Usually, when people think of solar energy, they envision those large, expensive solar panels on roofs and alongside highways. With a high initial investment (sometimes tens of thousands of dollars), the solar panels take many years to pay back their owners for the investment. But this is “active solar” – that is, using mechanical equipment like panels, pumps, and fans to get the most out of the omnipresent sun.
Passive solar energy is different. It gathers energy from the sun the old fashioned way – by allowing it to stream in through the windows, without the use of expensive solar panels. With a little intelligent design and planning, a passive solar home or building can get a full quarter of its heat from the sun alone.
Heating a Home with Passive Solar
For a home to gain a sizable fraction of its heat from the sun, its longest wall should be built facing due south. The ratio of window to floor space on this wall should be 7 – 8%. For example, a home of 2,000 square feet should have about 140 square feet of glass on the south-facing wall. Although that might not seem to be very much, keep in mind that the home needs to be kept warm in the winter, but also cool in the summer.
Outside the south-facing wall, make sure there are not too many tall trees or shrubs that might obstruct the sun. Inside the southern wall, use an absorber to soak up the sun and transfer the heat to the thermal mass behind or below it to distribute that heat.
What exactly is thermal mass? Imagine leaning against a stone fireplace the sun has been shining on for several hours. Even after the sun goes down, the stone fireplace radiates a bit of leftover heat. A liquid or solid that absorbs the sun's heat and radiates it later on. This design element is crucial for heating a home using passive solar energy – the more thermal mass a home has, the better passive solar will work. Thick concrete floors, brick, tiles, or masonry elements provide a home with better solar mass. And by the way, don't forget that the darker it is, the more heat will be absorbed; light colors reflect 80 – 85% of the sun's light, making these colors poor interior choices for a home using passive solar for its winter heat.
Keeping a Passive Solar Home Cool
If the builder of the passive solar home is not cautious, all those south-facing windows can be disastrous when summertime rolls around. To keep a home cool in the summertime using passive solar technologies, the first tip to remember is not to exceed the 7 – 8% glass exposure already mentioned on the south-facing wall. Too much glass will lead to an uncomfortable overheating problem.
The second tip is to utilize the right sized overhangs on the southern wall to let the sun in during the winter, but keep it out during the summer. In the winter time, the sun hangs low in the sky, so a small overhang over south-facing windows will not obstruct it. During the summertime, the sun is much higher in the sky, and the same overhang blocks the sun from southern windows. Insulated drapes, shutters, and blinds can also help keep the strong summer sun from overheating the home.
Landscaping is another great way to protect the home from overheating during the summertime. With some forethought, trees and vines can shade a home during the summer months, without blocking the sun in the winter.
When building a new home, a little extra planning will go a long way in creating a house that will be energy efficient through its use of passive solar energy.
K. N. Singer - There are some pros and some cons to being a jack-of-all-trades and master of none. The pros are that I can and do write about anything ...
