How to use a simple, cheap, passive solar design

Stop. If you don't have Southerly facing windows, this blog post is probably not for you!

Okay, that said... everyone has heard the term passive solar... right!? but just what the heck does it mean?

Simply put, passive solar is using design and building features that can gather heat from the sun during the day, and then release that heat slowly throughout the nighttime - helping to maintain a constant temperature, without expensive inputs from fossil fuel.

One of the easiest, most important, and most misunderstood aspects of passive solar is to take advantage of the South facing windows in your home to gather sun in the winter and block sun in the summer.

Unfortunately, most folks make the mistake to think that all you need is to have south facing windows, and, viola! you have passive solar. In fact, what you probably have is sky rocketing heating/cooling costs..!

What can you do about this? Luckily there is an easy solution to this dilemma. In the summer, we want to shade our homes from incoming heat, and in the winter we want to let it in. Right? What works to our advantage here, is that the sun is actually lower in the sky in the winter and as such can come in through a window that would be shaded by an overhang from the summer sun.

Great you say. But how much overhang do i need?

The answer to that lies almost entirely on where you are located, geographically speaking. And luckily for us, that can be calculated simply by punching in your town name and state into the bars for "feature name" and "state" here. (ed. note: write down the latitude and longtitude and elevation)

Take this newfound information here. When entering this information, you will want to know what the sun angle is at its highest... Summer solstice, and at its lowest... Winter solstice. To do this follow these simple steps:

1) Under "date" enter June 22
2) Under "time" enter 1200
3) Under "time basis" enter 24 hr.
4) Under "time zone", enter your time zone.
5) Under "time basis" choose “solar time”
6) Under "daylight savings" enter “no”
7) Under "zero azimuth" enter “South”.
8) Click on “Calculate”.

Great. You now have your summer high angle. Write this down.

9) Under "date" change to December 22 - recalculate.

Fantastic. You now have your winter low angle.

10) With these calculations in mind (and a few even more simple measurements on the outside of your home), you can now draw some simple lines and figure out exactly how much overhang you will need to block out that air conditioner killing summer sun, and soak up that warmth-giving winter light.


Now go forth and add on simple shades or build overhangs and see the cost of your monthly heating/cooling bills drop, and the value of your home increase. ...in fact, a little more work and you may actually be close to eligible for energy efficient financing packages for any future buyers of your home.

Heads-up to Michael Pulakamp for first putting together this simple two-step web-calculation.