Fall fades and passive solar kicks in

Boone Guyton

The sun’s arc is lower and still dropping pushing sunlight into our home about 8 feet.  These clear cool days are where the passive solar design really shines, so to speak.  We need very little back up heating and the sun-warmed floor radiates back the absorbed sun’s heat for hours. We also have an interior brick wall that absorbs more of the surplus to smooth out the temperature changes.  Even with a 24-degree night we can make it through till the next morning’s solar input.


The lot where we are building now is oriented exactly wrong for a good passive solar home.  It is narrow from Southeast to Northwest and long and open to the southwest. We did put the largest windows on the Southeast end to take some advantage though we did not make the glazing high solar heat gain which would have let more heat in but also been less insulating when the sun was not out or not hitting the glazing. As the south end faces 25 degrees east of South and the window glazing area less than 1% of the floor area, I figured it was not going to be a big gain at any rate.  The contrast between sitting in front of those windows in the sun and the high solar heat gain windows on our south side at home is huge. On a cold day during lunch I have often wished I chose differently.   We also will build a trellis on the Southwest side to shade for the summer. There is a good site for checking out the advantage and disadvantages of orientation and window glazing options at; http://www.efficientwindows.org/new_selection1.php

We were able to configure the roof to have a long solar exposure that will work for Solar PV system. By making the largest area a gable with the gable ends east and west and the South (really southeast) slope encompassing the porch we ended up with a large area for panels and plenty of sunlight hours to have an efficient system. One advantages of Solar PV is that it can handle a wide variation of orientation without diminishing efficiency much.  (see http://bit.ly/19bIgCZ )

A friend has the Sun Scout App on his I phone which gave us a quick easy display of where the sun would be during the year and what kind of exposure we would have.  We checked both before we began building and after the roof was on just to be sure.

Sun Scouth app – http://bit.ly/19T3bzb

Passive Solar is hard to beat. No moving parts and little extra cost for free heat.  But it works best within 15 degrees of true South so many lots won’t work.  PV is more costly and more flexible and has dropped in price enough to incorporate even in a small home.  I do wish they would come up with an affordable window that would automatically change its solar heat gain to accommodate the seasonal need.