Deep Winter Greenhouse U of M Extension

deep-winter-greenhouse University of Minnesota Extension Link

From the site:
A Deep Winter Greenhouse (DWG) is a passive solar greenhouse designed to dramatically limit the amount of fossil fuel required to grow crops in northern latitudes. DWGs are oriented east-west with a south facing glazing wall specially angled depending on the latitude of the greenhouse to maximize solar energy on the shortest day of the year. Solar energy is stored in an underground thermal mass made up of an insulated rock bed that is covered with soil. Perforated drain tile that is laid out in the underground rock bed and distributed through the air through vents and fans that connect the air to the underground heat storage. Crops can be planted directly into the soil and through a system of suspended planters.

DWGs are utilized to grow cold hardy crops that thrive with minimal light throughout the middle of winter providing year-round production capacity for small scale farmers and gardeners. Crops well suited to DWG production include a variety of greens, herbs, broccoli, broccoli raab, kale, collards, Chinese cabbage, bok choy, and pea shoots. While fruiting crops like tomatoes, peppers, green beans, etc.. are not commonly grown in DWGs there is still lots of room for innovation and experimentation.