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  • heimdm
    replied
    Originally posted by khanh dam View Post
    I would stick build the shed. that way exact slope can be matched if you want
    The prebuilt building is around 20k (32' x 16') The stick built price I have is around 26k (26' x 16'). I am hoping in the next couple of weeks to get another stick-built quote. The stick built goes on a concrete pad. The pre-built goes on concrete but has its own floor. Because it has its own floor, I'd probably have to move the conduit so it comes through the wall instead of through the floor. If the stick-built price is close, I'll take that.

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  • khanh dam
    replied
    I would stick build the shed. that way exact slope can be matched if you want

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  • khanh dam
    replied
    Looking good! That’s going to be one huge open span under the panels

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  • heimdm
    replied
    Received stamped drawing for the structure today. Essentially there are 8 concrete pads that are 5' x 10' x 1'. They are located 18" below the surface. In this update the need for the concrete piers on top of the foundation was eliminated, which should make my concrete contractor happier. My aluminum fence runs close to some of these pads, so part of the fence might temporarily, have to come out.StructureOverview.png

    Foundation-Simple.png

    On another note, on the fence about doing a stick built shed next to the array or a pre-fab one. I found a nice pre-fab one from ezpb.com, their Austin model. The pitch would be 3/12 which is nearly identical to the array. My dimensions would be different than what is shown in the photo.
    ezfb.png

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  • khanh dam
    replied
    looks like the steel goes into the concrete foundation and sticks out of it, correct. Concrete guys have told me that the exposed steel will expand faster than the cool 60 degree ground concrete and can cause cracks around the poles? not sure if it really is an issue. maybe a thin foam wrap and then caulked on top to prevent water from getting in latter on or just diamond saw cut a control cut around each post.

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  • J.P.M.
    replied
    Originally posted by Mike90250 View Post
    Where you steel penetrates the 4" concrete pad, you need to leave an expansion space, or the microflexing of the steel and thermal effects will create a gap in an uncontrolled manner.
    I don't claim competence in reinforced concrete design but concrete and steel have coefficients of thermal expansion that are within 5 to 10 % of one another, that is, quite small. That usually makes the relative lateral or short span thermally induced axial movement quite small and so too the resulting thermally induced stresses over commonly seen temp. ranges and conditions.

    Induced stresses from usually local galvanic corrosion of the steel within the concrete (the resulting rust = iron oxide) has a greater volume than the steel) are usually a greater concern than the thermally induced stresses and can create (depending on length/thickness) a much larger tensile stress in the concrete than any thermal expansion. Most of those concerns deal with rebar, but structural members can be affected as well. Usually, a competent designer addresses those and other such concerns.

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  • heimdm
    replied
    If I am following correctly, Mike90250, there is a need to have a gap between the concrete and the base plate. Based on this schematic, I believe that is addressed.
    .baseplate.png

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  • Mike90250
    replied
    Where you steel penetrates the 4" concrete pad, you need to leave an expansion space, or the microflexing of the steel and thermal effects will create a gap in an uncontrolled manner.

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  • heimdm
    replied
    ss-prelim.png
    Received preliminary drawings/plans for the structure. The foundations are essentially a 5' x 12' x 1' pad with a 6" pier extending up, which is where the base plate and anchor will connect. The entire foundation will require just over 18 yards of concrete. My soil type has lots of limestone chunks, so a shallow foundation is preferred. At the moment the concrete anchors will be recessed. A concrete pad will be poured over the majority of the area covered by the panels. Hopefully, next week we will get finalized drawings and I can meet with my excavator/concrete contractor and get this moving forward.ss-prelim.png
    ss-foundation.png
    Last edited by heimdm; 02-14-2021, 10:17 PM.

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  • heimdm
    replied
    This week saw the arrival of 92 panels arrive by freight carrier. The panels came stacked 2 pallets high. Luckily, a local business with a skidsteer with forks was able to put all the pallets on the ground. They were kind enough not to charge. I have to pick up a pallet jack tomorrow to move them inside the garage, so we can inspect all the panels for damage. Next week, the temperatures are supposed to be near 10 degrees or less, so definitely want to have the panels in the garage for inspection.

    As far as the steel structure goes, the company that is building it is doing the design work, which hopefully will be completed in the next 2 weeks.

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  • heimdm
    replied
    Originally posted by khanh dam View Post
    sounds dumb. I put commercial sunpower panels on my picnic shelter roof. main difference is they are bigger than residential panels. Why the heck LG cares is anyone's guess.
    I spoke to a residential engineer today they said pergola rafters needed to be 2x8" steel tube with 1/8" wall spaced 40" on center to span 160" from south header to North header. OR two 2x12 wood rafters coupled together or two 2x8" with steel filch plate between the two or 2 aluminum self mating 2x10 beams. Designed for 115mph wind load and 25 degree tilt. I'm guesisng the 25 degree tilt is what makes it have to be so strong. Most pergolas are not tilted that much.
    The tilt is up to each project for sure. The guidance, I was given is a minimum of 5 degrees so that rain water does not pool on the panels. I would have desired a higher tilt, but settled at 15 at that prevents the panels on the high end from being above the raised deck on the back of the house. Our high side (north end) is about 14' above ground.

    My spacing is expected to be:
    North-South: 21'
    East-West: 22'8"

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  • khanh dam
    replied
    sounds dumb. I put commercial sunpower panels on my picnic shelter roof. main difference is they are bigger than residential panels. Why the heck LG cares is anyone's guess.
    I spoke to a residential engineer today they said pergola rafters needed to be 2x8" steel tube with 1/8" wall spaced 40" on center to span 160" from south header to North header. OR two 2x12 wood rafters coupled together or two 2x8" with steel filch plate between the two or 2 aluminum self mating 2x10 beams. Designed for 115mph wind load and 25 degree tilt. I'm guesisng the 25 degree tilt is what makes it have to be so strong. Most pergolas are not tilted that much.

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  • heimdm
    replied
    Update to yesterday setback. I ended up talking with the regional sales manager from LG for the Midwest. The deal with "commercial" Solar Panels is you can not put those on a primary residence (house). If you do ground mount or put them on a solar pergola/canopy that is perfectly. fine. LG will honor the 25/25 warranty for the product. However, they will not cover the labor cost. For the most part anytime you see LG panels and "commercial only" that is what is going on.

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  • heimdm
    replied
    A little setback today. Thought I had the LG bifacials all squared away. Distributor went to order them, and LG will only ship those modules for commercial projects. My backup module at this point is the REC Alpha Black module.

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  • bcroe
    replied
    Originally posted by heimdm View Post
    We are fed by 50 kvA transformer, and we are the only ones on it. Our angle will be 15 degree's, which optimally would be about 2x that. I am in southern indiana, which for the past 5 years, we have not got much snow. So, if there is an uptick in snow in the area in the next couple of years, you can blame me.

    We did add extra panels to make the winter performance not as bad. My intent is that we will underproduce during the winter months (Nov-Feb). Until 2032, we have net-metering. Once we get past that, we might add some panels at a steep angle on the ground, to offset winter (December, January). Bruce, what kind of performance do you get during the winter months? Trying to determine if the energy is worth hunting during a Midwest winter.

    The distance between the inverters and grid interconnect is about 75ft. Current design calls for 4/0 wire. Always appreciate your insights and feedback.
    75 feet with 25 more for both end terminations (mine took more than that), gives about a
    200 foot loop, 0.049 ohms per 1000 feet of copper 4/0 wire. With 36.8KW (92 400W panels),
    a lower angle Cos of .95, and an inverter + DC wire efficiency of 0.95, an inverter AC output
    of 33.2KW is possible. At 250VAC line that is 133A, causing around 1.3VAC drop in the loop,
    or 0.5% power loss, a pretty good number. Increase that by about 1.6 if the wire is aluminum.

    For my 42 Lat midwest, mid winter KWH production is about 1/3 my mid summer production.
    The main factors are much shorter days, much more prevalent clouding, and a poor seasonal
    elevation angle on fixed sections of the arrays. The seasonal increased clouding is the
    biggest thing, with cloud dispersed light the angle matters less. A few days ago the array
    under excellent sun produced about 57% of the best summer day ever, but 10% on the
    worst day.

    I clear snow after every storm, not so hard with my design. That will be nearly impossible for
    you, so a good part of winter production may be lost. That is a smaller part of the picture,
    but it is large enough to get me out pushing snow (manually), in between cleaning paths
    (with a tractor).

    I see no practical way to bring winter production up to summer levels, so net metering is
    the essential bridge here. It might be possible to reduce the need by building a new super
    insulated house.

    With a given ground area, the same energy may be collected by covering it with flat
    panels, or by a considerably reduced number of panels elevated to the angle to
    intercept that sunlight on a perpendicular. With optimal mounts costing more than
    panels these days, I see nothing wrong with using lots of flat mounted panels on
    that existing pergola.

    If you do add ground mount panels later, you might consider something like I built
    here after half a decade of experiments. The elevation may easily be changed
    seasonally, both for production and to minimize snow accumulation. This winter,
    this array has stayed snow free, while my conventional array required 5 cleanings.
    Note the high ground clearance to avoid snow accumulation.

    The next of these arrays will be 2 sided, to replace a decade old wooden support
    section. Going this route with string converters, you could arrange to collect a lot
    more energy with a lot more panels, while still using your original inverter plant
    and AC wiring. That is done here by east directly facing the rising sun, west
    facing the setting sun, with the other panels taking care of mid day and boosting
    output under clouds. Peak energy will not increase, but the number of production
    peak hours a day will jump. My best unclouded day produced 10.5 sun hours.
    Since only a fraction of the panels are at peak at any one time, the same inverters
    will handle near the same output, over a longer day.

    Expansion here is based on panel strings totaling 720 cells, about 360 VDC in
    summer, 420 in winter. I am less concerned with the exact panel arrangement
    or voltage specs, all my varied 720 cell strings play nicely together. Just need
    a combiner box with more inputs. Mine has 12 strings, will take 14.

    I see arrays of large X by Y panel numbers. These DO NOT save ground space,
    but they make it impossible to change the tilt or clear the snow. Designs here
    are for 2 high landscape mounted panels, set at a steep angle for winter, any
    convenient length, arrays. More panels = more length, NOT height. What snow
    does collect, is easily reached with a pusher. Yes more foundation and support
    structure is needed, my back and snow pushing mid winter dictate my tradeoff.
    good luck, Bruce Roe


    Array20Rear1.JPG

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