I have been following this subject with interest. I recall several years ago a documentary film from New Zealand about queen breeders there siting their banking colonies on the hot water themals and having a series of pipes in the bottom of the hive through which the hot water was pumped. This heated the hive and helped with the survival of the banked queens.
Whilst not being solar heat, some of the Kiwis on Bee-L may be able to give the list more details on the heating of the hives with the hot water. It may have applications in other cold parts of the beekeeping world.
Go the Aussies in the World Cup!!!
Trevor Weatherhead
AUSTRALIA