I've noticed that most thermally efficient constructions limit the use of windows due to glass' low [R-value](https://en.wikipedia.org/wiki/R-value_(insulation)). According to this, one is forced to choose between well-lit spaces or thermally efficient ones. 

Earthships, contrary to this, use plenty of windows facing the sun. Is this because the double panel glass corridor (used as a greenhouse) provides more thermal resistance than a glass wall alone? Since enclosed air cavities have higher R-values, I assume this to be the case. 

[![Earthship greenhouse](https://i.stack.imgur.com/Be7Od.jpg)](https://i.stack.imgur.com/Be7Od.jpg)

Under which conditions will this hold? What should be the dimensions of this corridor? Is the temperature inside the double panel wall bearable or is it too high to be used as a living space? Can window shades or deciduous trees be used to regulate temperature in these cases?