In compliance with codes, (local but possibly national), each window has to have an E value of .35 or greater. So this essentially means using a low E coating on a double with argon. http://en.wikipedia.org/wiki/Low-emissivity So solar gain will be reduced. But the question is, is this a good idea on south facing windows on a passive solar house? Could it be that less passive solar gain in the day is offset by the reduced loss at night when the sun isn't shining? Here is an interesting read on this topic. http://www.passivhaustagung.de/Passive_House_E/windows_passive_houses_06.html

Depends, Summer or Winter?

The principle is that the metalized coating reflects heat. Ideally in the Winter that coating should be facing inside, to reflect heat in. And in Summer it should be facing out. There is a window made in the EU that's reversible.

Per conversation with Jeld Wen windows, the coating should be on surface 3 of the glazing. This is the surface on the outside of the inside pane of glass.
When low e coatings are applied to surface 2 they reflect heat back to the outside. coatings are applied to both surfaces to reflect heat both ways and thus create a lower U value. The outside surface of the window is #1. The inside surface of a double pane window is surface #4. Look at the solar heat gain coefficient to find the factor for allowable sunlight transmission. This is for northern climates that do not have a large cooling requirement.

The reason for the insulating window in the beginning? Check out http://www.alpen.com
Amory Lovins is just installing new windows @ 6,000 ft. @ Rocky Mountain Institute - think they are about R=12
Alpen has research windows to almost R=18 .
There are hundreds if not thousands of combinations now to achieve almost any desired result. The new vacuum daylighting windows are soon to enter the mix. These will probably bring a mass of new attached solar greenhouses - just when they will be needed.
If you are building JUST to code, recall that the code is far behind the curve now. Naturally you know this as you mention passive.de web site - a must read for everyone.

While this may be true for the glass that Jeld Wen uses, each manufacturer has their own coatings that behave differently.

Saying that 'soft coat' behaves this way and 'hard coat' behaves that way or that coatings on #2 do this and coatings on #3 do that are generalizations that are not necessarily true for all glass.  Consult the manufacturer.

xexpat