Knowing Which Way is Up

You’ve finally decided to build your new solar house. All these books and magazines that you have been reading these last few months about efficient construction and renewable energy have inspired you and you’re ready to go.

So, you head out to your property and scout around for a good house site. Once you’ve found one you pull out your trusty scout compass and line it up so you’re facing south. You’ve been paying attention to all this stuff we’ve been writing in our columns and want to make sure your house is pointed in the right direction. You’re ready to start laying out your house, right?

Well, not exactly. You’ve been led a bit astray by your trusty scout compass. The north your compass points to is the north magnetic pole, which is actually located in the Queen Elizabeth Islands of the upper Hudson Bay region. This is some 830 miles from the north geographic pole, the north end of the axis around which the earth rotates. You want to face your house towards geographic south, the southern end of that axis, not magnetic south and your compass can have you pointed quite a ways off true geographic south, depending on where in the country you live.

The difference between the location of the geographic pole and the magnetic pole is called declination. There is a variation in declination across the U.S. of about 45 degrees and there can also be local variations. It is always best to have a recent topographic map of your area with the local declination if you plan to use a compass to orient your home and your solar panels.

A good quality compass will allow you to offset its dial to compensate for declination. Declination is expressed in terms of degrees, minutes and seconds. A compass face consists of 360 degrees, each degree is broken into 60 minutes and each minute into 60 seconds. The declination here in the Guffey area is currently 10 degrees, 53 minutes east, which means that the magnetic north pole is that much east of the geographic pole in relation to our location.

This means that the south your compass has you oriented towards is actually 10 degrees 53 minutes west of true solar south. Since magnetic north is east of geographic north, magnetic south will be west of geographic south.

You’ll also notice that I said currently. This is because the magnetic poles never stay in the same place for long. Each year the declination changes slightly. A good quality topographic map will always show the declination for the year the map was made.

There is also a way to use the sun to orient your house. You can pound a stake in the ground and watch the shadow at solar noon, the time when the sun is in line with the south geographic pole relative to your position. At solar noon the shadow will be pointing straight north. Be aware that solar noon and noon on the clock are not always the same. In the winter, during Standard Time, solar noon is indeed at 12. However, in the summer, during Daylight Savings Time, solar noon is at 1 p.m.

I can understand if you’re feeling a bit confused. My wife, Maggie, is a cartographer (mapmaker) and it took her a considerable amount of time and patience to get me to understand how it worked. I’m glad she did, though, because it allowed us to avoid a lot of arguments when we were laying out our house. ("Yeah, but Maggie, the compass says…").

This afternoon, when I walked down into the greenhouse at 1 p.m. the sunlight was pouring straight into the house and our PV panels were pumping out maximum current. It looks like we got it right, thanks to Maggie and her patience.

All Contents © 1998
Wagonmaker Press
Thomas W. Elliot


Return to Article List