Dear Solar Guy:

        What is the optimum angle of a roof for solar collection at
30-degrees North latitude (Austin)?  Do you have an easy answer ?   Thanks,

Anxious to Get Started, Austin, TX

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Dear Anxious,

I’ve been asked this many times before.  The response depends on the
application, and Anxious I really need more information, but will
assume a couple of possibilities.  The general recommendation for
collectors is latitude plus about 10 degrees, but the “optimum” will
vary somewhat with the application.

Anyway here goes.  Assume the following cases:


1. Solar water heating:  tilt of latitude plus 10 degrees (i.e.  40
degrees).

2. Space heating plus water heating:  tilt of about latitude plus 15
degrees.

3. Electricity (i.e.  PV panels):  tilt of about latitude plus 10
degrees.

However the actual tilts could be within 5-10 degrees of the above and
there would not be a great difference in long term performance.  The
chosen tilt will often be partially determined by the existing roof
slope, with aesthetics and wind loading being significant
considerations.  In all cases the best orientation is to face
collectors due south, but again one does not degrade performance much
if within 20 – 30 degrees of dues south. 

 The Solar Guy