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Does it matter if my solar panels face South or “True South”?

Avatar for Dave Llorens
Published on 01/15/2008 in
Updated 02/28/2019
Solar Power should Point True South

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!

Last modified: February 28, 2019

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Solaris
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Solaris

Just try to get the panels to face as true south as possible, and if there is shading — Microinverters!

Dick
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Dick

How can an article that has such a serious error stay on the internet for 8 years and still not be corrected? As many others have pointed out the correct way to find true south in San Francisco is to subtract the declination degrees not add them. Also any posts that refer to using a shadow at noon to find true south are only partly correct, what is actually needed is the “solar noon” or ,”sun transit” time which is adjusted for longitude (usually a minor adjustment) and daylight saving time (maybe an hour). Online sites such as http://aa.usno.navy.mil/data/docs/RS_OneDay.php will… Read more »

Ben Zientara
Admin

Thanks, Dick. I fixed the post!

-Ben

Skip
Guest
Skip

The E stands for east and it is to be subtracted not added

Oscar Moss
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Oscar Moss

Actually, the more critical consideration is the angle of latitude and time of the year.(date). I wrote a program probably 20 years ago called SOLAR.BAS that I put into the public domain. It calculated the precise angle of solar panel (the old water panels) position to maximize the output. Basically, add or subtract your latitude from the position of the sun. USGS has an online app that you plug in the long, lat. and date, and will tell you where the sun is. Just take it from there.

Joe
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Joe

I had and electric gate installed and it is a 12 volt system with a deep cyle battery. The installer said that he need to point the solar panel North. I was a little confused as I always thought the panel needed to be facing south. It actually facing North East. If I was to turn in around on the same bracket it is mounted to it would be facing South to South West. I believe this is what I should do. Can you tell me if I am right or wrong. It is only a 10 watt panel to… Read more »

Raja
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Raja

sir what is the reason for facing the solar panels towards south direction

RassleD
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RassleD

Guys, I just checked the NOAA site

http://www.ngdc.noaa.gov/geomagmodels/struts/calcDeclination

and found
Declination = 14° 16′ E changing by 0° 6′ W/year W/year for San Francisco.
It would appear to me that you subtract
this number from the magnetic north reading
to get true north because the needle is
pointing to the right of what they are calling
MN or magnetic north.

Lets say we were looking for 150 degrees.
Well, would we not really be looking for
150 – 14° 16′ or about 136 degrees?

John E Lavender
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John E Lavender

Dave, I know it is a bit late but I have only come across your method of finding south (or North) by the sun casting a shadow of a perpendicular pole or stick. You do know that the earths axial tilt is 32.26 degrees and if you were to pick out a nice tall perpendicular (‘Vertical’ to you) pole and every day, at high noon, place a stone (or some other suitable object) at the end of the poles shadow, at the end of a year you would have enscribed an oval of stones (or some other suitable objects) on… Read more »

Mike Wilhoit
Guest
Mike Wilhoit

Gentlemen,

Are there any figures on power loss as you move away from true south. My house is about 12 degrees west of true south. How bad does this hurt me.

Thanks,
Mike

Tor a.k.a. "Solar Fred"
Guest
Tor a.k.a. "Solar Fred"

Hey, Mike. It’s not going to hurt you all that much. You’re going to lose a little bit of power production, but that’s not a big deal. Your roof does NOT have to face exactly South, true or not. Plenty of systems get installed on Western systems and Eastern and South Eastern etc. North, now that’s a problem. Assuming you’ve got good subsidies, net metering, and good sun, it’s still going to be very cost effective for you. Being a few degrees off South will just mean that it will take you slightly longer for payback. Perhaps 10 years and… Read more »

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