What Is Passive Solar Energy?

When it comes to solar power, there are two kinds: passive and active.

In this article, we’re going to be looking at passive solar energy, and what it means for saving energy in your home.

What Is Passive Solar?

If you’ve ever sat in front of a sunny window on a cold winter’s day, then you’ve felt the power of passive solar energy. And, it’s warmth you got completely free.

According to Home Power Magazine, homeowners spend an average of $1300 per season heating their homes. And if you live in the northern climates, then you know that it’s usually much more than that.

The beautiful thing about passive solar is that you can use the power of the sun to heat your home, reducing or even completely eliminating your high monthly bills. Passive solar design not only saves you money, but it also helps reduce pollution by allowing you to use less energy.

The sun is always shining, which means that even on the coldest day we can still take advantage of the energy that’s constantly pouring down to Earth. Passive solar design uses building elements like windows, floors, and roofs to take advantage of the sun’s energy.

But, it doesn’t involve any “moving” or mechanical parts to move the heat around, which is why it’s called passive.

Passive solar energy can be used to heat an entire home, or simply heat water for a shower.

Passive Solar Heating

So, wondering how the sun could possibly heat your entire home?

Well, to understand how passive solar heating works you need to know how heat moves within a space.

First of all, heat always moves to colder areas, like a magnet, until there is no temperature difference between the two. Passive solar uses this basic law to heat areas large in scale, like your home, cheaply and efficiently.

For instance, a passive solar home often has very large, south-facing windows. As the sun is shining during the day, it’s heating up the floors and walls inside that portion of the house. Those floors and walls are specifically designed to absorb that heat. At night, when the home begins to cool down, that heat is released.

Simple and effective, right?

Now, passive solar design is used most often in new construction. But, existing buildings can be modified to take advantage of solar heat.

The U.S. Department of Energy lists 5 essential elements to passive solar design. All of the elements work independently, of course, but if you want a complete passive solar home, you need them all.

• Aperture- These are the windows that will be “collecting” the sunlight for your home. These windows usually need to face true south, and not be blocked by any trees. They need to get full sun for at least the majority of the day. You can help regulate your indoor temperature with insulated curtains or shades. But, these should be installed properly to help ensure that air can’t easily circulate behind the curtains and create a downdraft of cold air against the windows at night.

• Absorber- The absorber is a hard, dark material that absorbs the sunlight. It can be on a floor or roof, or even a water tank.

• Thermal Mass- Thermal mass can describe any material that can absorb a lot of heat. It’s different from the absorber: the absorber is a surface material, and the thermal mass is usually underneath the absorber. The thermal mass also works to stabilize indoor temperatures.

• Distribution- This is how your solar heat will circulate in your home. In strict passive solar homes, convection, conduction, and radiation are used to move heat. But, other homes can use fans and ducts to help move the heat.

• Control- It can be easy for passive solar homes to overheat, or be underheated, if there is no control. So, controls like roof overhangs and fans are used to keep a stable, comfortable temperature.

To see how a passive solar home works with all these elements, take a look at this illustration from the U.S. Department of Energy:

You can also clearly see how the control element works with this illustration, again, courtesy of the U.S. Department of Energy:

Passive Solar Daylighting

The sun can also be used to brighten your home, reducing your need for commercial lights. This is called “daylighting”, and many homes use this technique with skylights and large windows.

You can also use a clerestory, which is a row of windows close to the peak of your roof, to collect sunlight. The clerestory is often used in wide, open homes that allow the light to bounce off walls and spread out.

It’s important to realize, however, that skylights and clerestories need to be carefully sized and installed, or you could easily lose heat at night and gain too much during the day. Rather than having a comfortable indoor home environment, this imbalance could cause your home to either be too hot or too cold.

Consulting a professional who fully understands energy efficiency would be money well spent when designing your home. After all, it would be far more costly to fix these mistakes later on!

Passive solar design is slowly starting to catch on. Home Power Magazine estimates that using passive solar design in new home construction only adds around 5% to construction costs. And yet it can save at least 15-20% annually on heating and cooling costs. So, you can quickly make up your investment by building this way.