Reddit reviews Passive Annual Heat Storage: Improving the Design of Earth Shelters (2013 Revision)

http://www.motherearthnews.com/renewable-energy/passive-annual-heat-storage-zmaz85zsie.aspx#axzz3L4TMf2D6

Passive annual heat storage is your solution. I met a guy that made his earth home so efficient his house started getting too warm because he didn't account for the extra heat generated from his appliances. I have John Hait's book and love it.

http://www.amazon.com/gp/aw/d/0615905889/ref=pd_aw_sbs_1?pi=SL500_SY115&simLd=1

They grow banana trees and other tropical fruits inside the earthships in Taos, New Mexico. I'm not sure what climate zone that is, but it does get below zero in the winter. The design of the house keeps it 70 degrees inside all winter without heating. You can build an earth sheltered greenhouse in such a way that the surrounding mass of earth absorbs heat during the summer months and releases heat during the winter. It is possible to maintain pretty much whatever temperature you desire by adjusting the average annual temperature inside the greenhouse through venting or earth tubes.

Check out John Hait's book "Passive Annual Heat Storage," he does a really good job of explaining the science behind the concept, and how to build it without making some key mistakes. Here's a link to the book on Amazon:
http://amzn.com/0615905889

It is also possible to use earthworks as "sun traps." Think of a large U shaped berm, maybe 20 feet tall, oriented so the U opens towards the sun/south and with heat absorbing materials around the inside. Large boulders work great for absorbing heat, you can even build a rock wall to reflect light/heat toward the center of the U. In front of the berm you can build a pond to reflect light/heat into the U. All of these elements combine to create a micro-climate in the center of the U that is much warmer than the surrounding environment. I recently went to Paul Wheaton's land, where he is building something like this in hopes of being able to grow a lemon tree in Montana. Sepp Holzer has been growing citrus at high altitude in the Alps for years using these methods.

Another variation is the crater garden, which is exactly that, a large below grade garden in a crater like hole. The humidity from the plants inside the crater raises the temperature of the air, creating a warmer miocro-climate.

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