Hi I am putting a large great room addition on our house and am looking at passive solar heat. I am wondering if anyone could point me toward resources to find true North at my house and to find the solar path at my location. Once I know this then I need to find what size of awnings I need to shade my south facing windows in the summer. Any on-line resources for figuring this all out? Thanks, Mike

Local surveyors should be able to tell you where true North is.  Depending upon your location, it will probably be off of the compass North by a few degrees.  There may also be charts on the internet that show true North for your location.

If you are in the great American Midwest, true North is nearly identical to magnetic North, barring the effect of any local anomalies. In Missouri, for example, the difference is only a few degrees, probably less than you can accurately measure, so get a compass. The needle points North.

Here is a site that has a lot of solar tools on it.

http://www.builditsolar.com/Tools/tools.htm

As a 50+ year scouting veteran I suggest you check a BSA Handbook for Boys - you will find how to calculate magnetic declination using a compass to get true north. If you have a USGS map of your area it will give you the exact declination so that with a quality compass you can come within a few minutes.

Wikipedia gives you an explanation. http://en.wikipedia.org/wiki/Magnetic_declination
Another source - http://magnetic-declination.com/

This is all really overkill though since there are many other factors such as local terrain, other buildings and foliage that will have much more influence that being a few degrees to one side or the other. For example I have 11,000 foot mountain peaks rising less than half a mile east of my home so I can’t count on much in the early morning but the peaks on the other side of the valley are about 15 miles to my west. A slight correction favoring the west in my case would make sense.

Mike,

You can find the difference in magnetic north and true north, the one that will give you the relationship to the sun at:
http://www.ngdc.noaa.gov/geomagmodels/Declination.jsp
Then use a compass and the correction from this website to determne true north. Unless you are in Alaska, the declination will be fairly small.

To compute roof overhang or awning overhang, I like to use:
http://www.susdesign.com/overhang/
I think this is shareware, and I sent him a check for $25 to use a couple of his models, although I didn't see the cost when I just glanced at his website.

Good luck.

Posted By concretekax on 20 Feb 2012 07:25 PM
Hi I am putting a large great room addition on our house and am looking at passive solar heat. I am wondering if anyone could point me toward resources to find true North at my house and to find the solar path at my location. Once I know this then I need to find what size of awnings I need to shade my south facing windows in the summer. Any on-line resources for figuring this all out? Thanks, Mike

During the winter, stick a thin metal rod or wood dowel ~3' high in the ground where it can receive direct sun from the south.  Use a spirit level to make sure that it is vertical.  On a sunny day from ~11:00 am to ~1:00 pm (wide range of time selected because it depends on where you are located within your time zone for solar noon) precisely mark the tip of the shadow ~every 10 minutes.  Measure the distance from the rod to the shadow marks and identify the one that is shortest.  This represents the sun's highest point in the sky.  A line drawn from your rod to the shadow mark closest to the rod represents true north within a few degrees.

Alternatively, if your local newspaper has sunrise and sunset times for every given day in your area, the middle of these two points will be solar noon.  Using the vertical rod, mark the shadow on the ground at solar noon.  This will represent a true north-south line within a few degrees.

Another option is to use the NOAA solar calculator here:  http://www.esrl.noaa.gov/gmd/grad/solcalc/

Thanks for all of the hints and ideas. I will definitely be trying some of these out.

The pole-star is about a half-degree from true north, so it doesn't take a rocket-scientist of an astronomer to get "close enough" for your purposes, and cannot be interfered with by local electromagnetic or magnetic issues. I've seen places in Colorado where ferrous rocks were enough to skew a compass more than 25 degrees off the average magnetic pole locally, but the stars stayed in the right places. :-)

To get a solar declination chart for your place, try this:

http://solardat.uoregon.edu/SunChartProgram.html

You can then use simple tools and paper & pencil to do your own site survey:

http://www.builditsolar.com/SiteSurvey/site_survey.htm