Six years ago New Zealand experienced the coldest week in recorded history, but our recently finished passive solar villa performed perfectly during the cold snap. Even with single-glazing in much of our home, it stayed warm during the frigid week without using any heat source other than the sun. (Of course the curtains and blinds did their job at night.)
Here is a blog post I wrote six years ago today that explains the great result:
Here is a blog post written a month later that explains how and why the sun can be used to heat a home in winter for free.