ASK THE EXPERTS: Finding True South

Magnetic Declination Map
Map of magnetic declination values in the United States.
Magnetic Declination Map

I have been reading Home Power for several years and love it. We are getting ready to build a new house in the country and will have a grid-tied PV system installed on the south-facing roof. My question is how to find “true south.” The magnetic declination at our location in central North Carolina is 8 degrees west. If I shoot an azimuth of 188 degrees and orient the south roof facing that azimuth would I be close enough for decent solar exposure? Is there a better way to find true south without buying additional equipment? Thanks in advance,

Frank Stump • via e-mail

Hello Frank, You have it right. True south for your location is at 188° magnetic. Magnetic south differs from true south because magnetic north—what compasses show—is based on the large mass of magnetic material in the northern part of the Earth. This mass is not centered on the geographical pole, so for each location, there is a correction (called “declination”) to convert to true north from compass/magnetic north.

I’m glad to see you’re thinking of the sun when you orient your new home. Most folks just think of the view from the living room window and can wind up building a home with poor solar exposure. In fact, plus or minus 10° either way doesn’t cause much loss in a fixed array (only about 2 percent).

In addition to solar-electricity, I hope you’ll also consider passive solar design and solar hot water for your new home. Both of these are very effective solar technologies! Thanks for reading Home Power

Richard PerezHome Power

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