So, what is the difference between “True South” and “Magnetic South,” anyway? Well, if you imagine the axis that the earth rotates around, the point at which that pokes out of the earth in the middle of Antarctica, that’s true south. But when you hold up a compass you aren’t really finding “true” north or south, you can only find “magnetic south,” which is the direction towards the south pole of our earth’s geomagnetic field. Believe it or not, this point actually moves a few miles each year because the molten metal in the earth sloshes around.
YOU: “Dave, I think I know south is the best way to orient my solar panels (or north if you happen to live in the southern hemisphere), but do I want to face them magnetic south or true south??”
DAVE: TRUE SOUTH. We’re not concerned with the magnetic poles, just where the sun is.
YOU: “Well that’s great and all Dave, but my compass only shows me magnetic south, how the hell am I supposed to find True South? “
DAVE: Settle down, it’s gonna be ok. There are a few ways, but the most accurate is to find the magnetic declination in your area. (Australia, Canada, US, World). For example, I can tell from these sites that in San Francisco my current magnetic declination is (14° 33′ E). Since that number is magnetic, and I want to find “true,” I subtract about 14 degrees. So if my compass points to south at 180 degrees, TRUE SOUTH is about 194 degrees. Point your panels in that direction!
TIPS: Don’t have a compass? Here’s a simple old school way. When the sun is at its highest point in the sky “solar noon,” any shadow cast by a telephone pole or some other perfectly vertical object will run perfect TRUE north-south.
When taking a compass reading, never hold the compass near metal, as it will throw off your reading. Watch out for your belt buckle!