I saw it in person before I found the article. He heats it in winter on the coldest nights with an old wood burning stove. He also has several large drums of water to act as a heat sink. It seems rather effective, as well as inexpensive. It gets cold in winter around here.
I wonder if this particular greenhouse (geodesic dome) could be made into a propagation greenhouse? If you attached a misting system and could keep the inside a certain temp, I think that would be really cool and CHEAP!
One of the BBC "eco" shows did an experiment with a geodesic dome last year for propagation and tropical hydroculture. They used solar-powered pumps to keep the water circulating on the hydroculture side and to power a basic misting system. You could probably keep the temperature rather constant just by having dark containers of water in the dome.