Passive Solar in the Spring: I’ll Follow the Sun

Why use fossil fuels to heat your home if you can design it to take advantage of the fact that 75 to 80 percent of New Mexico days are sunny? We were fortunate enough to buy a passive solar home two years ago. It was professionally designed for the former owners, who told us they almost never used their furnace. Two wood-burning stoves do the trick on chilly evenings and the sun takes care of the rest. The owners warned us, however, that April would be the coolest month in the house, and September the hottest. And they were right.

passive solar NM home
Passive solar home in winter. See how many windows face south to soak up sun on a clear day?

Here’s why: A passive solar home has plenty of windows facing directly south. The windows collect warmth from the winter sun, which is lower than in the summer. With good thermal mass in the form of floor tile, bricks, concrete and other materials, the heat gets stored and then releases in the evening to help keep the house warm as temperatures drop. Other design factors, such as having few north-facing windows, keep cold air out and warm air in, as do tight seals and good insulation. Landscaping also helps; planting little but deciduous trees near the home’s foundation allows winter sun through, but provides summer shade.

 

trombe wall storing solar energy
A trombe wall soaks up and stores the heat from south-facing windows. Note how much more heat can enter when the sun is low. This illustration is from the U.S. Department of Energy.

We’ve got several trombe walls made of adobe bricks and tile floors in every room but the master bedroom. I can vouch for how well the system works; I had to open windows a few times in January on sunny, warmer days.

 

trombe wall in New Mexico home
This trombe wall warms a hallway and living area. The tiles and adobe bricks store heat efficiently.

But about March to April, the sun starts shifting its path in the sky and even though the days get longer, less sun comes in our windows. If it’s also partly cloudy or cool, the house warms up less than it does in December and January. That means we’re having fires on many spring evenings to take the chill off.

In summer, we open upper, clerestory windows as soon as the air outside cools off to circulate cool air throughout the house. Then we have to shut out the hot air come morning. We might also draw a few shades, especially on the east and west side of the house. Come September, the sun starts dipping in the sky and through our windows, warming up the house when temps outside can still be high.

Throughout the year, we’ve learned to work with the home’s design and the sun to make the most of how smart the house is at using natural energy so that we save on fuel, and especially fuel costs. In fact, I have nothing but an energy-efficient wall heater and a trombe wall in my office. I use a small space heater on cold winter mornings as needed. If it gets too warm in here, I can work outside under the shade of the apricot tree!

 

passive solar home in December
December sun striking opposite wall.

If you’re considering building a new home or a remodel, I strongly recommend passive solar as a way to warm and brighten your home and to save on annual energy costs. Learn more here.

Leave a Reply

Your email address will not be published. Required fields are marked *