Jennifer wrote:

I just realized I should probably shouldn't have been such a regional
chauvinist, sorry

In the north america, south-facing houses are recommended. I know next
to nothing about bats outside of NA.

Despite appearances (that I'm using news.indidual.net which is in
Germany), I'm not...

I can see some perceived advantage to an exposed location for warmth as
you say, but that's anthromophising their behavior at least partly if
not completely.

I just observed that the opening actually chosen contra-indicated the
supposition. Of course, a house eave vent supplies heating via another
mechanism, but they could have chosen one which did have sun in either
the morning or evening it they had thought that a significant criterion
as the particular house had all possibilities available.

BTW, I know nothing of bats outside of NA, either, and very little other
than observing the one colony that chose to reside in the house until I
had to clean it up to sell and the realtor freaked out.

Here we're too dry and no surface water which I understand is a required
portion of suitable habitat for them.