Here's the deal. I have a small 6x8 or so greenhouse that I've had four 3 or 4 years. I've never grown any plants inside but I would like to start growing nepenthes in it, and not just khasiana
I live in zone eight, and recently have been thinking about various methods of harnessing energy from the environment and using it as heat.
So far here are ideas I've come up with to keep my greenhouse at a comfortable 55-60 during december nights.
Caulk Caulk Caulk
Add insulation to the north wall, cover in plywood and paint black
Glaze all panels and add bubblewrap insulation
Insulate the floor.
Add gravel to the floor to act as a heatsink.
Make a solar water heater and use the hot water to somehow heat the greenhouse
Move my rain barrel inside, paint in black, fill with water and seal tightly.
Any more ideas, the more the better. My goal is to have zero heating costs after initial investment.