What is the variation you were already thinking of?
The Walipini looks like a take on the Passive Solar Thermal Greenhouse idea. It will use the thermal mass of the earth to help capture and store the energy from the sun during the day and release it back into the enclosed space at night. The angle of the translucent material being important that it is perpendicular to the angle of the sun at Winter Solstice for maximum winter soalr thermal energy accumulation.
I'm at work and don't have any links with me, but if you haven't already, do some searches on Passive Solar Thermal Greenhouses. There's lots of good information on them and I remember specifically some info on them in cold climates.
Sounds like a cool project you have going on! Best of luck to you!
