How to keep a greenhouse warm without heating?

A greenhouse can stay frost-free with no fuel if it stores the sun's heat. Glaze only the side facing the sun (south) and insulate the north wall and the roof slope behind it; insulate the ground around the edge down to frost depth. Give it thermal mass: barrels of water, stone or a brick wall in the sun, or pipes buried under the beds through which a small fan pushes the hot air from under the roof (a «climate battery»): the soil stores summer heat and gives it back in autumn and winter. On winter nights draw an insulating curtain over the glass. Such greenhouses in Canadian mountains stay around 0 °C at −20 °C outside. Draw your greenhouse on the plot drawing: the plan puts heat-loving crops in it.