Thanks again to all who frequent this site - such a great info source.  I'm in 'design/dreaming' mode on our 2200sf home that we hope to construct this year (if we can sell the current home....) 

Reading a LOT on passive solar, how it's just the greatest thing ever.  Here's my question - it's quite intuitive that the number of solar heating days available (i.e.- the sun being out) is a big factor in the effectiveness of passive solar.  So, suppose I build my house south facing with a huge bank of windows - in northern Wisconsin, climate zone 7. First of all - I have reservations that even with a ton of sunny days, the heat loss due to that volume of window area is going to outweight the benefit - no matter the thermal mass added inside the structure. Bear in mind my design temp is -25F.   Secondly - we can go for days, sometimes 2 weeks, with no sun at all.  So in a nutshell - is it safe to assume that in certain areas of the country, passive solar is a poor option?  Or am I totally missing something?

You are right, windows lose a lot of energy at night - especially in northern WI.

But, on the other hand, they also gain a lot of energy during the day.  Facing south, even a clear double glazed unit will, on average, gain more than it loses over your heating season. In general the better insulating the window the greater the net benefit ---  with one warning.

The best low E for passive solar is not the best insulating low E. This goes against all intuition. But in the north, the lowest heating bills come from south facing low E windows with the highest SHGC (not the lowest U).

Stephen Thwaites P.Eng.
Thermotech Fiberglass Fenestration

It is very important to look at the over all building heat loss as you design your passive solar home. As Stephen has mentioned, material selection is critical and the location of windows will effect the type of glass that you will want to use.
When you minimize the amount of heat energy that your home requires, it becomes much easier to obtain respectable solar fraction ( the percentage of heat that you procure from the sun). Having designed, built and lived in solar homes for nearly 30 years, I am partial to an indirect system (ie:sunspace) that will be allowed greater temperature fluctuations than the rest of the home. We also use our sunspace to extend our growing season.

Get familiar with your local climate data and think super insulated. You can see some examples of sunspaces that work very well at a similar latitude to yours (Montana). www.mysunspace.net

Passive solar technologies are means of using sunlight for useful energy without use of active mechanical systems (as contrasted to active solar). Such technologies convert sunlight into usable heat (water, air, thermal mass), cause air-movement for ventilating, or store heat for future use, with little use of other energy sources. --------------- gillberk

The Thermotech guy is right on. American window manufacturers are slow to catch on about high solar heat gain in the northern tier states being a good thing. The Canadians are already there. Also look at window quilts http://www.windowquilt.com/

Since we didn't have the money required at the time to import windows from Canada (although Thermotech makes nice stuff), and the custom-glaziers wanted far too much money, we actually ended up with double-pane clear glass in our great room. It does mean we have to have insulated shades that we lower at night to stop heat loss.

In the summer it's fine; it's the low winter sun that's actually a problem. Yesterday it topped out around 35, but the great room was about 78 due solely to the sun (the - partly solar thermal powered - radiant floors come on around 5:30, get the house to 70 and then shut off around 7 am, when the sun hits the windows). Any warmer and I'd have had to crack a window for a bit.

This summer we're going to extend the arbor that shades the deck in summer (a trellis with sliding nursery shade panels) far enough to shade in winter if we need it.

The rest of our windows are the standard lowE, low SHGC.

To me, passive solar is also about the pleasure a light, bright house brings, as much as the heat/cooling issues. Our house is designed on a long E-W axis, with most rooms facing south (on the north side we have a stair case, a bath room and a small guest bedroom; all other rooms are on the south).