One of the most comfortable houses I ever visited was largely heated passively by a big bank of windows on the south side that let the sun in during the winter. In summer, a broad overhang kept the sun out. Even without such an auspicious design, it's possible to harvest enough sunlight during the day in winter to feel a difference.
These shades have hollow chambers that provide dead airspace for insulation when closed,
and can open up or down to control the view while letting solar heat and light in during the day.