Panel Mounting on a pole barn

JohnWilliams
JohnWilliams Registered Users Posts: 5 ✭
in Solar Beginners Corner #1
I am building an off-grid system for my pole barn, which has modest electrical needs at this point (1 KWh/day measured with a Kill-a-watt) but will have higher needs later (eventual small shop). My building is too far away from the electrical pole to be feasible for an underground grid feed.

Initially I have a RV2012 inverter that I kept when I sold my RV. My plan is to eventually go to a XW4024 or 4048 in a year or two so I can get split phase and overload auto gen start and generator load sharing for heavy loads. Will probably look for a 4K Onan from an RV, but that is another thread...

Thus I am sizing the PV so that I can expand to 24 or 48 volts later. I plan to use a MPPT controller so that I can start deploying 250Wish panels. I will start with 2 or 3 panels to give me 750W of PV which is about the max for MPPT at 12V (depending on which controller I pick (Leaning towards Schneider 150-60 for eventual Xanbus with the xw inverter).

Now - the question. I have 2 options for PV mounting. I have 2 metal roof barns with suitable locations, about 100ft apart.

The shop barn (E/W roof with 3/12 pitch, metal) only allows an east facing orientation (due to shading mid afternoon on the west side) at 22 degrees of incline with the panels flat on the roof. Using PVWatts (So. Ill location), this shows 1057 KWh/yr (@ 1kw PV size). I ran PVWatts for 38.8 degrees due south and see 1266 KWh/yr. Roughly 200 KWh more. To do this I would have to elevate the north side of the panel off the roof with some sort of triangular mount. This would make the array much more at risk for high winds from the north. I am guessing this is not worth the risk. So, flat it is at 1057 KWh/yr. Shading is a concern. Now I don't see east shading until 4pm. In Winter may see shading shortly after noon. A worry.

The livestock barn is 100ft east of the shop with E/W slopes also, with a 4/12 pitch, but good unshaded west side exposure year round. So, I could place 1/2 the panels on the east side towards the peak, and 1/2 on the west side. PVwatts shows a combined number of 1083 KWh/yr. That number alone does not cause me to want to place them there, (more difficult install and have to run 125ft of wire underground to the inverter/battery location. However, I have been reading about east/west orientations being beneficial in less than optimal conditions, and the guarantee of no shading has me seriously considering this.

What would you do?
John
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Comments

  • Alaska Man
    Alaska Man Solar Expert Posts: 252 ✭✭
    #2
    Re: Panel Mounting on a pole barn

    My panels are mounted do south on the gable end of the house. If your roof slopes are East and West couldn't you mount them facing South or in a Southerly direction on the gable? Adding one more panel would make up for any loss you would have because they are straight up vertical. I have 4 Panels in the 250W range on one Midnight Classic 150. Two strings of two keeps me under the hyperVOC limit of the C.C. Just a thought.

    It's also a protected spot up against the building and under the roof overhang. I don't have to worry about snow.
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  • Alaska Man
    Alaska Man Solar Expert Posts: 252 ✭✭
    #3
    Re: Panel Mounting on a pole barn

    As an example:

    I actually have these mounted with a hinge on the top because it's easy for me to step out and angle them during the summer. Having done this I can tell you I only see about a 250W (One Panel) increase in the power produced when they are 90° to the sun.

    Attachment not found.
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  • AuricTech
    AuricTech Solar Expert Posts: 140 ✭✭
    #4
    Re: Panel Mounting on a pole barn

    Have you considered using the livestock barn for the entire installation (including inverter and battery bank), then running 120VAC power the 125' to the shop barn? That would give you much less voltage drop, using a much smaller/less expensive wire gauge.
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  • JohnWilliams
    JohnWilliams Registered Users Posts: 5 ✭
    #5
    Re: Panel Mounting on a pole barn
    AuricTech wrote: »
    Have you considered using the livestock barn for the entire installation (including inverter and battery bank), then running 120VAC power the 125' to the shop barn? That would give you much less voltage drop, using a much smaller/less expensive wire gauge.

    Thought about that but a bit worried about increased fire hazard with batteries in the barn. We have horses that stay in stalls at night in the winter. Also have hay stored upstairs in a loft. I think keeping the power center in the shop is safer overall. I can run THHN 4 or 6 AWG over to the shop and carry a full 60 amps. If I upgrade to 48 volts, that gives me 3K watt capability on 1 controller.

    John
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  • JohnWilliams
    JohnWilliams Registered Users Posts: 5 ✭
    #6
    Re: Panel Mounting on a pole barn
    Alaska Man wrote: »
    My panels are mounted do south on the gable end of the house. If your roof slopes are East and West couldn't you mount them facing South or in a Southerly direction on the gable? Adding one more panel would make up for any loss you would have because they are straight up vertical. I have 4 Panels in the 250W range on one Midnight Classic 150. Two strings of two keeps me under the hyperVOC limit of the C.C. Just a thought.

    It's also a protected spot up against the building and under the roof overhang. I don't have to worry about snow.

    South Gable has a large 12ft door that slides all the way across the end and is shaded more than 50% of the day.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #7
    Re: Panel Mounting on a pole barn
    JohnWilliams wrote: »
    I can run THHN 4 or 6 AWG over to the shop and carry a full 60 amps.
    Keep in mind that the NEC limits on current for wire size are based on wire heating only. A 2 volt voltage drop that is not very noticeable at 120V can correspond to losing 20% of your power on a 12V system. (One of the reasons that higher battery voltages are preferred. With a 48V battery bank you can use wires that are 1/4 the size and get the same percent voltage drop compared to a 24V system.
    SMA SB 3000, old BP panels.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,654 admin
    #8
    Re: Panel Mounting on a pole barn

    And 1/4 the wire diameter (surface area) is 6 AWG smaller (instead of 2 AWG wire, you can use 8 AWG wire).

    3 AWG change in wire gauge is 1/2 the square inches/mm of a cut wire (1/2 the amount of copper per unit length of wire).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • JohnWilliams
    JohnWilliams Registered Users Posts: 5 ✭
    #9
    Re: Panel Mounting on a pole barn

    Thanks for the info. I picked 4 AWG (at 75 C degrees heating) or 6 AWG (at 90 C degrees heating) for a max 60 amp run of 125 ft in buried conduit. I am sizing this for a 24v or most likely 48v system. At the start, I will be running my RV2012 with 3 250W Canadian Solar panels. Using a MPPT controller, you would never actually run 60 amps except on a record cold day, right? More like 50-55 amps... What size wire CU should I run? Am I overkill or under-sized?

    A second idea is to mount the 3 panels on the shop roof just because it is easier and then when I upgrade to 4000 watts or more, move to the livestock barn. I am really leaning towards 48V, when I do.

    This first system is mostly a trial system to help me understand the operational concepts, as well as learn the care and feeding of a battery bank...

    John
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