In message , Joe Fischer
writes

On the west slope roof there would be zero efficiency
until nearly noon, even if the panels have the north edge
of each higher than the south edge with the panels spaced
wide apart so they don't shade each other.

Due west certainly isn't great, but they'll go on working into the
evening longer, and our measurements of panels 45 degrees west of south
show useful heat gain from 9 am on sunny summer days.


The big advantage of the south facing wall mount
is the near optimum efficiency in winter, with the
possibility of extra reflections to exceed 100 percent
rating of the panels, and the reduction of thermal
energy in summer.

Hmmm... Little snow here, and only a few polished aluminium
driveways...


Cheers, J/.
--
John Beardmore