A passive solar building should ideally be rectangular in plan and oriented with the long axis running E/W. This allows one of the longer sides to face Solar North to maximise solar gain in winter. This also helps to minimise solar gain for the west wall in summer and it allows for more roof space facing north on which to mount solar PV or hot water panels.
How to find find Solar North? 1) Drive a tall stake into the ground (make sure it is plumb), 2) Observe the shadow of the stake at high noon (1pm during daylight savings time), 3) That’s it…the shadow of the stake points directly north/south.