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Thread: Magnetic Declination -- Compass skills

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    Senior Member tjwilhelm's Avatar
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    Default Magnetic Declination -- Compass skills

    I made this instructional video as part of my solar-photovoltaic course. Finding true south is considered an essential skill for solar site assessment.

    That said, the information here is also fully applicable to navigation/orienteering with a magnetic compass. The video explains the concept of magnetic declination and how to use it to find true north, as opposed to the often inaccurate magnetic north.

    Hope this is useful to a few folks:



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    Quality Control Director Ken's Avatar
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    Great post! Rep on the way.
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    Great demonstration TJ. Guess I gotta spread the love before I can give you some more rep.
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    Very educational. Thank you for the post.

    Off topic somewhat, but what degrees would solar site assessment be tailored too? I'm looking for something new to study..

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    Senior Member tjwilhelm's Avatar
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    Quote Originally Posted by JTD View Post
    Very educational. Thank you for the post.

    Off topic somewhat, but what degrees would solar site assessment be tailored too? I'm looking for something new to study..
    We offer an AAS degree in electrical technology that has a focus track in renewable energy. We use the ANSI accredited solar site assessment training and certificate exam from the MREA-- Midwest Renewable Energy Association.

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    Senior Member hunter63's Avatar
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    Very cool.......So true physical south is what panels are aligned at?....or that true south is a reference?

    Practical question:
    When I laid out the ordination of "The Place" our cabin, for the contractor....I used 12 degrees SE from N/S for the foundation Sonnet tubes.
    He thought I was nuts, but was paying cash....LOL.

    BTW inland from Mississippi River near Lacrosse 15 miles.

    Got this number for Ken Kerns book Owner Built home, I think....but I can't look it up as it got borrowed....and well you know how that goes....
    Anyway, the question is....was that a reasonable lay out for a south facing hill side, large over hang porch....shade in summer, sun on porch in winter?....Morning sun and afternoon shade?

    I hope I asked the correctly........No panels, passive only....at this point.

    Tried to Rep...says I gotta spread it around......
    Last edited by hunter63; 11-29-2013 at 05:57 PM. Reason: added comment
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    Senior Member tjwilhelm's Avatar
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    Howdy Hunter63,

    Here's the NOAA declination map from 2010: http://www.ngdc.noaa.gov/geomag/img/...tionMap_US.png

    They typically update the map every 3 years or so. Just to give you an idea of how much and how fast the magnetic north pole shifts around, here's a declination map from 2004: http://www.o-tmettowers.com/images/u...20magnetic.jpg

    Yes, solar-PV modules/panels are ideally oriented to face toward true south, if possible. If not possible, it's best to keep them facing within + or - 15 degrees of true south. Otherwise, performance is notably diminished. If you're within 12 degrees of true south, you're OK for sure.


    Quote Originally Posted by hunter63 View Post
    Very cool.......So true physical south is what panels are aligned at?....or that true south is a reference?

    Practical question:
    When I laid out the ordination of "The Place" our cabin, for the contractor....I used 12 degrees SE from N/S for the foundation Sonnet tubes.
    He thought I was nuts, but was paying cash....LOL.

    BTW inland from Mississippi River near Lacrosse 15 miles.

    Got this number for Ken Kerns book Owner Built home, I think....but I can't look it up as it got borrowed....and well you know how that goes....
    Anyway, the question is....was that a reasonable lay out for a south facing hill side, large over hang porch....shade in summer, sun on porch in winter?....Morning sun and afternoon shade?

    I hope I asked the correctly........No panels, passive only....at this point.

    Tried to Rep...says I gotta spread it around......

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    Senior Member hunter63's Avatar
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    Thanks......ideally some panels are being look at for the roof......after the insulation and new windows are done.
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    Evoking the 50 year old rule...
    First 50 years...worried about the small stuff...second 50 years....Not so much
    Member Wahoo Killer knives club....#27

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    Quote Originally Posted by tjwilhelm View Post
    We offer an AAS degree in electrical technology that has a focus track in renewable energy. We use the ANSI accredited solar site assessment training and certificate exam from the MREA-- Midwest Renewable Energy Association.
    Thanks for the info tjwilhelm!

  10. #10

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    Thats a good video for total beginners, to get the concept of declination in their heads, but the way it was explained, using a straight piece of string is not really correct. Mag Dec does not follow straight lines around the globe. Topo maps will have the Declination printed on them for the area you are in.

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  11. #11
    Senior Member tjwilhelm's Avatar
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    Quote Originally Posted by Enigma View Post
    Thats a good video for total beginners, to get the concept of declination in their heads, but the way it was explained, using a straight piece of string is not really correct. Mag Dec does not follow straight lines around the globe. Topo maps will have the Declination printed on them for the area you are in.
    True, Enigma. The compass needle does align with the "wonky," non-straight lines of flux. Also true, there are a number of resources that give occasionally updated numbers for the actual declination at locations all over the planet. That said, this video was made for beginners (solar site-assessment students); thus, the simplified explanation. I thought it would be easier to understand the simple, relative changes of the string positions, as opposed to something like the entire, global view (which is always changing) as shown in the map you attached, above. But, you are indeed correct.

  12. #12

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    All good. I just thought mentioning the "wonky" way it changes wouldn't be confusing for members of this forum. Topos (at least down here they do) also state the predicted rate of change yearly, so you can adjust Mag Dec according to how old your maps are.

    Sydney has about 11-12* Degrees easterly, Perth has almost 0*degrees, Wellington in New Zealand has about 22-23*Easterly
    Last edited by Enigma; 03-29-2015 at 04:57 AM.

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