Imagine a combo shed/greenhouse/cold pantry. A farmer in Nebraska grows oranges in winter. He dug a trench around a standard greenhouse about 5 to 6 feet deep and put in some 4" corrugated black pipe. The temperature in the ground is about 4 or 5 degrees Celcius and it barely changes from summer to winter. So you stay always stay above freezing in winter (and the greenhouse gets hotter when the sun shines), and in summer you can always keep cool. He runs it on a 12 Watt solar fan. Add some options, and you can go off-grid with a fully sustainable energy, food and water system. 

The simplest greenhouses are sheet plastic stretched over PVC plastic tubing bent in an arc. Fast, simple and inexpensive, but not good in high wind. The north side takes in only indirect ambient light, has little solar gain and significant heat loss. But you can imagine a shed with the greenhouse glass or plastic only on the sunny side. The north side is standard 2x4 construction, insulated, a place to store tools, pots and seeds.

A big problem with growing food in Canada is freezing. But you want to start plants early in the spring and grow well into  the fall. You don't think to put a shed partly into the ground, but if you do, it won't freeze. You'll extend the growing season. It's always +3 or +4 degrees C just 3' to 4' down in the ground, the same as the temperature in your refrigerator. What you have here is the idea of a root cellar. Yes, digging is work, but if you do it, your shed can have a walk-in cold pantry in it. A great place to stock up and save. Cold beer and watermelon in the summer, mmmm.

Why are you running an air conditioner in your house? All you need is a 4" pipe in a trench around your house with a small fan to bring the Earth-cooled air in. It's clean inside the pipe. Hot air from your house goes in, cools down, comes back as cold air. A thermostat controls the fan. A bit of digging, some low-cost pipe, a low-watt solar panel and 12 V battery, and you're permanently off grid. Forever. No more high electric bills.

A greenhouse need not be cheap, messy, dirty. Instead, think Sun Room. Morning coffee, a place to read a book. Even if the greenhouse is sunken, that lower part can be treated like a partial basement, a main floor above. An easy-to-sweep floor, with plants on the window side. All you want out of the basement is the ground heat, so it never freezes.  So often we think of plants as being on one working level. But with a greenhouse, you can do vertical gardening, hydroponics. Handy thing about a greenhouse is that the usual pests are kept out. No deer, no rabbits, no cutworms or moths.

A greenhouse with glass on the sunny side for solar gain,  and insulated shed walls on the shady side to reduce heat loss.. A greenhouse sunk into the ground will not freeze. Add buried 4" corrugated black plastic pipes with a fan to circulate 4 degree Celcius air. Add a water tank to catch rainwater and it could be used as  a heat sink. Use vertical gardening to maximize solar surface. Use mirrors to redirect light into shady locations, doubling solar intensity, doubling heat gain, doubling plant growth.A greenhouse with tools area, cold room pantry using 4 degree Celcius ground heat, which could be a beautiful sun room.