            Well that is nice to know that the split-rail thing is not marketing hype from REC. I bought 9 twinpeak 2's for the same reason. Well that and from what i could tell the company had some really good financials. So far I am very happy with the panels. I am getting NMOT values from the Array in mid Nov.
                            285Wx9 / MNClassic 150 / CSW4024 / TrojanL16H-ACx4

                            Comment


                            • #15
                              Am I the only one seeing only filenames (IMG_2716.jpg, etc.) in post #2 of this thread? I could see all of the photos in his previous thread and am not aware of any other threads where this exact quirk is appearing.

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